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#include <GDI.H>
Link against: gdi.lib

Class CGraphicsContext

class CGraphicsContext : public CBase;

Description

Abstract base class for all graphics contexts.

Created by a CGraphicsDevice.

Provides the 'context' in which you are drawing to an associated device, in the sense that it holds the settings for drawing, such as the pen and brush settings (e.g. color, line styles) and the font settings (e.g. bold, underline, italic). These settings are device-independent.

Also provides the clipping region (the visible drawing area).

The settings and clipping area can be updated while drawing.

This class also contains the main drawing functions, and all drawing is done through a CGraphicsContext.

The graphics context deals with pixels of device-dependent size and uses fonts with device-dependent size and representation. The sizes and fonts to be passed to the class functions therefore need to be converted from size-independent units to size-dependent units first. This is done by an MGraphicsDeviceMap derived class. This may be a TZoomFactor or the CGraphicsDevice.

See CGraphicsContext::Reset() for the default graphics context settings immediately after construction.

Derivation

Members

Defined in CGraphicsContext:

Inherited from CBase:

See also:

Member functions

Device()const

virtual CGraphicsDevice* Device() const=0;

Description

Gets a pointer to the graphics context's graphics device.

Return value

CGraphicsDevice *

A pointer to the graphics device.

SetOrigin(const TPoint &)

virtual void SetOrigin(const TPoint &aPos=TPoint(0, 0))=0;

Description

Sets the position of the co-ordinate origin.

All subsequent drawing operations are done relative to this origin.

Parameters

const TPoint &aPos

The origin. The default origin is TPoint(0,0) the top left corner of the screen.

SetDrawMode(TDrawMode)

virtual void SetDrawMode(TDrawMode aDrawingMode)=0;

Description

Sets the drawing mode.

The way that the pen and brush draw depends on the drawing mode. The drawing mode affects the colour that is actually drawn, because it defines the way that the current screen colour logically combines with the current pen colour and brush colour. There are many drawing modes, each giving different logical combinations of pen, brush and screen colours. Each mode is produced by ORing together different combinations of seven drawing mode components.

The three most important modes are TDrawMode::EDrawModePEN, TDrawMode::EDrawModeNOTSCREEN and TDrawMode::EDrawModeXOR. The default drawing mode is TDrawMode::EDrawModePEN.

The drawing mode is over-ridden for line and shape drawing functions when a wide pen line has been selected. It is forced to TDrawMode::EDrawModePEN. This is to prevent undesired effects at line joins (vertexes).

Notes:

TDrawMode::EDrawModeAND gives a "colour filter" effect. For example:

TDrawMode::EDrawModeOR gives a "colour boost" effect. For example:

TDrawMode::EDrawModeXOR gives an "Exclusive OR" effect. For example:

TDrawMode::EDrawModeWriteAlpha should not normally need to be used by client code. The following are exceptions:-

Note that if you have a transparent brush or source bitmap and you are drawing to a window, then it is a defect to use EDrawModeWriteAlpha.

Parameters

CGraphicsContext::TDrawMode aDrawingMode

The drawing mode.

See also:

SetClippingRect(const TRect &)

virtual void SetClippingRect(const TRect &aRect)=0;

Description

Sets the clipping rectangle.

The area of visible drawing depends on the clipping region. The default clipping rectangle is the full device area.

Parameters

const TRect &aRect

The clipping rectangle.

CancelClippingRect()

virtual void CancelClippingRect()=0;

Description

Cancels any clipping rectangle.

Clipping thus reverts to the full device area, the default.

See also:

Reset()

virtual void Reset()=0;

Description

Resets the graphics context to its default settings:

the drawing mode is TDrawMode::EDrawModePen (pen and brush colours used as they are)

there is no clipping rectangle

the pen settings are: black, solid, single pixel size

the brush style is null

no text font is selected

UseFont(const CFont *)

virtual void UseFont(const CFont *aFont)=0;

Description

Sets the device font to be used for text drawing.

If the font is already in memory, then that copy is shared.

Notes:

The CFont* argument must have been previously initialised by calling MGraphicsDeviceMap::GetNearestFontInTwips(CFont *&,const TFontSpec &) with the required font-specification. If the CFont* has not been initialised correctly, and therefore does not point to an available font-bitmap, then a panic is raised.

When the font is no longer required, use CGraphicsContext::DiscardFont() to free up the memory used. If CGraphicsContext::UseFont(const CFont *) is used again without using CGraphicsContext::DiscardFont() then the previous font is discarded automatically.

If no font has been selected, and an attempt is made to draw text with CGraphicsContext::DrawText(const TDesC &,const TPoint &), then a panic is raised.

Parameters

const CFont *aFont

A device font

See also:

DiscardFont()

virtual void DiscardFont()=0;

Description

Discards a font.

This frees up the memory used, if the font is not being shared.

The function can be called when no font is in use.

SetUnderlineStyle(TFontUnderline)

virtual void SetUnderlineStyle(TFontUnderline aUnderlineStyle)=0;

Description

Sets the underline style.

This is applied to all subsequently drawn text.

Parameters

TFontUnderline aUnderlineStyle

The underline style on or off.

SetStrikethroughStyle(TFontStrikethrough)

virtual void SetStrikethroughStyle(TFontStrikethrough aStrikethroughStyle)=0;

Description

Sets the strikethrough style.

This is applied to all subsequently drawn text.

Parameters

TFontStrikethrough aStrikethroughStyle

The strikethrough style on or off.

JustificationInPixels(TInt,TInt,TInt,TInt)

IMPORT_C static TInt JustificationInPixels(TInt aExcessPixels, TInt aTotalUnits, TInt aFirstUnit, TInt aNumUnits);

Description

Gets the amount of space in pixels by which to adjust letter or word spacing, given the total number of words and spaces, a start space, and the number of units to be adjusted.

The first two arguments are the number of pixels (character groups) and the number of units (word spaces) over which justification is to occur. The third argument specifies the current character group or word space, while the final argument specifies the number of units that are to be adjusted.

A panic occurs if aExcessPixels is 0, aTotalUnits is not greater than 0, or aFirstUnit is not less than aTotalUnits.

Parameters

TInt aExcessPixels

The number of pixels by which the width of the text is to be changed. It may be positive, in which case the text is stretched, or negative, in which case it is shrunk.

TInt aTotalUnits

The number of word spaces over which the change in width is to be distributed.

TInt aFirstUnit

The current unit — the character group or word space we are 'on'.

TInt aNumUnits

The number of units that are to be adjusted — starting at aFirstUnit.

Return value

TInt

The number of pixels to be added to the width of the current unit.

See also:

JustificationInPixels(TInt &,TInt &)

IMPORT_C static TInt JustificationInPixels(TInt &aExcessPixels, TInt &aTotalUnits);

Description

Gets the amount of space in pixels by which to adjust the current letter or word spacing, and also retrieves the number of excess pixels and word spaces remaining after the adjustment is performed.

The arguments are the number of remaining pixels (character groups) and units (word spaces) over which justification is to occur. The function can be called repetitively until the number of units is zero, and hence justification is complete. A panic occurs if the number of units is less than one or the amount of pixels is zero.

Parameters

TInt &aExcessPixels

The number of pixels by which the width of the text is to be changed. It may be positive, in which case the text is stretched, or negative, in which case it is shrunk. On return, this is equal to its old value minus the return value.

TInt &aTotalUnits

The number of word spaces over which the change in width is to be distributed. On return, this is reduced by one.

Return value

TInt

The number of pixels to be added to the width of the current unit.

See also:

SetWordJustification(TInt,TInt)

virtual void SetWordJustification(TInt aExcessWidth, TInt aNumGaps)=0;

Description

Adjusts the spaces between words to stretch or squeeze to a certain width.

The function is required by the Text Views API, and is not intended for regular use by developers.

The text line that is to be justified has a certain number of gaps (spaces) between the words. It also has a distance (in pixels) between the end of the last word and the actual end of the line (right hand margin, usually). These excess width pixels are distributed amongst the gaps between the words to achieve full justification of the text line. Spaces become fat spaces to keep underlining/strikethrough consistent. Pixels are distributed to the inter-word gaps starting from the left end of the string. The spacing between characters in each word remains unchanged.

After a call to CGraphicsContext::SetWordJustification(TInt,TInt), subsequent calls to either of the two CGraphicsContext::DrawText(const TDesC &,const TPoint &) functions are affected until the number of spaces specified by aNumSpaces is used up.

The easiest way to find out the excess width and number of spaces is to call CFont::MeasureText(const TDesC &,const TMeasureTextInput *,TMeasureTextOutput *)const. This function can also perform counting, which is finding how much of some text will fit into a given width.

Use CFont::TextCount(const TDesC &,TInt)const to return the excess width.

For example, in the string "To be, or not to be", there are five inter-word gaps. If there are six excess pixels they will be distributed in the proportion 2, 1, 1, 1, 1 between the words. If there are nine excess pixels they will be distributed in the proportion 2, 2, 2, 2, 1 between the words.

Notes:

If the excess width is zero, then calling CGraphicsContext::SetWordJustification(TInt,TInt) has no effect.

At first sight it may appear that CGraphicsContext::SetWordJustification(TInt,TInt) is not required because you can simply call CGraphicsContext::DrawText(const TDesC &,const TPoint &) for each word. However, underlined justified text does not work using this strategy you get a non-underlined gap between the space and the beginning of the next word.

Parameters

TInt aExcessWidth

The width (in pixels) to be distributed between the specified number of spaces. It may be positive, in which case the text is stretched, or negative, in which case it is shrunk.

TInt aNumGaps

The number of word spaces (characters with the code U+0020) over which the change in width is distributed.

SetCharJustification(TInt,TInt)

virtual void SetCharJustification(TInt aExcessWidth, TInt aNumChars)=0;

Description

Sets character justification.

This function is required by the Text Views API, and is not intended for regular use by developers.

It affects the strings of text used in the calls to CGraphicsContext::DrawText(const TDesC &,const TPoint &) that follow, until the number of characters drawn equals aNumChars.

The text line that is to be justified has a certain number of characters this includes the spaces between the words. It also has a distance (in pixels) between the end of the last word and the actual end of the line (right hand margin, usually). These excess width pixels are distributed amongst all the characters, increasing the gaps between them, to achieve full justification of the text line.

Use CFont::TextCount(const TDesC &,TInt)const to return the excess width.

Notes:

This function is provided to allow simulation of printer fonts on screen. Due to the fact that fully-scalable fonts are not used before v5, large printer fonts can be simulated by using the nearest smaller font and widening it slightly.

If the excess width is zero, then calling CGraphicsContext::SetCharJustification(TInt,TInt) has no effect.

CGraphicsContext::SetCharJustification(TInt,TInt) is required for WYSIWYG where the layout uses printer font metrics but screen fonts have to be drawn on the screen. Because continuously scalable typefaces (c.f. TrueType) are not used before v5 and because screen fonts are coarser and less numerous in their variety than the printer fonts, the best matching smaller screen font must be used with character justification to simulate the printer font on the screen.

There is also a situation where the gaps between characters on screen have to be reduced with character clipping. The screen font that best matches the printer font may have the required height, but has characters that are too wide. A line of text that works on the printer will then be too long on the screen, unless it is squashed horizontally. The number of pixels that overlap the end of the screen line must now be removed from the gaps between the characters, i.e. there is a negative excess width. This situation is especially important where adding a TAB on screen gives perfectly acceptable printout, but would push the last character of the line off the right hand side of the screen.

In practice what you do in printer layout mode is:

Calculate where the line breaks will come on the printer. To do this you use a printer font (which in practice means a table of character widths of the font that the printer will use).

Now change to use a screen font that is the closest font which is no taller that the printer font. In practice it will often be fatter maybe only for certain characters such as 'i'.

You have to recalculate the width of the characters using the screen fonts. You can do this using CFont::TextWidth() as you have already determined how many characters will fit on the line.

If, in the screen font, the characters are not as wide as the line then you can just use word justification to expand the line. You would only do this if the text is to be justified.

If, however, the characters are wider than the line then you would use character justification to clip each character. You would need to do this even if the line is not justified.

Thus, in practice, character justification will only very rarely be used to expand a line of characters.

Parameters

TInt aExcessWidth

The excess width (in pixels) to be distributed between the specified number of characters.

TInt aNumChars

The number of characters involved.

SetPenColor(const TRgb &)

virtual void SetPenColor(const TRgb &aColor)=0;

Description

Sets the pen colour.

The effective pen colour depends on the drawing mode. The default pen colour is black.

Note:

The pen is used to draw lines, the outlines of filled shapes, and text. The class provides member functions to set the colour of the pen, the style of line and the line size drawn.

Parameters

const TRgb &aColor

An RGB colour for the pen.

See also:

SetPenStyle(TPenStyle)

virtual void SetPenStyle(TPenStyle aPenStyle)=0;

Description

Sets the line drawing style for the pen.

There are 6 pen styles. If no pen style is set, then the default is TPenStyle::ESolidPen. To use a pen style, its full context must be given, e.g. for a null pen:

CGraphicsContext::TPenStyle::ENullPen Notes:

The pen is used to draw lines, the outlines of filled shapes, and text. CGraphicsContext member functions are provided to set the colour of the pen, the style of line and the line size drawn.

The TPenStyle::ENullPen style should be used if a border is not required around a filled shape.

Dotted and dashed pen styles have a device dependant implementation, always give single-pixel size lines on the screen whatever the pen size set by CGraphicsContext::SetPenSize(const TSize &) and can only be used for straight lines, polylines, non-rounded rectangles and polygons.

The dotted/dashed pattern is continued, without re-starting, for all consecutively drawn straight lines, i.e.

the outlines of rectangles the pattern starts in the top left corner. It is reset at the end of the function call.

the outlines of polygons the pattern starts at the first point. It is reset at the end of the function call.

polylines and straight lines the pattern starts at the first point initially. Consecutive calls to CGraphicsContext::DrawLine(const TPoint &,const TPoint &) and/or CGraphicsContext::DrawPolyLine(const CArrayFix< TPoint > *), whether the lines are concatenated or not, continue the pattern. It can be reset by a further call to CGraphicsContext::SetPenStyle(TPenStyle) using the same dotted/dashed style parameter.

Parameters

CGraphicsContext::TPenStyle aPenStyle

A pen style.

See also:

SetPenSize(const TSize &)

virtual void SetPenSize(const TSize &aSize)=0;

Description

Sets the line drawing size for the pen.

Lines of size greater than one pixel:

are drawn with rounded ends that extend beyond the end points, (as if the line is drawn using a circular pen tip of the specified size).

are always drawn in TDrawMode::EDrawModePEN mode, overriding whatever mode has been set using CGraphicsContext::SetDrawMode(TDrawMode).

Notes:

The pen is used to draw lines, the outlines of filled shapes, and text. The class provides member functions to set the colour of the pen, the style of line and the line size drawn.

Wide straight lines and arcs have rounded ends so that concatenated wide lines have smoothly rounded corners at the vertexes.

When lines are made wide, the extra strips of pixels are added equally to both sides of the line. This works precisely for lines of odd pixel size (3, 5, 7, etc.). Wide lines of even pixel size, (2, 4, 6, etc.), have the extra strip of pixels added to the right and/or below the line.

Wide outlines of ellipses and wide line arcs are drawn with the pixels distributed either side of a thin (single pixel wide) true ellipse constructed in the normal manner. Wide ellipses and arcs of even pixel size have the extra strip of pixels added to the right and/or below the curved line. This gives a slight asymmetry to ellipses.

If the pen style is dotted or dashed, the size specification is ignored: a single-pixel wide primitive is drawn, (this is device dependant).

A line size of zero is handled as if the pen style had been set to TPenStyle::ENullPen.

Parameters

const TSize &aSize

A line size. The default is 1 pixel.

SetBrushColor(const TRgb &)

virtual void SetBrushColor(const TRgb &aColor)=0;

Description

Sets the brush colour.

The effective brush colour depends on the drawing mode.

Notes:

The brush is used for filling shapes and the background of text boxes. The brush has colour, style, pattern and pattern origin parameters.

If no brush colour has been set, it defaults to white. However the default brush style is null, so when drawing to a window the default appears to be the window's background colour.

Parameters

const TRgb &aColor

An RGB colour for the brush.

See also:

SetBrushStyle(TBrushStyle)

virtual void SetBrushStyle(TBrushStyle aBrushStyle)=0;

Description

Sets the brush style.

Ten brush styles are provided, including six built-in hatching patterns. Note: The brush is used for filling shapes and the background of text boxes. The brush has colour, style, pattern and pattern origin parameters. Note: Use TBrushStyle::ENullBrush to draw the outline of a fillable shape on its own, without filling. Note: If the TBrushStyle::EPatternedBrush style is set, but no bitmap pattern has been selected using CGraphicsContext::UseBrushPattern(const CFbsBitmap *), then the function panics. Note: Hatching lines are done in the current pen colour, set using CGraphicsContext::SetPenColor(const TRgb &). The hatching pattern starts at the brush origin, set using CGraphicsContext::SetBrushOrigin(const TPoint &).

Parameters

CGraphicsContext::TBrushStyle aBrushStyle

A brush style.

See also:

SetBrushOrigin(const TPoint &)

virtual void SetBrushOrigin(const TPoint &aOrigin)=0;

Description

Sets the brush pattern origin.

This specifies the top left-hand corner position for the pattern tile around which copies of the pattern are tiled.

The brush pattern may be a built-in style, or a bitmap. To use a bitmap, the brush must have a pattern set and the brush style must be set to TBrushStyle::EPatternedBrush.

Notes

The brush is used for filling shapes and the background of text boxes. The brush has colour, style, pattern and pattern origin parameters.

If CGraphicsContext::SetBrushOrigin(const TPoint &) is not used, then the origin defaults to (0,0).

This brush origin remains in effect for all fillable shapes drawn subsequently, until a new brush origin is set. Shapes can thus be considered as windows onto a continuous pattern field (covering the whole clipping region of a screen device, or the whole device area of a printer).

Parameters

const TPoint &aOrigin

An origin point for the brush. The coordinates are relative to the rectangle to fill, i.e. specify 0,0 to align the pattern flush with the top and left hand sides of the rectangle.

See also:

UseBrushPattern(const CFbsBitmap *)

virtual void UseBrushPattern(const CFbsBitmap *aBitmap)=0;

Description

Sets the brush pattern to the specified bitmap.

For the brush to actually use the bitmap, TBrushStyle::EPatternedBrush must be used to set the brush style.

When the brush pattern is no longer required, use CGraphicsContext::DiscardBrushPattern() to free up the memory used, if the bitmap is not being shared. If CGraphicsContext::UseBrushPattern(const CFbsBitmap *) is used again without using CGraphicsContext::DiscardBrushPattern() then the previous pattern is discarded automatically.

Notes:

The brush is used for filling shapes and the background of text boxes. The brush has colour, style, pattern and pattern origin parameters.

When loading a bitmap, the bitmap is checked to see if it is already in memory. If the bitmap is already there, then that copy is shared.

The brush does not need to have a pattern set at all. There are several built-in hatching patterns which can be selected using CGraphicsContext::SetBrushStyle(TBrushStyle).

Parameters

const CFbsBitmap *aBitmap

A bitmap pattern for the brush.

See also:

DiscardBrushPattern()

virtual void DiscardBrushPattern()=0;

Description

Discards a non-built-in brush pattern.

This frees up the memory used by the bitmap, if it is not being shared by another process.

Notes:

The brush is used for filling shapes and the background of text boxes. The brush has colour, style, pattern and pattern origin parameters.

If CGraphicsContext::DiscardBrushPattern() is used, with no brush pattern set, then there is no effect.

MoveTo(const TPoint &)

virtual void MoveTo(const TPoint &aPoint)=0;

Description

Sets the drawing point relative to the co-ordinate origin.

A subsequent call to CGraphicsContext::DrawLineTo(const TPoint &) or CGraphicsContext::DrawLineBy(const TPoint &) uses the new drawing point as the start point for the line drawn.

Notes

The operations CGraphicsContext::DrawLine(const TPoint &,const TPoint &), CGraphicsContext::DrawLineTo(const TPoint &), CGraphicsContext::DrawLineBy(const TPoint &) and DrawPolyline() also change the internal drawing position to the last point of the drawn line(s).

The internal drawing position is set to the co-ordinate origin if no drawing or moving operations have yet taken place.

Parameters

const TPoint &aPoint

The new internal drawing position.

MoveBy(const TPoint &)

virtual void MoveBy(const TPoint &aVector)=0;

Description

Sets the drawing point relative to the current co-ordinates.

A subsequent call to CGraphicsContext::DrawLineTo(const TPoint &) or CGraphicsContext::DrawLineBy(const TPoint &) uses the new drawing point as the start point for the line drawn.

Notes

The operations CGraphicsContext::DrawLine(const TPoint &,const TPoint &), CGraphicsContext::DrawLineTo(const TPoint &), CGraphicsContext::DrawLineBy(const TPoint &) and DrawPolyline() also change the internal drawing position to the last point of the drawn line(s).

The internal drawing position is set to the co-ordinate origin if no drawing or moving operations have yet taken place.

Parameters

const TPoint &aVector

The amount by which the internal drawing position is to move.

Plot(const TPoint &)

virtual void Plot(const TPoint &aPoint)=0;

Description

Draws a single point. The point is drawn with the current pen settings using the current drawing mode.

Note:

If the pen size is greater than one pixel, a filled circle of the current pen colour is drawn, with the pen size as the diameter and the plotted point as the centre. If the pen size is an even number of pixels, the extra pixels are drawn below and to the right of the centre.

Parameters

const TPoint &aPoint

The point to be drawn.

See also:

DrawArc(const TRect &,const TPoint &,const TPoint &)

virtual void DrawArc(const TRect &aRect, const TPoint &aStart, const TPoint &aEnd)=0;

Description

Draws an arc.

The arc is considered a portion of an ellipse. The ellipse is defined by the TRect argument.

The pixels at both the start point and the end point are drawn.

The arc itself is the segment of the ellipse drawn in an anti-clockwise direction from the start point to the end point.

Notes:

A rectangle is used in the construction of the ellipse of which the arc is a segment. This rectangle is passed as an argument of type TRect.

A wide line arc is drawn with the pixels distributed either side of a true ellipse, in such a way that the outer edge of the line would touch the edge of the construction rectangle. In other words, the ellipse used to construct it is slightly smaller than that for a single pixel line size.

If the specified start or end point is at the centre of the ellipse, then the line that defines the start or end of the arc defaults to one extending vertically above the centre point.

If the start and end point are the same point or are points on the same line through the ellipse centre then a complete unfilled ellipse is drawn.

Parameters

const TRect &aRect

A rectangle in which to draw the ellipse, of which the arc is a segment.

const TPoint &aStart

The point defining the start of the arc. It defines one end of a line from the geometric centre of the ellipse. The point of intersection between this line and the ellipse defines the start point of the arc.

const TPoint &aEnd

The point defining the end of the arc. It defines one end of a second line from the geometric centre of the ellipse. The point of intersection between this line and the ellipse defines the end point of the arc.

See also:

DrawLine(const TPoint &,const TPoint &)

virtual void DrawLine(const TPoint &aPoint1, const TPoint &aPoint2)=0;

Description

Draws a straight line between two points.

Parameters

const TPoint &aPoint1

The point at the start of the line.

const TPoint &aPoint2

The point at the end of the line.

DrawLineTo(const TPoint &)

virtual void DrawLineTo(const TPoint &aPoint)=0;

Description

Draws a straight line from the current drawing point to a specified point.

Parameters

const TPoint &aPoint

The point at the end of the line.

See also:

DrawLineBy(const TPoint &)

virtual void DrawLineBy(const TPoint &aVector)=0;

Description

Draws a straight line relative to the current drawing point, using a vector.

The start point of the line is the current drawing point. The specified vector is added to the drawing point to give the end point of the line

Parameters

const TPoint &aVector

The vector to add to the current internal drawing position, giving the end point of the line.

See also:

DrawPolyLine(const CArrayFix< TPoint > *)

virtual void DrawPolyLine(const CArrayFix< TPoint > *aPointList)=0;

Description

Draws a polyline from a set of points in an array.

A polyline is a series of concatenated straight lines joining a set of points.

Parameters

const CArrayFix< TPoint > *aPointList

An array containing the points on the polyline.

DrawPolyLine(const TPoint *,TInt)

virtual void DrawPolyLine(const TPoint *aPointList, TInt aNumPoints)=0;

Description

Draws a polyline from a set of points in a list.

A polyline is a series of concatenated straight lines joining a set of points.

Parameters

const TPoint *aPointList

Pointer to a set of points on the polyline.

TInt aNumPoints

Number of points in the list.

DrawPie(const TRect &,const TPoint &,const TPoint &)

virtual void DrawPie(const TRect &aRect, const TPoint &aStart, const TPoint &aEnd)=0;

Description

Draws and fills a pie slice.

The pie slice is an area bounded by:

the arc of an ellipse drawn in an anticlockwise direction from the start point to the end point

the straight line drawn to the start point from the geometric centre of the ellipse.

the straight line to the end point from the geometric centre of the ellipse.

Notes:

A rectangle is used in the construction of the pie slice. This rectangle is passed as an argument of type TRect. The curved edge of the pie slice is an arc of an ellipse constructed within the rectangle.

The line drawn by the pen goes inside the specified rectangle.

The pixels at the end point of the arc are not drawn.

A wide line edged pie slice has the arc drawn with the pixels distributed either side of a true ellipse. This is done in such a way that the outer edge of the line touches the edge of the construction rectangle. In other words, the ellipse used to construct it is slightly smaller than that for a single pixel line size.

If the specified start or end point is at the centre of the ellipse, then the line that defines the start or end of the arc defaults to one extending vertically above the centre point.

If the start and end point are the same point or are points on the same line through the ellipse centre then a complete filled ellipse is drawn. A line is also drawn from the edge to the ellipse centre.

Parameters

const TRect &aRect

A rectangle in which to draw the ellipse bounding the pie slice.

const TPoint &aStart

A point defining the start of the arc bounding the pie slice. It defines one end of a line from the geometrical centre of the ellipse. The point of intersection between this line and the ellipse defines the start point of the arc.

const TPoint &aEnd

A point to define the end of the arc bounding the pie slice. It defines one end of a second line from the geometrical centre of the ellipse. The point of intersection between this line and the ellipse defines the end point of the arc.

DrawEllipse(const TRect &)

virtual void DrawEllipse(const TRect &aRect)=0;

Description

Draws and fills an ellipse.

The ellipse is drawn inside the rectangle defined by the TRect argument. Any rectangle that has odd pixel dimensions, has the bottom right corner trimmed to give even pixel dimensions before the ellipse is constructed.

Note:

A wide outline ellipse is drawn with the pixels distributed either side of a true ellipse, in such a way that the outer edge of the line touches the edge of the construction rectangle. In other words, the ellipse used to construct it is smaller than that for a single pixel line size.

Parameters

const TRect &aRect

The rectangle in which the ellipse is drawn.

DrawRect(const TRect &)

virtual void DrawRect(const TRect &aRect)=0;

Description

Draws and fills a rectangle.

Parameters

const TRect &aRect

The rectangle to be drawn.

DrawRoundRect(const TRect &,const TSize &)

virtual void DrawRoundRect(const TRect &aRect, const TSize &aCornerSize)=0;

Description

Draws and fills a rectangle with rounded corners.

The rounded corners are each constructed as an arc of an ellipse.

The line drawn by the pen, if any, goes inside the specified rectangle.

Notes:

Dotted and dashed pen styles cannot be used for the outline of a rounded rectangle.

If either corner size dimension is greater than half the corresponding rectangle length, the corner size dimension is reduced to half the rectangle size.

Parameters

const TRect &aRect

The rectangle to be drawn.

const TSize &aCornerSize

The dimensions of each corner.

See also:

DrawPolygon(const CArrayFix< TPoint > *,TFillRule)

virtual TInt DrawPolygon(const CArrayFix< TPoint > *aPointList, TFillRule aFillRule=EAlternate)=0;

Description

Draws and fills a polygon defined using an array of points.

The first point in the array defines the start of the first side of the polygon. The second point defines the second vertex (the end point of the first side and the start point of the second side).

The final side of the polygon is drawn using the last point from the array, and the line is drawn to the start point of the first side.

Self-crossing polygons are filled according to the specified fill rule.

Parameters

const CArrayFix< TPoint > *aPointList

An array of points, specifying the vertices of the polygon.

CGraphicsContext::TFillRule aFillRule

The fill rule. By default, this is TFillRule::EAlternate.

Return value

TInt

KErrNone, if successful; otherwise, another of the system-wide error codes.

DrawPolygon(const TPoint *,TInt,TFillRule)

virtual TInt DrawPolygon(const TPoint *aPointList, TInt aNumPoints, TFillRule aFillRule=EAlternate)=0;

Description

Draws and fills a polygon defined using a list of points.

The first point in the list defines the start of the first side of the polygon. The second point defines the second vertex (the end point of the first side and the start point of the second side).

The final side of the polygon is drawn using the last point from the list, and the line is drawn to the start point of the first side.

Self-crossing polygons are filled according to the specified fill rule.

Parameters

const TPoint *aPointList

Pointer to list of points, specifying the vertices of the polygon.

TInt aNumPoints

The number of points in the list.

CGraphicsContext::TFillRule aFillRule

The fill rule. By default this is TFillRule::EAlternate.

Return value

TInt

KErrNone, if successful; otherwise, another of the system-wide error codes.

DrawBitmap(const TPoint &,const CFbsBitmap *)

virtual void DrawBitmap(const TPoint &aTopLeft, const CFbsBitmap *aSource)=0;

Description

Draws a bitmap at the specified point.

The point specifies the top left hand corner of the bitmap. The bitmap is compressed or stretched based on its internally stored size in twips.

Notes:

This member function uses the bitmap's size in twips and does a stretch/compress blit using a linear DDA.

As this function scales the bitmap, it is unavoidably slow. Therefore, where possible, use CBitmapContext::BitBlt(const TPoint &,const CFbsBitmap *) instead. If the bitmap has to be scaled, consider creating another bitmap along with an CFbsBitmapDevice etc, doing CGraphicsContext::DrawBitmap(const TPoint &,const CFbsBitmap *) once and using BitBlt() subsequently.

Note that all bitmaps are clipped to the device boundaries.

Parameters

const TPoint &aTopLeft

The point where the top left pixel of the bitmap is to be drawn

const CFbsBitmap *aSource

A source bitmap

See also:

DrawBitmap(const TRect &,const CFbsBitmap *)

virtual void DrawBitmap(const TRect &aDestRect, const CFbsBitmap *aSource)=0;

Description

Draws a bitmap to fit a given rectangle.

The bitmap is compressed or stretched based on its internally stored size in pixels.

Notes:

This member function uses the bitmap's size in pixels and does a stretch/compress blit using a linear DDA.

As this function scales the bitmap, it is unavoidably slow. Therefore, where possible, use CBitmapContext::BitBlt(const TPoint &,const CFbsBitmap *) instead. If the bitmap has to be scaled, consider creating another bitmap along with an CFbsBitmapDevice etc., doing CGraphicsContext::DrawBitmap(const TPoint &,const CFbsBitmap *) once and using BitBlt() subsequently.

Note that all bitmaps are clipped to the device boundaries.

Parameters

const TRect &aDestRect

The rectangle within which the bitmap is to be drawn.

const CFbsBitmap *aSource

A source bitmap.

See also:

DrawBitmap(const TRect &,const CFbsBitmap *,const TRect &)

virtual void DrawBitmap(const TRect &aDestRect, const CFbsBitmap *aSource, const TRect &aSourceRect)=0;

Description

Draws a specified rectangle of a source bitmap to fit into a given destination rectangle.

Notes:

This member function uses rectangle sizes in pixels and does a stretch/compress blit using a linear DDA.

As this function scales the bitmap, it is unavoidably slow. Therefore, where possible, use CBitmapContext::BitBlt(const TPoint &,const CFbsBitmap *) instead. If the bitmap has to be scaled, consider creating another bitmap along with an CFbsBitmapDevice etc., doing CGraphicsContext::DrawBitmap(const TPoint &,const CFbsBitmap *) once and using BitBlt() subsequently.

Note that all bitmaps are clipped to the device boundaries.

Parameters

const TRect &aDestRect

The rectangle within which the bitmap is to be drawn.

const CFbsBitmap *aSource

A source bitmap.

const TRect &aSourceRect

The rectangle in the source bitmap that is copied to the destination rectangle.

See also:

DrawBitmapMasked(const TRect &,const CFbsBitmap *,const TRect &,const CFbsBitmap *,TBool)

virtual void DrawBitmapMasked(const TRect &aDestRect, const CFbsBitmap *aBitmap, const TRect &aSourceRect, const CFbsBitmap *aMaskBitmap, TBool aInvertMask)=0;

Description

Draws a specified rectangle of a source bitmap to fit into a given rectangle using a given mask.

Notes:

This member function uses rectangle sizes in pixels and does a stretch/compress blit using a linear DDA.

Parameters

const TRect &aDestRect

The rectangle within which the bitmap is to be drawn.

const CFbsBitmap *aBitmap

The source bitmap

const TRect &aSourceRect

The rectangle in the source bitmap that is to be drawn

const CFbsBitmap *aMaskBitmap

The mask to be applied to the source bitmap while drawing

TBool aInvertMask

Flag to indicate if the mask should be inverted.

DrawBitmapMasked(const TRect &,const CWsBitmap *,const TRect &,const CWsBitmap *,TBool)

virtual void DrawBitmapMasked(const TRect &aDestRect, const CWsBitmap *aBitmap, const TRect &aSourceRect, const CWsBitmap *aMaskBitmap, TBool aInvertMask)=0;

Description

Draws a specified rectangle from a wserv bitmap and its mask into another rectangle.

The function compresses/stretches the specified rectangle from the bitmap to fit the destination rectangle. The mask bitmap can be used as either a positive or negative mask. Masked pixels are not mapped to the destination rectangle.

A black and white (binary) mask bitmap is used. With aInvertMask=EFalse, black pixels in the mask bitmap stop corresponding pixels in the source bitmap from being transferred to the destination rectangle. With aInvertMask=ETrue, white pixels in the mask bitmap stop corresponding pixels in the source bitmap from being transferred to the destination rectangle.

Note: this member function uses rectangle sizes in pixels and does a stretch/compress blit using a linear DDA.

Parameters

const TRect &aDestRect

The rectangle within which the masked bitmap is to be drawn.

const CWsBitmap *aBitmap

A source wserv bitmap.

const TRect &aSourceRect

The rectangle in the source bitmap that is copied to the destination rectangle.

const CWsBitmap *aMaskBitmap

A mask wserv bitmap.

TBool aInvertMask

If false, a source pixel that is masked by a black pixel is not transferred to the destination rectangle. If true, then a source pixel that is masked by a white pixel is not transferred to the destination rectangle.

DrawText(const TDesC &,const TPoint &)

virtual void DrawText(const TDesC &aText, const TPoint &aPosition)=0;

Description

Draws text without a surrounding box.

The text baseline is aligned with the y co-ordinate of the specified point, and the left end of the text is aligned with the x co-ordinate of the specified point.

Note:

Text drawing is done with the pen, and is subject to the pen colour. The effective text colour also depends on the drawing mode. The size and style of the text depends on the font used. The layout of the text depends on the justification mode set.

Parameters

const TDesC16 &aText

The text string to be drawn.

const TPoint &aPosition

A point specifying the position of the left end of the text.

DrawText(const TDesC &,const TRect &,TInt,TTextAlign,TInt)

virtual void DrawText(const TDesC &aText, const TRect &aBox, TInt aBaselineOffset, TTextAlign aAlignment=ELeft, TInt aLeftMargin=0)=0;

Description

Draws text inside a box.

The surrounding box is filled with the current brush colour (not a pattern) and is drawn without any outline. The effective box colour depends on the drawing mode - if a brush colour has not been set then the brush defaults to white. The brush may be set to TBrushStyle::ENullBrush if text positioning relative to a box is required, but the box should not be filled.

The font used is that set by CGraphicsContext::UseFont(const CFont *). If no font is in use then a panic occurs.

The alignment of the text within the box can be specified.

Text drawn within a box is also clipped to that box. Unless you intend to clip the top off the text, aBaselineOffset should be greater than or equal to the ascent of the current font.

Offsets:

If the offset is negative, zero, or less than font height this is handled as would be expected, i.e. no text will be seen in the box in the first two instances, and the top of the text will be clipped in the latter case.

Margins:

For the drawing of right-aligned text, aLeftMargin indicates the margin from the right of aBox - where a positive value results in a leftwards offset.

Negative margins can be used to display portions of the text string clipped by the box. A negative margin for left aligned text would clip the start of the text string. Similarly, a negative margin for right aligned text would clip the end of the text string.

If the margin is greater than the width of the box then no text will be visible.

The margin is still honoured for centred text - centred text will not be centred in the box, unless the margin is zero.

Note:

Text drawing is done with the pen, and is thus subject to the pen colour. The effective text colour also depends on the drawing mode. The size and style of the text depends on the used font. The layout of the text depends on the justification mode set.

Parameters

const TDesC16 &aText

The text string to be drawn.

const TRect &aBox

The box to draw the text in.

TInt aBaselineOffset

An offset from the top of the box to the text baseline.

CGraphicsContext::TTextAlign aAlignment

The text alignment mode default is left aligned.

TInt aLeftMargin

The left margin for left-aligned text, or the right margin for right-aligned text default is zero.

DrawText(const TDesC &,const TPoint &,const TDrawTextParam &)

IMPORT_C virtual void DrawText(const TDesC &aText, const TPoint &aPosition, const TDrawTextParam &aParam);

Description

Draws the specified text at the given position using the parameters supplied.

Parameters

const TDesC16 &aText

The text to be drawn.

const TPoint &aPosition

The position to draw the text at.

const CGraphicsContext::TDrawTextParam &aParam

Parameters to use for text drawing.

Reserved()

IMPORT_C virtual void Reserved();

Description

Reserved function for future use.

DrawTextExtended(const TDesC &,const TPoint &,const TDrawTextExtendedParam &)

IMPORT_C TInt DrawTextExtended(const TDesC &aText, const TPoint &aPosition, const TDrawTextExtendedParam &aParam);

Description

Draws text, optionally changing its direction (right-to-left / left-to-right).

Apart from reordering the text, the function is the same as the two parameter variant of CGraphicsContext::DrawText(const TDesC &,const TPoint &), described above.

Parameters

const TDesC16 &aText

The text string to be drawn, optionally changing its direction (right-to-left / left-to-right).

const TPoint &aPosition

A point specifying the position of the left end of the text.

const CGraphicsContext::TDrawTextExtendedParam &aParam

Indicates whether the text should be drawn from right-to-left (for scripts like Arabic and Hebrew) or left-to-right.

Return value

TInt

KErrNoMemory indicates there was an OOM error when reordering the text; KErrNone if the reordering was successful.

MapColors(const TRect &,const TRgb *,TInt,TBool)

virtual void MapColors(const TRect &aRect, const TRgb *aColors, TInt aNumPairs, TBool aMapForwards)=0;

Description

Maps pixels in the specified rectangle. The function tries to match the colour of a pixel with one of the RGB values in an array of RGB pairs. If there is a match, the colour is changed to the value specified in the other RGB in the RGB pair.

Parameters

const TRect &aRect

The rectangle in which pixels are to be mapped.

const TRgb *aColors

A pointer to a set of RGB pairs.

TInt aNumPairs

The number of pairs

TBool aMapForwards

ETrue, mapping is done from the first RGB to the second RGB in the pair; EFalse, mapping is done from the second RGB to the first RGB in the pair.

SetClippingRegion(const TRegion &)

virtual TInt SetClippingRegion(const TRegion &aRegion)=0;

Description

Sets the clipping region.

Parameters

const TRegion &aRegion

Return value

TInt

KErrNone if successful; KErrArgument if the TRegion is not valid; KErrNoMemory if there is insufficient memory.

See also:

CancelClippingRegion()

virtual void CancelClippingRegion()=0;

Description

Cancels the current clipping region.

See also:

DrawTextVertical(const TDesC &,const TPoint &,TBool)

virtual void DrawTextVertical(const TDesC &aText, const TPoint &aPos, TBool aUp)=0;

Description

Draws vertical text in the specified direction.

Parameters

const TDesC16 &aText

The text to be drawn.

const TPoint &aPos

Point of origin of the text baseline.

TBool aUp

Direction. ETrue for up, EFalse for down.

DrawTextVertical(const TDesC &,const TRect &,TInt,TBool,TTextAlign,TInt)

virtual void DrawTextVertical(const TDesC &aText, const TRect &aBox, TInt aBaselineOffset, TBool aUp, TTextAlign aVert=ELeft, TInt aMargin=0)=0;

Description

Draws text vertically in the specified direction, within a box of the specified size.

Parameters

const TDesC16 &aText

The text to be drawn.

const TRect &aBox

The bounding box within which the text should be drawn, and which it is clipped to.

TInt aBaselineOffset

The height of the top of the characters from their text baseline.

TBool aUp

The direction. ETrue for up, EFalse for down.

CGraphicsContext::TTextAlign aVert

The text alignment.

TInt aMargin

The margin.

GetUnderlineMetrics(TInt &,TInt &)

IMPORT_C TInt GetUnderlineMetrics(TInt &aTop, TInt &aBottom);

Description

Parameters

TInt &aTop

TInt &aBottom

Return value

TInt

SetShadowColor(const TRgb &)

IMPORT_C TInt SetShadowColor(const TRgb &aShadowColor);

Description

Set the font's shadow colour

Parameters

const TRgb &aShadowColor

Shadow colour to be set.

Return value

TInt

KErrNone, if successful; otherwise, another of the system-wide errors.

GetShadowColor(TRgb &)

IMPORT_C TInt GetShadowColor(TRgb &aShadowColor);

Description

Get the font's shadow colour

Parameters

TRgb &aShadowColor

Shadow colour of the font returned by the funtion.

Return value

TInt

KErrNone, if successful; otherwise, another of the system-wide errors.

Reserved_CGraphicsContext_2()

protected: IMPORT_C virtual void Reserved_CGraphicsContext_2();

Description

A reserved virtual function for future use.

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Member structures

Struct TDrawTextParam

struct TDrawTextParam;

Description

Parameters to control the drawing of text.

Members

Defined in CGraphicsContext::TDrawTextParam:

Construction and destruction

TDrawTextParam()

inline TDrawTextParam();

Description

Reserved for future use.

Member data

iDirection

CFont::TTextDirection iDirection;

Description

the direction in which to draw the text.

iCharJustNum

TInt iCharJustNum;

Description

number of glyph groups to be letterspaced

iCharJustExcess

TInt iCharJustExcess;

Description

amount of space to be used for letterspacing

iWordJustNum

TInt iWordJustNum;

Description

number of spaces to be used for wordspacing

iWordJustExcess

TInt iWordJustExcess;

Description

amount of space to be used for wordspacing

Struct TDrawTextExtendedParam

struct TDrawTextExtendedParam : public CGraphicsContext::TDrawTextParam;

Description

Parameters for extended text drawing and measuring. It is used by CGraphicsContext::DrawTextExtended(const TDesC &,const TPoint &,const TDrawTextExtendedParam &) to indicate whether text should be drawn from right-to-left or left-to-right.

Derivation

Members

Defined in CGraphicsContext::TDrawTextExtendedParam:

Inherited from CGraphicsContext::TDrawTextParam:

Construction and destruction

TDrawTextExtendedParam()

inline TDrawTextExtendedParam();

Description

Constructor. Initialises iParRightToLeft to EFalse.

Member data

iParRightToLeft

TBool iParRightToLeft;

Description

ETrue if the text direction is right-to-left (for scripts like Arabic and Hebrew). EFalse if left-to-right.

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Member enumerations

Enum TTextAlign

TTextAlign

Description

Text alignment.

ELeft

Text is left-aligned.

ECenter

Text is centred.

ERight

Text is right-aligned.

Enum TDrawModeComponents

TDrawModeComponents

Description

Drawing mode components. This enum is not intended to be used directly, but provides components for the easy specification of drawing modes in the TDrawMode enum.

EInvertScreen

1

EXor

2

EOr

4

EAnd

8

ELogicalOp

14

EInvertPen

16

EPenmode

32

EWriteAlpha

64

Enum TDrawMode

TDrawMode

Description

Drawing modes.

This enum builds on the drawing mode components in the TDrawModeComponents enum.

If the pen colour is p, brush colour is b and screen colour is s, the effect of TDrawMode::EDrawModeAND is P=p&s and B=b&s. In other words, the effective colour of the pen on the screen, P, is that produced by the bitwise ANDing of the current screen colour and the current pen colour. The effect is similar for the effective brush colour, B.

The effective pen and brush colour are given in the table using the key Inputs: pen colour is p, brush colour is b and screen colour is s Outputs: effective brush colour is B, effective pen colour is P.

Some notes on using EDrawModeWriteAlpha:-

See also:

EDrawModeAND

Bitwise ANDs the pen and brush colours with the screen colour. P=p&s, B=b&s

EDrawModeNOTAND

Inverts the pen and brush colours before ANDing. P=(~p)&s, B=(~b)&s

EDrawModePEN

Uses both pen and brush colour as they are. P=p, B=b

EDrawModeANDNOT

Inverts the screen colour before ANDing. P=p&(~s), B=b&(~s)

EDrawModeXOR

Bitwise XORs the pen and brush colours with the screen colour. P=p^s, B=b^s

EDrawModeOR

Bitwise ORs the pen and brush colours with the screen colour. P=p|s, B=b|s

EDrawModeNOTANDNOT

Inverts the screen and pen and brush colours before ANDing. P=(~p)&(~s), B=(~b)&(~s)

EDrawModeNOTXOR

Inverts the pen and brush colours before XORing. P=(~p)^s, B=(~b)^s

EDrawModeNOTSCREEN

Inverts the colour of each pixel that is drawn over, (pen and brush attributes are ignored). P=~s, B=~s

EDrawModeNOTOR

Inverts the pen and brush colours before ORing. P=(~p)|s, B=(~b)|s

EDrawModeNOTPEN

Inverts the pen and brush colours. P=~p, B=~b

EDrawModeORNOT

Inverts the screen, pen and brush colours before ORing. P=p|(~s), B=b|(~s)

EDrawModeNOTORNOT

NOT OR NOT mode. P=(~p)|(~s), B=(~b)|(~s)

EDrawModeWriteAlpha

Writes alpha information in the source directly into the destination, rather than blending.

Enum TPenStyle

TPenStyle

Description

Pen styles. The screen pattern unit in each definition below describes the pattern drawn by the line 1 represents a pixel drawn, 0 represents a pixel that is not affected.

ENullPen

The pen does not draw. Screen pattern unit = 00...

ESolidPen

A solid line (default). Screen pattern unit = 11...

EDottedPen

A dotted line. Screen pattern unit = 1000...

EDashedPen

A dashed line. Screen pattern unit = 111000...

EDotDashPen

A line of alternating dashes and dots. Screen pattern unit = 1111001100...

EDotDotDashPen

A line of alternating single dashes and pairs of dots. Screen pattern unit = 11110011001100...

Enum TBrushStyle

TBrushStyle

Description

Brush styles.

ENullBrush

The brush fill has no effect (default).

ESolidBrush

The brush fills with a solid single colour, determined by CGraphicsContext::SetBrushColor(const TRgb &) and the drawing mode.

EPatternedBrush

The brush fills with a selected bitmap pattern, set by CGraphicsContext::UseBrushPattern(const CFbsBitmap *).

EVerticalHatchBrush

The brush fills with vertical hatching lines going from top to bottom.

EForwardDiagonalHatchBrush

The brush fills with diagonal hatching lines going from bottom left to top right.

EHorizontalHatchBrush

The brush fills with horizontal hatching lines going from left to right.

ERearwardDiagonalHatchBrush

The brush fills with rearward diagonal hatching lines going from top left to bottom right.

ESquareCrossHatchBrush

The brush fills with horizontal and vertical hatching lines going from left to right plus lines going from top to bottom giving the effect of a grid of small squares

EDiamondCrossHatchBrush

The brush fills with forward diagonal and rearward diagonal hatching lines going from bottom left to top right plus lines going from top left to bottom right giving the effect of a grid of small diamonds.

Enum TFillRule

TFillRule

Description

Rules used to fill self crossing polygons.

The filling of a polygon proceeds as follows: for a given point in the polygon, then

if the rule is TFillRule::EAlternate (default) and it has an odd winding number, then fill the surrounding area.

if the rule is TFillRule::EWinding and it has a winding number greater than zero, then fill the surrounding area.

EAlternate

Only fill areas with odd winding numbers.

EWinding

Fill areas with winding numbers greater than zero.

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