How to draw lines

The following example code demonstrates how to:

• draw a line a single pixel wide

• draw a line with a pen 3 pixels wide

• draw a line with a pen 30 pixels wide and 30 pixels high

• draw a thin dotted line

• draw a thin dot-dash line

The code assumes a common pair of pre-defined points are used for each of the line drawing examples:

...
// set up a pair of points for drawing diagonal lines
TPoint startPoint(50,50);
TPoint endPoint(590,190);
...

You can draw a thin line diagonally across the screen using DrawLine(). This illustrates how thin a single pixel width line is, and the visible stepping:

...
// draw a thin line from top left to bottom right 
gc.DrawLine(startPoint,endPoint);
...

• The line width is a single pixel by default.

1. Use SetPenSize() to increase the pen size to 3 pixels.

2. Use DrawLine() to draw a wide line diagonally across the screen.

// Set up a "bold" size for the pen tip to (default is 1,1)
TSize penSizeBold(3,3);
...
// draw a line from top left to bottom right 
gc.SetPenSize(penSizeBold);
gc.DrawLine(startPoint,endPoint);
...

1. Use SetPenWidth() to set the pen width to 30 pixels wide.

2. Use DrawLine() to draw a 30 pixel wide line, (x dimension), diagonally across the screen.

// Set up a "fat" size for the pen tip
TSize penSizeFat(30,30);
...
// draw a rather wide line from top left to bottom right,
// illustrating rounded ends and their clipping
gc.SetPenWidth(penSizeFat);
gc.DrawLine(startPoint,endPoint);
...

• the ends of wide lines are rounded

• the effective width of the line depends on the size of the pen tip, which is elliptical

• the rounded end of a wide line may be clipped to the window, even though the end point is within the window

1. Use SetPenStyle() to set the style of the pen to dotted.

2. Use DrawLine() to draw a thin dotted line diagonally across the screen.

...
// draw a dotted line from top left to bottom right 
gc.SetPenStyle(CGraphicsContext::EDottedPen);
gc.DrawLine(startPoint,endPoint);
...

• The pen style remains in effect until changed by another call to SetPenStyle() or the graphics context is reset to its default settings.

1. Use SetPenStyle() to set the style of the pen to dot-dashed.

2. Use DrawLine() to draw a thin dot-dashed line diagonally across the screen.

...
// draw a dot dash line from top left to bottom right 
gc.SetPenStyle(CGraphicsContext::EDotDashPen);
gc.DrawLine(startPoint,endPoint);
...