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Cairo: A Vector Graphics Library | ![]() |
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Top | Description |
cairo_path_t; union cairo_path_data_t; enum cairo_path_data_type_t; cairo_path_t * cairo_copy_path (cairo_t *cr); cairo_path_t * cairo_copy_path_flat (cairo_t *cr); void cairo_path_destroy (cairo_path_t *path); void cairo_append_path (cairo_t *cr, const cairo_path_t *path); cairo_bool_t cairo_has_current_point (cairo_t *cr); void cairo_get_current_point (cairo_t *cr, double *x, double *y); void cairo_new_path (cairo_t *cr); void cairo_new_sub_path (cairo_t *cr); void cairo_close_path (cairo_t *cr); void cairo_arc (cairo_t *cr, double xc, double yc, double radius, double angle1, double angle2); void cairo_arc_negative (cairo_t *cr, double xc, double yc, double radius, double angle1, double angle2); void cairo_curve_to (cairo_t *cr, double x1, double y1, double x2, double y2, double x3, double y3); void cairo_line_to (cairo_t *cr, double x, double y); void cairo_move_to (cairo_t *cr, double x, double y); void cairo_rectangle (cairo_t *cr, double x, double y, double width, double height); void cairo_glyph_path (cairo_t *cr, const cairo_glyph_t *glyphs, int num_glyphs); void cairo_text_path (cairo_t *cr, const char *utf8); void cairo_rel_curve_to (cairo_t *cr, double dx1, double dy1, double dx2, double dy2, double dx3, double dy3); void cairo_rel_line_to (cairo_t *cr, double dx, double dy); void cairo_rel_move_to (cairo_t *cr, double dx, double dy); void cairo_path_extents (cairo_t *cr, double *x1, double *y1, double *x2, double *y2);
Paths are the most basic drawing tools and are primarily used to implicitly generate simple masks.
typedef struct { cairo_status_t status; cairo_path_data_t *data; int num_data; } cairo_path_t;
A data structure for holding a path. This data structure serves as
the return value for cairo_copy_path()
and
cairo_copy_path_flat()
as well the input value for
cairo_append_path()
.
See cairo_path_data_t for hints on how to iterate over the actual data within the path.
The num_data member gives the number of elements in the data array. This number is larger than the number of independent path portions (defined in cairo_path_data_type_t), since the data includes both headers and coordinates for each portion.
cairo_status_t |
the current error status |
cairo_path_data_t * |
the elements in the path |
int |
the number of elements in the data array |
union cairo_path_data_t { struct { cairo_path_data_type_t type; int length; } header; struct { double x, y; } point; };
cairo_path_data_t is used to represent the path data inside a cairo_path_t.
The data structure is designed to try to balance the demands of efficiency and ease-of-use. A path is represented as an array of cairo_path_data_t, which is a union of headers and points.
Each portion of the path is represented by one or more elements in the array, (one header followed by 0 or more points). The length value of the header is the number of array elements for the current portion including the header, (ie. length == 1 + # of points), and where the number of points for each element type is as follows:
%CAIRO_PATH_MOVE_TO: 1 point %CAIRO_PATH_LINE_TO: 1 point %CAIRO_PATH_CURVE_TO: 3 points %CAIRO_PATH_CLOSE_PATH: 0 points
The semantics and ordering of the coordinate values are consistent
with cairo_move_to()
, cairo_line_to()
, cairo_curve_to()
, and
cairo_close_path()
.
Here is sample code for iterating through a ""
int i; cairo_path_t *path; cairo_path_data_t *data; path = cairo_copy_path (cr); for (i=0; i < path->num_data; i += path->data[i].header.length) { data = &path->data[i]; switch (data->header.type) { case CAIRO_PATH_MOVE_TO: do_move_to_things (data[1].point.x, data[1].point.y); break; case CAIRO_PATH_LINE_TO: do_line_to_things (data[1].point.x, data[1].point.y); break; case CAIRO_PATH_CURVE_TO: do_curve_to_things (data[1].point.x, data[1].point.y, data[2].point.x, data[2].point.y, data[3].point.x, data[3].point.y); break; case CAIRO_PATH_CLOSE_PATH: do_close_path_things (); break; } } cairo_path_destroy (path);
As of cairo 1.4, cairo does not mind if there are more elements in
a portion of the path than needed. Such elements can be used by
users of the cairo API to hold extra values in the path data
structure. For this reason, it is recommended that applications
always use data->header.length
to
iterate over the path data, instead of hardcoding the number of
elements for each element type.
typedef enum _cairo_path_data_type { CAIRO_PATH_MOVE_TO, CAIRO_PATH_LINE_TO, CAIRO_PATH_CURVE_TO, CAIRO_PATH_CLOSE_PATH } cairo_path_data_type_t;
cairo_path_data_t is used to describe the type of one portion of a path when represented as a cairo_path_t. See cairo_path_data_t for details.
cairo_path_t * cairo_copy_path (cairo_t *cr);
Creates a copy of the current path and returns it to the user as a cairo_path_t. See cairo_path_data_t for hints on how to iterate over the returned data structure.
This function will always return a valid pointer, but the result
will have no data (data==
and
NULL
num_data==0
), if either of the following
conditions hold:
path->status
will be set to
CAIRO_STATUS_NO_MEMORY
.cr
is already in an error state. In this case
path->status
will contain the same status that
would be returned by cairo_status()
.
In either case, path->status
will be set to
CAIRO_STATUS_NO_MEMORY
(regardless of what the error status in
cr
might have been).
|
a cairo context |
Returns : |
the copy of the current path. The caller owns the
returned object and should call cairo_path_destroy() when finished
with it.
|
cairo_path_t * cairo_copy_path_flat (cairo_t *cr);
Gets a flattened copy of the current path and returns it to the user as a cairo_path_t. See cairo_path_data_t for hints on how to iterate over the returned data structure.
This function is like cairo_copy_path()
except that any curves
in the path will be approximated with piecewise-linear
approximations, (accurate to within the current tolerance
value). That is, the result is guaranteed to not have any elements
of type CAIRO_PATH_CURVE_TO
which will instead be replaced by a
series of CAIRO_PATH_LINE_TO
elements.
This function will always return a valid pointer, but the result
will have no data (data==
and
NULL
num_data==0
), if either of the following
conditions hold:
path->status
will be set to
CAIRO_STATUS_NO_MEMORY
.cr
is already in an error state. In this case
path->status
will contain the same status that
would be returned by cairo_status()
.
|
a cairo context |
Returns : |
the copy of the current path. The caller owns the
returned object and should call cairo_path_destroy() when finished
with it.
|
void cairo_path_destroy (cairo_path_t *path);
Immediately releases all memory associated with path
. After a call
to cairo_path_destroy()
the path
pointer is no longer valid and
should not be used further.
Note: cairo_path_destroy()
should only be called with a
pointer to a cairo_path_t returned by a cairo function. Any path
that is created manually (ie. outside of cairo) should be destroyed
manually as well.
|
a path previously returned by either cairo_copy_path() or
cairo_copy_path_flat() .
|
void cairo_append_path (cairo_t *cr, const cairo_path_t *path);
Append the path
onto the current path. The path
may be either the
return value from one of cairo_copy_path()
or
cairo_copy_path_flat()
or it may be constructed manually. See
cairo_path_t for details on how the path data structure should be
initialized, and note that path->status
must be
initialized to CAIRO_STATUS_SUCCESS
.
|
a cairo context |
|
path to be appended |
cairo_bool_t cairo_has_current_point (cairo_t *cr);
Returns whether a current point is defined on the current path.
See cairo_get_current_point()
for details on the current point.
|
a cairo context |
Returns : |
whether a current point is defined. |
Since 1.6
void cairo_get_current_point (cairo_t *cr, double *x, double *y);
Gets the current point of the current path, which is conceptually the final point reached by the path so far.
The current point is returned in the user-space coordinate
system. If there is no defined current point or if cr
is in an
error status, x
and y
will both be set to 0.0. It is possible to
check this in advance with cairo_has_current_point()
.
Most path construction functions alter the current point. See the
following for details on how they affect the current point:
cairo_new_path()
, cairo_new_sub_path()
,
cairo_append_path()
, cairo_close_path()
,
cairo_move_to()
, cairo_line_to()
, cairo_curve_to()
,
cairo_rel_move_to()
, cairo_rel_line_to()
, cairo_rel_curve_to()
,
cairo_arc()
, cairo_arc_negative()
, cairo_rectangle()
,
cairo_text_path()
, cairo_glyph_path()
, cairo_stroke_to_path()
.
Some functions use and alter the current point but do not
otherwise change current path:
cairo_show_text()
.
Some functions unset the current path and as a result, current point:
cairo_fill()
, cairo_stroke()
.
|
a cairo context |
|
return value for X coordinate of the current point |
|
return value for Y coordinate of the current point |
void cairo_new_path (cairo_t *cr);
Clears the current path. After this call there will be no path and no current point.
|
a cairo context |
void cairo_new_sub_path (cairo_t *cr);
Begin a new sub-path. Note that the existing path is not affected. After this call there will be no current point.
In many cases, this call is not needed since new sub-paths are
frequently started with cairo_move_to()
.
A call to cairo_new_sub_path()
is particularly useful when
beginning a new sub-path with one of the cairo_arc()
calls. This
makes things easier as it is no longer necessary to manually
compute the arc's initial coordinates for a call to
cairo_move_to()
.
|
a cairo context |
Since 1.2
void cairo_close_path (cairo_t *cr);
Adds a line segment to the path from the current point to the
beginning of the current sub-path, (the most recent point passed to
cairo_move_to()
), and closes this sub-path. After this call the
current point will be at the joined endpoint of the sub-path.
The behavior of cairo_close_path()
is distinct from simply calling
cairo_line_to()
with the equivalent coordinate in the case of
stroking. When a closed sub-path is stroked, there are no caps on
the ends of the sub-path. Instead, there is a line join connecting
the final and initial segments of the sub-path.
If there is no current point before the call to cairo_close_path()
,
this function will have no effect.
Note: As of cairo version 1.2.4 any call to cairo_close_path()
will
place an explicit MOVE_TO element into the path immediately after
the CLOSE_PATH element, (which can be seen in cairo_copy_path()
for
example). This can simplify path processing in some cases as it may
not be necessary to save the "last move_to point" during processing
as the MOVE_TO immediately after the CLOSE_PATH will provide that
point.
|
a cairo context |
void cairo_arc (cairo_t *cr, double xc, double yc, double radius, double angle1, double angle2);
Adds a circular arc of the given radius
to the current path. The
arc is centered at (xc
, yc
), begins at angle1
and proceeds in
the direction of increasing angles to end at angle2
. If angle2
is
less than angle1
it will be progressively increased by 2*M_PI
until it is greater than angle1
.
If there is a current point, an initial line segment will be added
to the path to connect the current point to the beginning of the
arc. If this initial line is undesired, it can be avoided by
calling cairo_new_sub_path()
before calling cairo_arc()
.
Angles are measured in radians. An angle of 0.0 is in the direction
of the positive X axis (in user space). An angle of M_PI
/2.0 radians
(90 degrees) is in the direction of the positive Y axis (in
user space). Angles increase in the direction from the positive X
axis toward the positive Y axis. So with the default transformation
matrix, angles increase in a clockwise direction.
(To convert from degrees to radians, use degrees * (M_PI /
180.)
.)
This function gives the arc in the direction of increasing angles;
see cairo_arc_negative()
to get the arc in the direction of
decreasing angles.
The arc is circular in user space. To achieve an elliptical arc,
you can scale the current transformation matrix by different
amounts in the X and Y directions. For example, to draw an ellipse
in the box given by x
, y
, width
, height
:
cairo_save (cr); cairo_translate (cr, x + width / 2., y + height / 2.); cairo_scale (cr, width / 2., height / 2.); cairo_arc (cr, 0., 0., 1., 0., 2 * M_PI); cairo_restore (cr);
|
a cairo context |
|
X position of the center of the arc |
|
Y position of the center of the arc |
|
the radius of the arc |
|
the start angle, in radians |
|
the end angle, in radians |
void cairo_arc_negative (cairo_t *cr, double xc, double yc, double radius, double angle1, double angle2);
Adds a circular arc of the given radius
to the current path. The
arc is centered at (xc
, yc
), begins at angle1
and proceeds in
the direction of decreasing angles to end at angle2
. If angle2
is
greater than angle1
it will be progressively decreased by 2*M_PI
until it is less than angle1
.
See cairo_arc()
for more details. This function differs only in the
direction of the arc between the two angles.
|
a cairo context |
|
X position of the center of the arc |
|
Y position of the center of the arc |
|
the radius of the arc |
|
the start angle, in radians |
|
the end angle, in radians |
void cairo_curve_to (cairo_t *cr, double x1, double y1, double x2, double y2, double x3, double y3);
Adds a cubic Bézier spline to the path from the current point to
position (x3
, y3
) in user-space coordinates, using (x1
, y1
) and
(x2
, y2
) as the control points. After this call the current point
will be (x3
, y3
).
If there is no current point before the call to cairo_curve_to()
this function will behave as if preceded by a call to
cairo_move_to(cr
, x1
, y1
).
|
a cairo context |
|
the X coordinate of the first control point |
|
the Y coordinate of the first control point |
|
the X coordinate of the second control point |
|
the Y coordinate of the second control point |
|
the X coordinate of the end of the curve |
|
the Y coordinate of the end of the curve |
void cairo_line_to (cairo_t *cr, double x, double y);
Adds a line to the path from the current point to position (x
, y
)
in user-space coordinates. After this call the current point
will be (x
, y
).
If there is no current point before the call to cairo_line_to()
this function will behave as cairo_move_to(cr
, x
, y
).
|
a cairo context |
|
the X coordinate of the end of the new line |
|
the Y coordinate of the end of the new line |
void cairo_move_to (cairo_t *cr, double x, double y);
Begin a new sub-path. After this call the current point will be (x
,
y
).
|
a cairo context |
|
the X coordinate of the new position |
|
the Y coordinate of the new position |
void cairo_rectangle (cairo_t *cr, double x, double y, double width, double height);
Adds a closed sub-path rectangle of the given size to the current
path at position (x
, y
) in user-space coordinates.
This function is logically equivalent to:
cairo_move_to (cr, x, y); cairo_rel_line_to (cr, width, 0); cairo_rel_line_to (cr, 0, height); cairo_rel_line_to (cr, -width, 0); cairo_close_path (cr);
|
a cairo context |
|
the X coordinate of the top left corner of the rectangle |
|
the Y coordinate to the top left corner of the rectangle |
|
the width of the rectangle |
|
the height of the rectangle |
void cairo_glyph_path (cairo_t *cr, const cairo_glyph_t *glyphs, int num_glyphs);
Adds closed paths for the glyphs to the current path. The generated
path if filled, achieves an effect similar to that of
cairo_show_glyphs()
.
|
a cairo context |
|
array of glyphs to show |
|
number of glyphs to show |
void cairo_text_path (cairo_t *cr, const char *utf8);
Adds closed paths for text to the current path. The generated
path if filled, achieves an effect similar to that of
cairo_show_text()
.
Text conversion and positioning is done similar to cairo_show_text()
.
Like cairo_show_text()
, After this call the current point is
moved to the origin of where the next glyph would be placed in
this same progression. That is, the current point will be at
the origin of the final glyph offset by its advance values.
This allows for chaining multiple calls to to cairo_text_path()
without having to set current point in between.
Note: The cairo_text_path()
function call is part of what the cairo
designers call the "toy" text API. It is convenient for short demos
and simple programs, but it is not expected to be adequate for
serious text-using applications. See cairo_glyph_path()
for the
"real" text path API in cairo.
|
a cairo context |
|
a NUL-terminated string of text encoded in UTF-8, or NULL
|
void cairo_rel_curve_to (cairo_t *cr, double dx1, double dy1, double dx2, double dy2, double dx3, double dy3);
Relative-coordinate version of cairo_curve_to()
. All offsets are
relative to the current point. Adds a cubic Bézier spline to the
path from the current point to a point offset from the current
point by (dx3
, dy3
), using points offset by (dx1
, dy1
) and
(dx2
, dy2
) as the control points. After this call the current
point will be offset by (dx3
, dy3
).
Given a current point of (x, y), cairo_rel_curve_to(cr
, dx1
,
dy1
, dx2
, dy2
, dx3
, dy3
) is logically equivalent to
cairo_curve_to(cr
, x+dx1
, y+dy1
, x+dx2
, y+dy2
, x+dx3
, y+dy3
).
It is an error to call this function with no current point. Doing
so will cause cr
to shutdown with a status of
CAIRO_STATUS_NO_CURRENT_POINT
.
|
a cairo context |
|
the X offset to the first control point |
|
the Y offset to the first control point |
|
the X offset to the second control point |
|
the Y offset to the second control point |
|
the X offset to the end of the curve |
|
the Y offset to the end of the curve |
void cairo_rel_line_to (cairo_t *cr, double dx, double dy);
Relative-coordinate version of cairo_line_to()
. Adds a line to the
path from the current point to a point that is offset from the
current point by (dx
, dy
) in user space. After this call the
current point will be offset by (dx
, dy
).
Given a current point of (x, y), cairo_rel_line_to(cr
, dx
, dy
)
is logically equivalent to cairo_line_to(cr
, x + dx
, y + dy
).
It is an error to call this function with no current point. Doing
so will cause cr
to shutdown with a status of
CAIRO_STATUS_NO_CURRENT_POINT
.
|
a cairo context |
|
the X offset to the end of the new line |
|
the Y offset to the end of the new line |
void cairo_rel_move_to (cairo_t *cr, double dx, double dy);
Begin a new sub-path. After this call the current point will offset
by (x
, y
).
Given a current point of (x, y), cairo_rel_move_to(cr
, dx
, dy
)
is logically equivalent to cairo_move_to(cr
, x + dx
, y + dy
).
It is an error to call this function with no current point. Doing
so will cause cr
to shutdown with a status of
CAIRO_STATUS_NO_CURRENT_POINT
.
|
a cairo context |
|
the X offset |
|
the Y offset |
void cairo_path_extents (cairo_t *cr, double *x1, double *y1, double *x2, double *y2);
Computes a bounding box in user-space coordinates covering the points on the current path. If the current path is empty, returns an empty rectangle ((0,0), (0,0)). Stroke parameters, fill rule, surface dimensions and clipping are not taken into account.
Contrast with cairo_fill_extents()
and cairo_stroke_extents()
which
return the extents of only the area that would be "inked" by
the corresponding drawing operations.
The result of cairo_path_extents()
is defined as equivalent to the
limit of cairo_stroke_extents()
with CAIRO_LINE_CAP_ROUND
as the
line width approaches 0.0, (but never reaching the empty-rectangle
returned by cairo_stroke_extents()
for a line width of 0.0).
Specifically, this means that zero-area sub-paths such as
cairo_move_to()
;cairo_line_to()
segments, (even degenerate cases
where the coordinates to both calls are identical), will be
considered as contributing to the extents. However, a lone
cairo_move_to()
will not contribute to the results of
cairo_path_extents()
.
|
a cairo context |
|
left of the resulting extents |
|
top of the resulting extents |
|
right of the resulting extents |
|
bottom of the resulting extents |
Since 1.6