Paths

Paths — Creating paths and manipulating path data

Functions

Types and Values

Object Hierarchy


Description

Paths are the most basic drawing tools and are primarily used to implicitly generate simple masks.

Functions

cairo_copy_path ()

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==NULL and num_data==0), if either of the following conditions hold:

  1. If there is insufficient memory to copy the path. In this case path->status will be set to CAIRO_STATUS_NO_MEMORY.
  2. If cr is already in an error state. In this case path->status will contain the same status that would be returned by cairo_status().

Parameters

cr

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.

Since 1.0


cairo_copy_path_flat ()

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==NULL and num_data==0), if either of the following conditions hold:

  1. If there is insufficient memory to copy the path. In this case path->status will be set to CAIRO_STATUS_NO_MEMORY.
  2. If cr is already in an error state. In this case path->status will contain the same status that would be returned by cairo_status().

Parameters

cr

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.

Since 1.0


cairo_path_destroy ()

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 After a call to cairo_path_destroy() the path pointer is no longer valid and should not be used further.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.

Parameters

path

a path previously returned by either cairo_copy_path() or cairo_copy_path_flat().

 

Since 1.0


cairo_append_path ()

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.

Parameters

cr

a cairo context

 

path

path to be appended

 

Since 1.0


cairo_has_current_point ()

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.

Parameters

cr

a cairo context

 

Returns

whether a current point is defined.

Since 1.6


cairo_get_current_point ()

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().

Parameters

cr

a cairo context

 

x

return value for X coordinate of the current point

 

y

return value for Y coordinate of the current point

 

Since 1.0


cairo_new_path ()

void
cairo_new_path (cairo_t *cr);

Clears the current path. After this call there will be no path and no current point.

Parameters

cr

a cairo context

 

Since 1.0


cairo_new_sub_path ()

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().

Parameters

cr

a cairo context

 

Since 1.2


cairo_close_path ()

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.

Parameters

cr

a cairo context

 

Since 1.0


cairo_arc ()

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);

Parameters

cr

a cairo context

 

xc

X position of the center of the arc

 

yc

Y position of the center of the arc

 

radius

the radius of the arc

 

angle1

the start angle, in radians

 

angle2

the end angle, in radians

 

Since 1.0


cairo_arc_negative ()

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.

Parameters

cr

a cairo context

 

xc

X position of the center of the arc

 

yc

Y position of the center of the arc

 

radius

the radius of the arc

 

angle1

the start angle, in radians

 

angle2

the end angle, in radians

 

Since 1.0


cairo_curve_to ()

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 ).

Parameters

cr

a cairo context

 

x1

the X coordinate of the first control point

 

y1

the Y coordinate of the first control point

 

x2

the X coordinate of the second control point

 

y2

the Y coordinate of the second control point

 

x3

the X coordinate of the end of the curve

 

y3

the Y coordinate of the end of the curve

 

Since 1.0


cairo_line_to ()

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 ).

Parameters

cr

a cairo context

 

x

the X coordinate of the end of the new line

 

y

the Y coordinate of the end of the new line

 

Since 1.0


cairo_move_to ()

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 ).

Parameters

cr

a cairo context

 

x

the X coordinate of the new position

 

y

the Y coordinate of the new position

 

Since 1.0


cairo_rectangle ()

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);

Parameters

cr

a cairo context

 

x

the X coordinate of the top left corner of the rectangle

 

y

the Y coordinate to the top left corner of the rectangle

 

width

the width of the rectangle

 

height

the height of the rectangle

 

Since 1.0


cairo_glyph_path ()

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().

Parameters

cr

a cairo context

 

glyphs

array of glyphs to show

 

num_glyphs

number of glyphs to show

 

Since 1.0


cairo_text_path ()

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.

Parameters

cr

a cairo context

 

utf8

a NUL-terminated string of text encoded in UTF-8, or NULL

 

Since 1.0


cairo_rel_curve_to ()

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.

Parameters

cr

a cairo context

 

dx1

the X offset to the first control point

 

dy1

the Y offset to the first control point

 

dx2

the X offset to the second control point

 

dy2

the Y offset to the second control point

 

dx3

the X offset to the end of the curve

 

dy3

the Y offset to the end of the curve

 

Since 1.0


cairo_rel_line_to ()

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.

Parameters

cr

a cairo context

 

dx

the X offset to the end of the new line

 

dy

the Y offset to the end of the new line

 

Since 1.0


cairo_rel_move_to ()

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.

Parameters

cr

a cairo context

 

dx

the X offset

 

dy

the Y offset

 

Since 1.0


cairo_path_extents ()

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().

Parameters

cr

a cairo context

 

x1

left of the resulting extents

 

y1

top of the resulting extents

 

x2

right of the resulting extents

 

y2

bottom of the resulting extents

 

Since 1.6

Types and Values

cairo_path_t

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.

Members

cairo_status_t status;

the current error status

 

cairo_path_data_t *data;

the elements in the path

 

int num_data;

the number of elements in the data array

 

Since 1.0


union cairo_path_data_t

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 cairo_path_t:

     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.

Since 1.0


enum 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.

Members

CAIRO_PATH_MOVE_TO

A move-to operation, since 1.0

 

CAIRO_PATH_LINE_TO

A line-to operation, since 1.0

 

CAIRO_PATH_CURVE_TO

A curve-to operation, since 1.0

 

CAIRO_PATH_CLOSE_PATH

A close-path operation, since 1.0

 

Since 1.0