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Graphics Contexts

Graphics Contexts — Objects to encapsulate drawing properties

Types and Values

Object Hierarchy

    GObject
    ╰── GdkGC

Includes

#include <gdk/gdk.h>

Description

All drawing operations in GDK take a graphics context (GC) argument. A graphics context encapsulates information about the way things are drawn, such as the foreground color or line width. By using graphics contexts, the number of arguments to each drawing call is greatly reduced, and communication overhead is minimized, since identical arguments do not need to be passed repeatedly.

Most values of a graphics context can be set at creation time by using gdk_gc_new_with_values(), or can be set one-by-one using functions such as gdk_gc_set_foreground(). A few of the values in the GC, such as the dash pattern, can only be set by the latter method.

Functions

gdk_gc_new ()

GdkGC *
gdk_gc_new (GdkDrawable *drawable);

gdk_gc_new has been deprecated since version 2.22 and should not be used in newly-written code.

Use Cairo for rendering.

Create a new graphics context with default values.

Parameters

drawable

a GdkDrawable. The created GC must always be used with drawables of the same depth as this one.

 

Returns

the new graphics context.


gdk_gc_new_with_values ()

GdkGC *
gdk_gc_new_with_values (GdkDrawable *drawable,
                        GdkGCValues *values,
                        GdkGCValuesMask values_mask);

gdk_gc_new_with_values has been deprecated since version 2.22 and should not be used in newly-written code.

Use Cairo for rendering.

Create a new GC with the given initial values.

Parameters

drawable

a GdkDrawable. The created GC must always be used with drawables of the same depth as this one.

 

values

a structure containing initial values for the GC.

 

values_mask

a bit mask indicating which fields in values are set.

 

Returns

the new graphics context.


gdk_gc_get_screen ()

GdkScreen *
gdk_gc_get_screen (GdkGC *gc);

gdk_gc_get_screen is deprecated and should not be used in newly-written code.

Gets the GdkScreen for which gc was created

Parameters

gc

a GdkGC.

 

Returns

the GdkScreen for gc .

Since: 2.2


gdk_gc_ref ()

GdkGC *
gdk_gc_ref (GdkGC *gc);

gdk_gc_ref has been deprecated since version 2.0 and should not be used in newly-written code.

Use g_object_ref() instead.

Deprecated function; use g_object_ref() instead.

Parameters

gc

a GdkGC

 

Returns

the gc.


gdk_gc_unref ()

void
gdk_gc_unref (GdkGC *gc);

gdk_gc_unref has been deprecated since version 2.0 and should not be used in newly-written code.

Use g_object_unref() instead.

Decrement the reference count of gc .

Parameters

gc

a GdkGC

 

gdk_gc_set_values ()

void
gdk_gc_set_values (GdkGC *gc,
                   GdkGCValues *values,
                   GdkGCValuesMask values_mask);

gdk_gc_set_values has been deprecated since version 2.22 and should not be used in newly-written code.

Use Cairo for rendering.

Sets attributes of a graphics context in bulk. For each flag set in values_mask , the corresponding field will be read from values and set as the new value for gc . If you're only setting a few values on gc , calling individual "setter" functions is likely more convenient.

Parameters

gc

a GdkGC

 

values

struct containing the new values

 

values_mask

mask indicating which struct fields are to be used

 

gdk_gc_get_values ()

void
gdk_gc_get_values (GdkGC *gc,
                   GdkGCValues *values);

gdk_gc_get_values has been deprecated since version 2.22 and should not be used in newly-written code.

Use Cairo for rendering.

Retrieves the current values from a graphics context. Note that only the pixel values of the values->foreground and values->background are filled, use gdk_colormap_query_color() to obtain the rgb values if you need them.

Parameters

gc

a GdkGC.

 

values

the GdkGCValues structure in which to store the results.

 

gdk_gc_set_foreground ()

void
gdk_gc_set_foreground (GdkGC *gc,
                       const GdkColor *color);

gdk_gc_set_foreground has been deprecated since version 2.22 and should not be used in newly-written code.

Use gdk_cairo_set_source_color() to use a GdkColor as the source in Cairo.

Sets the foreground color for a graphics context. Note that this function uses color->pixel , use gdk_gc_set_rgb_fg_color() to specify the foreground color as red, green, blue components.

Parameters

gc

a GdkGC.

 

color

the new foreground color.

 

gdk_gc_set_background ()

void
gdk_gc_set_background (GdkGC *gc,
                       const GdkColor *color);

gdk_gc_set_background has been deprecated since version 2.22 and should not be used in newly-written code.

Use gdk_cairo_set_source_color() to use a GdkColor as the source in Cairo. Note that if you want to draw a background and a foreground in Cairo, you need to call drawing functions (like cairo_fill()) twice.

Sets the background color for a graphics context. Note that this function uses color->pixel , use gdk_gc_set_rgb_bg_color() to specify the background color as red, green, blue components.

Parameters

gc

a GdkGC.

 

color

the new background color.

 

gdk_gc_set_rgb_fg_color ()

void
gdk_gc_set_rgb_fg_color (GdkGC *gc,
                         const GdkColor *color);

gdk_gc_set_rgb_fg_color has been deprecated since version 2.22 and should not be used in newly-written code.

Use gdk_cairo_set_source_color() instead.

Set the foreground color of a GC using an unallocated color. The pixel value for the color will be determined using GdkRGB. If the colormap for the GC has not previously been initialized for GdkRGB, then for pseudo-color colormaps (colormaps with a small modifiable number of colors), a colorcube will be allocated in the colormap.

Calling this function for a GC without a colormap is an error.

Parameters

gc

a GdkGC

 

color

an unallocated GdkColor.

 

gdk_gc_set_rgb_bg_color ()

void
gdk_gc_set_rgb_bg_color (GdkGC *gc,
                         const GdkColor *color);

gdk_gc_set_rgb_bg_color has been deprecated since version 2.22 and should not be used in newly-written code.

Use gdk_cairo_set_source_color() instead.

Set the background color of a GC using an unallocated color. The pixel value for the color will be determined using GdkRGB. If the colormap for the GC has not previously been initialized for GdkRGB, then for pseudo-color colormaps (colormaps with a small modifiable number of colors), a colorcube will be allocated in the colormap.

Calling this function for a GC without a colormap is an error.

Parameters

gc

a GdkGC

 

color

an unallocated GdkColor.

 

gdk_gc_set_font ()

void
gdk_gc_set_font (GdkGC *gc,
                 GdkFont *font);

gdk_gc_set_font is deprecated and should not be used in newly-written code.

Sets the font for a graphics context. (Note that all text-drawing functions in GDK take a font argument; the value set here is used when that argument is NULL.)

Parameters

gc

a GdkGC.

 

font

the new font.

 

gdk_gc_set_function ()

void
gdk_gc_set_function (GdkGC *gc,
                     GdkFunction function);

gdk_gc_set_function has been deprecated since version 2.22 and should not be used in newly-written code.

Use cairo_set_operator() with Cairo.

Determines how the current pixel values and the pixel values being drawn are combined to produce the final pixel values.

Parameters

gc

a GdkGC.

 

function

the GdkFunction to use

 

gdk_gc_set_fill ()

void
gdk_gc_set_fill (GdkGC *gc,
                 GdkFill fill);

gdk_gc_set_fill has been deprecated since version 2.22 and should not be used in newly-written code.

You can achieve tiling in Cairo by using cairo_pattern_set_extend() on the source. For stippling, see the deprecation comments on gdk_gc_set_stipple().

Set the fill mode for a graphics context.

Parameters

gc

a GdkGC.

 

fill

the new fill mode.

 

gdk_gc_set_tile ()

void
gdk_gc_set_tile (GdkGC *gc,
                 GdkPixmap *tile);

gdk_gc_set_tile has been deprecated since version 2.22 and should not be used in newly-written code.

The following code snippet sets a tiling GdkPixmap as the source in Cairo:

1
cairo_pattern_set_extend (cairo_get_source (cr), CAIRO_EXTEND_REPEAT);]|

Set a tile pixmap for a graphics context. This will only be used if the fill mode is GDK_TILED.

Parameters

gc

a GdkGC.

 

tile

the new tile pixmap.

 

gdk_gc_set_stipple ()

void
gdk_gc_set_stipple (GdkGC *gc,
                    GdkPixmap *stipple);

gdk_gc_set_stipple has been deprecated since version 2.22 and should not be used in newly-written code.

Stippling has no direct replacement in Cairo. If you want to achieve an identical look, you can use the stipple bitmap as a mask. Most likely, this involves rendering the source to an intermediate surface using cairo_push_group() first, so that you can then use cairo_mask() to achieve the stippled look.

Set the stipple bitmap for a graphics context. The stipple will only be used if the fill mode is GDK_STIPPLED or GDK_OPAQUE_STIPPLED.

Parameters

gc

a GdkGC.

 

stipple

the new stipple bitmap.

 

gdk_gc_set_ts_origin ()

void
gdk_gc_set_ts_origin (GdkGC *gc,
                      gint x,
                      gint y);

gdk_gc_set_ts_origin has been deprecated since version 2.22 and should not be used in newly-written code.

You can set the origin for tiles and stipples in Cairo by changing the source's matrix using cairo_pattern_set_matrix(). Or you can specify it with gdk_cairo_set_source_pixmap() as shown in the example for gdk_gc_set_tile().

Set the origin when using tiles or stipples with the GC. The tile or stipple will be aligned such that the upper left corner of the tile or stipple will coincide with this point.

Parameters

gc

a GdkGC.

 

x

the x-coordinate of the origin.

 

y

the y-coordinate of the origin.

 

gdk_gc_set_clip_origin ()

void
gdk_gc_set_clip_origin (GdkGC *gc,
                        gint x,
                        gint y);

gdk_gc_set_clip_origin has been deprecated since version 2.22 and should not be used in newly-written code.

Use cairo_translate() before applying the clip path in Cairo.

Sets the origin of the clip mask. The coordinates are interpreted relative to the upper-left corner of the destination drawable of the current operation.

Parameters

gc

a GdkGC.

 

x

the x-coordinate of the origin.

 

y

the y-coordinate of the origin.

 

gdk_gc_set_clip_mask ()

void
gdk_gc_set_clip_mask (GdkGC *gc,
                      GdkBitmap *mask);

gdk_gc_set_clip_mask has been deprecated since version 2.22 and should not be used in newly-written code.

Use cairo_mask() instead.

Sets the clip mask for a graphics context from a bitmap. The clip mask is interpreted relative to the clip origin. (See gdk_gc_set_clip_origin()).

Parameters

gc

the GdkGC.

 

mask

a bitmap.

 

gdk_gc_set_clip_rectangle ()

void
gdk_gc_set_clip_rectangle (GdkGC *gc,
                           const GdkRectangle *rectangle);

gdk_gc_set_clip_rectangle has been deprecated since version 2.22 and should not be used in newly-written code.

Use cairo_rectangle() and cairo_clip() in Cairo.

Sets the clip mask for a graphics context from a rectangle. The clip mask is interpreted relative to the clip origin. (See gdk_gc_set_clip_origin()).

Parameters

gc

a GdkGC.

 

rectangle

the rectangle to clip to.

 

gdk_gc_set_clip_region ()

void
gdk_gc_set_clip_region (GdkGC *gc,
                        const GdkRegion *region);

gdk_gc_set_clip_region has been deprecated since version 2.22 and should not be used in newly-written code.

Use gdk_cairo_region() and cairo_clip() in Cairo.

Sets the clip mask for a graphics context from a region structure. The clip mask is interpreted relative to the clip origin. (See gdk_gc_set_clip_origin()).

Parameters

gc

a GdkGC.

 

region

the GdkRegion.

 

gdk_gc_set_subwindow ()

void
gdk_gc_set_subwindow (GdkGC *gc,
                      GdkSubwindowMode mode);

gdk_gc_set_subwindow has been deprecated since version 2.22 and should not be used in newly-written code.

There is no replacement. If you need to control subwindows, you must use drawing operations of the underlying window system manually. Cairo will always use GDK_INCLUDE_INFERIORS on sources and masks and GDK_CLIP_BY_CHILDREN on targets.

Sets how drawing with this GC on a window will affect child windows of that window.

Parameters

gc

a GdkGC.

 

mode

the subwindow mode.

 

gdk_gc_set_exposures ()

void
gdk_gc_set_exposures (GdkGC *gc,
                      gboolean exposures);

gdk_gc_set_exposures has been deprecated since version 2.22 and should not be used in newly-written code.

There is no replacement. If you need to control exposures, you must use drawing operations of the underlying window system or use gdk_window_invalidate_rect(). Cairo will never generate exposures.

Sets whether copying non-visible portions of a drawable using this graphics context generate exposure events for the corresponding regions of the destination drawable. (See gdk_draw_drawable()).

Parameters

gc

a GdkGC.

 

exposures

if TRUE, exposure events will be generated.

 

gdk_gc_set_line_attributes ()

void
gdk_gc_set_line_attributes (GdkGC *gc,
                            gint line_width,
                            GdkLineStyle line_style,
                            GdkCapStyle cap_style,
                            GdkJoinStyle join_style);

gdk_gc_set_line_attributes has been deprecated since version 2.22 and should not be used in newly-written code.

Use the Cairo functions cairo_set_line_width(), cairo_set_line_join(), cairo_set_line_cap() and cairo_set_dash() to affect the stroking behavior in Cairo. Keep in mind that the default attributes of a cairo_t are different from the default attributes of a GdkGC.

Sets various attributes of how lines are drawn. See the corresponding members of GdkGCValues for full explanations of the arguments.

Parameters

gc

a GdkGC.

 

line_width

the width of lines.

 

line_style

the dash-style for lines.

 

cap_style

the manner in which the ends of lines are drawn.

 

join_style

the in which lines are joined together.

 

gdk_gc_set_dashes ()

void
gdk_gc_set_dashes (GdkGC *gc,
                   gint dash_offset,
                   gint8 dash_list[],
                   gint n);

gdk_gc_set_dashes has been deprecated since version 2.22 and should not be used in newly-written code.

Use cairo_set_dash() to set the dash in Cairo.

Sets the way dashed-lines are drawn. Lines will be drawn with alternating on and off segments of the lengths specified in dash_list . The manner in which the on and off segments are drawn is determined by the line_style value of the GC. (This can be changed with gdk_gc_set_line_attributes().)

The dash_offset defines the phase of the pattern, specifying how many pixels into the dash-list the pattern should actually begin.

Parameters

gc

a GdkGC.

 

dash_offset

the phase of the dash pattern.

 

dash_list

an array of dash lengths.

 

n

the number of elements in dash_list .

 

gdk_gc_copy ()

void
gdk_gc_copy (GdkGC *dst_gc,
             GdkGC *src_gc);

gdk_gc_copy has been deprecated since version 2.22 and should not be used in newly-written code.

Use Cairo for drawing. cairo_save() and cairo_restore() can be helpful in cases where you'd have copied a GdkGC.

Copy the set of values from one graphics context onto another graphics context.

Parameters

dst_gc

the destination graphics context.

 

src_gc

the source graphics context.

 

gdk_gc_set_colormap ()

void
gdk_gc_set_colormap (GdkGC *gc,
                     GdkColormap *colormap);

gdk_gc_set_colormap has been deprecated since version 2.22 and should not be used in newly-written code.

There is no replacement. Cairo handles colormaps automatically, so there is no need to care about them.

Sets the colormap for the GC to the given colormap. The depth of the colormap's visual must match the depth of the drawable for which the GC was created.

Parameters

gc

a GdkGC

 

colormap

a GdkColormap

 

gdk_gc_get_colormap ()

GdkColormap *
gdk_gc_get_colormap (GdkGC *gc);

gdk_gc_get_colormap has been deprecated since version 2.22 and should not be used in newly-written code.

There is no replacement. Cairo handles colormaps automatically, so there is no need to care about them.

Retrieves the colormap for a given GC, if it exists. A GC will have a colormap if the drawable for which it was created has a colormap, or if a colormap was set explicitely with gdk_gc_set_colormap.

Parameters

gc

a GdkGC

 

Returns

the colormap of gc , or NULL if gc doesn't have one.


gdk_gc_offset ()

void
gdk_gc_offset (GdkGC *gc,
               gint x_offset,
               gint y_offset);

gdk_gc_offset has been deprecated since version 2.22 and should not be used in newly-written code.

There is no direct replacement, as this is just a convenience function for gdk_gc_set_ts_origin and gdk_gc_set_clip_origin().

Offset attributes such as the clip and tile-stipple origins of the GC so that drawing at x - x_offset, y - y_offset with the offset GC has the same effect as drawing at x, y with the original GC.

Parameters

gc

a GdkGC

 

x_offset

amount by which to offset the GC in the X direction

 

y_offset

amount by which to offset the GC in the Y direction

 

Types and Values

GdkGC

typedef struct _GdkGC GdkGC;

The GdkGC structure represents a graphics context. It is an opaque structure with no user-visible elements.


struct GdkGCValues

struct GdkGCValues {
  GdkColor	    foreground;
  GdkColor	    background;
  GdkFont	   *font;
  GdkFunction	    function;
  GdkFill	    fill;
  GdkPixmap	   *tile;
  GdkPixmap	   *stipple;
  GdkPixmap	   *clip_mask;
  GdkSubwindowMode  subwindow_mode;
  gint		    ts_x_origin;
  gint		    ts_y_origin;
  gint		    clip_x_origin;
  gint		    clip_y_origin;
  gint		    graphics_exposures;
  gint		    line_width;
  GdkLineStyle	    line_style;
  GdkCapStyle	    cap_style;
  GdkJoinStyle	    join_style;
};

The GdkGCValues structure holds a set of values used to create or modify a graphics context.

Members

GdkColor foreground;

the foreground color. Note that gdk_gc_get_values() only sets the pixel value.

 

GdkColor background;

the background color. Note that gdk_gc_get_values() only sets the pixel value.

 

GdkFont *font;

the default font.

 

GdkFunction function;

the bitwise operation used when drawing.

 

GdkFill fill;

the fill style.

 

GdkPixmap *tile;

the tile pixmap.

 

GdkPixmap *stipple;

the stipple bitmap.

 

GdkPixmap *clip_mask;

the clip mask bitmap.

 

GdkSubwindowMode subwindow_mode;

the subwindow mode.

 

gint ts_x_origin;

the x origin of the tile or stipple.

 

gint ts_y_origin;

the y origin of the tile or stipple.

 

gint clip_x_origin;

the x origin of the clip mask.

 

gint clip_y_origin;

the y origin of the clip mask.

 

gint graphics_exposures;

whether graphics exposures are enabled.

 

gint line_width;

the line width.

 

GdkLineStyle line_style;

the way dashed lines are drawn.

 

GdkCapStyle cap_style;

the way the ends of lines are drawn.

 

GdkJoinStyle join_style;

the way joins between lines are drawn.

 

enum GdkGCValuesMask

A set of bit flags used to indicate which fields GdkGCValues structure are set.

Members

GDK_GC_FOREGROUND

the foreground is set.

 

GDK_GC_BACKGROUND

the background is set.

 

GDK_GC_FONT

the font is set.

 

GDK_GC_FUNCTION

the function is set.

 

GDK_GC_FILL

the fill is set.

 

GDK_GC_TILE

the tile is set.

 

GDK_GC_STIPPLE

the stipple is set.

 

GDK_GC_CLIP_MASK

the clip_mask is set.

 

GDK_GC_SUBWINDOW

the subwindow_mode is set.

 

GDK_GC_TS_X_ORIGIN

the ts_x_origin is set.

 

GDK_GC_TS_Y_ORIGIN

the ts_y_origin is set.

 

GDK_GC_CLIP_X_ORIGIN

the clip_x_origin is set.

 

GDK_GC_CLIP_Y_ORIGIN

the clip_y_origin is set.

 

GDK_GC_EXPOSURES

the graphics_exposures is set.

 

GDK_GC_LINE_WIDTH

the line_width is set.

 

GDK_GC_LINE_STYLE

the line_style is set.

 

GDK_GC_CAP_STYLE

the cap_style is set.

 

GDK_GC_JOIN_STYLE

the join_style is set.

 

enum GdkFunction

Determines how the bit values for the source pixels are combined with the bit values for destination pixels to produce the final result. The sixteen values here correspond to the 16 different possible 2x2 truth tables. Only a couple of these values are usually useful; for colored images, only GDK_COPY, GDK_XOR and GDK_INVERT are generally useful. For bitmaps, GDK_AND and GDK_OR are also useful.

Members

GDK_COPY

dst = src

 

GDK_INVERT

dst = NOT dst

 

GDK_XOR

dst = src XOR dst

 

GDK_CLEAR

dst = 0

 

GDK_AND

dst = dst AND src

 

GDK_AND_REVERSE

dst = src AND (NOT dst)

 

GDK_AND_INVERT

dst = (NOT src) AND dst

 

GDK_NOOP

dst = dst

 

GDK_OR

dst = src OR dst

 

GDK_EQUIV

dst = (NOT src) XOR dst

 

GDK_OR_REVERSE

dst = src OR (NOT dst)

 

GDK_COPY_INVERT

dst = NOT src

 

GDK_OR_INVERT

dst = (NOT src) OR dst

 

GDK_NAND

dst = (NOT src) OR (NOT dst)

 

GDK_NOR

dst = (NOT src) AND (NOT dst)

 

GDK_SET

dst = 1

 

gdk_gc_destroy

#define gdk_gc_destroy                 g_object_unref

gdk_gc_destroy is deprecated and should not be used in newly-written code.

Use g_object_unref() instead

This function is obsolete and should not be used.


enum GdkFill

Determines how primitives are drawn.

Members

GDK_SOLID

draw with the foreground color.

 

GDK_TILED

draw with a tiled pixmap.

 

GDK_STIPPLED

draw using the stipple bitmap. Pixels corresponding to bits in the stipple bitmap that are set will be drawn in the foreground color; pixels corresponding to bits that are not set will be left untouched.

 

GDK_OPAQUE_STIPPLED

draw using the stipple bitmap. Pixels corresponding to bits in the stipple bitmap that are set will be drawn in the foreground color; pixels corresponding to bits that are not set will be drawn with the background color.

 

enum GdkSubwindowMode

Determines how drawing onto a window will affect child windows of that window.

Members

GDK_CLIP_BY_CHILDREN

only draw onto the window itself.

 

GDK_INCLUDE_INFERIORS

draw onto the window and child windows.

 

enum GdkLineStyle

Determines how lines are drawn.

Members

GDK_LINE_SOLID

lines are drawn solid.

 

GDK_LINE_ON_OFF_DASH

even segments are drawn; odd segments are not drawn.

 

GDK_LINE_DOUBLE_DASH

even segments are normally. Odd segments are drawn in the background color if the fill style is GDK_SOLID, or in the background color masked by the stipple if the fill style is GDK_STIPPLED.

 

enum GdkCapStyle

Determines how the end of lines are drawn.

Members

GDK_CAP_NOT_LAST

the same as GDK_CAP_BUTT for lines of non-zero width. for zero width lines, the final point on the line will not be drawn.

 

GDK_CAP_BUTT

the ends of the lines are drawn squared off and extending to the coordinates of the end point.

 

GDK_CAP_ROUND

the ends of the lines are drawn as semicircles with the diameter equal to the line width and centered at the end point.

 

GDK_CAP_PROJECTING

the ends of the lines are drawn squared off and extending half the width of the line beyond the end point.

 

enum GdkJoinStyle

Determines how the joins between segments of a polygon are drawn.

Members

GDK_JOIN_MITER

the sides of each line are extended to meet at an angle.

 

GDK_JOIN_ROUND

the sides of the two lines are joined by a circular arc.

 

GDK_JOIN_BEVEL

the sides of the two lines are joined by a straight line which makes an equal angle with each line.

 
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