Cairo drawing utils

Cairo drawing utils — Auxiliary and impedance matching functions for Cairo drawing

Functions

void gwy_cairo_set_source_rgba ()
cairo_pattern_t * gwy_cairo_pattern_create_gradient ()
void gwy_cairo_checker_rectangle ()
void gwy_cairo_line ()
void gwy_cairo_ellipse ()
void gwy_cairo_cross ()
void gwy_cairo_times ()
void gwy_cairo_asterisk ()
void gwy_cairo_square ()
void gwy_cairo_diamond ()
void gwy_cairo_triangle_up ()
void gwy_cairo_triangle_down ()
void gwy_cairo_triangle_left ()
void gwy_cairo_triangle_right ()
void gwy_cairo_draw_symbol ()
void gwy_cairo_draw_symbols ()
void gwy_cairo_draw_line ()
void gwy_cairo_region_add_line ()
void gwy_cairo_region_add_crectangle ()
void gwy_cairo_region_add_erectangle ()
void gwy_cairo_region_add_ellipse ()
void gwy_cairo_region_add_layout ()
void gwy_cairo_draw_or_add_thin_line ()
void gwy_cairo_draw_or_add_layout ()

Types and Values

enum GwySymbolType
enum GwyLineStyle

Includes

#include <libgwyui/gwyui.h>

Description

Drawing primitives for simple geometrical shapes such as gwy_cairo_cross() or gwy_cairo_triangle_up() are namely useful for drawing markes and symbols on graphs because they are visually centered on given coordinates. Nevertheless, the sizes are given as natural parameters. Use gwy_cairo_draw_symbol() to visually uniform sizes.

Functions

gwy_cairo_set_source_rgba()

void
gwy_cairo_set_source_rgba (cairo_t *cr,
                           const GwyRGBA *rgba);

Sets the source patter of a Cairo context to GwyRGBA color.

This is a convenience function that is exactly equivalent to

1
 
cairo_set_source_rgba(cr, rgba->r, rgba->g, rgba->b, rgba->a);

Parameters

cr

A Cairo drawing context.

  

rgba

An RGBA colour.

  

gwy_cairo_pattern_create_gradient()

cairo_pattern_t *
gwy_cairo_pattern_create_gradient (GwyGradient *gradient,
                                   GtkPositionType towards,
                                   gboolean use_alpha);

Creates a linear Cairo pattern corresponding to a false colour gradient.

The pattern is always along the interval [0,1] in either horizontal or vertical direction and either towards 1 or towards 0, depending on the value of towards .

Parameters

gradient

A false colour gradient.

  

towards

Gradient direction in the plane.

  

use_alpha

TRUE to use the alpha components and create a possibly semitransparent pattern; FALSE to render all colours with full opacity.

  

Returns

A newly created linear Cairo pattern.

[transfer full]

gwy_cairo_checker_rectangle()

void
gwy_cairo_checker_rectangle (cairo_t *cr,
                             const GwyRGBA *even,
                             const GwyRGBA *odd,
                             gint width,
                             gint height,
                             gint size);

gwy_cairo_line()

void
gwy_cairo_line (cairo_t *cr,
                gdouble xfrom,
                gdouble yfrom,
                gdouble xto,
                gdouble yto);

Adds a straight line subpath to a Cairo context.

A new subpath is started, but it is not terminated. Use cairo_new_sub_path() or other subpath-terminating primitive afterwards if necessary. All parameters are in user coordinates.

This function does cairo_move_to() and cairo_line_to() in a single call, simplifying common line drawing a bit.

Parameters

cr

A Cairo drawing context.

  

xfrom

X-coordinate of start point of the line.

  

yfrom

Y-coordinate of start point of the line.

  

xto

X-coordinate of end point of the line.

  

yto

Y-coordinate of end point of the line.

  

gwy_cairo_ellipse()

void
gwy_cairo_ellipse (cairo_t *cr,
                   gdouble x,
                   gdouble y,
                   gdouble xr,
                   gdouble yr);

Adds a closed elliptical subpath to a Cairo context.

A new subpath is started and closed. The ellipse is approximated using Bezier curves, on the other hand, it does not rely on transformations. All parameters are in user coordinates.

Parameters

cr

A Cairo drawing context.

  

x

Centre x-coordinate.

  

y

Centre y-coordinate.

  

xr

Horizontal half-axis length.

  

yr

Vertical half-axis length.

  

gwy_cairo_cross()

void
gwy_cairo_cross (cairo_t *cr,
                 gdouble x,
                 gdouble y,
                 gdouble halfside);

Adds a cross-shaped subpath to a Cairo context.

A new subpath is started and terminated. All parameters are in user coordinates.

Parameters

cr

A Cairo drawing context.

  

x

Centre x-coordinate.

  

y

Centre y-coordinate.

  

halfside

Length of the cross arm (from centre to end), i.e. half of the side of the smallest square containing the cross.

  

gwy_cairo_times()

void
gwy_cairo_times (cairo_t *cr,
                 gdouble x,
                 gdouble y,
                 gdouble halfside);

Adds a times-shaped subpath to a Cairo context.

A new subpath is started and terminated. All parameters are in user coordinates.

Parameters

cr

A Cairo drawing context.

  

x

Centre x-coordinate.

  

y

Centre y-coordinate.

  

halfside

Half of the side of the smallest square containing the cross.

  

gwy_cairo_asterisk()

void
gwy_cairo_asterisk (cairo_t *cr,
                    gdouble x,
                    gdouble y,
                    gdouble halfside);

Adds a rightward pointing triangle-shaped subpath to a Cairo context.

A new subpath is started and terminated. All parameters are in user coordinates.

Parameters

cr

A Cairo drawing context.

  

x

Centre x-coordinate.

  

y

Centre y-coordinate.

  

halfside

Half of the side of the containing square.

  

gwy_cairo_square()

void
gwy_cairo_square (cairo_t *cr,
                  gdouble x,
                  gdouble y,
                  gdouble halfside);

Adds a square-shaped subpath to a Cairo context.

A new subpath is started and closed. All parameters are in user coordinates.

Parameters

cr

A Cairo drawing context.

  

x

Centre x-coordinate.

  

y

Centre y-coordinate.

  

halfside

Half of the side of the square.

  

gwy_cairo_diamond()

void
gwy_cairo_diamond (cairo_t *cr,
                   gdouble x,
                   gdouble y,
                   gdouble halfside);

Adds a diamond-shaped subpath to a Cairo context.

A new subpath is started and closed. All parameters are in user coordinates.

Parameters

cr

A Cairo drawing context.

  

x

Centre x-coordinate.

  

y

Centre y-coordinate.

  

halfside

Half of the side of the containing square.

  

gwy_cairo_triangle_up()

void
gwy_cairo_triangle_up (cairo_t *cr,
                       gdouble x,
                       gdouble y,
                       gdouble halfside);

Adds an upward pointing triangle-shaped subpath to a Cairo context.

A new subpath is started and closed. All parameters are in user coordinates.

Parameters

cr

A Cairo drawing context.

  

x

Centre x-coordinate.

  

y

Centre y-coordinate.

  

halfside

Half of the side of the containing square.

  

gwy_cairo_triangle_down()

void
gwy_cairo_triangle_down (cairo_t *cr,
                         gdouble x,
                         gdouble y,
                         gdouble halfside);

Adds a downward pointing triangle-shaped subpath to a Cairo context.

A new subpath is started and closed. All parameters are in user coordinates.

Parameters

cr

A Cairo drawing context.

  

x

Centre x-coordinate.

  

y

Centre y-coordinate.

  

halfside

Half of the side of the containing square.

  

gwy_cairo_triangle_left()

void
gwy_cairo_triangle_left (cairo_t *cr,
                         gdouble x,
                         gdouble y,
                         gdouble halfside);

Adds a leftward pointing triangle-shaped subpath to a Cairo context.

A new subpath is started and closed. All parameters are in user coordinates.

Parameters

cr

A Cairo drawing context.

  

x

Centre x-coordinate.

  

y

Centre y-coordinate.

  

halfside

Half of the side of the containing square.

  

gwy_cairo_triangle_right()

void
gwy_cairo_triangle_right (cairo_t *cr,
                          gdouble x,
                          gdouble y,
                          gdouble halfside);

Adds a rightward pointing triangle-shaped subpath to a Cairo context.

A new subpath is started and closed. All parameters are in user coordinates.

Parameters

cr

A Cairo drawing context.

  

x

Centre x-coordinate.

  

y

Centre y-coordinate.

  

halfside

Half of the side of the containing square.

  

gwy_cairo_draw_symbol()

void
gwy_cairo_draw_symbol (cairo_t *cr,
                       gdouble x,
                       gdouble y,
                       GwySymbolType symbol_type,
                       gdouble size,
                       const GwyRGBA *color);

Draws a graph symbol on a drawable.

Consider using gwy_cairo_draw_symbols() if you are drawing many symbols.

Parameters

cr

Cairo context.

  

x

X coordinate of the point.

  

y

Y coordinate of the point.

  

symbol_type

Symbol type.

  

size

Symbol size.

  

color

Symbol color. If NULL, the color is not set.

[nullable]

gwy_cairo_draw_symbols()

void
gwy_cairo_draw_symbols (cairo_t *cr,
                        const GwyXY *coords,
                        guint n,
                        GwySymbolType symbol_type,
                        gdouble size,
                        const GwyRGBA *color);

Draws multiple graph symbols.

Parameters

cr

Cairo context.

  

coords

Point coordinates, as concatenated pairs (x, y).

  

n

The number of points.

  

symbol_type

Symbol type.

  

size

Symbol size.

  

color

Symbol color. If NULL, the color is not set.

[nullable]

gwy_cairo_draw_line()

void
gwy_cairo_draw_line (cairo_t *cr,
                     gdouble x_from,
                     gdouble y_from,
                     gdouble x_to,
                     gdouble y_to,
                     GwyLineStyle line_style,
                     gdouble width,
                     const GwyRGBA *color);

Draws a line segment on a drawable.

Parameters

cr

Cairo context.

  

x_from

x coordinate of the start point of the line

  

y_from

y coordinate of the start point of the line

  

x_to

x coordinate of the end point of the line

  

y_to

y coordinate of the end point of the line

  

line_style

Line style.

  

width

Line width.

  

color

Line color. If NULL, the color is not set.

[nullable]

gwy_cairo_region_add_line()

void
gwy_cairo_region_add_line (cairo_region_t *region,
                           gdouble xfrom,
                           gdouble yfrom,
                           gdouble xto,
                           gdouble yto,
                           gdouble lw);

Updates a Cairo region by adding the area containing an arbitrary straight line.

Parameters

region

Cario region to update.

  

xfrom

X-coordinate of start point of the line.

  

yfrom

Y-coordinate of start point of the line.

  

xto

X-coordinate of end point of the line.

  

yto

Y-coordinate of end point of the line.

  

lw

Line width.

  

gwy_cairo_region_add_crectangle()

void
gwy_cairo_region_add_crectangle (cairo_region_t *region,
                                 gdouble xc,
                                 gdouble yc,
                                 gdouble xr,
                                 gdouble yr,
                                 gdouble lw);

Updates a Cairo region by adding the area containing a rectangle given the centre and half-size.

Parameters

region

Cario region to update.

  

xc

X-coordinate of rectangle centre.

  

yc

Y-coordinate of rectangle centre.

  

xr

Half of X-size of the rectangle.

  

yr

Half of y-size of the rectangle.

  

lw

Line width.

  

gwy_cairo_region_add_erectangle()

void
gwy_cairo_region_add_erectangle (cairo_region_t *region,
                                 gdouble x1,
                                 gdouble y1,
                                 gdouble x2,
                                 gdouble y2,
                                 gdouble lw);

Updates a Cairo region by adding the area containing a rectangle given two opposite corners.

Parameters

region

Cario region to update.

  

x1

X-coordinate of one rectangle corner.

  

y1

Y-coordinate of one rectangle corner.

  

x2

X-coordinate of the opposite rectangle corner.

  

y2

Y-coordinate of the opposite rectangle corner.

  

lw

Line width.

  

gwy_cairo_region_add_ellipse()

void
gwy_cairo_region_add_ellipse (cairo_region_t *region,
                              gdouble xc,
                              gdouble yc,
                              gdouble xr,
                              gdouble yr,
                              gdouble lw);

Updates a Cairo region by adding the area containing an ellipse given the centre and semi-axes.

Parameters

region

Cario region to update.

  

xc

X-coordinate of ellipse centre.

  

yc

Y-coordinate of ellipse centre.

  

xr

X-semiaxis of the ellipse.

  

yr

Y-semiaxis of the ellipse.

  

lw

Line width.

  

gwy_cairo_region_add_layout()

void
gwy_cairo_region_add_layout (cairo_region_t *region,
                             PangoLayout *layout,
                             gdouble x,
                             gdouble y);

Updates a Cairo region by adding the area containing a Pango layout.

The area corresponds to the text being drawn with pango_cairo_show_layout() after moving to (x , y ).

Parameters

region

Cario region to update.

  

layout

Pango layout to render at context's current coordinates.

  

x

Text origin x-coordinate.

  

y

Text origin y-coordinate.

  

gwy_cairo_draw_or_add_thin_line()

void
gwy_cairo_draw_or_add_thin_line (cairo_t *cr,
                                 cairo_region_t *region,
                                 gdouble xfrom,
                                 gdouble yfrom,
                                 gdouble xto,
                                 gdouble yto);

Draws a line and/or updates a Cairo region to add the line's area.

This is a convenience function wrapping gwy_cairo_line() and gwy_cairo_region_add_line(). Either one or both are called, depending on which of cr and region are non-NULL. The line is must be thin.

Parameters

cr

A Cairo drawing context, or NULL.

  

region

Cario region to update, or NULL.

  

xfrom

X-coordinate of start point of the line.

  

yfrom

Y-coordinate of start point of the line.

  

xto

X-coordinate of end point of the line.

  

yto

Y-coordinate of end point of the line.

  

gwy_cairo_draw_or_add_layout()

void
gwy_cairo_draw_or_add_layout (cairo_t *cr,
                              cairo_region_t *region,
                              PangoLayout *layout,
                              gdouble x,
                              gdouble y);

Renders a Pango layout and/or updates a Cairo region to add the text's area.

The coordinates have the effect of cairo_move_to() to the specified point. Normally, this function would not be called in the middle of drawing a path. Still, be aware the Cairo context position is modified.

This is a convenience function wrapping pango_cairo_show_layout() and gwy_cairo_region_add_layout(). Either one or both are called, depending on which of cr and region are non-NULL.

Parameters

cr

A Cairo drawing context, or NULL.

  

region

Cario region to update, or NULL.

  

layout

Pango layout to render at context's current coordinates.

  

x

Text origin x-coordinate.

  

y

Text origin y-coordinate.

  

Types and Values

enum GwySymbolType

Members

GWY_SYMBOL_SQUARE

    

GWY_SYMBOL_CROSS

    

GWY_SYMBOL_CIRCLE

    

GWY_SYMBOL_STAR

    

GWY_SYMBOL_TIMES

    

GWY_SYMBOL_TRIANGLE_UP

    

GWY_SYMBOL_TRIANGLE_DOWN

    

GWY_SYMBOL_DIAMOND

    

GWY_SYMBOL_FILLED_SQUARE

    

GWY_SYMBOL_DISC

    

GWY_SYMBOL_FILLED_CIRCLE

    

GWY_SYMBOL_FILLED_TRIANGLE_UP

    

GWY_SYMBOL_FILLED_TRIANGLE_DOWN

    

GWY_SYMBOL_FILLED_DIAMOND

    

GWY_SYMBOL_TRIANGLE_LEFT

    

GWY_SYMBOL_FILLED_TRIANGLE_LEFT

    

GWY_SYMBOL_TRIANGLE_RIGHT

    

GWY_SYMBOL_FILLED_TRIANGLE_RIGHT

    

GWY_SYMBOL_ASTERISK

    

enum GwyLineStyle

Members

GWY_LINE_SOLID

    

GWY_LINE_DASH

    

GWY_LINE_DASH_SPARSE

    

GWY_LINE_DASH_DENSE

    

GWY_LINE_DOT

    

GWY_LINE_DOT_SPARSE

    

GWY_LINE_DASH_DOT

    
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