Gnome User Interface Library Reference Manual
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# gnome-canvas-util

## Name

gnome-canvas-util -- Auxiliary canvas functions.

## Synopsis

    #include <gnome.h>

    struct      GnomeCanvasPoints;
    GnomeCanvasPoints* gnome_canvas_points_new  (int num_points);
    void        gnome_canvas_points_free        (GnomeCanvasPoints *points);
    int         gnome_canvas_get_miter_points   (double x1,
                                                 double y1,
                                                 double x2,
                                                 double y2,
                                                 double x3,
                                                 double y3,
                                                 double width,
                                                 double *mx1,
                                                 double *my1,
                                                 double *mx2,
                                                 double *my2);
    void        gnome_canvas_get_butt_points    (double x1,
                                                 double y1,
                                                 double x2,
                                                 double y2,
                                                 double width,
                                                 int project,
                                                 double *bx1,
                                                 double *by1,
                                                 double *bx2,
                                                 double *by2);
    double      gnome_canvas_polygon_to_point   (double *poly,
                                                 int num_points,
                                                 double x,
                                                 double y);
    void        gnome_canvas_render_svp         (GnomeCanvasBuf *buf,
                                                 ArtSVP *svp,
                                                 guint32 rgba);
    void        gnome_canvas_update_svp         (GnomeCanvas *canvas,
                                                 ArtSVP **p_svp,
                                                 ArtSVP *new_svp);
    void        gnome_canvas_update_svp_clip    (GnomeCanvas *canvas,
                                                 ArtSVP **p_svp,
                                                 ArtSVP *new_svp,
                                                 ArtSVP *clip_svp);
    void        gnome_canvas_item_reset_bounds  (GnomeCanvasItem *item);
    void        gnome_canvas_item_update_svp    (GnomeCanvasItem *item,
                                                 ArtSVP **p_svp,
                                                 ArtSVP *new_svp);
    void        gnome_canvas_item_update_svp_clip
                                                (GnomeCanvasItem *item,
                                                 ArtSVP **p_svp,
                                                 ArtSVP *new_svp,
                                                 ArtSVP *clip_svp);
    void        gnome_canvas_item_request_redraw_svp
                                                (GnomeCanvasItem *item,
                                                 const ArtSVP *svp);
    void        gnome_canvas_update_bbox        (GnomeCanvasItem *item,
                                                 int x1,
                                                 int y1,
                                                 int x2,
                                                 int y2);
    void        gnome_canvas_buf_ensure_buf     (GnomeCanvasBuf *buf);
    GdkImlibImage* gnome_canvas_load_alpha      (char *file);
    void        gnome_canvas_destroy_image      (GdkImlibImage *image);

## Description

These miscellaneous functions are useful with the GnomeCanvas.

## Details

### struct GnomeCanvasPoints

    typedef struct {
    	int num_points;
    	double *coords;
    	int ref_count;
    } GnomeCanvasPoints;

### gnome_canvas_points_new ()

    GnomeCanvasPoints* gnome_canvas_points_new  (int num_points);

Creates a structure that should be used to pass an array of points to items.

`num_points` : | The number of points to allocate space for in the array.
Returns : | A newly-created array of points. It should be filled in by the user.

### gnome_canvas_points_free ()

    void        gnome_canvas_points_free        (GnomeCanvasPoints *points);

Decreases the reference count of the specified points structure. If it reaches zero, then the structure is freed.

`points` : | A canvas points structure.

### gnome_canvas_get_miter_points ()

    int         gnome_canvas_get_miter_points   (double x1,
                                                 double y1,
                                                 double x2,
                                                 double y2,
                                                 double x3,
                                                 double y3,
                                                 double width,
                                                 double *mx1,
                                                 double *my1,
                                                 double *mx2,
                                                 double *my2);

Given three points forming an angle, computes the coordinates of the inside and outside points of the mitered corner formed by a line of a given width at that angle.

`x1` : | X coordinate of the first point
`y1` : | Y coordinate of the first point
`x2` : | X coordinate of the second (angle) point
`y2` : | Y coordinate of the second (angle) point
`x3` : | X coordinate of the third point
`y3` : | Y coordinate of the third point
`width` : | Width of the line
`mx1` : | The X coordinate of the first miter point is returned here.
`my1` : | The Y coordinate of the first miter point is returned here.
`mx2` : | The X coordinate of the second miter point is returned here.
`my2` : | The Y coordinate of the second miter point is returned here.
Returns : | FALSE if the angle is less than 11 degrees (this is the same threshold as X uses. If this occurs, the return points are not modified. Otherwise, returns TRUE.

### gnome_canvas_get_butt_points ()

    void        gnome_canvas_get_butt_points    (double x1,
                                                 double y1,
                                                 double x2,
                                                 double y2,
                                                 double width,
                                                 int project,
                                                 double *bx1,
                                                 double *by1,
                                                 double *bx2,
                                                 double *by2);

Computes the butt points of a line segment.

`x1` : | X coordinate of first point in the line
`y1` : | Y cooordinate of first point in the line
`x2` : | X coordinate of second point (endpoint) of the line
`y2` : | Y coordinate of second point (endpoint) of the line
`width` : | Width of the line
`project` : | Whether the butt points should project out by width/2 distance
`bx1` : | X coordinate of first butt point is returned here
`by1` : | Y coordinate of first butt point is returned here
`bx2` : | X coordinate of second butt point is returned here
`by2` : | Y coordinate of second butt point is returned here

### gnome_canvas_polygon_to_point ()

    double      gnome_canvas_polygon_to_point   (double *poly,
                                                 int num_points,
                                                 double x,
                                                 double y);

Computes the distance between a point and a polygon.

`poly` : | Vertices of the polygon. X coordinates are in the even indices, and Y coordinates are in the odd indices
`num_points` : | Number of points in the polygon
`x` : | X coordinate of the point
`y` : | Y coordinate of the point
Returns : | The distance from the point to the polygon, or zero if the point is inside the polygon.

### gnome_canvas_render_svp ()

    void        gnome_canvas_render_svp         (GnomeCanvasBuf *buf,
                                                 ArtSVP *svp,
                                                 guint32 rgba);

Render the svp over the buf.

`buf` : | the canvas buffer to render over
`svp` : | the vector path to render
`rgba` : | the rgba color to render

### gnome_canvas_update_svp ()

    void        gnome_canvas_update_svp         (GnomeCanvas *canvas,
                                                 ArtSVP **p_svp,
                                                 ArtSVP *new_svp);

Sets the svp to the new value, requesting repaint on what's changed. This function takes responsibility for freeing new_svp.

`canvas` : | the canvas containing the svp that needs updating.
`p_svp` : | a pointer to the existing svp
`new_svp` : | the new svp

### gnome_canvas_update_svp_clip ()

    void        gnome_canvas_update_svp_clip    (GnomeCanvas *canvas,
                                                 ArtSVP **p_svp,
                                                 ArtSVP *new_svp,
                                                 ArtSVP *clip_svp);

Sets the svp to the new value, clipping if necessary, and requesting repaint on what's changed. This function takes responsibility for freeing new_svp.

`canvas` : | the canvas containing the svp that needs updating.
`p_svp` : | a pointer to the existing svp
`new_svp` : | the new svp
`clip_svp` : | a clip path, if non-null

### gnome_canvas_item_reset_bounds ()

    void        gnome_canvas_item_reset_bounds  (GnomeCanvasItem *item);

Resets the bounding box of a canvas item to an empty rectangle.

`item` : | A canvas item

### gnome_canvas_item_update_svp ()

    void        gnome_canvas_item_update_svp    (GnomeCanvasItem *item,
                                                 ArtSVP **p_svp,
                                                 ArtSVP *new_svp);

Sets the svp to the new value, requesting repaint on what's changed. This function takes responsibility for freeing new_svp. This routine also adds the svp's bbox to the item's.

`item` : | the canvas item containing the svp that needs updating.
`p_svp` : | a pointer to the existing svp
`new_svp` : | the new svp

### gnome_canvas_item_update_svp_clip ()

    void        gnome_canvas_item_update_svp_clip
                                                (GnomeCanvasItem *item,
                                                 ArtSVP **p_svp,
                                                 ArtSVP *new_svp,
                                                 ArtSVP *clip_svp);

Sets the svp to the new value, clipping if necessary, and requesting repaint on what's changed. This function takes responsibility for freeing new_svp.

`item` : | the canvas item containing the svp that needs updating.
`p_svp` : | a pointer to the existing svp
`new_svp` : | the new svp
`clip_svp` : | a clip path, if non-null

### gnome_canvas_item_request_redraw_svp ()

    void        gnome_canvas_item_request_redraw_svp
                                                (GnomeCanvasItem *item,
                                                 const ArtSVP *svp);

Request redraw of the svp if in aa mode, or the entire item in in xlib mode.

`item` : | the item containing the svp
`svp` : | the svp that needs to be redrawn

### gnome_canvas_update_bbox ()

    void        gnome_canvas_update_bbox        (GnomeCanvasItem *item,
                                                 int x1,
                                                 int y1,
                                                 int x2,
                                                 int y2);

Sets the bbox to the new value, requesting full repaint.

`item` : |
`x1` : | Left coordinate of the new bounding box
`y1` : | Top coordinate of the new bounding box
`x2` : | Right coordinate of the new bounding box
`y2` : | Bottom coordinate of the new bounding box

### gnome_canvas_buf_ensure_buf ()

    void        gnome_canvas_buf_ensure_buf     (GnomeCanvasBuf *buf);

`buf` : |

### gnome_canvas_load_alpha ()

    GdkImlibImage* gnome_canvas_load_alpha      (char *file);

This routine loads a PNG file with full alpha transparency and

`file` : | filename to load
Returns : | a (GdkImlibImage *). Note that images created by this routine are not intended to be passed to GdkImlib, we just use this to remain compatible with the GnomeCanvasImage Canvas item. Use this with GdkImlib at your own risk. To release images loaded by gnome_canvas_load_alpha, use gnome_canvas_destroy_image preferably although it works with imlib now, in the future this might not be the case.

### gnome_canvas_destroy_image ()

    void        gnome_canvas_destroy_image      (GdkImlibImage *image);

Do not pass a regular GdkImlibImage to this routine, only pass GdkImlibImage pointer that were created by gnome_canvas_load_alpha

`image` : | A GdkImlibImage allocated by gnome_canvas_load_alpha

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