path: root/libgnomecanvas/gnome-canvas-util.c

/*
 * Copyright (C) 1997, 1998, 1999, 2000 Free Software Foundation
 * All rights reserved.
 *
 * This file is part of the Gnome Library.
 *
 * The Gnome Library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * The Gnome Library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with the Gnome Library; see the file COPYING.LIB.  If not,
 * write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */
/*
  @NOTATION@
 */
/* Miscellaneous utility functions for the GnomeCanvas widget
 *
 * GnomeCanvas is basically a port of the Tk toolkit's most excellent canvas
 * widget.  Tk is copyrighted by the Regents of the University of California,
 * Sun Microsystems, and other parties.
 *
 *
 * Author: Federico Mena <federico@nuclecu.unam.mx>
 */

#include <config.h>

/* needed for M_PI_2 under 'gcc -ansi -predantic' on GNU/Linux */
#ifndef _BSD_SOURCE
#  define _BSD_SOURCE 1
#endif
#include <sys/types.h>

#include <glib.h>
#include <math.h>
#include "gnome-canvas.h"
#include "gnome-canvas-util.h"
#include <libart_lgpl/art_uta.h>
#include <libart_lgpl/art_svp.h>
#include <libart_lgpl/art_svp_ops.h>
#include <libart_lgpl/art_rgb.h>
#include <libart_lgpl/art_rgb_svp.h>
#include <libart_lgpl/art_uta_svp.h>
#include <libart_lgpl/art_rect_svp.h>

/**
 * gnome_canvas_get_miter_points:
 * @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.
 *
 * 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.
 *
 * Return value: 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.
 **/
gint
gnome_canvas_get_miter_points (gdouble x1,
                               gdouble y1,
                               gdouble x2,
                               gdouble y2,
                               gdouble x3,
                               gdouble y3,
                               gdouble width,
                               gdouble *mx1,
                               gdouble *my1,
                               gdouble *mx2,
                               gdouble *my2)
{
    gdouble theta1;     /* angle of segment p2-p1 */
    gdouble theta2;     /* angle of segment p2-p3 */
    gdouble theta;      /* angle between line segments */
    gdouble theta3;     /* angle that bisects theta1 and theta2 and points to p1 */
    gdouble dist;       /* distance of miter points from p2 */
    gdouble dx, dy;     /* x and y offsets corresponding to dist */

#define ELEVEN_DEGREES (11.0 * G_PI / 180.0)

    if (y2 == y1)
        theta1 = (x2 < x1) ? 0.0 : G_PI;
    else if (x2 == x1)
        theta1 = (y2 < y1) ? G_PI_2 : -G_PI_2;
    else
        theta1 = atan2 (y1 - y2, x1 - x2);

    if (y3 == y2)
        theta2 = (x3 > x2) ? 0 : G_PI;
    else if (x3 == x2)
        theta2 = (y3 > y2) ? G_PI_2 : -G_PI_2;
    else
        theta2 = atan2 (y3 - y2, x3 - x2);

    theta = theta1 - theta2;

    if (theta > G_PI)
        theta -= 2.0 * G_PI;
    else if (theta < -G_PI)
        theta += 2.0 * G_PI;

    if ((theta < ELEVEN_DEGREES) && (theta > -ELEVEN_DEGREES))
        return FALSE;

    dist = 0.5 * width / sin (0.5 * theta);
    if (dist < 0.0)
        dist = -dist;

    theta3 = (theta1 + theta2) / 2.0;
    if (sin (theta3 - (theta1 + G_PI)) < 0.0)
        theta3 += G_PI;

    dx = dist * cos (theta3);
    dy = dist * sin (theta3);

    *mx1 = x2 + dx;
    *mx2 = x2 - dx;
    *my1 = y2 + dy;
    *my2 = y2 - dy;

    return TRUE;
}

/**
 * gnome_canvas_get_butt_points:
 * @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
 *
 * Computes the butt points of a line segment.
 **/
void
gnome_canvas_get_butt_points (gdouble x1, gdouble y1, gdouble x2, gdouble y2,
                  gdouble width, gint project,
                  gdouble *bx1, gdouble *by1, gdouble *bx2, gdouble *by2)
{
    gdouble length;
    gdouble dx, dy;

    width *= 0.5;
    dx = x2 - x1;
    dy = y2 - y1;
    length = sqrt (dx * dx + dy * dy);

    if (length < GNOME_CANVAS_EPSILON) {
        *bx1 = *bx2 = x2;
        *by1 = *by2 = y2;
    } else {
        dx = -width * (y2 - y1) / length;
        dy = width * (x2 - x1) / length;

        *bx1 = x2 + dx;
        *bx2 = x2 - dx;
        *by1 = y2 + dy;
        *by2 = y2 - dy;

        if (project) {
            *bx1 += dy;
            *bx2 += dy;
            *by1 -= dx;
            *by2 -= dx;
        }
    }
}

/**
 * gnome_canvas_polygon_to_point:
 * @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
 *
 * Computes the distance between a point and a polygon.
 *
 * Return value: The distance from the point to the polygon, or zero if the
 * point is inside the polygon.
 **/
gdouble
gnome_canvas_polygon_to_point (gdouble *poly, gint num_points, gdouble x, gdouble y)
{
    gdouble best;
    gint intersections;
    gint i;
    gdouble *p;
    gdouble dx, dy;

    /* Iterate through all the edges in the polygon, updating best and
     * intersections.
     *
     * When computing intersections, include left X coordinate of line
     * within its range, but not Y coordinate.  Otherwise if the point
     * lies exactly below a vertex we'll count it as two intersections. */

    best = 1.0e36;
    intersections = 0;

    for (i = num_points, p = poly; i > 1; i--, p += 2) {
        gdouble px, py, dist;

        /* Compute the point on the current edge closest to the
         * point and update the intersection count.  This must be
         * done separately for vertical edges, horizontal edges,
         * and others. */

        if (p[2] == p[0]) {
            /* Vertical edge */

            px = p[0];

            if (p[1] >= p[3]) {
                py = MIN (p[1], y);
                py = MAX (py, p[3]);
            } else {
                py = MIN (p[3], y);
                py = MAX (py, p[1]);
            }
        } else if (p[3] == p[1]) {
            /* Horizontal edge */

            py = p[1];

            if (p[0] >= p[2]) {
                px = MIN (p[0], x);
                px = MAX (px, p[2]);

                if ((y < py) && (x < p[0]) && (x >= p[2]))
                    intersections++;
            } else {
                px = MIN (p[2], x);
                px = MAX (px, p[0]);

                if ((y < py) && (x < p[2]) && (x >= p[0]))
                    intersections++;
            }
        } else {
            gdouble m1, b1, m2, b2;
            gint lower;

            /* Diagonal edge.  Convert the edge to a line equation (y = m1*x + b1), then
             * compute a line perpendicular to this edge but passing through the point,
             * (y = m2*x + b2).
             */

            m1 = (p[3] - p[1]) / (p[2] - p[0]);
            b1 = p[1] - m1 * p[0];

            m2 = -1.0 / m1;
            b2 = y - m2 * x;

            px = (b2 - b1) / (m1 - m2);
            py = m1 * px + b1;

            if (p[0] > p[2]) {
                if (px > p[0]) {
                    px = p[0];
                    py = p[1];
                } else if (px < p[2]) {
                    px = p[2];
                    py = p[3];
                }
            } else {
                if (px > p[2]) {
                    px = p[2];
                    py = p[3];
                } else if (px < p[0]) {
                    px = p[0];
                    py = p[1];
                }
            }

            lower = (m1 * x + b1) > y;

            if (lower && (x >= MIN (p[0], p[2])) && (x < MAX (p[0], p[2])))
                intersections++;
        }

        /* Compute the distance to the closest point, and see if that is the best so far */

        dx = x - px;
        dy = y - py;
        dist = sqrt (dx * dx + dy * dy);
        if (dist < best)
            best = dist;
    }

    /* We've processed all the points.  If the number of
     * intersections is odd, the point is inside the polygon. */

    if (intersections & 0x1)
        return 0.0;
    else
        return best;
}

/* Here are some helper functions for aa rendering: */

/**
 * gnome_canvas_update_svp:
 * @canvas: the canvas containing the svp that needs updating.
 * @p_svp: a pointer to the existing svp
 * @new_svp: the new svp
 *
 * Sets the svp to the new value, requesting repaint on what's changed. This
 * function takes responsibility for freeing new_svp.
 **/
void
gnome_canvas_update_svp (GnomeCanvas *canvas, ArtSVP **p_svp, ArtSVP *new_svp)
{
    ArtSVP *old_svp;
    ArtSVP *diff G_GNUC_UNUSED;
    ArtUta *repaint_uta;

    old_svp = *p_svp;

    if (old_svp != NULL) {
        ArtDRect bb;
        art_drect_svp (&bb, old_svp);
        if ((bb.x1 - bb.x0) * (bb.y1 - bb.y0) > (64 * 64)) {
            repaint_uta = art_uta_from_svp (old_svp);
            gnome_canvas_request_redraw_uta (canvas, repaint_uta);
        } else {
            ArtIRect ib;
            art_drect_to_irect (&ib, &bb);
            gnome_canvas_request_redraw (canvas, ib.x0, ib.y0, ib.x1, ib.y1);
        }
        art_svp_free (old_svp);
    }

    if (new_svp != NULL) {
        ArtDRect bb;
        art_drect_svp (&bb, new_svp);
        if ((bb.x1 - bb.x0) * (bb.y1 - bb.y0) > (64 * 64)) {
            repaint_uta = art_uta_from_svp (new_svp);
            gnome_canvas_request_redraw_uta (canvas, repaint_uta);
        } else {
            ArtIRect ib;
            art_drect_to_irect (&ib, &bb);
            gnome_canvas_request_redraw (canvas, ib.x0, ib.y0, ib.x1, ib.y1);
        }
    }

    *p_svp = new_svp;
}

/**
 * gnome_canvas_update_svp_clip:
 * @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
 *
 * 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.
 **/
void
gnome_canvas_update_svp_clip (GnomeCanvas *canvas,
                              ArtSVP **p_svp,
                              ArtSVP *new_svp,
                              ArtSVP *clip_svp)
{
    ArtSVP *clipped_svp;

    if (clip_svp != NULL) {
        clipped_svp = art_svp_intersect (new_svp, clip_svp);
        art_svp_free (new_svp);
    } else {
        clipped_svp = new_svp;
    }
    gnome_canvas_update_svp (canvas, p_svp, clipped_svp);
}

/**
 * gnome_canvas_item_reset_bounds:
 * @item: A canvas item
 *
 * Resets the bounding box of a canvas item to an empty rectangle.
 **/
void
gnome_canvas_item_reset_bounds (GnomeCanvasItem *item)
{
    item->x1 = 0.0;
    item->y1 = 0.0;
    item->x2 = 0.0;
    item->y2 = 0.0;
}

/**
 * gnome_canvas_item_update_svp:
 * @item: the canvas item containing the svp that needs updating.
 * @p_svp: a pointer to the existing svp
 * @new_svp: the 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.
 **/
void
gnome_canvas_item_update_svp (GnomeCanvasItem *item, ArtSVP **p_svp, ArtSVP *new_svp)
{
    ArtDRect bbox;

    gnome_canvas_update_svp (item->canvas, p_svp, new_svp);
    if (new_svp) {
        bbox.x0 = item->x1;
        bbox.y0 = item->y1;
        bbox.x1 = item->x2;
        bbox.y1 = item->y2;
        art_drect_svp_union (&bbox, new_svp);
        item->x1 = bbox.x0;
        item->y1 = bbox.y0;
        item->x2 = bbox.x1;
        item->y2 = bbox.y1;
    }
}

/**
 * gnome_canvas_item_update_svp_clip:
 * @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
 *
 * 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.
 **/
void
gnome_canvas_item_update_svp_clip (GnomeCanvasItem *item,
                                   ArtSVP **p_svp,
                                   ArtSVP *new_svp,
                                   ArtSVP *clip_svp)
{
    ArtSVP *clipped_svp;

    if (clip_svp != NULL) {
        clipped_svp = art_svp_intersect (new_svp, clip_svp);
        art_svp_free (new_svp);
    } else {
        clipped_svp = new_svp;
    }

    gnome_canvas_item_update_svp (item, p_svp, clipped_svp);
}

/**
 * gnome_canvas_item_request_redraw_svp
 * @item: the item containing the svp
 * @svp: the svp that needs to be redrawn
 *
 * Request redraw of the svp if in aa mode, or the entire item in in xlib mode.
 **/
void
gnome_canvas_item_request_redraw_svp (GnomeCanvasItem *item, const ArtSVP *svp)
{
    gnome_canvas_request_redraw (item->canvas, item->x1, item->y1, item->x2, item->y2);
}

/**
 * gnome_canvas_update_bbox:
 * @item: the canvas item needing update
 * @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
 *
 * Sets the bbox to the new value, requesting full repaint.
 **/
void
gnome_canvas_update_bbox (GnomeCanvasItem *item, gint x1, gint y1, gint x2, gint y2)
{
    gnome_canvas_request_redraw (item->canvas, item->x1, item->y1, item->x2, item->y2);
    item->x1 = x1;
    item->y1 = y1;
    item->x2 = x2;
    item->y2 = y2;
    gnome_canvas_request_redraw (item->canvas, item->x1, item->y1, item->x2, item->y2);
}

/**
 * gnome_canvas_join_gdk_to_art
 * @gdk_join: a join type, represented in GDK format
 *
 * Convert from GDK line join specifier to libart.
 *
 * Return value: The line join specifier in libart format.
 **/
ArtPathStrokeJoinType
gnome_canvas_join_gdk_to_art (GdkJoinStyle gdk_join)
{
    switch (gdk_join) {
    case GDK_JOIN_MITER:
        return ART_PATH_STROKE_JOIN_MITER;

    case GDK_JOIN_ROUND:
        return ART_PATH_STROKE_JOIN_ROUND;

    case GDK_JOIN_BEVEL:
        return ART_PATH_STROKE_JOIN_BEVEL;

    default:
        g_assert_not_reached ();
        return ART_PATH_STROKE_JOIN_MITER; /* shut up the compiler */
    }
}

/**
 * gnome_canvas_cap_gdk_to_art
 * @gdk_cap: a cap type, represented in GDK format
 *
 * Convert from GDK line cap specifier to libart.
 *
 * Return value: The line cap specifier in libart format.
 **/
ArtPathStrokeCapType
gnome_canvas_cap_gdk_to_art (GdkCapStyle gdk_cap)
{
    switch (gdk_cap) {
    case GDK_CAP_BUTT:
    case GDK_CAP_NOT_LAST:
        return ART_PATH_STROKE_CAP_BUTT;

    case GDK_CAP_ROUND:
        return ART_PATH_STROKE_CAP_ROUND;

    case GDK_CAP_PROJECTING:
        return ART_PATH_STROKE_CAP_SQUARE;

    default:
        g_assert_not_reached ();
        return ART_PATH_STROKE_CAP_BUTT; /* shut up the compiler */
    }
}

/**
 * gnome_canvas_cairo_create_scratch:
 *
 * Create a scratch #cairo_t. This is useful for measuring purposes or
 * calling functions like cairo_in_fill().
 *
 * Returns: A new cairo_t. Destroy with cairo_destroy() after use.
 **/
cairo_t *
gnome_canvas_cairo_create_scratch (void)
{
        cairo_surface_t *surface;
        cairo_t *cr;

        surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, 0, 0);
        cr = cairo_create (surface);
        cairo_surface_destroy (surface);

        return cr;
}