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Rewrite trim_rect() for robustness.

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The previous version dealt adequately with rectangles _partially_
overlapping the edge of the canvas, but doesn't correctly handle a
rectangle that's completely out of bounds in one direction. Replace
with a complete rewrite which is more easily seen to be correct. Also,
while I'm at it, add a missing condition to draw_update() so that we
don't even bother calling the Javascript half of it on any rectangle
that's been trimmed into nonexistence.

[originally from svn r9800]
This commit is contained in:
Simon Tatham
2013-04-01 16:23:03 +00:00
parent bce3f1bd26
commit 01471b5dc9
1 changed files with 21 additions and 17 deletions
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38
emcc.c
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@ -416,27 +416,30 @@ static void js_blitter_free(void *handle, blitter *bl)
static void trim_rect(int *x, int *y, int *w, int *h)
{
int x0, x1, y0, y1;
/*
* Reduce the size of the copied rectangle to stop it going
* outside the bounds of the canvas.
*/
if (*x < 0) {
*w += *x;
*x = 0;
}
if (*y < 0) {
*h += *y;
*y = 0;
}
if (*w > canvas_w - *x)
*w = canvas_w - *x;
if (*h > canvas_h - *y)
*h = canvas_h - *y;
if (*w < 0)
*w = 0;
if (*h < 0)
*h = 0;
/* Transform from x,y,w,h form into coordinates of all edges */
x0 = *x;
y0 = *y;
x1 = *x + *w;
y1 = *y + *h;
/* Clip each coordinate at both extremes of the canvas */
x0 = (x0 < 0 ? 0 : x0 > canvas_w ? canvas_w : x0);
x1 = (x1 < 0 ? 0 : x1 > canvas_w ? canvas_w : x1);
y0 = (y0 < 0 ? 0 : y0 > canvas_h ? canvas_h : y0);
y1 = (y1 < 0 ? 0 : y1 > canvas_h ? canvas_h : y1);
/* Transform back into x,y,w,h to return */
*x = x0;
*y = y0;
*w = x1 - x0;
*h = y1 - y0;
}
static void js_blitter_save(void *handle, blitter *bl, int x, int y)
@ -458,7 +461,8 @@ static void js_blitter_load(void *handle, blitter *bl, int x, int y)
static void js_draw_update(void *handle, int x, int y, int w, int h)
{
trim_rect(&x, &y, &w, &h);
js_canvas_draw_update(x, y, w, h);
if (w > 0 && h > 0)
js_canvas_draw_update(x, y, w, h);
}
static void js_end_draw(void *handle)