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polygon: Simplify code for edge clipping

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Add some comments about what's going on and clean up the branches by
sharing common computations.
This commit is contained in:
Andrea Canciani 2011-07-27 18:57:59 +02:00
parent de25fec06b
commit 6aa6b7daa8
1 changed files with 31 additions and 45 deletions
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76
src/cairo-polygon.c
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@ -288,67 +288,53 @@ _add_clipped_edge (cairo_polygon_t *polygon,
const int top, const int bottom,
const int dir)
{
cairo_point_t p[2];
int top_y, bot_y;
cairo_point_t bot_left, top_right;
cairo_fixed_t top_y, bot_y;
int n;
for (n = 0; n < polygon->num_limits; n++) {
const cairo_box_t *limits = &polygon->limits[n];
cairo_fixed_t pleft, pright;
if (top >= limits->p2.y)
continue;
if (bottom <= limits->p1.y)
continue;
if (p1->x >= limits->p1.x && p2->x >= limits->p1.x &&
p1->x <= limits->p2.x && p2->x <= limits->p2.x)
{
top_y = top;
if (top_y < limits->p1.y)
top_y = limits->p1.y;
bot_left.x = limits->p1.x;
bot_left.y = limits->p2.y;
bot_y = bottom;
if (bot_y > limits->p2.y)
bot_y = limits->p2.y;
top_right.x = limits->p2.x;
top_right.y = limits->p1.y;
/* The useful region */
top_y = MAX (top, limits->p1.y);
bot_y = MIN (bottom, limits->p2.y);
/* The projection of the edge on the horizontal axis */
pleft = MIN (p1->x, p2->x);
pright = MAX (p1->x, p2->x);
if (limits->p1.x <= pleft && pright <= limits->p2.x) {
/* Projection of the edge completely contained in the box:
* clip vertically by restricting top and bottom */
_add_edge (polygon, p1, p2, top_y, bot_y, dir);
}
else if (p1->x <= limits->p1.x && p2->x <= limits->p1.x)
{
p[0].x = limits->p1.x;
p[0].y = limits->p1.y;
top_y = top;
if (top_y < p[0].y)
top_y = p[0].y;
} else if (pright <= limits->p1.x) {
/* Projection of the edge to the left of the box:
* replace with the left side of the box (clipped top/bottom) */
p[1].x = limits->p1.x;
p[1].y = limits->p2.y;
bot_y = bottom;
if (bot_y > p[1].y)
bot_y = p[1].y;
_add_edge (polygon, &limits->p1, &bot_left, top_y, bot_y, dir);
} else if (limits->p2.x <= pleft) {
/* Projection of the edge to the right of the box:
* replace with the right side of the box (clipped top/bottom) */
_add_edge (polygon, &p[0], &p[1], top_y, bot_y, dir);
}
else if (p1->x >= limits->p2.x && p2->x >= limits->p2.x)
{
p[0].x = limits->p2.x;
p[0].y = limits->p1.y;
top_y = top;
if (top_y < p[0].y)
top_y = p[0].y;
p[1].x = limits->p2.x;
p[1].y = limits->p2.y;
bot_y = bottom;
if (bot_y > p[1].y)
bot_y = p[1].y;
_add_edge (polygon, &p[0], &p[1], top_y, bot_y, dir);
}
else
{
int left_y, right_y;
_add_edge (polygon, &top_right, &limits->p2, top_y, bot_y, dir);
} else {
/* The edge and the box intersect in a generic way */
cairo_fixed_t left_y, right_y;
int p1_y, p2_y;
cairo_point_t p[2];
left_y = _cairo_edge_compute_intersection_y_for_x (p1, p2,
limits->p1.x);