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gl-renderer: Improve clipper documentation 

Add clipper_clip() documentation and improve comments a tiny bit.

Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
This commit is contained in:
Loïc Molinari 2023-05-25 15:24:32 +02:00 committed by Pekka Paalanen
parent 42205628bf
commit 309a546165
2 changed files with 15 additions and 7 deletions
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13
libweston/vertex-clipping.c
View File

@ -291,6 +291,9 @@ clip_polygon_bottom(struct clip_context *ctx, const struct polygon8 *src,
return ctx->vertices - dst;
}
/* General purpose polygon clipping algorithm based on Sutherland-Hodgman:
* https://www.codeguru.com/cplusplus/polygon-clipping/
*/
WESTON_EXPORT_FOR_TESTS int
clipper_clip(const struct clipper_vertex *polygon,
size_t polygon_len,
@ -360,7 +363,7 @@ clipper_quad_clip(struct clipper_quad *quad,
{
int i, n;
/* Simple case: quad edges are parallel to clipping box edges, there
/* Aligned case: quad edges are parallel to clipping box edges, there
* will be either four or zero edges. We just need to clamp the quad
* edges to the clipping box edges and test for non-zero area:
*/
@ -378,18 +381,14 @@ clipper_quad_clip(struct clipper_quad *quad,
return 0;
}
/* Transformed case: first, simple bounding box check to discard early a
/* Unaligned case: first, simple bounding box check to discard early a
* quad that does not intersect with the clipping box:
*/
if ((quad->bbox[0].x >= box[1].x) || (quad->bbox[1].x <= box[0].x) ||
(quad->bbox[0].y >= box[1].y) || (quad->bbox[1].y <= box[0].y))
return 0;
/* Then, use a general polygon clipping algorithm to clip the quad with
* each side of the surface rect. The algorithm is Sutherland-Hodgman,
* as explained in
* https://www.codeguru.com/cplusplus/polygon-clipping/
* but without looking at any of that code.
/* Then use our general purpose clipping algorithm:
*/
n = clipper_clip(quad->polygon, 4, box, vertices);

9
libweston/vertex-clipping.h
View File

@ -39,6 +39,15 @@ struct clipper_quad {
bool axis_aligned;
};
/*
* General purpose clipping function. Compute the boundary vertices of the
* intersection of a 'polygon' and a clipping 'box'. 'polygon' points to an
* array of 'polygon_len' vertices, less than or equal to 8, defining a convex
* polygon of any winding order. 'box' points to an array of 2 vertices where
* the values of the 1st vertex are less than or equal to the values of the 2nd
* vertex. Up to 16 resulting vertices, using 'polygon' winding order, are
* written to 'vertices'. The return value is the number of vertices created.
*/
int
clipper_clip(const struct clipper_vertex *polygon,
size_t polygon_len,