diff options
author | Manuel Stoeckl <code@mstoeckl.com> | 2023-10-01 16:25:39 -0400 |
---|---|---|
committer | Simon Ser <contact@emersion.fr> | 2023-10-05 11:45:32 +0000 |
commit | d180f4d9b3fab72ff1bad881c91b004c905299c3 (patch) | |
tree | 0db65ca8def31d644852826ea4b9000eb6697264 /util | |
parent | d817ebb80f8b0f1a27152104525d4b5a8c38e56d (diff) |
util: add struct to track union of rectangles
The new struct rect_union is designed to make it easier to
efficiently accumulate a list of rectangles, and then operate
on an exact cover of their union.
Using rect_union, the times needed to added t rectangles, and then
compute their exact cover will be O(t), and something between Ω(t) and
O(t^2), depending on the rectangle arrangement. If one tries to do
the same by storing a pixman_region32_t and updating it with
pixman_region32_union_rect(), then total time needed would be between
Ω(t^2) and O(t^3), depending on the input. Without changing the public
API (data structure + rectangle ordering rules) for pixman_region32_t,
it is impossible to improve its worst case time.
Diffstat (limited to 'util')
-rw-r--r-- | util/meson.build | 1 | ||||
-rw-r--r-- | util/rect_union.c | 91 |
2 files changed, 92 insertions, 0 deletions
diff --git a/util/meson.build b/util/meson.build index 1cd7f65c..1c3dcd5a 100644 --- a/util/meson.build +++ b/util/meson.build @@ -5,6 +5,7 @@ wlr_files += files( 'env.c', 'global.c', 'log.c', + 'rect_union.c', 'region.c', 'set.c', 'shm.c', diff --git a/util/rect_union.c b/util/rect_union.c new file mode 100644 index 00000000..8cd26d76 --- /dev/null +++ b/util/rect_union.c @@ -0,0 +1,91 @@ +#include <limits.h> +#include "util/rect_union.h" + +static void box_union(pixman_box32_t *dst, pixman_box32_t box) { + dst->x1 = dst->x1 < box.x1 ? dst->x1 : box.x1; + dst->y1 = dst->y1 < box.y1 ? dst->y1 : box.y1; + dst->x2 = dst->x2 > box.x2 ? dst->x2 : box.x2; + dst->y2 = dst->y2 > box.y2 ? dst->y2 : box.y2; +} + +static bool box_empty_or_invalid(pixman_box32_t box) { + return box.x1 >= box.x2 || box.y1 >= box.y2; +} + +void rect_union_init(struct rect_union *ru) { + *ru = (struct rect_union) { + .alloc_failure = false, + .bounding_box = (pixman_box32_t) { + .x1 = INT_MAX, + .x2 = INT_MIN, + .y1 = INT_MAX, + .y2 = INT_MIN, + } + }; + pixman_region32_init(&ru->region); + wl_array_init(&ru->unsorted); +}; + +void rect_union_finish(struct rect_union *ru) { + pixman_region32_fini(&ru->region); + wl_array_release(&ru->unsorted); +} + +static void handle_alloc_failure(struct rect_union *ru) { + ru->alloc_failure = true; + wl_array_release(&ru->unsorted); + wl_array_init(&ru->unsorted); +} + +void rect_union_add(struct rect_union *ru, pixman_box32_t box) { + if (box_empty_or_invalid(box)) { + return; + } + + box_union(&ru->bounding_box, box); + + if (!ru->alloc_failure) { + pixman_box32_t *entry = wl_array_add(&ru->unsorted, sizeof(*entry)); + if (entry) { + *entry = box; + } else { + handle_alloc_failure(ru); + } + } +} + +const pixman_region32_t *rect_union_evaluate(struct rect_union *ru) { + if (ru->alloc_failure) { + goto bounding_box; + } + + int nrects = (int)(ru->unsorted.size / sizeof(pixman_box32_t)); + pixman_region32_t reg; + bool ok = pixman_region32_init_rects(®, ru->unsorted.data, nrects); + if (!ok) { + handle_alloc_failure(ru); + goto bounding_box; + } + ok = pixman_region32_union(®, ®, &ru->region); + if (!ok) { + pixman_region32_fini(®); + handle_alloc_failure(ru); + goto bounding_box; + } + pixman_region32_fini(&ru->region); + // pixman_region32_t is safe to move + ru->region = reg; + wl_array_release(&ru->unsorted); + wl_array_init(&ru->unsorted); + + return &ru->region; +bounding_box: + pixman_region32_fini(&ru->region); + if (box_empty_or_invalid(ru->bounding_box)) { + pixman_region32_init(&ru->region); + } else { + pixman_region32_init_with_extents(&ru->region, &ru->bounding_box); + } + return &ru->region; +} + |