mirror of
https://gitlab.freedesktop.org/wlroots/wlroots.git
synced 2025-11-03 09:01:40 -05:00
d180f4d9b3
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.
76 lines
2.5 KiB
C
76 lines
2.5 KiB
C
#ifndef UTIL_RECT_UNION_H
|
|
#define UTIL_RECT_UNION_H
|
|
|
|
#include <stdlib.h>
|
|
#include <stdbool.h>
|
|
#include <pixman.h>
|
|
#include <wayland-util.h>
|
|
|
|
/**
|
|
* `struct rect_union` is a data structure to efficiently accumulate a number
|
|
* of rectangles and then, when needed, compute a disjoint cover of their union.
|
|
* (That is: produce a list of disjoint rectangles which covers every point
|
|
* that was contained in one of the added rectangles.)
|
|
*
|
|
* Add rectangles to the union with `rect_union_add()`; to compute the disjoint
|
|
* union, run `rect_union_evaluate()`, which will place the result in `.region`.
|
|
* If there were any allocation failures, `.region` will instead contain the
|
|
* bounding box for the entire list of rectangles.
|
|
*
|
|
* Example usage:
|
|
*
|
|
* struct rect_union r;
|
|
* rect_union_init(&r);
|
|
* for (j in ...) {
|
|
* rect_union_add(&r, box[j]);
|
|
* }
|
|
* const pixman_region32_t *reg = rect_union_evaluate(&r);
|
|
* int nboxes;
|
|
* pixman_box32_t *boxes = pixman_region32_rectangles(reg, nboxes);
|
|
* for (int i = 0; i < nboxes; i++) {
|
|
* do_stuff(boxes[i]);
|
|
* }
|
|
* rect_union_destroy(&r);
|
|
*
|
|
*/
|
|
struct rect_union {
|
|
pixman_box32_t bounding_box; // Always up-to-date bounding box
|
|
pixman_region32_t region; // Updated only on _evaluate()
|
|
|
|
struct wl_array unsorted; // pixman_box32_t
|
|
bool alloc_failure; // If this is true, fall back to computing a bounding box
|
|
};
|
|
|
|
/**
|
|
* Initialize *r, disregarding any previous contents.
|
|
*/
|
|
void rect_union_init(struct rect_union *r);
|
|
|
|
/**
|
|
* Free heap data associated with *r; should only be called after rect_union_init.
|
|
* Leaves *r in an invalid state.
|
|
*/
|
|
void rect_union_finish(struct rect_union *r);
|
|
|
|
/**
|
|
* Add a rectangle to the union. If `box` is empty or invalid (x2 > x1 || y2 > y1),
|
|
* do nothing.
|
|
*
|
|
* Amortized time: O(1)
|
|
*/
|
|
void rect_union_add(struct rect_union *r, pixman_box32_t box);
|
|
|
|
/**
|
|
* Compute an exact cover of the rectangles added so far, and return
|
|
* a pointer to a pixman_region32_t giving that cover. The pointer will
|
|
* remain valid until the next time *r is modified. If there was an allocation
|
|
* failure, this function may return a single-rectangle bounding box instead.
|
|
*
|
|
* This may be called multiple times and interleaved with rect_union_add().
|
|
*
|
|
* Worst case time: O(t^2), where t is the number of rectangles in the list.
|
|
* Best case time: O(t), if rectangles are disjoint and have y-x band structure
|
|
*/
|
|
const pixman_region32_t *rect_union_evaluate(struct rect_union *r);
|
|
|
|
#endif
|