Fix damage tracking for rotated surfaces

It was broken because the damage extents were rotated about its
own center, not about the center of the surface.

This adds a new wlr_region_rotated_bounds that rotates regions.
This allows us to have only one code path (for both non-rotated
views and rotated views) and optimizes rendering for rotated
views.

1 files changed, 49 insertions, 0 deletions

diff --git a/util/region.c b/util/region.c
index 88e38fd2..38f84c5e 100644
--- a/util/region.c
+++ b/util/region.c
@@ -128,3 +128,52 @@ void wlr_region_expand(pixman_region32_t *dst, pixman_region32_t *src,
 	pixman_region32_init_rects(dst, dst_rects, nrects);
 	free(dst_rects);
 }
+
+void wlr_region_rotated_bounds(pixman_region32_t *dst, pixman_region32_t *src,
+		float rotation, int ox, int oy) {
+	if (rotation == 0) {
+		pixman_region32_copy(dst, src);
+		return;
+	}
+
+	int nrects;
+	pixman_box32_t *src_rects = pixman_region32_rectangles(src, &nrects);
+
+	pixman_box32_t *dst_rects = malloc(nrects * sizeof(pixman_box32_t));
+	if (dst_rects == NULL) {
+		return;
+	}
+
+	for (int i = 0; i < nrects; ++i) {
+		double x1 = src_rects[i].x1 - ox;
+		double y1 = src_rects[i].y1 - oy;
+		double x2 = src_rects[i].x2 - ox;
+		double y2 = src_rects[i].y2 - oy;
+
+		double rx1 = x1 * cos(rotation) - y1 * sin(rotation);
+		double ry1 = x1 * sin(rotation) + y1 * cos(rotation);
+
+		double rx2 = x2 * cos(rotation) - y1 * sin(rotation);
+		double ry2 = x2 * sin(rotation) + y1 * cos(rotation);
+
+		double rx3 = x2 * cos(rotation) - y2 * sin(rotation);
+		double ry3 = x2 * sin(rotation) + y2 * cos(rotation);
+
+		double rx4 = x1 * cos(rotation) - y2 * sin(rotation);
+		double ry4 = x1 * sin(rotation) + y2 * cos(rotation);
+
+		x1 = fmin(fmin(rx1, rx2), fmin(rx3, rx4));
+		y1 = fmin(fmin(ry1, ry2), fmin(ry3, ry4));
+		x2 = fmax(fmax(rx1, rx2), fmax(rx3, rx4));
+		y2 = fmax(fmax(ry1, ry2), fmax(ry3, ry4));
+
+		dst_rects[i].x1 = floor(ox + x1);
+		dst_rects[i].x2 = ceil(ox + x2);
+		dst_rects[i].y1 = floor(oy + y1);
+		dst_rects[i].y2 = ceil(oy + y2);
+	}
+
+	pixman_region32_fini(dst);
+	pixman_region32_init_rects(dst, dst_rects, nrects);
+	free(dst_rects);
+}