Implement pointer-constraints protocol in wlroots and rootston

1 files changed, 71 insertions, 0 deletions

diff --git a/util/region.c b/util/region.c
index 38f84c5e..76df71f3 100644
--- a/util/region.c
+++ b/util/region.c
@@ -1,5 +1,8 @@
+#include <assert.h>
 #include <math.h>
+#include <limits.h>
 #include <stdlib.h>
+#include <wlr/types/wlr_box.h>
 #include <wlr/util/region.h>
 
 void wlr_region_scale(pixman_region32_t *dst, pixman_region32_t *src,
@@ -177,3 +180,71 @@ void wlr_region_rotated_bounds(pixman_region32_t *dst, pixman_region32_t *src,
 	pixman_region32_init_rects(dst, dst_rects, nrects);
 	free(dst_rects);
 }
+
+static void region_confine(pixman_region32_t *region, double x1, double y1, double x2,
+		double y2, double *x2_out, double *y2_out, pixman_box32_t box) {
+	double x_clamped = fmax(fmin(x2, box.x2 - 1), box.x1);
+	double y_clamped = fmax(fmin(y2, box.y2 - 1), box.y1);
+
+	// If the target coordinates are above box.{x,y}2 - 1, but less than
+	// box.{x,y}2, then they are still within the box.
+	if (floor(x_clamped) == floor(x2) && floor(y_clamped) == floor(y2)) {
+		*x2_out = x2;
+		*y2_out = y2;
+		return;
+	}
+
+	double dx = x2 - x1;
+	double dy = y2 - y1;
+
+	// We use fabs to avoid negative zeroes and thus avoid a bug
+	// with negative infinity.
+	double delta = fmin(fabs(x_clamped - x1) / fabs(dx), fabs(y_clamped - y1) / fabs(dy));
+
+	// We clamp it again due to precision errors.
+	double x = fmax(fmin(delta * dx + x1, box.x2 - 1), box.x1);
+	double y = fmax(fmin(delta * dy + y1, box.y2 - 1), box.y1);
+
+	// Go one unit past the boundary to find an adjacent box.
+	int x_ext = floor(x) + (dx == 0 ? 0 : dx > 0 ? 1 : -1);
+	int y_ext = floor(y) + (dy == 0 ? 0 : dy > 0 ? 1 : -1);
+
+	if (pixman_region32_contains_point(region, x_ext, y_ext, &box)) {
+		return region_confine(region, x1, y1, x2, y2, x2_out, y2_out, box);
+	} else if (dx == 0 || dy == 0) {
+		*x2_out = x;
+		*y2_out = y;
+	} else {
+		bool bordering_x = x == box.x1 || x == box.x2 - 1;
+		bool bordering_y = y == box.y1 || y == box.y2 - 1;
+
+		if ((bordering_x && bordering_y) || (!bordering_x && !bordering_y)) {
+			double x2_potential, y2_potential;
+			double tmp1, tmp2;
+			region_confine(region, x, y, x, y2, &tmp1, &y2_potential, box);
+			region_confine(region, x, y, x2, y, &x2_potential, &tmp2, box);
+			if (fabs(x2_potential - x) > fabs(y2_potential - y)) {
+				*x2_out = x2_potential;
+				*y2_out = y;
+			} else {
+				*x2_out = x;
+				*y2_out = y2_potential;
+			}
+		} else if (bordering_x) {
+			return region_confine(region, x, y, x, y2, x2_out, y2_out, box);
+		} else if (bordering_y) {
+			return region_confine(region, x, y, x2, y, x2_out, y2_out, box);
+		}
+	}
+}
+
+bool wlr_region_confine(pixman_region32_t *region, double x1, double y1, double x2,
+		double y2, double *x2_out, double *y2_out) {
+	pixman_box32_t box;
+	if (pixman_region32_contains_point(region, x1, y1, &box)) {
+		region_confine(region, x1, y1, x2, y2, x2_out, y2_out, box);
+		return true;
+	} else {
+		return false;
+	}
+}