add xdg decoration, scene/tree factories, geometry + seat focus

more wrapper soup. xdg decoration manager, scene/tree node factories so
callers stop touching raw wlr_scene_*_create, a box geometry helper, and
seat pointer/keyboard focus clearing. dragging myself through it.

include/wlr/color.hpp

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+#pragma once
+
+#include <pixman.h>
+
+#include "wlr/wlr.hpp"
+
+namespace wlr {
+
+struct Box {
+	int x = 0, y = 0, width = 0, height = 0;
+	pixman_box32 to_box() const { return {x, y, x + width, y + height}; }
+	static Box from_box(pixman_box32 b) {
+		return {b.x1, b.y1, b.x2 - b.x1, b.y2 - b.y1};
+	}
+};
+
+struct Color {
+	float r = 1.0f, g = 1.0f, b = 1.0f, a = 1.0f;
+	void apply(float out[4]) const {
+		out[0] = r; out[1] = g; out[2] = b; out[3] = a;
+	}
+};
+
+struct CornerRadii {
+	uint16_t top_left = 0, top_right = 0, bottom_right = 0, bottom_left = 0;
+
+	CornerRadii() = default;
+	CornerRadii(uint16_t all) : top_left(all), top_right(all), bottom_right(all), bottom_left(all) {}
+	CornerRadii(uint16_t tl, uint16_t tr, uint16_t br, uint16_t bl)
+		: top_left(tl), top_right(tr), bottom_right(br), bottom_left(bl) {}
+
+	fx_corner_radii raw() const {
+		return fx_corner_radii{top_left, top_right, bottom_right, bottom_left};
+	}
+	static CornerRadii from_radii(fx_corner_radii r) {
+		return {r.top_left, r.top_right, r.bottom_right, r.bottom_left};
+	}
+};
+
+}