Pond: Allow windows to blur what's behind them

Work in progress. Adds a new window hint to blur contents behind a window. It currently uses an approximated gaussian blur by applying 3 passes of a box blur. There are currently a few visual artifacts (such as when moving the cursor around a blurred window) due to the way partial redraws work.

Author: byteduck

libraries/libgraphics/Framebuffer.cpp

@@ -225,6 +225,79 @@ void Framebuffer::copy_blitting_flipped(const Framebuffer& other, Rect other_are
 	}
 }
 
+void Framebuffer::blur(Gfx::Rect area, int radius) const {
+	int window_size = radius * 2 + 1;
+
+	auto do_pass = [&]() { ;
+		// First, apply blur horizontally.
+		for(int y = area.y; y < area.y + area.height; y++) {
+			int window[3] = {0, 0, 0};
+			Color window_preblur[window_size];
+			int preblur_index = 0;
+
+			// Populate window
+			for(int i = -radius; i <= radius; i++) {
+				auto color = data[(std::min(std::max(area.x + i, 0), width - 1)) + y * width];
+				window_preblur[i + radius] = color;
+				window[0] += color.r;
+				window[1] += color.g;
+				window[2] += color.b;
+			}
+
+			for(int x = area.x; x < area.x + area.width; x++) {
+				data[x + y * width] = {
+						(uint8_t) (window[0] / window_size),
+						(uint8_t) (window[1] / window_size),
+						(uint8_t) (window[2] / window_size),
+				};
+				auto window_add = data[(std::min(x + 5, width - 1)) + y * width];
+				auto window_sub = window_preblur[preblur_index];
+				preblur_index++;
+				preblur_index %= window_size;
+				window_preblur[((preblur_index - 1) % window_size + window_size) % window_size] = window_add;
+				window[0] += (int) window_add.r - (int) window_sub.r;
+				window[1] += (int) window_add.g - (int) window_sub.g;
+				window[2] += (int) window_add.b - (int) window_sub.b;
+			}
+		}
+
+		// Then, apply blur vertically.
+		for(int x = area.x; x < area.x + area.width; x++) {
+			int window[3] = {0, 0, 0};
+			Color window_preblur[window_size];
+			int preblur_index = 0;
+
+			// Populate window
+			for(int i = -radius; i <= radius; i++) {
+				auto color = data[(x + std::min(std::max(area.y + i, 0), height - 1)) * width];
+				window_preblur[i + radius] = color;
+				window[0] += color.r;
+				window[1] += color.g;
+				window[2] += color.b;
+			}
+
+			for(int y = area.y; y < area.y + area.height; y++) {
+				data[x + y * width] = {
+						(uint8_t) (window[0] / window_size),
+						(uint8_t) (window[1] / window_size),
+						(uint8_t) (window[2] / window_size),
+				};
+				auto window_add = data[x + (std::min(y + 5, height - 1)) * width];
+				auto window_sub = window_preblur[preblur_index];
+				preblur_index++;
+				preblur_index %= window_size;
+				window_preblur[((preblur_index - 1) % window_size + window_size) % window_size] = window_add;
+				window[0] += (int) window_add.r - (int) window_sub.r;
+				window[1] += (int) window_add.g - (int) window_sub.g;
+				window[2] += (int) window_add.b - (int) window_sub.b;
+			}
+		}
+	};
+
+	for(int i = 0; i < 3; i++)
+		do_pass();
+}
+
 void Framebuffer::copy_tiled(const Framebuffer& other, Rect other_area, const Point& pos) const {
 	//Make sure self_area is in bounds of the framebuffer
 	Rect self_area = {pos.x, pos.y, other_area.width, other_area.height};

libraries/libgraphics/Framebuffer.h

@@ -93,6 +93,13 @@ namespace Gfx {
 		 */
 		void copy_blitting_flipped(const Framebuffer& other, Rect other_area, const Point& pos, bool flip_h, bool flip_v) const;
 
+		/**
+		 * Blurs an area of this framebuffer with an approximated gaussian blur.
+		 * @param area The area to blur.
+		 * @param radius The blur radius.
+		 */
+		void blur(Rect area, int radius = 4) const;
+
 		/**
 		 * Identical to ::copy(), but will tile the Image.
 		 */

services/pond/Window.h

@@ -271,6 +271,17 @@ class Window {
 
 	/**
 	 * Gets the shadow framebuffers for drawing shadows.
+	 * Sets whether the window should blur contents behind it.
+	 */
+	void set_blur_behind(bool blur);
+
+	/**
+	 * Returns whether the window blurs contents behind it.
+	 */
+	bool blurs_behind() const;
+
+	/**
+	 * Gets the shadow framebuffer for drawing shadows.
 	 */
 	Gfx::Framebuffer* shadow_buffers() { return _shadow_buffers; }