Add shaders for texture damage checking

shaders/texture-damage-fragment.glsl

@@ -0,0 +1,44 @@
+precision mediump float;
+
+uniform sampler2D tex0;
+uniform sampler2D tex1;
+
+varying vec2 v_texture;
+varying float v_width;
+varying float v_height;
+
+float get_pixel_damage(vec2 coord)
+{
+	vec3 diff = texture2D(tex0, coord).rgb - texture2D(tex1, coord).rgb;
+
+	vec3 absdiff = ceil(abs(diff));
+
+	return clamp(absdiff.r + absdiff.g + absdiff.b, 0.0, 1.0);
+}
+
+float get_damage(vec2 coord)
+{
+	float x_off = 2.0 / v_width;
+	float y_off = 2.0 / v_height;
+
+	float ix = v_width * (1.0 + coord.x) * 2.0;
+	float iy = v_height * (1.0 + coord.y) * 2.0;
+
+	float x_start = mod(ix, 32.0) / v_width / 2.0;
+	float y_start = mod(iy, 32.0) / v_height / 2.0;
+
+	float color = 0.0;
+	for (float y = 0.0; y < 32.0; y += 1.0)
+		for (float x = 0.0; x < 32.0; x += 1.0) {
+			color += get_pixel_damage(vec2(coord.x - x_start + x * x_off,
+						       coord.y - y_start + y * y_off));
+		}
+
+	return clamp(color, 0.0, 1.0);
+}
+
+void main()
+{
+	float color = get_damage(v_texture);
+	gl_FragColor = vec4(color, color, color, 1.0);
+}

shaders/texture-damage-vertex.glsl

@@ -0,0 +1,15 @@
+attribute vec2 pos;
+attribute vec2 texture;
+attribute float width;
+attribute float height;
+
+varying vec2 v_texture;
+varying float v_width;
+varying float v_height;
+
+void main() {
+	v_texture = texture;
+	v_width = width;
+	v_height = height;
+	gl_Position = vec4(pos, 0, 1);
+}