made visual updates

pixeldither.gdshader

@@ -0,0 +1,75 @@
+shader_type canvas_item;
+
+uniform bool shader_enabled = true;
+
+uniform sampler2D palette;
+uniform sampler2D SCREEN_TEXTURE: hint_screen_texture, filter_linear_mipmap;
+uniform bool dithering = false;
+uniform int dithering_size : hint_range(1, 16) = 2;
+uniform int resolution_scale : hint_range(1, 64) = 2;
+uniform int quantization_level : hint_range(2, 64) = 64;
+
+int dithering_pattern(ivec2 fragcoord) {
+	const int pattern[] = {
+		-4, +0, -3, +1,
+		+2, -2, +3, -1,
+		-3, +1, -4, +0,
+		+3, -1, +2, -2
+	};
+	int x = fragcoord.x % 4;
+	int y = fragcoord.y % 4;
+	return pattern[y * 4 + x] * dithering_size;
+}
+
+float color_distance(vec3 a, vec3 b) {
+	vec3 diff = a - b;
+	return dot(diff, diff);
+}
+
+vec3 quantize_color(vec3 color, int levels) {
+	if (levels <= 1) return vec3(0.0);
+	float step = 1.0 / float(levels - 1);
+	return round(color / step) * step;
+}
+
+void fragment() {
+	vec4 final_color;
+
+	if (!shader_enabled) {
+		final_color = texture(SCREEN_TEXTURE, UV);
+	} else {
+		vec2 tex_size = vec2(textureSize(SCREEN_TEXTURE, 0));
+
+		if (tex_size.x <= 0.0 || tex_size.y <= 0.0) {
+			final_color = vec4(0.0);
+		} else {
+			ivec2 texel_coord = ivec2(floor(UV * tex_size / float(resolution_scale)));
+			vec3 color = texelFetch(SCREEN_TEXTURE, texel_coord * resolution_scale, 0).rgb;
+
+			if (dithering) {
+				int dither = dithering_pattern(texel_coord);
+				color += vec3(float(dither) / 255.0);
+			}
+			color = clamp(color, 0.0, 1.0);
+			color = quantize_color(color, quantization_level);
+
+			int palette_size = 64;
+			float closest_distance = 9999.0;
+			vec4 closest_color = vec4(0.0);
+
+			for (int i = 0; i < palette_size; i++) {
+				float u = float(i) / float(palette_size - 1);
+				vec3 palette_color = texture(palette, vec2(u, 0.0)).rgb;
+				float dist = color_distance(color, palette_color);
+				if (dist < closest_distance) {
+					closest_distance = dist;
+					closest_color = vec4(palette_color, 1.0);
+				}
+			}
+
+			final_color = closest_color;
+		}
+	}
+
+	COLOR = final_color;
+}