256 colour pixelation

This shader is designed to create a retro-gaming look by limiting colours and pixelating a canvas item’s appearance.

By default a range of 256 colours may be output by this shader. That is to say black, white, and 254 others. The Red, Green and Blue channels are individually stepped by the cube-root of 255, resulting in an even distribution of available colours.

The pixelation effect divides the texture’s x and y dimensions individually, both defaulting to 32 divisions. Setting this on a per-object basis allows the apparent resolution of each part to be matched.

Shader code

shader_type canvas_item;

uniform int resX = 32;
uniform int resY = 32;

// 0.100392156862 is the cube root of 255
uniform vec3 rgb255 = vec3(0.100392156862, 0.100392156862, 0.100392156862);

void fragment() {
	float uvX = UV.x - mod(UV.x * float(resX), 1) / float(resX);
	float uvY = UV.y - mod(UV.y * float(resY), 1) / float(resY);
	vec2 grid_uv = vec2(uvX, uvY);
	
	vec4 col = texture(TEXTURE, grid_uv);
	
	if(col.r < 1.0 && col.g < 1.0 && col.b < 1.0) {
		vec3 remainder = mod(col.rgb, rgb255);
		col.rgb = col.rgb - remainder;
	}
	
	COLOR = col;
}

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