ChocolateBird/shaders/palette_shader.gdshader

shader_type canvas_item;
//uniform usampler2D tex;
uniform sampler2D palette;
const float index_scale = 255.0 / 16.0;

void fragment() {
	// GLES3
	/*uint color_idx = uint(textureLod(TEXTURE, UV, 0.0).r * 255.0);
	COLOR = texelFetch(palette, ivec2(int(color_idx), 0), 0);
	if (color_idx == uint(0))
		COLOR.a = 0.0;*/
	// GLES2
	float color_idx16 = texture(TEXTURE, UV).r * index_scale;
	float row = trunc(color_idx16) / 16.0;
	float col = fract(color_idx16);
	COLOR = texture(palette, vec2(col, row));
	COLOR.a = step(0.000001, color_idx16);  // Branchless transparency
}