//SHADER ORIGINALY CREADED BY "abelcamarena" FROM SHADERTOY
//MODIFIED AND PORTED TO GODOT BY AHOPNESS (@ahopness)
//LICENSE : CC0
//COMATIBLE WITH : GLES2, GLES3, WEBGL
//SHADERTOY LINK : https://www.shadertoy.com/view/tsKGDm

shader_type canvas_item;

uniform sampler2D SCREEN_TEXTURE : hint_screen_texture, filter_linear_mipmap;

uniform float SCREEN_WIDTH = 320.; // Lower num - bigger pixels (this will be the screen width)
uniform float COLOR_FACTOR :hint_range(0., 10.) = 4.;   // Higher num - higher colors quality
uniform float DITHERING_STRENTH :hint_range(0., .07) = 0.005; // Be carefull with this one, dithering can get messy really easily

int PSXDither(ivec2 fragcoord) {
    const int dither_table[16] = {
        -4, +0, -3, +1, 
        +2, -2, +3, -1, 
        -3, +1, -4, +0, 
        +3, -1, +2, -2
    };
	
	const int dither_table2[16] = {
        +0, +8, 2, +10, 
        +12, -4, +14, +6, 
        +3, +11, +1, +9, 
        +15, +7, +13, +5
    };
	
	const int dither_table_8[64] = {
		0, 32, 8, 40, 2, 34, 10, 42,
		48, 16, 56, 24, 50, 18, 58, 26,
		12, 44, 4, 36, 14, 46, 6, 38,
		60, 28, 52, 20, 62, 30, 54, 22,
		3, 35, 11, 43, 1, 33, 9, 41,
		51, 19, 59, 27, 49, 17, 57, 25, 
		15, 47, 7, 39, 13, 45, 5, 37,
		63, 31, 55, 23, 61, 29, 53, 21
	};
    
    int x = fragcoord.x % 4;
    int y = fragcoord.y % 4;
    
    return dither_table_8[y * 4 + x];
}

void fragment(){                  
    // Reduce pixels            
    vec2 size = SCREEN_WIDTH * SCREEN_PIXEL_SIZE.xy/SCREEN_PIXEL_SIZE.x;
    vec2 coor = floor( UV * size) ;
    vec2 uv =  FRAGCOORD.xy / (1.0 / SCREEN_PIXEL_SIZE).xy;
    
    // Get source color
    vec3 col = texture(SCREEN_TEXTURE, uv).xyz;     
    
    // Dithering
    col += float(PSXDither(ivec2(FRAGCOORD.xy))) * DITHERING_STRENTH;
    
    // Reduce colors    
    col = floor(col * COLOR_FACTOR) / COLOR_FACTOR;    
    
    // Output to screen
    COLOR = vec4(col,1.);
}