ProjectArcade

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// Bicubic (Mitchell–Netravali, B=1/3, C=1/3) upscaling shader.
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#ifdef GL_ES
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precision mediump float;
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precision mediump int;
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#endif
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uniform sampler2D sampler0;
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varying vec2 v_position;
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uniform vec2 u_texelDelta;
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uniform vec2 u_pixelDelta;
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const vec2 HALF_PIXEL = vec2(0.5, 0.5);
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vec3 rgb(int inputX, int inputY)
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{
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	return texture2D(sampler0, (vec2(inputX, inputY) + HALF_PIXEL) * u_texelDelta).xyz;
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}
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// Mitchell–Netravali coefficients, multiplied by 18.
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float A(float x) {return ((-7.0*x+15.0)*x-9.0)*x+1.0;}
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float B(float x) {return (21.0*x-36.0)*x*x+16.0;}
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float C(float x) {return ((-21.0*x+27.0)*x+9.0)*x+1.0;}
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float D(float x) {return (7.0*x-6.0)*x*x;}
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vec3 interpolateHorizontally(vec2 inputPos, ivec2 inputPosFloor, int dy) {
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	vec3 ret = vec3(0.0);
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	float x = inputPos.x - float(inputPosFloor.x);
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	ret += A(x) * rgb(inputPosFloor.x - 1, inputPosFloor.y + dy);
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        ret += B(x) * rgb(inputPosFloor.x    , inputPosFloor.y + dy);
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        ret += C(x) * rgb(inputPosFloor.x + 1, inputPosFloor.y + dy);
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        ret += D(x) * rgb(inputPosFloor.x + 2, inputPosFloor.y + dy);
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	return ret;
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}
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vec4 process(vec2 outputPos) {
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	vec2 inputPos = outputPos / u_texelDelta - HALF_PIXEL;
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	ivec2 inputPosFloor = ivec2(inputPos);
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        vec3 ret = vec3(0.0);
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	float y = inputPos.y - float(inputPosFloor.y);
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	ret += A(y) * interpolateHorizontally(inputPos, inputPosFloor, -1);
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	ret += B(y) * interpolateHorizontally(inputPos, inputPosFloor,  0);
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	ret += C(y) * interpolateHorizontally(inputPos, inputPosFloor, +1);
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	ret += D(y) * interpolateHorizontally(inputPos, inputPosFloor, +2);
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	return vec4(ret / 324.0, 1.0);
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}
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void main()
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{
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        gl_FragColor.rgba = process(v_position);
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}
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