SameBoy/Shaders/SmoothBilinear.fsh

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vec4 filter(sampler2D image)
{
vec2 texCoord = vec2(gl_FragCoord.x, uResolution.y - gl_FragCoord.y) / uResolution;
vec2 pixel = texCoord * textureDimensions - vec2(0.5, 0.5);
vec4 q11 = texture2D(image, vec2(floor(pixel.x) / textureDimensions.x, floor(pixel.y) / textureDimensions.y));
vec4 q12 = texture2D(image, vec2(floor(pixel.x) / textureDimensions.x, ceil(pixel.y) / textureDimensions.y));
vec4 q21 = texture2D(image, vec2(ceil(pixel.x) / textureDimensions.x, floor(pixel.y) / textureDimensions.y));
vec4 q22 = texture2D(image, vec2(ceil(pixel.x) / textureDimensions.x, ceil(pixel.y) / textureDimensions.y));
vec2 smooth = smoothstep(0., 1., fract(pixel));
vec4 r1 = mix(q11, q21, fract(smooth.x));
vec4 r2 = mix(q12, q22, fract(smooth.x));
return mix (r1, r2, fract(smooth.y));
}