54 lines
2.1 KiB
Plaintext
54 lines
2.1 KiB
Plaintext
// Object position in screen space. Allows the noise to
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// have a constant screen-space size, without being
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// affected by the widget layout/position.
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uniform highp vec2 objCoord;
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// Magic, well-known 2d random function; makes perlin-like noise
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highp vec2 random(highp vec2 uv){
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uv = vec2( dot(uv, vec2(127.1,311.7) ),
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dot(uv, vec2(269.5,183.3) ) );
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return -1.0 + 2.0 * fract(sin(uv) * 43758.5453123);
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}
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highp float noise(highp vec2 uv) {
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highp vec2 uv_i = floor(uv);
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highp vec2 uv_f = fract(uv);
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highp vec2 t = smoothstep(0.0, 1.0, uv_f);
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// Sample the random function and run a bilinear filter to smooth it out
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highp float tl = dot( random(uv_i + vec2(0.0,0.0) ), uv_f - vec2(0.0,0.0) );
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highp float tr = dot( random(uv_i + vec2(1.0,0.0) ), uv_f - vec2(1.0,0.0) );
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highp float bl = dot( random(uv_i + vec2(0.0,1.0) ), uv_f - vec2(0.0,1.0) );
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highp float br = dot( random(uv_i + vec2(1.0,1.0) ), uv_f - vec2(1.0,1.0) );
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highp float tA = mix( tl, tr, t.x );
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highp float tB = mix( bl, br, t.x );
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return mix( tA, tB, t.y ) + 0.5;
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}
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void fragment() {
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// Stamps have orientation, and the texture sampling is nearest
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// pixel, so run a bilinear filter to smooth out the edges.
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{
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highp vec4 tl = texture2D(TEXTURE, UV);
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highp vec4 tr = texture2D(TEXTURE, UV + vec2(TEXTURE_PIXEL_SIZE.x, 0.0));
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highp vec4 bl = texture2D(TEXTURE, UV + vec2(0.0, TEXTURE_PIXEL_SIZE.y));
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highp vec4 br = texture2D(TEXTURE, UV + TEXTURE_PIXEL_SIZE);
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highp vec2 textureSize = 1.0 / TEXTURE_PIXEL_SIZE;
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highp vec2 f = fract( UV * textureSize );
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highp vec4 tA = mix( tl, tr, f.x );
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highp vec4 tB = mix( bl, br, f.x );
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COLOR = mix( tA, tB, f.y );
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}
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// Add a bit of noise to mimic imperfect contact with the paper
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{
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highp float stampNoise = noise((FRAGCOORD.xy - objCoord) * vec2(0.03, 0.03)) *
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noise((FRAGCOORD.xy - objCoord) * vec2(0.08, 0.08));
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COLOR.a *= min(0.9, 0.4 + smoothstep(0.05, 0.3, stampNoise));
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}
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}
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