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// Vignette: the window's corners fall a little into shade, in linear light,
// so the eye settles on the middle. Round, whatever the window's shape;
// nothing within half the way to a corner is touched. At most 28% at the
// far corners (level 3), and never more than pardesCap, so text and its
// selection keep their own contrast or 4.5. Tags, grips, notices and the
// cursor are left alone (pardesSpare): the focus indicators never darken.
// It is a Shadertoy file: pardes puts its prefix before it.
float strength() { return min(pardesByLevel(0.10, 0.18, 0.28), pardesCap); }
vec3 toLinear(vec3 c) {
return mix(pow((c + 0.055) / 1.055, vec3(2.4)), c / 12.92, lessThanEqual(c, vec3(0.04045)));
}
vec3 toSrgb(vec3 c) {
c = max(c, vec3(0.0));
return mix(1.055 * pow(c, vec3(1.0 / 2.4)) - 0.055, c * 12.92, lessThanEqual(c, vec3(0.0031308)));
}
float ign(vec2 p) {
return fract(52.9829189 * fract(dot(p, vec2(0.06711056, 0.00583715))));
}
void mainImage(out vec4 fragColor, in vec2 fragCoord) {
vec2 uv = fragCoord / iResolution.xy;
vec4 frame = texture(iChannel0, uv);
if (pardesSpared(fragCoord)) {
fragColor = frame;
return;
}
// 0 at the middle, 1 at a corner, on a circle's measure.
vec2 half_size = 0.5 * iResolution.xy;
float r = length(fragCoord - half_size) / length(half_size);
float shade = strength() * pow(smoothstep(0.5, 1.0, r), 1.5);
vec3 srgb = toSrgb(toLinear(frame.rgb) * (1.0 - shade));
srgb += (ign(fragCoord) - 0.5) / 255.0 * step(1e-4, shade);
fragColor = vec4(clamp(srgb, 0.0, 1.0), frame.a);
}
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