-// Compress to sRGB gamma curve.
+// Compress gamma curve.
+
+uniform float PREFIX(linear_scale);
+uniform float PREFIX(c0), PREFIX(c1), PREFIX(c2), PREFIX(c3), PREFIX(c4);
+uniform float PREFIX(beta);
vec4 FUNCNAME(vec2 tc) {
vec4 x = INPUT(tc);
- x.r = texture1D(PREFIX(compression_curve_tex), x.r).x;
- x.g = texture1D(PREFIX(compression_curve_tex), x.g).x;
- x.b = texture1D(PREFIX(compression_curve_tex), x.b).x;
+ // We could reasonably get values outside (0.0, 1.0), but the formulas below
+ // are not valid outside that range, so clamp before we do anything else.
+ x.rgb = clamp(x.rgb, 0.0, 1.0);
+
+ vec3 a = x.rgb * PREFIX(linear_scale);
+
+ // Fourth-order polynomial approximation to pow(). See the .cpp file for details.
+ vec3 s = sqrt(x.rgb);
+ vec3 b = PREFIX(c0) + (PREFIX(c1) + (PREFIX(c2) + (PREFIX(c3) + PREFIX(c4) * s) * s) * s) * s;
+
+ vec3 f = vec3(greaterThan(x.rgb, vec3(PREFIX(beta))));
+ x = vec4(mix(a, b, f), x.a);
return x;
}