1 // Copyright 2024 Google LLC.
2 // Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
3 #include "tools/fiddle/examples.h"
4 REG_FIDDLE(SkSL_LinearSRGB, 256, 128, false, 0) {
draw(SkCanvas * canvas)5 void draw(SkCanvas* canvas) {
6 // Make a simple lighting effect:
7 auto litEffect = SkRuntimeEffect::MakeForShader(SkString(R"(
8 layout(color) uniform vec3 surfaceColor;
9 uniform int doLinearLighting;
10
11 vec3 normal_at(vec2 p) {
12 p = (p / 128) * 2 - 1;
13 float len2 = dot(p, p);
14 vec3 n = (len2 > 1) ? vec3(0, 0, 1) : vec3(p, sqrt(1 - len2));
15 return normalize(n);
16 }
17
18 vec4 main(vec2 p) {
19 vec3 n = normal_at(p);
20 vec3 l = normalize(vec3(-1, -1, 0.5));
21 vec3 C = surfaceColor;
22
23 if (doLinearLighting != 0) { C = toLinearSrgb(C); }
24 C *= saturate(dot(n, l));
25 if (doLinearLighting != 0) { C = fromLinearSrgb(C); }
26
27 return C.rgb1;
28 })")).effect;
29 SkRuntimeShaderBuilder builder(litEffect);
30 builder.uniform("surfaceColor") = SkV3{0.8, 0.8, 0.8};
31 SkPaint paint;
32
33 // FIRST: Draw the lit sphere without converting to linear sRGB.
34 // This produces INCORRECT light falloff.
35 builder.uniform("doLinearLighting") = 0;
36 paint.setShader(builder.makeShader());
37 canvas->drawRect({0,0,128,128}, paint);
38
39 // SECOND: Draw the lit sphere with math done in linear sRGB.
40 // This produces sharper falloff, which is CORRECT.
41 builder.uniform("doLinearLighting") = 1;
42 paint.setShader(builder.makeShader());
43 canvas->translate(128, 0);
44 canvas->drawRect({0,0,128,128}, paint);
45 }
46 } // END FIDDLE
47