void draw(SkCanvas* canvas) {

  // Make a simple lighting effect:

  auto litEffect = SkRuntimeEffect::MakeForShader(SkString(R"(

    layout(color) uniform vec3 surfaceColor;

    uniform int doLinearLighting;

​

    vec3 normal_at(vec2 p) {

      p = (p / 128) * 2 - 1;

      float len2 = dot(p, p);

      vec3 n = (len2 > 1) ? vec3(0, 0, 1) : vec3(p, sqrt(1 - len2));

      return normalize(n);

    }

​

    vec4 main(vec2 p) {

      vec3 n = normal_at(p);

      vec3 l = normalize(vec3(-1, -1, 0.5));

      vec3 C = surfaceColor;

​

      if (doLinearLighting != 0) { C = toLinearSrgb(C); }

      C *= saturate(dot(n, l));

      if (doLinearLighting != 0) { C = fromLinearSrgb(C); }

​

      return C.rgb1;

    })")).effect;

  SkRuntimeShaderBuilder builder(litEffect);

  builder.uniform("surfaceColor") = SkV3{0.8, 0.8, 0.8};

  SkPaint paint;

​

  // FIRST: Draw the lit sphere without converting to linear sRGB.

  // This produces INCORRECT light falloff.

  builder.uniform("doLinearLighting") = 0;

  paint.setShader(builder.makeShader());

  canvas->drawRect({0,0,128,128}, paint);

​

  // SECOND: Draw the lit sphere with math done in linear sRGB.

  // This produces sharper falloff, which is CORRECT.

  builder.uniform("doLinearLighting") = 1;

  paint.setShader(builder.makeShader());

  canvas->translate(128, 0);

  canvas->drawRect({0,0,128,128}, paint);

}