src/sksl/sksl_shared.sksl

// Intrinsics that are available to public SkSL (SkRuntimeEffect)

// See "The OpenGL ES Shading Language, Section 8"

// 8.1 : Angle and Trigonometry Functions
$pure $genType  radians($genType  degrees);
$pure $genHType radians($genHType degrees);
$pure $genType  degrees($genType  radians);
$pure $genHType degrees($genHType radians);

$pure $genType  sin($genType  angle);
$pure $genHType sin($genHType angle);
$pure $genType  cos($genType  angle);
$pure $genHType cos($genHType angle);
$pure $genType  tan($genType  angle);
$pure $genHType tan($genHType angle);

$pure $genType  asin($genType  x);
$pure $genHType asin($genHType x);
$pure $genType  acos($genType  x);
$pure $genHType acos($genHType x);
$pure $genType  atan($genType  y, $genType  x);
$pure $genHType atan($genHType y, $genHType x);
$pure $genType  atan($genType  y_over_x);
$pure $genHType atan($genHType y_over_x);

// 8.1 : Angle and Trigonometry Functions (GLSL ES 3.0)
$pure $es3 $genType  sinh($genType x);
$pure $es3 $genHType sinh($genHType x);
$pure $es3 $genType  cosh($genType x);
$pure $es3 $genHType cosh($genHType x);
$pure $es3 $genType  tanh($genType x);
$pure $es3 $genHType tanh($genHType x);
$pure $es3 $genType  asinh($genType x);
$pure $es3 $genHType asinh($genHType x);
$pure $es3 $genType  acosh($genType x);
$pure $es3 $genHType acosh($genHType x);
$pure $es3 $genType  atanh($genType x);
$pure $es3 $genHType atanh($genHType x);

// 8.2 : Exponential Functions
$pure $genType  pow($genType  x, $genType  y);
$pure $genHType pow($genHType x, $genHType y);
$pure $genType  exp($genType  x);
$pure $genHType exp($genHType x);
$pure $genType  log($genType  x);
$pure $genHType log($genHType x);
$pure $genType  exp2($genType  x);
$pure $genHType exp2($genHType x);
$pure $genType  log2($genType  x);
$pure $genHType log2($genHType x);

$pure $genType  sqrt($genType  x);
$pure $genHType sqrt($genHType x);
$pure $genType  inversesqrt($genType  x);
$pure $genHType inversesqrt($genHType x);

// 8.3 : Common Functions
$pure $genType  abs($genType  x);
$pure $genHType abs($genHType x);
$pure $genType  sign($genType  x);
$pure $genHType sign($genHType x);
$pure $genType  floor($genType  x);
$pure $genHType floor($genHType x);
$pure $genType  ceil($genType  x);
$pure $genHType ceil($genHType x);
$pure $genType  fract($genType  x);
$pure $genHType fract($genHType x);
$pure $genType  mod($genType  x, float     y);
$pure $genType  mod($genType  x, $genType  y);
$pure $genHType mod($genHType x, half      y);
$pure $genHType mod($genHType x, $genHType y);

$pure $genType  min($genType  x, $genType  y);
$pure $genType  min($genType  x, float     y);
$pure $genHType min($genHType x, $genHType y);
$pure $genHType min($genHType x, half      y);
$pure $genType  max($genType  x, $genType  y);
$pure $genType  max($genType  x, float     y);
$pure $genHType max($genHType x, $genHType y);
$pure $genHType max($genHType x, half      y);
$pure $genType  clamp($genType  x, $genType  minVal, $genType  maxVal);
$pure $genType  clamp($genType  x, float     minVal, float     maxVal);
$pure $genHType clamp($genHType x, $genHType minVal, $genHType maxVal);
$pure $genHType clamp($genHType x, half      minVal, half      maxVal);
$pure $genType  saturate($genType  x);  // SkSL extension
$pure $genHType saturate($genHType x);  // SkSL extension
$pure $genType  mix($genType  x, $genType  y, $genType a);
$pure $genType  mix($genType  x, $genType  y, float a);
$pure $genHType mix($genHType x, $genHType y, $genHType a);
$pure $genHType mix($genHType x, $genHType y, half a);
$pure $genType  step($genType  edge, $genType x);
$pure $genType  step(float     edge, $genType x);
$pure $genHType step($genHType edge, $genHType x);
$pure $genHType step(half      edge, $genHType x);
$pure $genType  smoothstep($genType  edge0, $genType  edge1, $genType  x);
$pure $genType  smoothstep(float     edge0, float     edge1, $genType  x);
$pure $genHType smoothstep($genHType edge0, $genHType edge1, $genHType x);
$pure $genHType smoothstep(half      edge0, half      edge1, $genHType x);

// 8.3 : Common Functions (GLSL ES 3.0)
$pure $es3 $genIType abs($genIType x);
$pure $es3 $genIType sign($genIType x);
$pure $es3 $genIType floatBitsToInt ($genType  value);
$pure $es3 $genUType floatBitsToUint($genType  value);
$pure $es3 $genType  intBitsToFloat ($genIType value);
$pure $es3 $genType  uintBitsToFloat($genUType value);
$pure $es3 $genType  trunc($genType  x);
$pure $es3 $genHType trunc($genHType x);
$pure $es3 $genType  round($genType  x);
$pure $es3 $genHType round($genHType x);
$pure $es3 $genType  roundEven($genType  x);
$pure $es3 $genHType roundEven($genHType x);
$pure $es3 $genIType min($genIType x, $genIType y);
$pure $es3 $genIType min($genIType x, int y);
$pure $es3 $genUType min($genUType x, $genUType y);
$pure $es3 $genUType min($genUType x, uint y);
$pure $es3 $genIType max($genIType x, $genIType y);
$pure $es3 $genIType max($genIType x, int y);
$pure $es3 $genUType max($genUType x, $genUType y);
$pure $es3 $genUType max($genUType x, uint y);
$pure $es3 $genIType clamp($genIType x, $genIType minVal, $genIType maxVal);
$pure $es3 $genIType clamp($genIType x, int minVal, int maxVal);
$pure $es3 $genUType clamp($genUType x, $genUType minVal, $genUType maxVal);
$pure $es3 $genUType clamp($genUType x, uint minVal, uint maxVal);
$pure $es3 $genType  mix($genType  x, $genType  y, $genBType a);
$pure $es3 $genHType mix($genHType x, $genHType y, $genBType a);

// 8.3 : Common Functions (GLSL ES 3.0) -- cannot be used in constant-expressions
$pure $es3 $genBType isnan($genType  x);
$pure $es3 $genBType isnan($genHType x);
$pure $es3 $genBType isinf($genType  x);
$pure $es3 $genBType isinf($genHType x);
$pure $es3 $genType  modf($genType  x, out $genType  i);
$pure $es3 $genHType modf($genHType x, out $genHType i);

// 8.4 : Floating-Point Pack and Unpack Functions (GLSL ES 3.0)
$pure $es3 uint packUnorm2x16(float2 v);
$pure $es3 float2 unpackUnorm2x16(uint p);

// 8.5 : Geometric Functions
$pure float length($genType  x);
$pure half  length($genHType x);
$pure float distance($genType  p0, $genType  p1);
$pure half  distance($genHType p0, $genHType p1);
$pure float dot($genType  x, $genType  y);
$pure half  dot($genHType x, $genHType y);
$pure float3 cross(float3 x, float3 y);
$pure half3  cross(half3  x, half3  y);
$pure $genType  normalize($genType  x);
$pure $genHType normalize($genHType x);
$pure $genType  faceforward($genType  N, $genType  I, $genType  Nref);
$pure $genHType faceforward($genHType N, $genHType I, $genHType Nref);
$pure $genType  reflect($genType  I, $genType  N);
$pure $genHType reflect($genHType I, $genHType N);
$pure $genType  refract($genType  I, $genType  N, float eta);
$pure $genHType refract($genHType I, $genHType N, half eta);

// 8.6 : Matrix Functions
$pure $squareMat  matrixCompMult($squareMat  x, $squareMat  y);
$pure $squareHMat matrixCompMult($squareHMat x, $squareHMat y);
$pure $es3 $mat   matrixCompMult($mat x, $mat y);
$pure $es3 $hmat  matrixCompMult($hmat x, $hmat y);

// 8.6 : Matrix Functions (GLSL 1.4, poly-filled by SkSL as needed)
$pure $squareMat  inverse($squareMat  m);
$pure $squareHMat inverse($squareHMat m);

// 8.6 : Matrix Functions (GLSL ES 3.0)
$pure $es3 float       determinant($squareMat m);
$pure $es3 half        determinant($squareHMat m);
$pure $es3 $squareMat  transpose($squareMat  m);
$pure $es3 $squareHMat transpose($squareHMat m);
$pure $es3 float2x3    transpose(float3x2 m);
$pure $es3 half2x3     transpose(half3x2  m);
$pure $es3 float2x4    transpose(float4x2 m);
$pure $es3 half2x4     transpose(half4x2  m);
$pure $es3 float3x2    transpose(float2x3 m);
$pure $es3 half3x2     transpose(half2x3  m);
$pure $es3 float3x4    transpose(float4x3 m);
$pure $es3 half3x4     transpose(half4x3  m);
$pure $es3 float4x2    transpose(float2x4 m);
$pure $es3 half4x2     transpose(half2x4  m);
$pure $es3 float4x3    transpose(float3x4 m);
$pure $es3 half4x3     transpose(half3x4  m);
$pure $es3 $squareMat  outerProduct($vec   c, $vec   r);
$pure $es3 $squareHMat outerProduct($hvec  c, $hvec  r);
$pure $es3 float2x3    outerProduct(float3 c, float2 r);
$pure $es3 half2x3     outerProduct(half3  c, half2  r);
$pure $es3 float3x2    outerProduct(float2 c, float3 r);
$pure $es3 half3x2     outerProduct(half2  c, half3  r);
$pure $es3 float2x4    outerProduct(float4 c, float2 r);
$pure $es3 half2x4     outerProduct(half4  c, half2  r);
$pure $es3 float4x2    outerProduct(float2 c, float4 r);
$pure $es3 half4x2     outerProduct(half2  c, half4  r);
$pure $es3 float3x4    outerProduct(float4 c, float3 r);
$pure $es3 half3x4     outerProduct(half4  c, half3  r);
$pure $es3 float4x3    outerProduct(float3 c, float4 r);
$pure $es3 half4x3     outerProduct(half3  c, half4  r);

// 8.7 : Vector Relational Functions
$pure $bvec lessThan($vec  x, $vec  y);
$pure $bvec lessThan($hvec x, $hvec y);
$pure $bvec lessThan($ivec x, $ivec y);
$pure $bvec lessThan($svec x, $svec y);
$pure $bvec lessThanEqual($vec  x, $vec  y);
$pure $bvec lessThanEqual($hvec x, $hvec y);
$pure $bvec lessThanEqual($ivec x, $ivec y);
$pure $bvec lessThanEqual($svec x, $svec y);
$pure $bvec greaterThan($vec  x, $vec  y);
$pure $bvec greaterThan($hvec x, $hvec y);
$pure $bvec greaterThan($ivec x, $ivec y);
$pure $bvec greaterThan($svec x, $svec y);
$pure $bvec greaterThanEqual($vec  x, $vec  y);
$pure $bvec greaterThanEqual($hvec x, $hvec y);
$pure $bvec greaterThanEqual($ivec x, $ivec y);
$pure $bvec greaterThanEqual($svec x, $svec y);
$pure $bvec equal($vec  x, $vec  y);
$pure $bvec equal($hvec x, $hvec y);
$pure $bvec equal($ivec x, $ivec y);
$pure $bvec equal($svec x, $svec y);
$pure $bvec equal($bvec x, $bvec y);
$pure $bvec notEqual($vec  x, $vec  y);
$pure $bvec notEqual($hvec x, $hvec y);
$pure $bvec notEqual($ivec x, $ivec y);
$pure $bvec notEqual($svec x, $svec y);
$pure $bvec notEqual($bvec x, $bvec y);

$pure $es3 $bvec lessThan($usvec x, $usvec y);
$pure $es3 $bvec lessThan($uvec x, $uvec y);
$pure $es3 $bvec lessThanEqual($uvec x, $uvec y);
$pure $es3 $bvec lessThanEqual($usvec x, $usvec y);
$pure $es3 $bvec greaterThan($uvec x, $uvec y);
$pure $es3 $bvec greaterThan($usvec x, $usvec y);
$pure $es3 $bvec greaterThanEqual($uvec x, $uvec y);
$pure $es3 $bvec greaterThanEqual($usvec x, $usvec y);
$pure $es3 $bvec equal($uvec x, $uvec y);
$pure $es3 $bvec equal($usvec x, $usvec y);
$pure $es3 $bvec notEqual($uvec x, $uvec y);
$pure $es3 $bvec notEqual($usvec x, $usvec y);

$pure bool  any($bvec x);
$pure bool  all($bvec x);
$pure $bvec not($bvec x);

// 8.9 : Fragment Processing Functions (GLSL ES 3.0)
$pure $es3 $genType  dFdx($genType p);
$pure $es3 $genType  dFdy($genType p);
$pure $es3 $genHType dFdx($genHType p);
$pure $es3 $genHType dFdy($genHType p);
$pure $es3 $genType  fwidth($genType p);
$pure $es3 $genHType fwidth($genHType p);


// SkSL utility functions

// The max() guards against division by zero when the incoming color is transparent black
$pure half4  unpremul(half4  color) { return half4 (color.rgb / max(color.a, 0.0001), color.a); }
$pure float4 unpremul(float4 color) { return float4(color.rgb / max(color.a, 0.0001), color.a); }

// Similar, but used for polar-space CSS colors
$export $pure half4 $unpremul_polar(half4 color) {
    return half4(color.r, color.gb / max(color.a, 0.0001), color.a);
}

// Convert RGBA -> HSLA (including unpremul).
//
// Based on work by Sam Hocevar, Emil Persson, and Ian Taylor [1][2][3].  High-level ideas:
//
//   - minimize the number of branches by sorting and computing the hue phase in parallel (vec4s)
//
//   - trade the third sorting branch for a potentially faster std::min and leaving 2nd/3rd
//     channels unsorted (based on the observation that swapping both the channels and the bias sign
//     has no effect under abs)
//
//   - use epsilon offsets for denominators, to avoid explicit zero-checks
//
// An additional trick we employ is deferring premul->unpremul conversion until the very end: the
// alpha factor gets naturally simplified for H and S, and only L requires a dedicated unpremul
// division (so we trade three divs for one).
//
// [1] http://lolengine.net/blog/2013/01/13/fast-rgb-to-hsv
// [2] http://lolengine.net/blog/2013/07/27/rgb-to-hsv-in-glsl
// [3] http://www.chilliant.com/rgb2hsv.html

$export $pure half4 $rgb_to_hsl(half3 c, half a) {
    half4 p = (c.g < c.b) ? half4(c.bg, -1,  2/3.0)
                          : half4(c.gb,  0, -1/3.0);
    half4 q = (c.r < p.x) ? half4(p.x, c.r, p.yw)
                          : half4(c.r, p.x, p.yz);

    // q.x  -> max channel value
    // q.yz -> 2nd/3rd channel values (unsorted)
    // q.w  -> bias value dependent on max channel selection

    const half kEps = 0.0001;
    half pmV = q.x;
    half pmC = pmV - min(q.y, q.z);
    half pmL = pmV - pmC * 0.5;
    half   H = abs(q.w + (q.y - q.z) / (pmC * 6 + kEps));
    half   S = pmC / (a + kEps - abs(pmL * 2 - a));
    half   L = pmL / (a + kEps);

    return half4(H, S, L, a);
}

// Convert HSLA -> RGBA (including clamp and premul).
//
// Based on work by Sam Hocevar, Emil Persson, and Ian Taylor [1][2][3].
//
// [1] http://lolengine.net/blog/2013/01/13/fast-rgb-to-hsv
// [2] http://lolengine.net/blog/2013/07/27/rgb-to-hsv-in-glsl
// [3] http://www.chilliant.com/rgb2hsv.html

$export $pure half3 $hsl_to_rgb(half3 hsl) {
    half      C = (1 - abs(2 * hsl.z - 1)) * hsl.y;
    half3     p = hsl.xxx + half3(0, 2/3.0, 1/3.0);
    half3     q = saturate(abs(fract(p) * 6 - 3) - 1);

    return (q - 0.5) * C + hsl.z;
}

$export $pure half4 $hsl_to_rgb(half3 hsl, half a) {
    return saturate(half4($hsl_to_rgb(hsl) * a, a));
}

// Color conversion functions used in gradient interpolation, based on
// https://www.w3.org/TR/css-color-4/#color-conversion-code
// TODO(skia:13108): For all of these, we can eliminate any linear math at the beginning
// (by removing the corresponding linear math at the end of the CPU code).
$export $pure half3 $css_lab_to_xyz(half3 lab) {
    const half k = 24389 / 27.0;
    const half e = 216 / 24389.0;

    half3 f;
    f[1] = (lab[0] + 16) / 116;
    f[0] = (lab[1] / 500) + f[1];
    f[2] = f[1] - (lab[2] / 200);

    half3 f_cubed = pow(f, half3(3));

    half3 xyz = half3(
        f_cubed[0] > e ? f_cubed[0] : (116 * f[0] - 16) / k,
        lab[0] > k * e ? f_cubed[1] : lab[0] / k,
        f_cubed[2] > e ? f_cubed[2] : (116 * f[2] - 16) / k
    );

    const half3 D50 = half3(0.3457 / 0.3585, 1.0, (1.0 - 0.3457 - 0.3585) / 0.3585);
    return xyz * D50;
}

// Skia stores all polar colors with hue in the first component, so this "LCH -> Lab" transform
// actually takes "HCL". This is also used to do the same polar transform for OkHCL to OkLAB.
// See similar comments & logic in SkGradientShaderBase.cpp.
$pure half3 $css_hcl_to_lab(half3 hcl) {
    return half3(
        hcl[2],
        hcl[1] * cos(radians(hcl[0])),
        hcl[1] * sin(radians(hcl[0]))
    );
}

$export $pure half3 $css_hcl_to_xyz(half3 hcl) {
    return $css_lab_to_xyz($css_hcl_to_lab(hcl));
}

$export $pure half3 $css_oklab_to_linear_srgb(half3 oklab) {
    half l_ = oklab.x + 0.3963377774 * oklab.y + 0.2158037573 * oklab.z,
         m_ = oklab.x - 0.1055613458 * oklab.y - 0.0638541728 * oklab.z,
         s_ = oklab.x - 0.0894841775 * oklab.y - 1.2914855480 * oklab.z;

    half l = l_*l_*l_,
         m = m_*m_*m_,
         s = s_*s_*s_;

    return half3(
        +4.0767416621 * l - 3.3077115913 * m + 0.2309699292 * s,
        -1.2684380046 * l + 2.6097574011 * m - 0.3413193965 * s,
        -0.0041960863 * l - 0.7034186147 * m + 1.7076147010 * s
    );
}

$export $pure half3 $css_okhcl_to_linear_srgb(half3 okhcl) {
    return $css_oklab_to_linear_srgb($css_hcl_to_lab(okhcl));
}

// TODO(skia:13108): Use our optimized version (though it has different range)
// Doing so might require fixing (re-deriving?) the math for the HWB version below
$export $pure half3 $css_hsl_to_srgb(half3 hsl) {
    hsl.x = mod(hsl.x, 360);
    if (hsl.x < 0) {
        hsl.x += 360;
    }

    hsl.yz /= 100;

    half3 k = mod(half3(0, 8, 4) + hsl.x/30, 12);
    half a = hsl.y * min(hsl.z, 1 - hsl.z);
    return hsl.z - a * clamp(min(k - 3, 9 - k), -1, 1);
}

$export $pure half3 $css_hwb_to_srgb(half3 hwb) {
    hwb.yz /= 100;
    if (hwb.y + hwb.z >= 1) {
        half gray = hwb.y / (hwb.y + hwb.z);
        return half3(gray);
    }
    half3 rgb = $css_hsl_to_srgb(half3(hwb.x, 100, 50));
    rgb *= (1 - hwb.y - hwb.z);
    rgb += hwb.y;
    return rgb;
}

/*
 * The actual output color space of this function depends on the input color space
 * (it might be sRGB, linear sRGB, or linear XYZ). The actual space is what's stored
 * in the gradient/SkColor4fXformer's fIntermediateColorSpace.
 */
$export $pure half4 $interpolated_to_rgb_unpremul(half4 color, int colorSpace, int doUnpremul) {
    const int kDestination = 0;
    const int kSRGBLinear  = 1;
    const int kLab         = 2;
    const int kOKLab       = 3;
    const int kLCH         = 4;
    const int kOKLCH       = 5;
    const int kSRGB        = 6;
    const int kHSL         = 7;
    const int kHWB         = 8;

    if (bool(doUnpremul)) {
        switch (colorSpace) {
            case kLab:
            case kOKLab: color = unpremul(color); break;
            case kLCH:
            case kOKLCH:
            case kHSL:
            case kHWB: color = $unpremul_polar(color); break;
        }
    }
    switch (colorSpace) {
        case kLab:   { color.rgb = $css_lab_to_xyz(color.rgb); break; }
        case kOKLab: { color.rgb = $css_oklab_to_linear_srgb(color.rgb); break; }
        case kLCH:   { color.rgb = $css_hcl_to_xyz(color.rgb); break; }
        case kOKLCH: { color.rgb = $css_okhcl_to_linear_srgb(color.rgb); break; }
        case kHSL:   { color.rgb = $css_hsl_to_srgb(color.rgb); break; }
        case kHWB:   { color.rgb = $css_hwb_to_srgb(color.rgb); break; }
    }
    return color;
}