src/sksl/sksl_graphite_frag.sksl

// Graphite-specific fragment shader code

const int $kTileModeClamp  = 0;
const int $kTileModeRepeat = 1;
const int $kTileModeMirror = 2;
const int $kTileModeDecal  = 3;

const int $kReadSwizzleNormalRGBA = 0;
const int $kReadSwizzleRGB1 = 1;
const int $kReadSwizzleRRRR = 2;
const int $kReadSwizzleRRR1 = 3;
const int $kReadSwizzleBGRA = 4;

const int $kFilterModeNearest = 0;
const int $kFilterModeLinear  = 1;

const int $kTFTypeSRGB  = 1;
const int $kTFTypePQ = 2;
const int $kTFTypeHLG = 3;
const int $kTFTypeHLGinv = 4;

const int $kColorSpaceXformFlagUnpremul = 0x1;
const int $kColorSpaceXformFlagLinearize = 0x2;
const int $kColorSpaceXformFlagGamutTransform = 0x4;
const int $kColorSpaceXformFlagEncode = 0x8;
const int $kColorSpaceXformFlagPremul = 0x10;

$pure half4 sk_error() {
    return half4(1.0, 0.0, 1.0, 1.0);
}

$pure half4 sk_passthrough(half4 color) {
    return color;
}

$pure half4 sk_solid_shader(float4 colorParam) {
    return half4(colorParam);
}

$pure half4 $apply_swizzle(int swizzleType, half4 color) {
    half4 resultantColor = color;
    switch (swizzleType) {
        case $kReadSwizzleNormalRGBA:
            break;
        case $kReadSwizzleRGB1:
            resultantColor = color.rgb1;
            break;
        case $kReadSwizzleRRRR:
            resultantColor = color.rrrr;
            break;
        case $kReadSwizzleRRR1:
            resultantColor = color.rrr1;
            break;
        case $kReadSwizzleBGRA:
            resultantColor = color.bgra;
            break;
    }
    return resultantColor;
}

$pure half $apply_xfer_fn(int kind, half x, half cs[7]) {
    half G = cs[0], A = cs[1], B = cs[2], C = cs[3], D = cs[4], E = cs[5], F = cs[6];
    half s = sign(x);
    x = abs(x);
    switch (kind) {
        case $kTFTypeSRGB:
            x = (x < D) ? (C * x) + F
                        : pow(A * x + B, G) + E;
            break;
        case $kTFTypePQ:
            x = pow(max(A + B * pow(x, C), 0) / (D + E * pow(x, C)), F);
            break;
        case $kTFTypeHLG:
            x = (x * A <= 1) ? pow(x * A, B)
                             : exp((x - E) * C) + D;
            x *= (F + 1);
            break;
        case $kTFTypeHLGinv:
            x /= (F + 1);
            x = (x <= 1) ? A * pow(x, B)
                         : C * log(x - D) + E;
            break;
    }
    return s * x;
}

// TODO(b/239548614) need to plumb Graphite equivalent of fColorSpaceMathNeedsFloat.
// This would change 'color' from half4 to float4
$pure half4 sk_color_space_transform(half4 color,
                                     int flags,
                                     int srcKind,
                                     half srcCoeffs[7],
                                     half3x3 gamutTransform,
                                     int dstKind,
                                     half dstCoeffs[7]) {
    if (bool(flags & $kColorSpaceXformFlagUnpremul)) {
        color = unpremul(color);
    }

    if (bool(flags & $kColorSpaceXformFlagLinearize)) {
        color.r = $apply_xfer_fn(srcKind, color.r, srcCoeffs);
        color.g = $apply_xfer_fn(srcKind, color.g, srcCoeffs);
        color.b = $apply_xfer_fn(srcKind, color.b, srcCoeffs);
    }
    if (bool(flags & $kColorSpaceXformFlagGamutTransform)) {
        color.rgb = gamutTransform * color.rgb;
    }
    if (bool(flags & $kColorSpaceXformFlagEncode)) {
        color.r = $apply_xfer_fn(dstKind, color.r, dstCoeffs);
        color.g = $apply_xfer_fn(dstKind, color.g, dstCoeffs);
        color.b = $apply_xfer_fn(dstKind, color.b, dstCoeffs);
    }

    if (bool(flags & $kColorSpaceXformFlagPremul)) {
        color.rgb *= color.a;
    }
    return color;
}

$pure float $tile(int tileMode, float f, float low, float high) {
    switch (tileMode) {
        case $kTileModeClamp:
            return clamp(f, low, high);

        case $kTileModeRepeat: {
            float length = high - low;
            return (mod(f - low, length) + low);
        }
        case $kTileModeMirror: {
            float length = high - low;
            float length2 = 2 * length;
            float tmp = mod(f - low, length2);
            return (mix(tmp, length2 - tmp, step(length, tmp)) + low);
        }
        default:  // $kTileModeDecal
            // Decal is handled later.
            return f;
    }
}

$pure half4 $sample_image(float2 pos,
                          float2 imgSize,
                          float4 subset,
                          int tileModeX,
                          int tileModeY,
                          int filterMode,
                          int readSwizzle,
                          sampler2D s) {
    // Do hard-edge shader transitions to the border color for nearest-neighbor decal tiling at the
    // subset boundaries. Snap the input coordinates to nearest neighbor before comparing to the
    // subset rect, to avoid GPU interpolation errors. See https://crbug.com/skia/10403.
    if (tileModeX == $kTileModeDecal && filterMode == $kFilterModeNearest) {
        float snappedX = floor(pos.x) + 0.5;
        if (snappedX < subset.x || snappedX > subset.z) {
            return half4(0);
        }
    }
    if (tileModeY == $kTileModeDecal && filterMode == $kFilterModeNearest) {
        float snappedY = floor(pos.y) + 0.5;
        if (snappedY < subset.y || snappedY > subset.w) {
            return half4(0);
        }
    }

    pos.x = $tile(tileModeX, pos.x, subset.x, subset.z);
    pos.y = $tile(tileModeY, pos.y, subset.y, subset.w);

    // Clamp to an inset subset to prevent sampling neighboring texels when coords fall exactly at
    // texel boundaries.
    float4 insetClamp;
    if (filterMode == $kFilterModeNearest) {
        insetClamp = float4(floor(subset.xy) + 0.5, ceil(subset.zw) - 0.5);
    } else {
        insetClamp = float4(subset.xy + 0.5, subset.zw - 0.5);
    }
    float2 clampedPos = clamp(pos, insetClamp.xy, insetClamp.zw);
    half4 color = sample(s, clampedPos / imgSize);
    color = $apply_swizzle(readSwizzle, color);

    if (filterMode == $kFilterModeLinear) {
        // Remember the amount the coord moved for clamping. This is used to implement shader-based
        // filtering for repeat and decal tiling.
        half2 error = half2(pos - clampedPos);
        half2 absError = abs(error);

        // Do 1 or 3 more texture reads depending on whether both x and y tiling modes are repeat
        // and whether we're near a single subset edge or a corner. Then blend the multiple reads
        // using the error values calculated above.
        bool sampleExtraX = tileModeX == $kTileModeRepeat;
        bool sampleExtraY = tileModeY == $kTileModeRepeat;
        if (sampleExtraX || sampleExtraY) {
            float extraCoordX;
            float extraCoordY;
            half4 extraColorX;
            half4 extraColorY;
            if (sampleExtraX) {
                extraCoordX = error.x > 0 ? insetClamp.x : insetClamp.z;
                extraColorX = sample(s, float2(extraCoordX, clampedPos.y) / imgSize);
                extraColorX = $apply_swizzle(readSwizzle, extraColorX);
            }
            if (sampleExtraY) {
                extraCoordY = error.y > 0 ? insetClamp.y : insetClamp.w;
                extraColorY = sample(s, float2(clampedPos.x, extraCoordY) / imgSize);
                extraColorY = $apply_swizzle(readSwizzle, extraColorY);
            }
            if (sampleExtraX && sampleExtraY) {
                half4 extraColorXY = sample(s, float2(extraCoordX, extraCoordY) / imgSize);
                extraColorXY = $apply_swizzle(readSwizzle, extraColorXY);
                color = mix(mix(color, extraColorX, absError.x),
                            mix(extraColorY, extraColorXY, absError.x),
                            absError.y);
            } else if (sampleExtraX) {
                color = mix(color, extraColorX, absError.x);
            } else if (sampleExtraY) {
                color = mix(color, extraColorY, absError.y);
            }
        }

        // Do soft edge shader filtering for decal tiling and linear filtering using the error
        // values calculated above.
        if (tileModeX == $kTileModeDecal) {
            color *= max(1 - absError.x, 0);
        }
        if (tileModeY == $kTileModeDecal) {
            color *= max(1 - absError.y, 0);
        }
    }

    return color;
}

$pure half4 $cubic_filter_image(float2 pos,
                                float2 imgSize,
                                float4 subset,
                                int tileModeX,
                                int tileModeY,
                                float4x4 coeffs,
                                int readSwizzle,
                                sampler2D s) {
    // Determine pos's fractional offset f between texel centers.
    float2 f = fract(pos - 0.5);
    // Sample 16 points at 1-pixel intervals from [p - 1.5 ... p + 1.5].
    pos -= 1.5;
    // Snap to texel centers to prevent sampling neighboring texels.
    pos = floor(pos) + 0.5;

    float4 wx = coeffs * float4(1.0, f.x, f.x * f.x, f.x * f.x * f.x);
    float4 wy = coeffs * float4(1.0, f.y, f.y * f.y, f.y * f.y * f.y);
    float4 color = float4(0);
    for (int y = 0; y < 4; ++y) {
        float4 rowColor = float4(0);
        for (int x = 0; x < 4; ++x) {
            rowColor += wx[x] * $sample_image(pos + float2(x, y), imgSize, subset,
                                              tileModeX, tileModeY, $kFilterModeNearest,
                                              readSwizzle, s);
        }
        color += wy[y] * rowColor;
    }
    return half4(color);
}

$pure half4 sk_image_shader(float2 coords,
                            float2 imgSize,
                            float4 subset,
                            int tileModeX,
                            int tileModeY,
                            int filterMode,
                            int useCubic,
                            float4x4 cubicCoeffs,
                            int readSwizzle,
                            int csXformFlags,
                            int csXformSrcKind,
                            half csXformSrcCoeffs[7],
                            half3x3 csXformGamutTransform,
                            int csXformDstKind,
                            half csXformDstCoeffs[7],
                            sampler2D s) {
    half4 sampleColor = (useCubic != 0)
        ? $cubic_filter_image(coords, imgSize, subset, tileModeX, tileModeY, cubicCoeffs,
                              readSwizzle, s)
        : $sample_image(coords, imgSize, subset, tileModeX, tileModeY, filterMode, readSwizzle, s);
    return sk_color_space_transform(sampleColor, csXformFlags, csXformSrcKind, csXformSrcCoeffs,
                                    csXformGamutTransform, csXformDstKind, csXformDstCoeffs);
}

$pure float2 $tile_grad(int tileMode, float2 t) {
    switch (tileMode) {
        case $kTileModeClamp:
            t.x = clamp(t.x, 0, 1);
            break;

        case $kTileModeRepeat:
            t.x = fract(t.x);
            break;

        case $kTileModeMirror: {
            float t_1 = t.x - 1;
            t.x = t_1 - 2 * floor(t_1 * 0.5) - 1;
            if (sk_Caps.mustDoOpBetweenFloorAndAbs) {
                // At this point the expected value of tiled_t should between -1 and 1, so this
                // clamp has no effect other than to break up the floor and abs calls and make sure
                // the compiler doesn't merge them back together.
                t.x = clamp(t.x, -1, 1);
            }
            t.x = abs(t.x);
            break;
        }

        case $kTileModeDecal:
            if (t.x < 0 || t.x > 1) {
                return float2(0, -1);
            }
            break;
    }

    return t;
}

$pure half4 $colorize_grad_4(float4 colorsParam[4], float offsetsParam[4], float2 t) {
    if (t.y < 0) {
        return half4(0);

    } else if (t.x <= offsetsParam[0]) {
        return half4(colorsParam[0]);
    } else if (t.x < offsetsParam[1]) {
        return half4(mix(colorsParam[0], colorsParam[1], (t.x             - offsetsParam[0]) /
                                                         (offsetsParam[1] - offsetsParam[0])));
    } else if (t.x < offsetsParam[2]) {
        return half4(mix(colorsParam[1], colorsParam[2], (t.x             - offsetsParam[1]) /
                                                         (offsetsParam[2] - offsetsParam[1])));
    } else if (t.x < offsetsParam[3]) {
        return half4(mix(colorsParam[2], colorsParam[3], (t.x             - offsetsParam[2]) /
                                                         (offsetsParam[3] - offsetsParam[2])));
    } else {
        return half4(colorsParam[3]);
    }
}

$pure half4 $colorize_grad_8(float4 colorsParam[8], float offsetsParam[8], float2 t) {
    if (t.y < 0) {
        return half4(0);

    // Unrolled binary search through intervals
    // ( .. 0), (0 .. 1), (1 .. 2), (2 .. 3), (3 .. 4), (4 .. 5), (5 .. 6), (6 .. 7), (7 .. ).
    } else if (t.x < offsetsParam[4]) {
        if (t.x < offsetsParam[2]) {
            if (t.x <= offsetsParam[0]) {
                return half4(colorsParam[0]);
            } else if (t.x < offsetsParam[1]) {
                return half4(mix(colorsParam[0], colorsParam[1],
                                 (t.x             - offsetsParam[0]) /
                                 (offsetsParam[1] - offsetsParam[0])));
            } else {
                return half4(mix(colorsParam[1], colorsParam[2],
                                 (t.x             - offsetsParam[1]) /
                                 (offsetsParam[2] - offsetsParam[1])));
            }
        } else {
            if (t.x < offsetsParam[3]) {
                return half4(mix(colorsParam[2], colorsParam[3],
                                 (t.x             - offsetsParam[2]) /
                                 (offsetsParam[3] - offsetsParam[2])));
            } else {
                return half4(mix(colorsParam[3], colorsParam[4],
                                 (t.x             - offsetsParam[3]) /
                                 (offsetsParam[4] - offsetsParam[3])));
            }
        }
    } else {
        if (t.x < offsetsParam[6]) {
            if (t.x < offsetsParam[5]) {
                return half4(mix(colorsParam[4], colorsParam[5],
                                 (t.x             - offsetsParam[4]) /
                                 (offsetsParam[5] - offsetsParam[4])));
            } else {
                return half4(mix(colorsParam[5], colorsParam[6],
                                 (t.x             - offsetsParam[5]) /
                                 (offsetsParam[6] - offsetsParam[5])));
            }
        } else {
            if (t.x < offsetsParam[7]) {
                return half4(mix(colorsParam[6], colorsParam[7],
                                 (t.x             - offsetsParam[6]) /
                                 (offsetsParam[7] - offsetsParam[6])));
            } else {
                return half4(colorsParam[7]);
            }
        }
    }
}

$pure float2 $linear_grad_layout(float2 point0Param, float2 point1Param, float2 pos) {
    pos -= point0Param;
    float2 delta = point1Param - point0Param;
    float t = dot(pos, delta) / dot(delta, delta);
    return float2(t, 1);
}

$pure float2 $radial_grad_layout(float2 centerParam, float radiusParam, float2 pos) {
    float t = distance(pos, centerParam) / radiusParam;
    return float2(t, 1);
}

$pure float2 $sweep_grad_layout(float2 centerParam, float biasParam, float scaleParam, float2 pos) {
    pos -= centerParam;

    // Some devices incorrectly implement atan2(y,x) as atan(y/x). In actuality it is
    // atan2(y,x) = 2 * atan(y / (sqrt(x^2 + y^2) + x)). To work around this we pass in
    // (sqrt(x^2 + y^2) + x) as the second parameter to atan2 in these cases. We let the device
    // handle the undefined behavior if the second parameter is 0, instead of doing the divide
    // ourselves and calling atan with the quotient.
    float angle = sk_Caps.atan2ImplementedAsAtanYOverX ? 2 * atan(-pos.y, length(pos) - pos.x)
                                                       : atan(-pos.y, -pos.x);

    // 0.1591549430918 is 1/(2*pi), used since atan returns values [-pi, pi]
    float t = (angle * 0.1591549430918 + 0.5 + biasParam) * scaleParam;
    return float2(t, 1);
}

$pure float3x3 $map_to_unit_x(float2 p0, float2 p1) {
    // Returns a matrix that maps [p0, p1] to [(0, 0), (1, 0)]. Results are undefined if p0 = p1.
    // From skia/src/core/SkMatrix.cpp, SkMatrix::setPolyToPoly.
    return float3x3(
        0, -1,  0,
        1,  0,  0,
        0,  0,  1
    ) * inverse(float3x3(
        p1.y - p0.y, p0.x - p1.x, 0,
        p1.x - p0.x, p1.y - p0.y, 0,
               p0.x,        p0.y, 1
    ));
}

$pure float2 $conical_grad_layout(float2 point0Param,
                                  float2 point1Param,
                                  float radius0Param,
                                  float radius1Param,
                                  float2 pos) {
    const float SK_ScalarNearlyZero = 1.0 / (1 << 12);
    float dCenter = distance(point0Param, point1Param);
    float dRadius = radius1Param - radius0Param;

    // Degenerate case: a radial gradient (p0 = p1).
    bool radial = dCenter < SK_ScalarNearlyZero;

    // Degenerate case: a strip with bandwidth 2r (r0 = r1).
    bool strip = abs(dRadius) < SK_ScalarNearlyZero;

    if (radial) {
        if (strip) {
            // The start and end inputs are the same in both position and radius.
            // We don't expect to see this input, but just in case we avoid dividing by zero.
            return float2(0, -1);
        }

        float scale = 1 / dRadius;
        float scaleSign = sign(dRadius);
        float bias = radius0Param / dRadius;

        float2 pt = (pos - point0Param) * scale;
        float t = length(pt) * scaleSign - bias;
        return float2(t, 1);

    } else if (strip) {
        float3x3 transform = $map_to_unit_x(point0Param, point1Param);
        float r = radius0Param / dCenter;
        float r_2 = r * r;

        float2 pt = (transform * pos.xy1).xy;
        float t = r_2 - pt.y * pt.y;
        if (t < 0) {
            return float2(0, -1);
        }
        t = pt.x + sqrt(t);
        return float2(t, 1);

    } else {
        // See https://skia.org/docs/dev/design/conical/ for details on how this algorithm works.
        // Calculate f and swap inputs if necessary (steps 1 and 2).
        float f = radius0Param / (radius0Param - radius1Param);

        bool isSwapped = abs(f - 1) < SK_ScalarNearlyZero;
        if (isSwapped) {
            float2 tmpPt = point0Param;
            point0Param = point1Param;
            point1Param = tmpPt;
            f = 0;
        }

        // Apply mapping from [Cf, C1] to unit x, and apply the precalculations from steps 3 and 4,
        // all in the same transformation.
        float2 Cf = point0Param * (1 - f) + point1Param * f;
        float3x3 transform = $map_to_unit_x(Cf, point1Param);

        float scaleX = abs(1 - f);
        float scaleY = scaleX;
        float r1 = abs(radius1Param - radius0Param) / dCenter;
        bool isFocalOnCircle = abs(r1 - 1) < SK_ScalarNearlyZero;
        if (isFocalOnCircle) {
            scaleX *= 0.5;
            scaleY *= 0.5;
        } else {
            scaleX *= r1 / (r1 * r1 - 1);
            scaleY /= sqrt(abs(r1 * r1 - 1));
        }
        transform = float3x3(
            scaleX, 0, 0,
            0, scaleY, 0,
            0, 0, 1
        ) * transform;

        float2 pt = (transform * pos.xy1).xy;

        // Continue with step 5 onward.
        float invR1 = 1 / r1;
        float dRadiusSign = sign(1 - f);
        bool isWellBehaved = !isFocalOnCircle && r1 > 1;

        float x_t = -1;
        if (isFocalOnCircle) {
            x_t = dot(pt, pt) / pt.x;
        } else if (isWellBehaved) {
            x_t = length(pt) - pt.x * invR1;
        } else {
            float temp = pt.x * pt.x - pt.y * pt.y;
            if (temp >= 0) {
                if (isSwapped || dRadiusSign < 0) {
                    x_t = -sqrt(temp) - pt.x * invR1;
                } else {
                    x_t = sqrt(temp) - pt.x * invR1;
                }
            }
        }

        if (!isWellBehaved && x_t < 0) {
            return float2(0, -1);
        }

        float t = f + dRadiusSign * x_t;
        if (isSwapped) {
            t = 1 - t;
        }
        return float2(t, 1);
    }
}

$pure half4 sk_linear_grad_4_shader(float2 coords,
                                    float4 colorsParam[4],
                                    float offsetsParam[4],
                                    float2 point0Param,
                                    float2 point1Param,
                                    int tileMode,
                                    int colorSpace,
                                    int doUnpremul) {
    float2 t = $linear_grad_layout(point0Param, point1Param, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_4(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_linear_grad_8_shader(float2 coords,
                                    float4 colorsParam[8],
                                    float offsetsParam[8],
                                    float2 point0Param,
                                    float2 point1Param,
                                    int tileMode,
                                    int colorSpace,
                                    int doUnpremul) {
    float2 t = $linear_grad_layout(point0Param, point1Param, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_8(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_radial_grad_4_shader(float2 coords,
                                    float4 colorsParam[4],
                                    float offsetsParam[4],
                                    float2 centerParam,
                                    float radiusParam,
                                    int tileMode,
                                    int colorSpace,
                                    int doUnpremul) {
    float2 t = $radial_grad_layout(centerParam, radiusParam, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_4(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_radial_grad_8_shader(float2 coords,
                                    float4 colorsParam[8],
                                    float offsetsParam[8],
                                    float2 centerParam,
                                    float radiusParam,
                                    int tileMode,
                                    int colorSpace,
                                    int doUnpremul) {
    float2 t = $radial_grad_layout(centerParam, radiusParam, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_8(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_sweep_grad_4_shader(float2 coords,
                                   float4 colorsParam[4],
                                   float offsetsParam[4],
                                   float2 centerParam,
                                   float biasParam,
                                   float scaleParam,
                                   int tileMode,
                                   int colorSpace,
                                   int doUnpremul) {
    float2 t = $sweep_grad_layout(centerParam, biasParam, scaleParam, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_4(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_sweep_grad_8_shader(float2 coords,
                                   float4 colorsParam[8],
                                   float offsetsParam[8],
                                   float2 centerParam,
                                   float biasParam,
                                   float scaleParam,
                                   int tileMode,
                                   int colorSpace,
                                   int doUnpremul) {
    float2 t = $sweep_grad_layout(centerParam, biasParam, scaleParam, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_8(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_conical_grad_4_shader(float2 coords,
                                     float4 colorsParam[4],
                                     float offsetsParam[4],
                                     float2 point0Param,
                                     float2 point1Param,
                                     float radius0Param,
                                     float radius1Param,
                                     int tileMode,
                                     int colorSpace,
                                     int doUnpremul) {
    float2 t = $conical_grad_layout(point0Param, point1Param, radius0Param, radius1Param, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_4(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_conical_grad_8_shader(float2 coords,
                                     float4 colorsParam[8],
                                     float offsetsParam[8],
                                     float2 point0Param,
                                     float2 point1Param,
                                     float radius0Param,
                                     float radius1Param,
                                     int tileMode,
                                     int colorSpace,
                                     int doUnpremul) {
    float2 t = $conical_grad_layout(point0Param, point1Param, radius0Param, radius1Param, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_8(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_matrix_colorfilter(half4 colorIn, float4x4 m, float4 v, int inHSLA) {
    if (bool(inHSLA)) {
        colorIn = $rgb_to_hsl(colorIn.rgb, colorIn.a); // includes unpremul
    } else {
        colorIn = unpremul(colorIn);
    }

    half4 colorOut = half4((m * colorIn) + v);

    if (bool(inHSLA)) {
        colorOut = $hsl_to_rgb(colorOut.rgb, colorOut.a); // includes clamp and premul
    } else {
        colorOut = saturate(colorOut);
        colorOut.rgb *= colorOut.a;
    }

    return colorOut;
}

// This method computes the 4 x-coodinates ([0..1]) that should be used to look
// up in the Perlin noise shader's noise table.
$pure half4 noise_helper(half2 noiseVec,
                         half2 stitchData,
                         int stitching,
                         sampler2D permutationSampler) {
    const half kBlockSize = 256.0;

    half4 floorVal;
    floorVal.xy = floor(noiseVec);
    floorVal.zw = floorVal.xy + half2(1);

    // Adjust frequencies if we're stitching tiles
    if (bool(stitching)) {
        if (floorVal.x >= stitchData.x) { floorVal.x -= stitchData.x; };
        if (floorVal.y >= stitchData.y) { floorVal.y -= stitchData.y; };
        if (floorVal.z >= stitchData.x) { floorVal.z -= stitchData.x; };
        if (floorVal.w >= stitchData.y) { floorVal.w -= stitchData.y; };
    }

    half sampleX = sample(permutationSampler, half2(floorVal.x/kBlockSize, 0.5)).r;
    half sampleY = sample(permutationSampler, half2(floorVal.z/kBlockSize, 0.5)).r;

    half2 latticeIdx = half2(sampleX, sampleY);

    const half kInv255 = 0.003921569;   // 1.0 / 255.0

    // Aggressively round to the nearest exact (N / 255) floating point values.
    // This prevents rounding errors on some platforms (e.g., Tegras)
    latticeIdx = floor(latticeIdx * half2(255.0) + half2(0.5)) * half2(kInv255);

    // Get (x,y) coordinates with the permuted x
    half4 noiseXCoords = kBlockSize*latticeIdx.xyxy + floorVal.yyww;

    noiseXCoords /= half4(kBlockSize);
    return noiseXCoords;
}

// TODO: Move this to sksl_shared.sksl and try to share with Ganesh
$pure half4 noise_function(half2 noiseVec,
                           half4 noiseXCoords,
                           sampler2D noiseSampler) {

    half2 fractVal = fract(noiseVec);

    // smooth curve : t^2*(3 - 2*t)
    half2 noiseSmooth = fractVal*fractVal*(half2(3) - 2*fractVal);

    // This is used to convert the two 16bit integers packed into rgba 8 bit input into
    // a [-1,1] vector
    const half kInv256 = 0.00390625;  // 1.0 / 256.0

    half4 result;

    for (int channel = 0; channel < 4; channel++) {

        // There are 4 lines in the noise texture, put y coords at center of each.
        half chanCoord = (half(channel) + 0.5) / 4.0;

        half4 sampleA = sample(noiseSampler, half2(noiseXCoords.x, chanCoord));
        half4 sampleB = sample(noiseSampler, half2(noiseXCoords.y, chanCoord));
        half4 sampleC = sample(noiseSampler, half2(noiseXCoords.w, chanCoord));
        half4 sampleD = sample(noiseSampler, half2(noiseXCoords.z, chanCoord));

        half2 uv;
        half2 tmpFractVal = fractVal;

        // Compute u, at offset (0,0)
        uv.x = dot((sampleA.ga + sampleA.rb*kInv256)*2 - half2(1), tmpFractVal);

        // Compute v, at offset (-1,0)
        tmpFractVal.x -= 1.0;
        uv.y = dot((sampleB.ga + sampleB.rb*kInv256)*2 - half2(1), tmpFractVal);

        // Compute 'a' as a linear interpolation of 'u' and 'v'
        half2 ab;
        ab.x = mix(uv.x, uv.y, noiseSmooth.x);

        // Compute v, at offset (-1,-1)
        tmpFractVal.y -= 1.0;
        uv.y = dot((sampleC.ga + sampleC.rb*kInv256)*2 - half2(1), tmpFractVal);

        // Compute u, at offset (0,-1)
        tmpFractVal.x += 1.0;
        uv.x = dot((sampleD.ga + sampleD.rb*kInv256)*2 - half2(1), tmpFractVal);

        // Compute 'b' as a linear interpolation of 'u' and 'v'
        ab.y = mix(uv.x, uv.y, noiseSmooth.x);

        // Compute the noise as a linear interpolation of 'a' and 'b'
        result[channel] =  mix(ab.x, ab.y, noiseSmooth.y);
    }

    return result;
}

// permutationSampler is [kBlockSize x 1] A8
// noiseSampler is [kBlockSize x 4] RGBA8 premul
$pure half4 perlin_noise_shader(float2 coords,
                                float2 baseFrequency,
                                float2 stitchDataIn,
                                int noiseType,
                                int numOctaves,
                                int stitching,
                                sampler2D permutationSampler,
                                sampler2D noiseSampler) {
    const int kFractalNoise_Type = 0;
    const int kTurbulence_Type = 1;

    // There are rounding errors if the floor operation is not performed here
    half2 noiseVec = half2(floor(coords.xy) * baseFrequency);

    // Clear the color accumulator
    half4 color = half4(0);

    half2 stitchData = half2(stitchDataIn);

    half ratio = 1.0;

    // Loop over all octaves
    for (int octave = 0; octave < numOctaves; ++octave) {
        half4 noiseXCoords = noise_helper(noiseVec, stitchData, stitching, permutationSampler);

        half4 tmp = noise_function(noiseVec, noiseXCoords, noiseSampler);

        if (noiseType != kFractalNoise_Type) {
            // For kTurbulence_Type the result is: abs(noise[-1,1])
            tmp = abs(tmp);
        }

        tmp *= ratio;
        color += tmp;

        noiseVec *= half2(2.0);
        ratio *= 0.5;
        stitchData *= half2(2.0);
    }

    if (noiseType == kFractalNoise_Type) {
        // For kFractalNoise_Type the result is: noise[-1,1] * 0.5 + 0.5
        color = color * half4(0.5) + half4(0.5);
    }

    // Clamp values
    color = saturate(color);

    // Pre-multiply the result
    return half4(color.rgb * color.aaa, color.a);
}

$pure half4 sk_blend(int blendMode, half4 src, half4 dst) {
    const int kClear      = 0;
    const int kSrc        = 1;
    const int kDst        = 2;
    const int kSrcOver    = 3;
    const int kDstOver    = 4;
    const int kSrcIn      = 5;
    const int kDstIn      = 6;
    const int kSrcOut     = 7;
    const int kDstOut     = 8;
    const int kSrcATop    = 9;
    const int kDstATop    = 10;
    const int kXor        = 11;
    const int kPlus       = 12;
    const int kModulate   = 13;
    const int kScreen     = 14;
    const int kOverlay    = 15;
    const int kDarken     = 16;
    const int kLighten    = 17;
    const int kColorDodge = 18;
    const int kColorBurn  = 19;
    const int kHardLight  = 20;
    const int kSoftLight  = 21;
    const int kDifference = 22;
    const int kExclusion  = 23;
    const int kMultiply   = 24;
    const int kHue        = 25;
    const int kSaturation = 26;
    const int kColor      = 27;
    const int kLuminosity = 28;

    switch (blendMode) {
        case kClear:      { return blend_clear(src, dst); }
        case kSrc:        { return blend_src(src, dst); }
        case kDst:        { return blend_dst(src, dst); }
        case kSrcOver:    { return blend_porter_duff(half4(1, 0,  0, -1), src, dst); }
        case kDstOver:    { return blend_porter_duff(half4(0, 1, -1,  0), src, dst); }
        case kSrcIn:      { return blend_porter_duff(half4(0, 0,  1,  0), src, dst); }
        case kDstIn:      { return blend_porter_duff(half4(0, 0,  0,  1), src, dst); }
        case kSrcOut:     { return blend_porter_duff(half4(0, 0, -1,  0), src, dst); }
        case kDstOut:     { return blend_porter_duff(half4(0, 0,  0, -1), src, dst); }
        case kSrcATop:    { return blend_porter_duff(half4(0, 0,  1, -1), src, dst); }
        case kDstATop:    { return blend_porter_duff(half4(0, 0, -1,  1), src, dst); }
        case kXor:        { return blend_porter_duff(half4(0, 0, -1, -1), src, dst); }
        case kPlus:       { return blend_porter_duff(half4(1, 1,  0,  0), src, dst); }
        case kModulate:   { return blend_modulate(src, dst); }
        case kScreen:     { return blend_screen(src, dst); }
        case kOverlay:    { return blend_overlay(/*flip=*/0, src, dst); }
        case kDarken:     { return blend_darken(/*mode=*/1, src, dst); }
        case kLighten:    { return blend_darken(/*mode=*/-1, src, dst); }
        case kColorDodge: { return blend_color_dodge(src, dst); }
        case kColorBurn:  { return blend_color_burn(src, dst); }
        case kHardLight:  { return blend_overlay(/*flip=*/1, src, dst); }
        case kSoftLight:  { return blend_soft_light(src, dst); }
        case kDifference: { return blend_difference(src, dst); }
        case kExclusion:  { return blend_exclusion(src, dst); }
        case kMultiply:   { return blend_multiply(src, dst); }
        case kHue:        { return blend_hslc(/*flipSat=*/half2(0, 1), src, dst); }
        case kSaturation: { return blend_hslc(/*flipSat=*/half2(1), src, dst); }
        case kColor:      { return blend_hslc(/*flipSat=*/half2(0), src, dst); }
        case kLuminosity: { return blend_hslc(/*flipSat=*/half2(1, 0), src, dst); }
        default: return half4(0);  // Avoids 'blend can exit without returning a value' error
    }
}

$pure half4 sk_blend_shader(int blendMode, half4 dst, half4 src) {
    return sk_blend(blendMode, src, dst);
}

$pure half4 porter_duff_blend_shader(half4 blendOp, half4 dst, half4 src) {
    return blend_porter_duff(blendOp, src, dst);
}

$pure half4 sk_blend_colorfilter(half4 dstColor, int blendMode, float4 srcColor) {
    return sk_blend(blendMode, half4(srcColor), dstColor);
}

$pure half4 sk_table_colorfilter(half4 inColor, sampler2D s) {
    half4 coords = unpremul(inColor) * 255.0/256.0 + 0.5/256.0;
    half4 color = half4(sample(s, half2(coords.r, 3.0/8.0)).r,
                        sample(s, half2(coords.g, 5.0/8.0)).r,
                        sample(s, half2(coords.b, 7.0/8.0)).r,
                        1);
    return color * sample(s, half2(coords.a, 1.0/8.0)).r;
}

$pure half4 sk_gaussian_colorfilter(half4 inColor) {
    half factor = 1 - inColor.a;
    factor = exp(-factor * factor * 4) - 0.018;
    return half4(factor);
}


///////////////////////////////////////////////////////////////////////////////////////////////////
// Support functions for analytic round rectangles

// Calculates 1/|∇| in device space by applying the chain rule to a local gradient vector and the
// 2x2 Jacobian describing the transform from local-to-device space. For non-perspective, this is
// equivalent to the "normal matrix", or the inverse transpose. For perspective, J should be
//    W(u,v) [m00' - m20'u  m01' - m21'u] derived from the first two columns of the 3x3 inverse.
//           [m10' - m20'v  m11' - m21'v]
$pure float inverse_grad_len(float2 localGrad, float2x2 jacobian) {
    // NOTE: By chain rule, the local gradient is on the left side of the Jacobian matrix
    float2 devGrad = localGrad * jacobian;
    // NOTE: This uses the L2 norm, which is more accurate than the L1 norm used by fwidth().
    // TODO: Switch to L1 since it is a 2x perf improvement according to Xcode with little visual
    // impact, but start with L2 to measure the change separately from the algorithmic update.
    // return 1.0 / (abs(devGrad.x) + abs(devGrad.y));
    return inversesqrt(dot(devGrad, devGrad));
}

// Returns distance from both sides of a stroked circle or ellipse. Elliptical coverage is
// only accurate if strokeRadius = 0. A positive value represents the interior of the stroke.
$pure float2 elliptical_distance(float2 uv, float2 radii, float strokeRadius, float2x2 jacobian) {
    // We do need to evaluate up to two circle equations: one with
    //    R = cornerRadius(r)+strokeRadius(s), and another with R = r-s.
    // This can be consolidated into a common evaluation against a circle of radius sqrt(r^2+s^2):
    //    (x/(r+/-s))^2 + (y/(r+/-s))^2 = 1
    //    x^2 + y^2 = (r+/-s)^2
    //    x^2 + y^2 = r^2 + s^2 +/- 2rs
    //    (x/sqrt(r^2+s^2))^2 + (y/sqrt(r^2+s^2)) = 1 +/- 2rs/(r^2+s^2)
    // The 2rs/(r^2+s^2) is the "width" that adjusts the implicit function to the outer or inner
    // edge of the stroke. For fills and hairlines, s = 0, which means these operations remain valid
    // for elliptical corners where radii holds the different X and Y corner radii.
    float2 invR2 = 1.0 / (radii * radii + strokeRadius*strokeRadius);
    float2 normUV = invR2 * uv;
    float invGradLength = inverse_grad_len(normUV, jacobian);

    // Since normUV already includes 1/r^2 in the denominator, dot with just 'uv' instead.
    float f = 0.5 * invGradLength * (dot(uv, normUV) - 1.0);

    // This is 0 for fills/hairlines, which are the only types that allow
    // elliptical corners (strokeRadius == 0). For regular strokes just use X.
    float width = radii.x * strokeRadius * invR2.x * invGradLength;
    return float2(width - f, width + f);
}

// Accumulates the minimum (and negative maximum) of the outer and inner corner distances in 'dist'
// for a possibly elliptical corner with 'radii' and relative pixel location specified by
// 'cornerEdgeDist'. The corner's basis relative to the jacobian is defined in 'xyFlip'.
void corner_distance(inout float2 dist,
                     float2x2 jacobian,
                     float2 strokeParams,
                     float2 cornerEdgeDist,
                     float2 xyFlip,
                     float2 radii) {
    float2 uv = radii - cornerEdgeDist;
    // NOTE: For mitered corners uv > 0 only if it's stroked, and in that case the
    // subsequent conditions skip calculating anything.
    if (uv.x > 0.0 && uv.y > 0.0) {
        if ((radii.x > 0.0 && radii.y > 0.0) ||
            (strokeParams.x > 0.0 && strokeParams.y < 0.0 /* round-join */)) {
            // A rounded corner so incorporate outer elliptical distance if we're within the
            // quarter circle.
            float2 d = elliptical_distance(uv * xyFlip, radii, strokeParams.x, jacobian);
            if (radii.x - strokeParams.x <= 0.0) {
                d.y = 1.0; // disregard inner curve since it's collapsed into an inner miter.
            } else {
                d.y *= -1.0; // Negate so that "min" accumulates the maximum value instead
            }
            dist = min(dist, d);
        } else if (strokeParams.y == 0.0 /* bevel-join */) {
            // Bevels are--by construction--interior mitered, so inner distance is based
            // purely on the edge distance calculations, but the outer distance is to a 45-degree
            // line and not the vertical/horizontal lines of the other edges.
            float bevelDist = (strokeParams.x - uv.x - uv.y) * inverse_grad_len(xyFlip, jacobian);
            dist.x = min(dist.x, bevelDist);
        } // Else it's a miter so both inner and outer distances are unmodified
    } // Else we're not affected by the corner so leave distances unmodified
}

// Accumulates the minimum (and negative maximum) of the outer and inner corner distances into 'd',
// for all four corners of a [round] rectangle. 'edgeDists' should be ordered LTRB with positive
// distance representing the interior of the edge. 'xRadii' and 'yRadii' should hold the per-corner
// elliptical radii, ordered TL, TR, BR, BL.
void corner_distances(inout float2 d,
                      float2x2 J,
                      float2 stroke, // {radii, joinStyle}, see StrokeStyle struct definition
                      float4 edgeDists,
                      float4 xRadii,
                      float4 yRadii) {
    corner_distance(d, J, stroke, edgeDists.xy, float2(-1.0, -1.0), float2(xRadii[0], yRadii[0]));
    corner_distance(d, J, stroke, edgeDists.zy, float2( 1.0, -1.0), float2(xRadii[1], yRadii[1]));
    corner_distance(d, J, stroke, edgeDists.zw, float2( 1.0,  1.0), float2(xRadii[2], yRadii[2]));
    corner_distance(d, J, stroke, edgeDists.xw, float2(-1.0,  1.0), float2(xRadii[3], yRadii[3]));
}