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

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

half4 sk_passthrough(half4 color) {
    return color;
}

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

// The localMatrix is passed to the child by the glue code. This snippet just needs to bubble the
// child's output back up. Local coordinates are passed in from the default glue code and can
// just be ignored here.
half4 sk_local_matrix_shader(float4, float4x4, half4 childResult) {
    return childResult;
}

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;
    }
}

half4 sk_image_shader(float4 coords,
                      float4x4 preLocal,
                      float4 subset,
                      int tileModeX,
                      int tileModeY,
                      int filterMode,
                      int imgWidth,
                      int imgHeight,
                      sampler2D s) {
    float2 pos = (preLocal * coords).xy;

    // 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 / float2(imgWidth, imgHeight));

    // Remember the amount the coord moved for clamping. This will be used to implement shader-based
    // filtering for repeat and decal tiling.
    half2 error = half2(pos - clampedPos);

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

    return color;
}

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;
}

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]);
    }
}

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]);
            }
        }
    }
}

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);
}

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

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);
}

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
    ));
}

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);
    }
}

half4 sk_linear_grad_4_shader(float4 coords,
                              float4x4 preLocal,
                              float4 colorsParam[4],
                              float offsetsParam[4],
                              float2 point0Param,
                              float2 point1Param,
                              int tileMode) {
    float2 pos = (preLocal * coords).xy;
    float2 t = $linear_grad_layout(point0Param, point1Param, pos);
    t = $tile_grad(tileMode, t);
    return $colorize_grad_4(colorsParam, offsetsParam, t);
}

half4 sk_linear_grad_8_shader(float4 coords,
                              float4x4 preLocal,
                              float4 colorsParam[8],
                              float offsetsParam[8],
                              float2 point0Param,
                              float2 point1Param,
                              int tileMode) {
    float2 pos = (preLocal * coords).xy;
    float2 t = $linear_grad_layout(point0Param, point1Param, pos);
    t = $tile_grad(tileMode, t);
    return $colorize_grad_8(colorsParam, offsetsParam, t);
}

half4 sk_radial_grad_4_shader(float4 coords,
                              float4x4 preLocal,
                              float4 colorsParam[4],
                              float offsetsParam[4],
                              float2 centerParam,
                              float radiusParam,
                              int tileMode) {
    float2 pos = (preLocal * coords).xy;
    float2 t = $radial_grad_layout(centerParam, radiusParam, pos);
    t = $tile_grad(tileMode, t);
    return $colorize_grad_4(colorsParam, offsetsParam, t);
}

half4 sk_radial_grad_8_shader(float4 coords,
                              float4x4 preLocal,
                              float4 colorsParam[8],
                              float offsetsParam[8],
                              float2 centerParam,
                              float radiusParam,
                              int tileMode) {
    float2 pos = (preLocal * coords).xy;
    float2 t = $radial_grad_layout(centerParam, radiusParam, pos);
    t = $tile_grad(tileMode, t);
    return $colorize_grad_8(colorsParam, offsetsParam, t);
}

half4 sk_sweep_grad_4_shader(float4 coords,
                             float4x4 preLocal,
                             float4 colorsParam[4],
                             float offsetsParam[4],
                             float2 centerParam,
                             float biasParam,
                             float scaleParam,
                             int tileMode) {
    float2 pos = (preLocal * coords).xy;
    float2 t = $sweep_grad_layout(centerParam, biasParam, scaleParam, pos);
    t = $tile_grad(tileMode, t);
    return $colorize_grad_4(colorsParam, offsetsParam, t);
}

half4 sk_sweep_grad_8_shader(float4 coords,
                             float4x4 preLocal,
                             float4 colorsParam[8],
                             float offsetsParam[8],
                             float2 centerParam,
                             float biasParam,
                             float scaleParam,
                             int tileMode) {
    float2 pos = (preLocal * coords).xy;
    float2 t = $sweep_grad_layout(centerParam, biasParam, scaleParam, pos);
    t = $tile_grad(tileMode, t);
    return $colorize_grad_8(colorsParam, offsetsParam, t);
}

half4 sk_conical_grad_4_shader(float4 coords,
                               float4x4 preLocal,
                               float4 colorsParam[4],
                               float offsetsParam[4],
                               float2 point0Param,
                               float2 point1Param,
                               float radius0Param,
                               float radius1Param,
                               int tileMode) {
    float2 pos = (preLocal * coords).xy;
    float2 t = $conical_grad_layout(point0Param, point1Param, radius0Param, radius1Param, pos);
    t = $tile_grad(tileMode, t);
    return $colorize_grad_4(colorsParam, offsetsParam, t);
}

half4 sk_conical_grad_8_shader(float4 coords,
                               float4x4 preLocal,
                               float4 colorsParam[8],
                               float offsetsParam[8],
                               float2 point0Param,
                               float2 point1Param,
                               float radius0Param,
                               float radius1Param,
                               int tileMode) {
    float2 pos = (preLocal * coords).xy;
    float2 t = $conical_grad_layout(point0Param, point1Param, radius0Param, radius1Param, pos);
    t = $tile_grad(tileMode, t);
    return $colorize_grad_8(colorsParam, offsetsParam, t);
}

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;
}

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
    }
}

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

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

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;
}

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