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Commit 6183c97e authored by Romain Guy's avatar Romain Guy
Browse files

Bowing my head in shame, going back to gamma interpolated gradients 

Frankengradients (linearly interpolated RGB, gamma interpolated alpha) look
fantastic but unfortunately create sligh compatibility issues. For instance,
a gradient from 0xffea1030 to 0x00ea1030 (opaque to alpha, with a single
color) blended on top of 0xff101010 would not look the same as a single
opaque gradient from 0xffea1030 to 0xff101010. The difference is hardly
noticeable on simple gradients but it could cause confusion amongst app
developers. Their life is hard enough as it is, let's be good to them.

My crusade against the gamma world is not over and one day I shall
be the victor. I am patience.

Bug: 35485208
Test: UiRendering.ShaderTests, UiRendering.GradientTests, manual testing
Change-Id: I8204e60cdf0a6b12dfe22638d30ca9622687000e
parent 0d86d7eb

libs/hwui/FloatColor.h

+7 −6
Original line number Diff line number Diff line
@@ -38,13 +38,14 @@ struct FloatColor { 
    }



    // "color" is a gamma-encoded sRGB color

    // After calling this method, the color is stored as a linear color. The color

    // is not pre-multiplied.

    void setUnPreMultipliedSRGB(uint32_t color) {

    // After calling this method, the color is stored as a un-premultiplied linear color

    // if linear blending is enabled. Otherwise, the color is stored as a un-premultiplied

    // gamma-encoded sRGB color

    void setUnPreMultiplied(uint32_t color) {

        a = ((color >> 24) & 0xff) / 255.0f;

        r = EOCF_sRGB(((color >> 16) & 0xff) / 255.0f);

        g = EOCF_sRGB(((color >>  8) & 0xff) / 255.0f);

        b = EOCF_sRGB(((color      ) & 0xff) / 255.0f);

        r = EOCF(((color >> 16) & 0xff) / 255.0f);

        g = EOCF(((color >>  8) & 0xff) / 255.0f);

        b = EOCF(((color      ) & 0xff) / 255.0f);

    }



    bool isNotBlack() {

libs/hwui/GradientCache.cpp

+10 −13
Original line number Diff line number Diff line
@@ -189,9 +189,9 @@ void GradientCache::mixBytes(const FloatColor& start, const FloatColor& end, 
        float amount, uint8_t*& dst) const {

    float oppAmount = 1.0f - amount;

    float a = start.a * oppAmount + end.a * amount;

    *dst++ = uint8_t(a * OECF_sRGB((start.r * oppAmount + end.r * amount)) * 255.0f);

    *dst++ = uint8_t(a * OECF_sRGB((start.g * oppAmount + end.g * amount)) * 255.0f);

    *dst++ = uint8_t(a * OECF_sRGB((start.b * oppAmount + end.b * amount)) * 255.0f);

    *dst++ = uint8_t(a * OECF(start.r * oppAmount + end.r * amount) * 255.0f);

    *dst++ = uint8_t(a * OECF(start.g * oppAmount + end.g * amount) * 255.0f);

    *dst++ = uint8_t(a * OECF(start.b * oppAmount + end.b * amount) * 255.0f);

    *dst++ = uint8_t(a * 255.0f);

}
@@ -201,17 +201,14 @@ void GradientCache::mixFloats(const FloatColor& start, const FloatColor& end, 
    float a = start.a * oppAmount + end.a * amount;

    float* d = (float*) dst;

#ifdef ANDROID_ENABLE_LINEAR_BLENDING

    // We want to stay linear

    *d++ = a * (start.r * oppAmount + end.r * amount);

    *d++ = a * (start.g * oppAmount + end.g * amount);

    *d++ = a * (start.b * oppAmount + end.b * amount);

#else

    // What we're doing to the alpha channel here is technically incorrect

    // but reproduces Android's old behavior when the alpha was pre-multiplied

    // with gamma-encoded colors

    a = EOCF_sRGB(a);

    *d++ = a * OECF_sRGB(start.r * oppAmount + end.r * amount);

    *d++ = a * OECF_sRGB(start.g * oppAmount + end.g * amount);

    *d++ = a * OECF_sRGB(start.b * oppAmount + end.b * amount);

    *d++ = a * OECF(start.r * oppAmount + end.r * amount);

    *d++ = a * OECF(start.g * oppAmount + end.g * amount);

    *d++ = a * OECF(start.b * oppAmount + end.b * amount);

#endif

    *d++ = a;

    dst += 4 * sizeof(float);
@@ -232,10 +229,10 @@ void GradientCache::generateTexture(uint32_t* colors, float* positions, 
    ChannelMixer mix = gMixers[mUseFloatTexture];



    FloatColor start;

    start.setUnPreMultipliedSRGB(colors[0]);

    start.setUnPreMultiplied(colors[0]);



    FloatColor end;

    end.setUnPreMultipliedSRGB(colors[1]);

    end.setUnPreMultiplied(colors[1]);



    int currentPos = 1;

    float startPos = positions[0];
@@ -250,7 +247,7 @@ void GradientCache::generateTexture(uint32_t* colors, float* positions, 


            currentPos++;



            end.setUnPreMultipliedSRGB(colors[currentPos]);

            end.setUnPreMultiplied(colors[currentPos]);

            distance = positions[currentPos] - startPos;

        }

libs/hwui/ProgramCache.cpp

+22 −19
Original line number Diff line number Diff line
@@ -202,23 +202,26 @@ const char* gFS_Gradient_Functions = R"__SHADER__( 
)__SHADER__";

const char* gFS_Gradient_Preamble[2] = {

        // Linear framebuffer

        "\nvec4 dither(const vec4 color) {\n"

        "    return color + (triangleNoise(gl_FragCoord.xy * screenSize.xy) / 255.0);\n"

        "}\n"

        "\nvec4 gammaMix(const vec4 a, const vec4 b, float v) {\n"

        "    vec4 c = mix(a, b, v);\n"

        "    c.a = EOTF_sRGB(c.a);\n" // This is technically incorrect but preserves compatibility

        "    return vec4(OETF_sRGB(c.rgb) * c.a, c.a);\n"

        "}\n",

        R"__SHADER__(

        vec4 dither(const vec4 color) {

            return color + (triangleNoise(gl_FragCoord.xy * screenSize.xy) / 255.0);

        }

        vec4 gradientMix(const vec4 a, const vec4 b, float v) {

            vec4 c = mix(a, b, v);

            return vec4(c.rgb * c.a, c.a);

        }

        )__SHADER__",

        // sRGB framebuffer

        "\nvec4 dither(const vec4 color) {\n"

        "    vec3 dithered = sqrt(color.rgb) + (triangleNoise(gl_FragCoord.xy * screenSize.xy) / 255.0);\n"

        "    return vec4(dithered * dithered, color.a);\n"

        "}\n"

        "\nvec4 gammaMix(const vec4 a, const vec4 b, float v) {\n"

        "    vec4 c = mix(a, b, v);\n"

        "    return vec4(c.rgb * c.a, c.a);\n"

        "}\n"

        R"__SHADER__(

        vec4 dither(const vec4 color) {

            vec3 dithered = sqrt(color.rgb) + (triangleNoise(gl_FragCoord.xy * screenSize.xy) / 255.0);

            return vec4(dithered * dithered, color.a);

        }

        vec4 gradientMixMix(const vec4 a, const vec4 b, float v) {

            vec4 c = mix(a, b, v);

            return vec4(c.rgb * c.a, c.a);

        }

        )__SHADER__",

};



// Uses luminance coefficients from Rec.709 to choose the appropriate gamma
@@ -272,19 +275,19 @@ const char* gFS_Main_FetchGradient[6] = { 
        // Linear

        "    vec4 gradientColor = texture2D(gradientSampler, linear);\n",



        "    vec4 gradientColor = gammaMix(startColor, endColor, clamp(linear, 0.0, 1.0));\n",

        "    vec4 gradientColor = gradientMix(startColor, endColor, clamp(linear, 0.0, 1.0));\n",



        // Circular

        "    vec4 gradientColor = texture2D(gradientSampler, vec2(length(circular), 0.5));\n",



        "    vec4 gradientColor = gammaMix(startColor, endColor, clamp(length(circular), 0.0, 1.0));\n",

        "    vec4 gradientColor = gradientMix(startColor, endColor, clamp(length(circular), 0.0, 1.0));\n",



        // Sweep

        "    highp float index = atan(sweep.y, sweep.x) * 0.15915494309; // inv(2 * PI)\n"

        "    vec4 gradientColor = texture2D(gradientSampler, vec2(index - floor(index), 0.5));\n",



        "    highp float index = atan(sweep.y, sweep.x) * 0.15915494309; // inv(2 * PI)\n"

        "    vec4 gradientColor = gammaMix(startColor, endColor, clamp(index - floor(index), 0.0, 1.0));\n"

        "    vec4 gradientColor = gradientMix(startColor, endColor, clamp(index - floor(index), 0.0, 1.0));\n"

};

const char* gFS_Main_FetchBitmap =

        "    vec4 bitmapColor = OETF(texture2D(bitmapSampler, outBitmapTexCoords));\n";

libs/hwui/SkiaShader.cpp

+2 −2
Original line number Diff line number Diff line
@@ -173,8 +173,8 @@ bool tryStoreGradient(Caches& caches, const SkShader& shader, const Matrix4 mode 
        outData->gradientSampler = 0;

        outData->gradientTexture = nullptr;



        outData->startColor.setUnPreMultipliedSRGB(gradInfo.fColors[0]);

        outData->endColor.setUnPreMultipliedSRGB(gradInfo.fColors[1]);

        outData->startColor.setUnPreMultiplied(gradInfo.fColors[0]);

        outData->endColor.setUnPreMultiplied(gradInfo.fColors[1]);

    }



    return true;