tests/SRGBReadWritePixelsTest.cpp

/*
 * Copyright 2015 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "Test.h"
#if SK_SUPPORT_GPU
#include "GrCaps.h"
#include "GrContext.h"
#include "GrContextPriv.h"
#include "GrSurfaceContext.h"
#include "SkCanvas.h"
#include "SkGr.h"
#include "SkSurface.h"

// using anonymous namespace because these functions are used as template params.
namespace {
/** convert 0..1 srgb value to 0..1 linear */
float srgb_to_linear(float srgb) {
    if (srgb <= 0.04045f) {
        return srgb / 12.92f;
    } else {
        return powf((srgb + 0.055f) / 1.055f, 2.4f);
    }
}

/** convert 0..1 linear value to 0..1 srgb */
float linear_to_srgb(float linear) {
    if (linear <= 0.0031308) {
        return linear * 12.92f;
    } else {
        return 1.055f * powf(linear, 1.f / 2.4f) - 0.055f;
    }
}
}

/** tests a conversion with an error tolerance */
template <float (*CONVERT)(float)> static bool check_conversion(uint32_t input, uint32_t output,
                                                                float error) {
    // alpha should always be exactly preserved.
    if ((input & 0xff000000) != (output & 0xff000000)) {
        return false;
    }

    for (int c = 0; c < 3; ++c) {
        uint8_t inputComponent = (uint8_t) ((input & (0xff << (c*8))) >> (c*8));
        float lower = SkTMax(0.f, (float) inputComponent - error);
        float upper = SkTMin(255.f, (float) inputComponent + error);
        lower = CONVERT(lower / 255.f);
        upper = CONVERT(upper / 255.f);
        SkASSERT(lower >= 0.f && lower <= 255.f);
        SkASSERT(upper >= 0.f && upper <= 255.f);
        uint8_t outputComponent = (output & (0xff << (c*8))) >> (c*8);
        if (outputComponent < SkScalarFloorToInt(lower * 255.f) ||
            outputComponent > SkScalarCeilToInt(upper * 255.f)) {
            return false;
        }
    }
    return true;
}

/** tests a forward and backward conversion with an error tolerance */
template <float (*FORWARD)(float), float (*BACKWARD)(float)>
static bool check_double_conversion(uint32_t input, uint32_t output, float error) {
    // alpha should always be exactly preserved.
    if ((input & 0xff000000) != (output & 0xff000000)) {
        return false;
    }

    for (int c = 0; c < 3; ++c) {
        uint8_t inputComponent = (uint8_t) ((input & (0xff << (c*8))) >> (c*8));
        float lower = SkTMax(0.f, (float) inputComponent - error);
        float upper = SkTMin(255.f, (float) inputComponent + error);
        lower = FORWARD(lower / 255.f);
        upper = FORWARD(upper / 255.f);
        SkASSERT(lower >= 0.f && lower <= 255.f);
        SkASSERT(upper >= 0.f && upper <= 255.f);
        uint8_t upperComponent = SkScalarCeilToInt(upper * 255.f);
        uint8_t lowerComponent = SkScalarFloorToInt(lower * 255.f);
        lower = SkTMax(0.f, (float) lowerComponent - error);
        upper = SkTMin(255.f, (float) upperComponent + error);
        lower = BACKWARD(lowerComponent / 255.f);
        upper = BACKWARD(upperComponent / 255.f);
        SkASSERT(lower >= 0.f && lower <= 255.f);
        SkASSERT(upper >= 0.f && upper <= 255.f);
        upperComponent = SkScalarCeilToInt(upper * 255.f);
        lowerComponent = SkScalarFloorToInt(lower * 255.f);

        uint8_t outputComponent = (output & (0xff << (c*8))) >> (c*8);
        if (outputComponent < lowerComponent || outputComponent > upperComponent) {
            return false;
        }
    }
    return true;
}

static bool check_srgb_to_linear_conversion(uint32_t srgb, uint32_t linear, float error) {
    return check_conversion<srgb_to_linear>(srgb, linear, error);
}

static bool check_linear_to_srgb_conversion(uint32_t linear, uint32_t srgb, float error) {
    return check_conversion<linear_to_srgb>(linear, srgb, error);
}

static bool check_linear_to_srgb_to_linear_conversion(uint32_t input, uint32_t output, float error) {
    return check_double_conversion<linear_to_srgb, srgb_to_linear>(input, output, error);
}

static bool check_srgb_to_linear_to_srgb_conversion(uint32_t input, uint32_t output, float error) {
    return check_double_conversion<srgb_to_linear, linear_to_srgb>(input, output, error);
}

typedef bool (*CheckFn) (uint32_t orig, uint32_t actual, float error);

void read_and_check_pixels(skiatest::Reporter* reporter, GrSurfaceContext* context,
                           uint32_t* origData,
                           const SkImageInfo& dstInfo, CheckFn checker, float error,
                           const char* subtestName) {
    int w = dstInfo.width();
    int h = dstInfo.height();
    SkAutoTMalloc<uint32_t> readData(w * h);
    memset(readData.get(), 0, sizeof(uint32_t) * w * h);

    if (!context->readPixels(dstInfo, readData.get(), 0, 0, 0)) {
        ERRORF(reporter, "Could not read pixels for %s.", subtestName);
        return;
    }

    for (int j = 0; j < h; ++j) {
        for (int i = 0; i < w; ++i) {
            uint32_t orig = origData[j * w + i];
            uint32_t read = readData[j * w + i];

            if (!checker(orig, read, error)) {
                ERRORF(reporter, "Expected 0x%08x, read back as 0x%08x in %s at %d, %d).",
                       orig, read, subtestName, i, j);
                return;
            }
        }
    }
}

// TODO: Add tests for copySurface between srgb/linear textures. Add tests for unpremul/premul
// conversion during read/write along with srgb/linear conversions.
DEF_GPUTEST_FOR_RENDERING_CONTEXTS(SRGBReadWritePixels, reporter, ctxInfo) {
    GrContext* context = ctxInfo.grContext();
#if defined(GOOGLE3)
    // Stack frame size is limited in GOOGLE3.
    static const int kW = 63;
    static const int kH = 63;
#else
    static const int kW = 255;
    static const int kH = 255;
#endif
    uint32_t origData[kW * kH];
    for (int j = 0; j < kH; ++j) {
        for (int i = 0; i < kW; ++i) {
            origData[j * kW + i] = (j << 24) | (i << 16) | (i << 8) | i;
        }
    }

    const SkImageInfo iiSRGBA = SkImageInfo::Make(kW, kH, kRGBA_8888_SkColorType,
                                                  kPremul_SkAlphaType,
                                                  SkColorSpace::MakeSRGB());
    const SkImageInfo iiRGBA = SkImageInfo::Make(kW, kH, kRGBA_8888_SkColorType,
                                                 kPremul_SkAlphaType);
    GrSurfaceDesc desc;
    desc.fFlags = kRenderTarget_GrSurfaceFlag;
    desc.fOrigin = kBottomLeft_GrSurfaceOrigin;
    desc.fWidth = kW;
    desc.fHeight = kH;
    desc.fConfig = kSRGBA_8888_GrPixelConfig;
    if (context->caps()->isConfigRenderable(desc.fConfig, false) &&
        context->caps()->isConfigTexturable(desc.fConfig)) {

        sk_sp<GrSurfaceContext> sContext = context->contextPriv().makeDeferredSurfaceContext(
                                                                             desc, GrMipMapped::kNo,
                                                                             SkBackingFit::kExact,
                                                                             SkBudgeted::kNo);
        if (!sContext) {
            ERRORF(reporter, "Could not create SRGBA surface context.");
            return;
        }

        float error = context->caps()->shaderCaps()->floatPrecisionVaries() ? 1.2f  : 0.5f;

        // Write srgba data and read as srgba and then as rgba
        if (sContext->writePixels(iiSRGBA, origData, 0, 0, 0)) {
            // For the all-srgba case, we allow a small error only for devices that have
            // precision variation because the srgba data gets converted to linear and back in
            // the shader.
            float smallError = context->caps()->shaderCaps()->floatPrecisionVaries() ? 1.f : 0.0f;
            read_and_check_pixels(reporter, sContext.get(), origData, iiSRGBA,
                                  check_srgb_to_linear_to_srgb_conversion, smallError,
                                  "write/read srgba to srgba texture");
            read_and_check_pixels(reporter, sContext.get(), origData, iiRGBA,
                                  check_srgb_to_linear_conversion, error,
                                  "write srgba/read rgba with srgba texture");
        } else {
            ERRORF(reporter, "Could not write srgba data to srgba texture.");
        }

        // Now verify that we can write linear data
        if (sContext->writePixels(iiRGBA, origData, 0, 0, 0)) {
            // We allow more error on GPUs with lower precision shader variables.
            read_and_check_pixels(reporter, sContext.get(), origData, iiSRGBA,
                                  check_linear_to_srgb_conversion, error,
                                  "write rgba/read srgba with srgba texture");
            read_and_check_pixels(reporter, sContext.get(), origData, iiRGBA,
                                  check_linear_to_srgb_to_linear_conversion, error,
                                  "write/read rgba with srgba texture");
        } else {
            ERRORF(reporter, "Could not write rgba data to srgba texture.");
        }

        desc.fConfig = kRGBA_8888_GrPixelConfig;
        sContext = context->contextPriv().makeDeferredSurfaceContext(desc,
                                                                     GrMipMapped::kNo,
                                                                     SkBackingFit::kExact,
                                                                     SkBudgeted::kNo);
        if (!sContext) {
            ERRORF(reporter, "Could not create RGBA surface context.");
            return;
        }

        // Write srgba data to a rgba texture and read back as srgba and rgba
        if (sContext->writePixels(iiSRGBA, origData, 0, 0, 0)) {
#if 0
            // We don't support this conversion (read from untagged source into tagged destination.
            // If we decide there is a meaningful way to implement this, restore this test.
            read_and_check_pixels(reporter, sContext.get(), origData, iiSRGBA,
                                  check_srgb_to_linear_to_srgb_conversion, error,
                                  "write/read srgba to rgba texture");
#endif
            // We expect the sRGB -> linear write to do no sRGB conversion (to match the behavior of
            // drawing tagged sources). skbug.com/6547. So the data we read should still contain
            // sRGB encoded values.
            //
            // srgb_to_linear_to_srgb is a proxy for the expected identity transform.
            read_and_check_pixels(reporter, sContext.get(), origData, iiRGBA,
                                  check_srgb_to_linear_to_srgb_conversion, error,
                                  "write srgba/read rgba to rgba texture");
        } else {
            ERRORF(reporter, "Could not write srgba data to rgba texture.");
        }

        // Write rgba data to a rgba texture and read back as srgba
        if (sContext->writePixels(iiRGBA, origData, 0, 0, 0)) {
            read_and_check_pixels(reporter, sContext.get(), origData, iiSRGBA,
                                  check_linear_to_srgb_conversion, 1.2f,
                                  "write rgba/read srgba to rgba texture");
        } else {
            ERRORF(reporter, "Could not write rgba data to rgba texture.");
        }
    }
}
#endif