tests/SRGBMipMapTest.cpp

/*
 * Copyright 2016 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 "GrDrawContext.h"
#include "SkCanvas.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;
    }
}
}

static bool check_value(U8CPU value, U8CPU expected, U8CPU error) {
    if (value >= expected) {
        return (value - expected) <= error;
    } else {
        return (expected - value) <= error;
    }
}

void read_and_check_pixels(skiatest::Reporter* reporter, GrTexture* texture, U8CPU expected,
                           U8CPU error, const char* subtestName) {
    int w = texture->width();
    int h = texture->height();
    SkAutoTMalloc<uint32_t> readData(w * h);
    memset(readData.get(), 0, sizeof(uint32_t) * w * h);
    if (!texture->readPixels(0, 0, w, h, texture->config(), readData.get())) {
        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 read = readData[j * w + i];

            bool success =
                check_value(read & 0xff, expected, error) &&
                check_value((read >> 8) & 0xff, expected, error) &&
                check_value((read >> 16) & 0xff, expected, error);

            if (!success) {
                ERRORF(reporter, "Expected 0xff%02x%02x%02x, read back as 0x%08x in %s at %d, %d.",
                       expected, expected, expected, read, subtestName, i, j);
                return;
            }
        }
    }
}

DEF_GPUTEST_FOR_GL_RENDERING_CONTEXTS(SRGBMipMaps, reporter, ctxInfo) {
    GrContext* context = ctxInfo.grContext();
    if (!context->caps()->srgbSupport()) {
        return;
    }

    const int rtS = 16;
    const int texS = rtS * 2;

    // Fill texture with a dither of black and 60% sRGB (~ 32.5% linear) gray. Although there is
    // only one likely failure mode (doing a direct downsample of the sRGB values), this pattern
    // maximizes the minimum error across all three conceivable failure modes:
    // 1) Likely incorrect:
    //      (A + B) / 2
    // 2) No input decode, decode output:
    //      linear_to_srgb((A + B) / 2)
    // 3) Decode input, no output encode:
    //      (srgb_to_linear(A) + srgb_to_linear(B)) / 2

    const U8CPU srgb60 = sk_float_round2int(0.6f * 255.0f);
    static const SkPMColor colors[2] = {
        SkPackARGB32(0xFF, srgb60, srgb60, srgb60),
        SkPackARGB32(0xFF, 0x00, 0x00, 0x00)
    };
    uint32_t texData[texS * texS];
    for (int y = 0; y < texS; ++y) {
        for (int x = 0; x < texS; ++x) {
            texData[y * texS + x] = colors[(x + y) % 2];
        }
    }

    // We can be pretty generous with the error detection, thanks to the choice of input.
    // The closest likely failure mode is off by > 0.1, so anything that encodes within
    // 10/255 of optimal is more than good enough for this test.
    const U8CPU expectedSRGB = sk_float_round2int(
        linear_to_srgb(srgb_to_linear(srgb60 / 255.0f) / 2.0f) * 255.0f);
    const U8CPU expectedLinear = srgb60 / 2;
    const U8CPU error = 10;

    // Create our test texture
    GrSurfaceDesc desc;
    desc.fFlags = kNone_GrSurfaceFlags;
    desc.fConfig = kSkiaGamma8888_GrPixelConfig;
    desc.fWidth = texS;
    desc.fHeight = texS;

    GrTextureProvider* texProvider = context->textureProvider();
    SkAutoTUnref<GrTexture> texture(texProvider->createTexture(desc, SkBudgeted::kNo, texData, 0));

    // Create two draw contexts (L32 and S32)
    sk_sp<SkColorSpace> srgbColorSpace = SkColorSpace::NewNamed(SkColorSpace::kSRGB_Named);
    sk_sp<GrDrawContext> l32DrawContext = context->makeDrawContext(SkBackingFit::kExact, rtS, rtS,
                                                                   kSkia8888_GrPixelConfig,
                                                                   nullptr);
    sk_sp<GrDrawContext> s32DrawContext = context->makeDrawContext(SkBackingFit::kExact, rtS, rtS,
                                                                   kSkiaGamma8888_GrPixelConfig,
                                                                   std::move(srgbColorSpace));

    SkRect rect = SkRect::MakeWH(SkIntToScalar(rtS), SkIntToScalar(rtS));
    GrNoClip noClip;
    GrPaint paint;
    paint.setPorterDuffXPFactory(SkXfermode::kSrc_Mode);
    GrTextureParams mipMapParams(SkShader::kRepeat_TileMode, GrTextureParams::kMipMap_FilterMode);
    paint.addColorTextureProcessor(texture, nullptr, SkMatrix::MakeScale(0.5f), mipMapParams);

    // 1) Draw texture to S32 surface (should generate/use sRGB mips)
    paint.setGammaCorrect(true);
    s32DrawContext->drawRect(noClip, paint, SkMatrix::I(), rect);
    read_and_check_pixels(reporter, s32DrawContext->asTexture().get(), expectedSRGB, error,
                          "first render of sRGB");

    // 2) Draw texture to L32 surface (should generate/use linear mips)
    paint.setGammaCorrect(false);
    l32DrawContext->drawRect(noClip, paint, SkMatrix::I(), rect);
    read_and_check_pixels(reporter, l32DrawContext->asTexture().get(), expectedLinear, error,
                          "re-render as linear");

    // 3) Go back to sRGB
    paint.setGammaCorrect(true);
    s32DrawContext->drawRect(noClip, paint, SkMatrix::I(), rect);
    read_and_check_pixels(reporter, s32DrawContext->asTexture().get(), expectedSRGB, error,
                          "re-render as sRGB");
}
#endif