New GM that exercises gamma-correctness in various parts of the pipeline.

gm/gamma.cpp

Index: gm/gamma.cpp
diff --git a/gm/gamma.cpp b/gm/gamma.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..c874db6969ac8a52a73460ff9c7d392e08c6c97f
--- /dev/null
+++ b/gm/gamma.cpp
@@ -0,0 +1,166 @@
+/*
+ * 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 "gm.h"
+
+#include "Resources.h"
+#include "SkGradientShader.h"
+
+DEF_SIMPLE_GM(gamma, canvas, 500, 200) {
+    SkPaint p;
+    const SkScalar sz = 50.0f;
+    const int szInt = SkScalarTruncToInt(sz);
+    const SkScalar tx = sz + 5.0f;
+    const SkRect r = SkRect::MakeXYWH(0, 0, sz, sz);
+    SkShader::TileMode rpt = SkShader::kRepeat_TileMode;
+
+    SkBitmap ditherBmp;
+    ditherBmp.allocN32Pixels(2, 2);
+    SkPMColor* pixels = reinterpret_cast<SkPMColor*>(ditherBmp.getPixels());
+    pixels[0] = pixels[3] = SkPackARGB32(0xFF, 0xFF, 0xFF, 0xFF);
+    pixels[1] = pixels[2] = SkPackARGB32(0xFF, 0, 0, 0);
+
+    SkBitmap linearGreyBmp;
+    SkImageInfo linearGreyInfo = SkImageInfo::MakeN32(szInt, szInt, kOpaque_SkAlphaType,
+                                                      kLinear_SkColorProfileType);
+    linearGreyBmp.allocPixels(linearGreyInfo);
+    linearGreyBmp.eraseARGB(0xFF, 0x7F, 0x7F, 0x7F);
+
+    SkBitmap srgbGreyBmp;
+    SkImageInfo srgbGreyInfo = SkImageInfo::MakeN32(szInt, szInt, kOpaque_SkAlphaType,
+                                                    kSRGB_SkColorProfileType);
+    srgbGreyBmp.allocPixels(srgbGreyInfo);
+    srgbGreyBmp.eraseARGB(0xFF, 0xBC, 0xBC, 0xBC);
+
+    SkPaint textPaint;
+    textPaint.setColor(SK_ColorWHITE);
+
+    // Helpers:
+    auto advance = [&]() {
+        canvas->translate(tx, 0);
+        p.reset();
+    };
+
+    auto nextRect = [&](const char* label, const char* label2) {
+        canvas->drawRect(r, p);
+        canvas->drawText(label, strlen(label), 0, sz + textPaint.getFontSpacing(), textPaint);
+        if (label2) {
+            canvas->drawText(label2, strlen(label2), 0, sz + 2 * textPaint.getFontSpacing(),
+                             textPaint);
+        }
+        advance();
+    };
+
+    auto nextBitmap = [&](const SkBitmap& bmp, const char* label) {
+        canvas->drawBitmap(bmp, 0, 0);
+        canvas->drawText(label, strlen(label), 0, sz + textPaint.getFontSpacing(), textPaint);
+        advance();
+    };
+
+    auto nextXferRect = [&](SkColor srcColor, SkXfermode::Mode mode, SkColor dstColor) {
+        p.setColor(dstColor);
+        canvas->drawRect(r, p);
+        p.setColor(srcColor);
+        p.setXfermodeMode(mode);
+        canvas->drawRect(r, p);
+
+        SkString srcText = SkStringPrintf("%08X", srcColor);
+        SkString dstText = SkStringPrintf("%08X", dstColor);
+        canvas->drawText(srcText.c_str(), srcText.size(), 0, sz + textPaint.getFontSpacing(),
+                         textPaint);
+        const char* modeName = SkXfermode::ModeName(mode);
+        canvas->drawText(modeName, strlen(modeName), 0, sz + 2 * textPaint.getFontSpacing(),
+                         textPaint);
+        canvas->drawText(dstText.c_str(), dstText.size(), 0, sz + 3 * textPaint.getFontSpacing(),
+                         textPaint);
+        advance();
+    };
+
+    // Necessary for certain Xfermodes to work:
+    canvas->clear(SK_ColorTRANSPARENT);
+
+    // *Everything* should be perceptually 50% grey. Only the first rectangle
+    // is guaranteed to draw that way, though.
+    canvas->save();
+
+    // Black/white dither, pixel perfect. This is ground truth.
+    p.setShader(SkShader::CreateBitmapShader(
+        ditherBmp, rpt, rpt))->unref();
+    p.setFilterQuality(SkFilterQuality::kNone_SkFilterQuality);
+    nextRect("Dither", "Reference");
+
+    // Black/white dither, sampled at half-texel offset. Tests bilerp.
+    // NOTE: We need to apply a non-identity scale and/or rotation to trick
+    // the raster pipeline into *not* snapping to nearest.
+    SkMatrix offsetMatrix = SkMatrix::Concat(
+        SkMatrix::MakeScale(-1.0f), SkMatrix::MakeTrans(0.5f, 0.0f));
+    p.setShader(SkShader::CreateBitmapShader(
+        ditherBmp, rpt, rpt, &offsetMatrix))->unref();
+    p.setFilterQuality(SkFilterQuality::kMedium_SkFilterQuality);
+    nextRect("Dither", "Bilerp");
+
+    // Black/white dither, scaled down by 2x. Tests minification.
+    SkMatrix scaleMatrix = SkMatrix::MakeScale(0.5f);
+    p.setShader(SkShader::CreateBitmapShader(
+        ditherBmp, rpt, rpt, &scaleMatrix))->unref();
+    p.setFilterQuality(SkFilterQuality::kMedium_SkFilterQuality);
+    nextRect("Dither", "Scale");
+
+    // 50% grey via paint color.
+    p.setColor(0xff7f7f7f);
+    nextRect("Color", 0);
+
+    // Black -> White gradient, scaled to sample just the middle.
+    // Tests gradient interpolation.
+    SkPoint points[2] = {
+        SkPoint::Make(0 - (sz * 10), 0),
+        SkPoint::Make(sz + (sz * 10), 0)
+    };
+    SkColor colors[2] = { SK_ColorBLACK, SK_ColorWHITE };
+    p.setShader(SkGradientShader::CreateLinear(
+        points, colors, nullptr, 2, SkShader::kClamp_TileMode))->unref();
+    nextRect("Gradient", 0);
+
+    // 50% grey from linear bitmap, with drawBitmap
+    nextBitmap(linearGreyBmp, "Lnr BMP");
+
+    // 50% grey from sRGB bitmap, with drawBitmap
+    nextBitmap(srgbGreyBmp, "sRGB BMP");
+
+    // Bitmap wrapped in a shader (linear):
+    p.setShader(SkShader::CreateBitmapShader(linearGreyBmp, rpt, rpt))->unref();
+    p.setFilterQuality(SkFilterQuality::kMedium_SkFilterQuality);
+    nextRect("Lnr BMP", "Shader");
+
+    // Bitmap wrapped in a shader (sRGB):
+    p.setShader(SkShader::CreateBitmapShader(srgbGreyBmp, rpt, rpt))->unref();
+    p.setFilterQuality(SkFilterQuality::kMedium_SkFilterQuality);
+    nextRect("sRGB BMP", "Shader");
+
+    // Carriage return.
+    canvas->restore();
+    canvas->translate(0, 2 * sz);
+
+    const U8CPU sqrtHalf = 0xB4;
+    const SkColor sqrtHalfAlpha = SkColorSetARGB(sqrtHalf, 0, 0, 0);
+    const SkColor sqrtHalfWhite = SkColorSetARGB(0xFF, sqrtHalf, sqrtHalf, sqrtHalf);
+
+    // Xfermode tests.
+    nextXferRect(0x7fffffff, SkXfermode::kSrcOver_Mode, SK_ColorBLACK);
+    nextXferRect(0x7f000000, SkXfermode::kSrcOver_Mode, SK_ColorWHITE);
+
+    nextXferRect(SK_ColorBLACK, SkXfermode::kDstOver_Mode, 0x7fffffff);
+    nextXferRect(SK_ColorWHITE, SkXfermode::kSrcIn_Mode, 0x7fff00ff);
+    nextXferRect(0x7fff00ff, SkXfermode::kDstIn_Mode, SK_ColorWHITE);
+    nextXferRect(sqrtHalfWhite, SkXfermode::kSrcIn_Mode, sqrtHalfAlpha);
+    nextXferRect(sqrtHalfAlpha, SkXfermode::kDstIn_Mode, sqrtHalfWhite);
+
+    nextXferRect(0xff3f3f3f, SkXfermode::kPlus_Mode, 0xff3f3f3f);
+    nextXferRect(sqrtHalfWhite, SkXfermode::kModulate_Mode, sqrtHalfWhite);
+
+    canvas->restore();
+}