Implement Porter Duff XP with a blend table

gm/aaxfermodes.cpp

Index: gm/aaxfermodes.cpp
diff --git a/gm/aaxfermodes.cpp b/gm/aaxfermodes.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..b8101cb59ee3870c9ceb55b3206b6678cf4ccb45
--- /dev/null
+++ b/gm/aaxfermodes.cpp
@@ -0,0 +1,211 @@
+
+/*
+ * 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 "SkArithmeticMode.h"
+#include "SkShader.h"
+#include "SkXfermode.h"
+
+enum {
+    kXfermodeCount = SkXfermode::kLastMode + 2, // All xfermodes plus arithmetic mode.
+    kShapeSize = 22,
+    kShapeSpacing = 36,
+    kShapeTypeSpacing = 4 * kShapeSpacing/3,
+    kPaintSpacing = 2 * kShapeSpacing,
+    kPadding = (kPaintSpacing - kShapeSpacing) / 2,
+
+    kPaintWidth = 3*kShapeSpacing + 2*kShapeTypeSpacing + kShapeSize,
+    kPaintPadding = kPaintSpacing - kShapeSize,
+};
+
+static const SkColor kBGColor = SkColorSetARGB(200, 210, 184, 135);
+
+static const SkColor kShapeColors[3] = {
+    SkColorSetARGB(130, 255, 0, 128),   // input color unknown
+    SkColorSetARGB(255, 0, 255, 255),   // input color opaque
+    SkColorSetARGB(255, 255, 255, 255)  // input solid white
+};
+
+enum Shape {
+    kSquare_Shape,
+    kDiamond_Shape,
+    kOval_Shape,
+
+    kLast_Shape = kOval_Shape
+};
+
+namespace skiagm {
+
+static void draw_shape(SkCanvas* canvas, Shape shape, const SkColor color, size_t xfermodeIdx);
+
+/**
+ * Verifies AA works properly on all Xfermodes, including arithmetic, with various color invariants.
+ */
+class AAXfermodesGM : public GM {
+public:
+    AAXfermodesGM() {}
+
+protected:
+    SkString onShortName() override {
+        return SkString("aaxfermodes");
+    }
+
+    SkISize onISize() override {
+        return SkISize::Make(3*kPaintWidth + 2*kPaintPadding + 2*kPadding,
+                             (2 + SkXfermode::kLastCoeffMode) * kShapeSpacing + 2*kPadding);
+    }
+
+    void onDraw(SkCanvas* canvas) override {
+        SkPaint checkerPaint;
+        checkerPaint.setAntiAlias(false);
+        checkerPaint.setStyle(SkPaint::kFill_Style);
+        checkerPaint.setShader(fCheckerShader);
+        canvas->drawPaint(checkerPaint);
+
+        canvas->saveLayer(NULL, NULL);
+        canvas->drawColor(kBGColor, SkXfermode::kSrc_Mode);
+
+        canvas->translate(kPadding + kShapeSize/2, kPadding + kShapeSpacing + kShapeSize/2);
+
+        for (size_t colorIdx = 0; colorIdx < SK_ARRAY_COUNT(kShapeColors); colorIdx++) {
+            SkColor color = kShapeColors[colorIdx];
+
+            for (size_t shapeIdx = 0; shapeIdx <= kLast_Shape; shapeIdx++) {
+                Shape shape = static_cast<Shape>(shapeIdx);
+                canvas->save();
+
+                for (size_t xfermodeIdx = 0; xfermodeIdx < kXfermodeCount; xfermodeIdx++) {
+                    draw_shape(canvas, shape, color, xfermodeIdx);
+
+                    if (xfermodeIdx == SkXfermode::kLastCoeffMode) {
+                        // New column.
+                        canvas->restore();
+                        canvas->translate(kShapeSpacing, 0);
+                        canvas->save();
+                    } else {
+                        canvas->translate(0, kShapeSpacing);
+                    }
+                }
+
+                canvas->restore();
+                canvas->translate(shape != kLast_Shape ? kShapeTypeSpacing : kPaintSpacing, 0);
+            }
+        }
+
+        canvas->restore();
+
+        SkPaint textPaint;
+        textPaint.setAntiAlias(true);
+        sk_tool_utils::set_portable_typeface(&textPaint);
+        textPaint.setTextAlign(SkPaint::kCenter_Align);
+        textPaint.setFakeBoldText(true);
+        textPaint.setTextSize(21 * kShapeSize/32);
+
+        canvas->translate(kPadding + kPaintWidth/2,
+                          kPadding + kShapeSize/2 + textPaint.getTextSize()/4);
+        canvas->drawText("input color unknown", sizeof("input color unknown") - 1, 0, 0, textPaint);
+
+        canvas->translate(kPaintWidth + kPaintPadding, 0);
+        canvas->drawText("input color opaque", sizeof("input color opaque") - 1, 0, 0, textPaint);
+
+        canvas->translate(kPaintWidth + kPaintPadding, 0);
+        canvas->drawText("input solid white", sizeof("input solid white") - 1, 0, 0, textPaint);
+    }
+
+private:
+    void onOnceBeforeDraw() override {
+        static const uint32_t kCheckerData[] = {
+            SkPackARGB32(0xff, 0xc0, 0xc0, 0xc0),
+            SkPackARGB32(0xff, 0xff, 0xff, 0xff),
+            SkPackARGB32(0xff, 0xff, 0xff, 0xff),
+            SkPackARGB32(0xff, 0xc0, 0xc0, 0xc0)
+        };
+        SkBitmap checker;
+        checker.allocN32Pixels(2, 2, true);
+        memcpy(checker.getPixels(), kCheckerData, sizeof(kCheckerData));
+
+        SkMatrix lm;
+        lm.setScale(SkIntToScalar(10), SkIntToScalar(10));
+        fCheckerShader.reset(SkShader::CreateBitmapShader(checker,
+                                                          SkShader::kRepeat_TileMode,
+                                                          SkShader::kRepeat_TileMode,
+                                                          &lm));
+    }
+
+    SkAutoTUnref<SkShader> fCheckerShader;
+
+    typedef GM INHERITED;
+};
+
+static void draw_shape(SkCanvas* canvas, Shape shape, const SkColor color, size_t xfermodeIdx) {
+    SkPaint shapePaint;
+    shapePaint.setAntiAlias(kSquare_Shape != shape);
+    shapePaint.setColor(color);
+
+    SkAutoTUnref<SkXfermode> xfermode;
+    if (xfermodeIdx <= SkXfermode::kLastMode) {
+        SkXfermode::Mode mode = static_cast<SkXfermode::Mode>(xfermodeIdx);
+        xfermode.reset(SkXfermode::Create(mode));
+    } else {
+        xfermode.reset(SkArithmeticMode::Create(+1.0f, +0.25f, -0.5f, +0.1f));
+    }
+    shapePaint.setXfermode(xfermode);
+
+    if (xfermodeIdx == SkXfermode::kPlus_Mode) {
+        // Check for overflow and dim the src and dst colors if we need to, otherwise we might get
+        // confusing AA artifacts.
+        int maxSum = SkTMax(SkTMax(SkColorGetA(kBGColor) + SkColorGetA(color),
+                                   SkColorGetR(kBGColor) + SkColorGetR(color)),
+                            SkTMax(SkColorGetG(kBGColor) + SkColorGetG(color),
+                                   SkColorGetB(kBGColor) + SkColorGetB(color)));
+
+        if (maxSum > 255) {
+            SkPaint dimPaint;
+            dimPaint.setARGB(255 * 255 / maxSum, 0, 0, 0);
+            dimPaint.setAntiAlias(false);
+            dimPaint.setXfermode(SkXfermode::Create(SkXfermode::kDstIn_Mode));
+            canvas->drawRectCoords(-kShapeSpacing/2, -kShapeSpacing/2,
+                                   kShapeSpacing/2, kShapeSpacing/2, dimPaint);
+
+            shapePaint.setAlpha(255 * shapePaint.getAlpha() / maxSum);
+        }
+    }
+
+    switch (shape) {
+        case kSquare_Shape:
+            canvas->drawRectCoords(-kShapeSize/2, -kShapeSize/2, kShapeSize/2, kShapeSize/2,
+                                   shapePaint);
+            break;
+
+        case kDiamond_Shape:
+            canvas->save();
+            canvas->rotate(45);
+            canvas->drawRectCoords(-kShapeSize/2, -kShapeSize/2, kShapeSize/2, kShapeSize/2,
+                                   shapePaint);
+            canvas->restore();
+            break;
+
+        case kOval_Shape:
+            canvas->save();
+            canvas->rotate((511 * xfermodeIdx + 257) % 360);
+            canvas->drawArc(SkRect::MakeLTRB(-kShapeSize/2, -1.4f * kShapeSize/2,
+                                             kShapeSize/2, 1.4f * kShapeSize/2),
+                            0, 360, true, shapePaint);
+            canvas->restore();
+            break;
+
+        default:
+            SkFAIL("Invalid shape.");
+    }
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+static GM* MyFactory(void*) { return new AAXfermodesGM; }
+static GMRegistry reg(MyFactory);
+
+}