Luminance-to-alpha color filter (SkLumaColorFilter).

gm/lumafilter.cpp

Index: gm/lumafilter.cpp
diff --git a/gm/lumafilter.cpp b/gm/lumafilter.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..69a4f073f0a200258854ca941bac0c089a89c764
--- /dev/null
+++ b/gm/lumafilter.cpp
@@ -0,0 +1,152 @@
+/*
+ * Copyright 2013 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 "SkCanvas.h"
+#include "SkGradientShader.h"
+#include "SkLumaColorFilter.h"
+
+static SkScalar kSize   = 80;
+static SkScalar kInset  = 10;
+static SkColor  kColor1 = SkColorSetARGB(0xff, 0xff, 0xff, 0);
+static SkColor  kColor2 = SkColorSetARGB(0xff, 0x80, 0xff, 0);
+
+static void draw_label(SkCanvas* canvas, const char* label,
+                       const SkPoint& offset) {
+    SkPaint paint;
+    size_t len = strlen(label);
+
+    SkScalar width = paint.measureText(label, len);
+    canvas->drawText(label, len, offset.x() - width / 2, offset.y(),
+                     paint);
+}
+
+static void draw_scene(SkCanvas* canvas, SkColorFilter* filter,
+                       SkXfermode::Mode mode, SkShader* s1,
+                       SkShader* s2) {
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    SkRect r, c, bounds = SkRect::MakeWH(kSize, kSize);
+
+    c = bounds;
+    c.fRight = bounds.centerX();
+    canvas->drawRect(bounds, paint);
+
+    canvas->saveLayer(&bounds, NULL);
+
+    r = bounds;
+    r.inset(kInset, 0);
+    paint.setShader(s1);
+    paint.setColor(s1 ? SK_ColorBLACK : SkColorSetA(kColor1, 0x80));
+    canvas->drawOval(r, paint);
+    if (!s1) {
+        canvas->save();
+        canvas->clipRect(c);
+        paint.setColor(kColor1);
+        canvas->drawOval(r, paint);
+        canvas->restore();
+    }
+
+    SkPaint xferPaint;
+    xferPaint.setXfermodeMode(mode);
+    canvas->saveLayer(&bounds, &xferPaint);
+
+    r = bounds;
+    r.inset(0, kInset);
+    paint.setShader(s2);
+    paint.setColor(s2 ? SK_ColorBLACK : SkColorSetA(kColor2, 0x80));
+    paint.setColorFilter(filter);
+    canvas->drawOval(r, paint);
+    if (!s2) {
+        canvas->save();
+        canvas->clipRect(c);
+        paint.setColor(kColor2);
+        canvas->drawOval(r, paint);
+        canvas->restore();
+    }
+
+    canvas->restore();
+    canvas->restore();
+}
+
+class LumaFilterGM : public skiagm::GM {
+public:
+    LumaFilterGM() {
+        SkColor  g1Colors[] = { kColor1, SkColorSetA(kColor1, 0x20) };
+        SkColor  g2Colors[] = { kColor2, SkColorSetA(kColor2, 0x20) };
+        SkPoint  g1Points[] = { { 0, 0 }, { 0,     100 } };
+        SkPoint  g2Points[] = { { 0, 0 }, { kSize, 0   } };
+        SkScalar pos[] = { 0.2f, 1.0f };
+
+        fFilter.reset(SkLumaColorFilter::Create());
+        fGr1.reset(SkGradientShader::CreateLinear(g1Points,
+                                                  g1Colors,
+                                                  pos,
+                                                  SK_ARRAY_COUNT(g1Colors),
+                                                  SkShader::kClamp_TileMode));
+        fGr2.reset(SkGradientShader::CreateLinear(g2Points,
+                                                  g2Colors,
+                                                  pos,
+                                                  SK_ARRAY_COUNT(g2Colors),
+                                                  SkShader::kClamp_TileMode));
+    }
+
+protected:
+    virtual SkString onShortName() SK_OVERRIDE {
+        return SkString("lumafilter");
+    }
+
+    virtual SkISize onISize() SK_OVERRIDE {
+        return SkISize::Make(600, 420);
+    }
+
+    virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        SkXfermode::Mode modes[] = { SkXfermode::kSrcOver_Mode,
+                                     SkXfermode::kDstOver_Mode,
+                                     SkXfermode::kSrcATop_Mode,
+                                     SkXfermode::kDstATop_Mode,
+                                     SkXfermode::kSrcIn_Mode,
+                                     SkXfermode::kDstIn_Mode,
+                                   };
+        struct {
+            SkShader*   fShader1;
+            SkShader*   fShader2;
+        } shaders[] = {
+            { NULL, NULL },
+            { NULL, fGr2 },
+            { fGr1, NULL },
+            { fGr1, fGr2 },
+        };
+
+        SkScalar gridStep = kSize + 2 * kInset;
+        for (size_t i = 0; i < SK_ARRAY_COUNT(modes); ++i) {
+            draw_label(canvas, SkXfermode::ModeName(modes[i]),
+                       SkPoint::Make(gridStep * (0.5f + i), 20));
+        }
+
+        for (size_t i = 0; i < SK_ARRAY_COUNT(shaders); ++i) {
+            canvas->save();
+            canvas->translate(kInset, gridStep * i + 30);
+            for (size_t m = 0; m < SK_ARRAY_COUNT(modes); ++m) {
+                draw_scene(canvas, fFilter, modes[m], shaders[i].fShader1,
+                           shaders[i].fShader2);
+                canvas->translate(gridStep, 0);
+            }
+            canvas->restore();
+        }
+    }
+
+private:
+    SkAutoTUnref<SkColorFilter> fFilter;
+    SkAutoTUnref<SkShader>      fGr1, fGr2;
+
+    typedef skiagm::GM INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+DEF_GM( return SkNEW(LumaFilterGM); )