add new gm to test overlapping lcd text

BUG=skia:

Review URL: https://codereview.chromium.org/1358563002

gm/lcdoverlap.cpp

@@ -0,0 +1,100 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+
+/*
+ * Tests overlapping LCD text
+ */
+
+#include "gm.h"
+#include "SkCanvas.h"
+#include "SkSurface.h"
+#include "SkTextBlob.h"
+
+namespace skiagm {
+
+static const int kWidth = 750;
+static const int kHeight = 750;
+
+class LcdOverlapGM : public skiagm::GM {
+public:
+    LcdOverlapGM() {
+        const int kPointSize = 25;
+        fTextHeight = SkIntToScalar(kPointSize);
+    }
+
+protected:
+    SkString onShortName() override {
+        return SkString("lcdoverlap");
+    }
+
+    void onOnceBeforeDraw() override {
+        // build text blob
+        SkTextBlobBuilder builder;
+
+        SkPaint paint;
+        sk_tool_utils::set_portable_typeface(&paint);
+        paint.setTextSize(32);
+        const char* text = "able was I ere I saw elba";
+        paint.setAntiAlias(true);
+        paint.setSubpixelText(true);
+        paint.setLCDRenderText(true);
+        sk_tool_utils::add_to_text_blob(&builder, text, paint, 0, 0);
+        fBlob.reset(builder.build());
+    }
+
+    SkISize onISize() override { return SkISize::Make(kWidth, kHeight); }
+
+    void drawTestCase(SkCanvas* canvas, SkScalar x, SkScalar y, SkXfermode::Mode mode,
+                      SkXfermode::Mode mode2) {
+        const SkColor colors[] {
+                SK_ColorRED,
+                SK_ColorGREEN,
+                SK_ColorBLUE,
+                SK_ColorYELLOW,
+                SK_ColorCYAN,
+                SK_ColorMAGENTA,
+        };
+
+        SkAutoTUnref<SkXfermode> xfermode(SkXfermode::Create(mode));
+        SkAutoTUnref<SkXfermode> xfermode2(SkXfermode::Create(mode2));
+        for (size_t i = 0; i < SK_ARRAY_COUNT(colors); i++) {
+            canvas->save();
+            canvas->translate(x, y);
+            canvas->rotate(360.0f / SK_ARRAY_COUNT(colors) * i);
+            canvas->translate(-fBlob->bounds().width() / 2.0f + 0.5f, 0);
+
+            SkPaint textPaint;
+            textPaint.setColor(colors[i]);
+            textPaint.setXfermode(i % 2 == 0 ? xfermode : xfermode2);
+            canvas->drawTextBlob(fBlob, 0, 0, textPaint);
+            canvas->restore();
+        }
+    }
+
+    void onDraw(SkCanvas* canvas) override {
+        SkScalar offsetX = kWidth / 4.0f;
+        SkScalar offsetY = kHeight / 4.0f;
+        drawTestCase(canvas, offsetX, offsetY,  SkXfermode::kSrc_Mode, SkXfermode::kSrc_Mode);
+        drawTestCase(canvas, 3 * offsetX, offsetY,  SkXfermode::kSrcOver_Mode,
+                     SkXfermode::kSrcOver_Mode);
+        drawTestCase(canvas, offsetX, 3 * offsetY,  SkXfermode::kHardLight_Mode,
+                     SkXfermode::kLuminosity_Mode);
+        drawTestCase(canvas, 3 * offsetX, 3 * offsetY,  SkXfermode::kSrcOver_Mode,
+                     SkXfermode::kSrc_Mode);
+    }
+
+private:
+    SkScalar fTextHeight;
+    SkAutoTUnref<const SkTextBlob> fBlob;
+    typedef skiagm::GM INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+DEF_GM( return new LcdOverlapGM; )
+}