SkPDF: with opaque draws, treat SRC mode as SRC_OVER

tests/skpdf_opaquesrcmodetosrcover.cpp

+/*
+ * 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 "SkCanvas.h"
+#include "SkDocument.h"
+#include "SkStream.h"
+#include "Test.h"
+
+static void run_test(SkWStream* out, SkXfermode::Mode mode, U8CPU alpha) {
+    SkAutoTUnref<SkDocument> pdfDoc(SkDocument::CreatePDF(out));
+    SkCanvas* c = pdfDoc->beginPage(612.0f, 792.0f);
+    SkPaint black;
+    SkPaint background;
+    background.setColor(SK_ColorWHITE);
+    background.setAlpha(alpha);
+    background.setXfermodeMode(mode);
+    c->drawRect(SkRect::MakeWH(612.0f, 792.0f), background);
+    c->drawRect(SkRect::MakeXYWH(36.0f, 36.0f, 9.0f, 9.0f), black);
+    c->drawRect(SkRect::MakeXYWH(72.0f, 72.0f, 468.0f, 648.0f), background);
+    c->drawRect(SkRect::MakeXYWH(108.0f, 108.0f, 9.0f, 9.0f), black);
+    pdfDoc->close();
+}
+
+// http://crbug.com/473572
+DEF_TEST(SkPDF_OpaqueSrcModeToSrcOver, r) {
+    SkDynamicMemoryWStream srcMode;
+    SkDynamicMemoryWStream srcOverMode;
+
+    U8CPU alpha = SK_AlphaOPAQUE;
+    run_test(&srcMode, SkXfermode::kSrc_Mode, alpha);
+    run_test(&srcOverMode, SkXfermode::kSrcOver_Mode, alpha);
+    REPORTER_ASSERT(r, srcMode.getOffset() == srcOverMode.getOffset());
+    // The two PDFs should be equal because they have an opaque alpha.
+
+    srcMode.reset();
+    srcOverMode.reset();
+
+    alpha = 0x80;
+    run_test(&srcMode, SkXfermode::kSrc_Mode, alpha);
+    run_test(&srcOverMode, SkXfermode::kSrcOver_Mode, alpha);
+    REPORTER_ASSERT(r, srcMode.getOffset() > srcOverMode.getOffset());
+    // The two PDFs should not be equal because they have a non-opaque alpha.
+}