Make the canvas draw looper internal layer not part of SkCanvas save count

tests/DrawLooperTest.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 "SkColorFilter.h"
+#include "SkColorFilterImageFilter.h"
+#include "SkDrawLooper.h"
+#include "Test.h"
+
+/* Tests for SkDrawLooper -related APIs and implementations. */
+
+namespace {
+/*
+ *  Subclass that caused an assert at the time of writing.
+ */
+class GetSaveCountAssertLooper : public SkDrawLooper {
+public:
+    GetSaveCountAssertLooper(skiatest::Reporter* reporter)
+        : fReporter(reporter) {
+    }
+
+    SkDrawLooper::Context* createContext(SkCanvas*, void* storage) const override {
+        return SkNEW_PLACEMENT_ARGS(storage, GetSaveCountAssertLooperContext, (fReporter));
+    }
+
+    size_t contextSize() const override { return sizeof(GetSaveCountAssertLooperContext); }
+
+#ifndef SK_IGNORE_TO_STRING
+    void toString(SkString* str) const override {
+        str->append("GetSaveCountAssertLooper:");
+    }
+#endif
+
+    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(GetSaveCountAssertLooper);
+
+private:
+    class GetSaveCountAssertLooperContext : public SkDrawLooper::Context {
+    public:
+        GetSaveCountAssertLooperContext(skiatest::Reporter* reporter)
+            : fReporter(reporter)
+            , fOnce(0) {
+        }
+
+        bool next(SkCanvas* canvas, SkPaint* p) override {
+            // 1st test: Getting the save count would assert in SkCanvas at the time of writing.
+            // 2nd test: test the sentence from SkCanvas.h:
+            //   This will equal # save() calls - # restore() calls + 1.
+            REPORTER_ASSERT(fReporter, 1 == canvas->getSaveCount());
+
+            SkASSERT(p->getColor() == SK_ColorRED);
+            // Set the color green so the test knows payload was run. We use this color in order to
+            // try to express the expectation that Skia can not away the color filter. Due to
+            // non-pm-to-pm-to-non-pm conversions, this probably is not exactly correct.
+            p->setColor(SkColorSetARGB(255, 0, 254, 0));
+            return fOnce++ < 1;
+        }
+    private:
+        skiatest::Reporter* fReporter;
+        int fOnce;
+    };
+    mutable skiatest::Reporter* fReporter;
+};
+
+SkFlattenable* GetSaveCountAssertLooper::CreateProc(SkReadBuffer&) {
+    SkASSERT(false);
+    return SkNEW_ARGS(GetSaveCountAssertLooper, (NULL));
+}
+
+}
+
+DEF_TEST(SkCanvas_GetSaveCountInDrawLooperAssert, reporter) {
+    SkBitmap dst;
+    dst.allocN32Pixels(10, 10);
+    dst.eraseColor(SK_ColorTRANSPARENT);
+
+    SkCanvas canvas(dst);
+    SkPaint  paint;
+    {
+        SkAutoTUnref<SkColorFilter> addGreenCF(
+            SkColorFilter::CreateModeFilter(SkColorSetARGB(64, 0, 4, 0), SkXfermode::kPlus_Mode));
+        SkAutoTUnref<SkImageFilter> addGreenIF(
+            SkColorFilterImageFilter::Create(addGreenCF));
+
+        // This would trigger the assert upon a draw. It is a color filter that adds (roughly) 1 to
+        // the green component.
+        paint.setImageFilter(addGreenIF);
+
+        SkAutoTUnref<SkDrawLooper> looper(SkNEW_ARGS(GetSaveCountAssertLooper, (reporter)));
+        paint.setLooper(looper);
+    }
+    paint.setColor(SK_ColorRED);
+    paint.setStrokeWidth(1);
+    paint.setStyle(SkPaint::kStroke_Style);
+    canvas.drawPoint(0, 0, paint);
+
+    uint32_t pixel = 0;
+    SkImageInfo info = SkImageInfo::Make(1, 1, kBGRA_8888_SkColorType, kUnpremul_SkAlphaType);
+    canvas.readPixels(info, &pixel, 4, 0, 0);
+    REPORTER_ASSERT(reporter, pixel == SK_ColorGREEN);
+}