Proactive SkPixelRef invalidation

tests/PixelRefTest.cpp

+#include "Test.h"
+#include "TestClassDef.h"
+
+#include "SkPixelRef.h"
+#include "SkMallocPixelRef.h"
+
+namespace {
+
+class TestListener : public SkPixelRef::GenIDChangeListener {
+public:
+    explicit TestListener(int* ptr) : fPtr(ptr) {}
+    void onChange() SK_OVERRIDE { (*fPtr)++; }
+private:
+    int* fPtr;
+};
+
+}  // namespace
+
+DEF_TEST(PixelRef_GenIDChange, r) {
+    SkMallocPixelRef pixelRef(NULL, 0, NULL);  // We don't really care about the pixels here.
+
+    // Register a listener.
+    int count = 0;
+    pixelRef.addGenIDChangeListener(SkNEW_ARGS(TestListener, (&count)));
+    REPORTER_ASSERT(r, 0 == count);
+
+    // No one has looked at our pixelRef's generation ID, so invalidating it doesn't make sense.
+    // (An SkPixelRef tree falls in the forest but there's nobody around to hear it.  Do we care?)
+    pixelRef.notifyPixelsChanged();
+    REPORTER_ASSERT(r, 0 == count);
+
+    // Force the generation ID to be calculated.
+    REPORTER_ASSERT(r, 0 != pixelRef.getGenerationID());
+
+    // Our listener was dropped in the first call to notifyPixelsChanged().  This is a no-op.
+    pixelRef.notifyPixelsChanged();
+    REPORTER_ASSERT(r, 0 == count);
+
+    // Force the generation ID to be recalculated, then add a listener.
+    REPORTER_ASSERT(r, 0 != pixelRef.getGenerationID());
+    pixelRef.addGenIDChangeListener(SkNEW_ARGS(TestListener, (&count)));
+    pixelRef.notifyPixelsChanged();
+    REPORTER_ASSERT(r, 1 == count);
+
+    // Quick check that NULL is safe.
+    REPORTER_ASSERT(r, 0 != pixelRef.getGenerationID());
+    pixelRef.addGenIDChangeListener(NULL);
+    pixelRef.notifyPixelsChanged();
+}