Sketch splitting SkPicture into an interface and SkBigPicture.

src/core/SkMiniRecorder.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 "SkLazyPtr.h"
+#include "SkMiniRecorder.h"
+#include "SkPicture.h"
+#include "SkRecordDraw.h"
+#include "SkTextBlob.h"
+
+using namespace SkRecords;
+
+class SkEmptyPicture final : public SkPicture {
+public:
+    void playback(SkCanvas*, AbortCallback*) const override { }
+
+    size_t approximateBytesUsed() const override { return sizeof(*this); }
+    int    approximateOpCount()   const override { return 0; }
+    SkRect cullRect()             const override { return SkRect::MakeEmpty(); }
+    bool   hasText()              const override { return false; }
+    int    numSlowPaths()         const override { return 0; }
+    bool   willPlayBackBitmaps()  const override { return false; }
+    bool   suitableForGpuRasterization(GrContext*, const char**) const override { return true; }
+};
+SK_DECLARE_STATIC_LAZY_PTR(SkEmptyPicture, gEmptyPicture);
+
+template <typename T>
+class SkMiniPicture final : public SkPicture {
+public:
+    SkMiniPicture(SkRect cull, T* op) : fCull(cull) {
+        memcpy(&fOp, op, sizeof(fOp));  // We take ownership of op's guts.
+    }
+
+    void playback(SkCanvas* c, AbortCallback*) const override {
+        SkRecords::Draw(c, nullptr, nullptr, 0, nullptr)(fOp);
+    }
+
+    size_t approximateBytesUsed() const override { return sizeof(*this); }
+    int    approximateOpCount()   const override { return 1; }
+    SkRect cullRect()             const override { return fCull; }
+
+    // TODO: These trivial implementations are not all correct for all types.
+    // But I suspect these will never be called on SkMiniPictures, so assert for now.
+    bool   hasText()              const override { SkASSERT(false); return false; }
+    int    numSlowPaths()         const override { SkASSERT(false); return 0; }
+    bool   willPlayBackBitmaps()  const override { SkASSERT(false); return false; }
+    bool   suitableForGpuRasterization(GrContext*, const char**) const override {
+        SkASSERT(false);
+        return true;
+    }
+
+private:
+    SkRect fCull;
+    T      fOp;
+};
+
+
+SkMiniRecorder::SkMiniRecorder() : fState(State::kEmpty) {}
+SkMiniRecorder::~SkMiniRecorder() {
+    // We've done something wrong if no one's called detachAsPicture().
+    SkASSERT(fState == State::kEmpty);
+}
+
+#define TRY_TO_STORE(Type, ...)                    \
+    if (fState != State::kEmpty) { return false; } \
+    fState = State::k##Type;                       \
+    new (fBuffer.get()) Type(__VA_ARGS__);         \
+    return true
+
+bool SkMiniRecorder::drawRect(const SkRect& rect, const SkPaint& paint) {
+    TRY_TO_STORE(DrawRect, paint, rect);
+}
+
+bool SkMiniRecorder::drawPath(const SkPath& path, const SkPaint& paint) {
+    TRY_TO_STORE(DrawPath, paint, path);
+}
+
+bool SkMiniRecorder::drawTextBlob(const SkTextBlob* b, SkScalar x, SkScalar y, const SkPaint& p) {
+    TRY_TO_STORE(DrawTextBlob, p, b, x, y);
+}
+#undef TRY_TO_STORE
+
+#define CASE(Type)               \
+    case State::k##Type:         \
+        fState = State::kEmpty;  \
+        return SkNEW_ARGS(SkMiniPicture<Type>, (cull, reinterpret_cast<Type*>(fBuffer.get())))
+
+SkPicture* SkMiniRecorder::detachAsPicture(const SkRect& cull) {
+    switch (fState) {
+        case State::kEmpty: return SkRef(gEmptyPicture.get());
+        CASE(DrawPath);
+        CASE(DrawRect);
+        CASE(DrawTextBlob);
+    }
+    SkASSERT(false);
+    return NULL;
+}
+#undef CASE