use new template class SkTLazy for deferred paint initialization

git-svn-id: http://skia.googlecode.com/svn/trunk@1070 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 77 insertions, 0 deletions

diff --git a/include/core/SkTLazy.h b/include/core/SkTLazy.h
new file mode 100644
index 0000000000..94e64150e1
--- /dev/null
+++ b/include/core/SkTLazy.h
@@ -0,0 +1,77 @@
+/*
+    Copyright 2011 Google Inc.
+
+    Licensed under the Apache License, Version 2.0 (the "License");
+    you may not use this file except in compliance with the License.
+    You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+    See the License for the specific language governing permissions and
+    limitations under the License.
+ */
+
+
+#ifndef SkTLazy_DEFINED
+#define SkTLazy_DEFINED
+
+#include "SkTypes.h"
+
+/**
+ *  Efficient way to defer allocating/initializing a class until it is needed
+ *  (if ever).
+ */
+template <typename T> class SkTLazy {
+public:
+    SkTLazy() : fPtr(NULL) {}
+
+    explicit SkTLazy(const T* src) : fPtr(NULL) {
+        if (src) {
+            fPtr = new (fStorage) T(*src);
+        }
+    }
+
+    SkTLazy(const SkTLazy<T>& src) : fPtr(NULL) {
+        const T* ptr = src.get();
+        if (ptr) {
+            fPtr = new (fStorage) T(*ptr);
+        }
+    }
+
+    ~SkTLazy() {
+        if (fPtr) {
+            fPtr->~T();
+        }
+    }
+
+    /**
+     *  Copy src into this, and return a pointer to a copy of it. Note this
+     *  will always return the same pointer, so if it is called on a lazy that
+     *  has already been initialized, then this will copy over the previous
+     *  contents.
+     */
+    T* set(const T& src) {
+        if (fPtr) {
+            *fPtr = src;
+        } else {
+            fPtr = new (fStorage) T(src);
+        }
+        return fPtr;
+    }
+    
+    /**
+     *  Returns either NULL, or a copy of the object that was passed to
+     *  set() or the constructor.
+     */
+    T* get() const { return fPtr; }
+    
+private:
+    T*   fPtr; // NULL or fStorage
+    char fStorage[sizeof(T)];
+};
+
+#endif
+