Compile-time initialize special SkMatrices.

src/core/SkMatrix.cpp

Index: src/core/SkMatrix.cpp
diff --git a/src/core/SkMatrix.cpp b/src/core/SkMatrix.cpp
index 8778f78f4105f833a7cb10f5cb48b137f625a1b2..95662fc4cd42bca1edfb286e94089494b6e5a206 100644
--- a/src/core/SkMatrix.cpp
+++ b/src/core/SkMatrix.cpp
@@ -7,9 +7,10 @@
 
 #include "SkMatrix.h"
 #include "SkFloatBits.h"
-#include "SkLazyPtr.h"
 #include "SkString.h"
 
+#include <stddef.h>

[reed1, 2014/06/02 18:39:50]

is this not already included (directly/indirectly) by SkTypes.h?

[mtklein, 2014/06/02 18:40:31]

Nope.  offsetof wasn't defined until I included this.

+
 // In a few places, we performed the following
 //      a * b + c * d + e
 // as
@@ -1560,31 +1561,38 @@ bool SkMatrix::getMinMaxScales(SkScalar scaleFactors[2]) const {
 
 namespace {
 
-SkMatrix* create_identity() {
-    SkMatrix* m = SkNEW(SkMatrix);
-    m->reset();
-    return m;
-}
+struct PODMatrix {
+    SkScalar matrix[9];
+    uint32_t typemask;
 
-SkMatrix* create_invalid() {
-    SkMatrix* m = SkNEW(SkMatrix);
-    m->setAll(SK_ScalarMax, SK_ScalarMax, SK_ScalarMax,
-              SK_ScalarMax, SK_ScalarMax, SK_ScalarMax,
-              SK_ScalarMax, SK_ScalarMax, SK_ScalarMax);
-    m->getType();  // Force the type to be computed.
-    return m;
-}
+    const SkMatrix& asSkMatrix() const { return *reinterpret_cast<const SkMatrix*>(this); }

[bungeman-skia, 2014/06/02 17:46:32]

This cast is implementation defined. Of course, we'd break all over the place if
this didn't work. We already assert that they have the same sizeof, so they
should have the same alignment constraints as well.

+};
+SK_COMPILE_ASSERT(sizeof(PODMatrix) == sizeof(SkMatrix), PODMatrixSizeMismatch);
 
 }  // namespace
 
 const SkMatrix& SkMatrix::I() {
-    SK_DECLARE_STATIC_LAZY_PTR(SkMatrix, identity, create_identity);
-    return *identity.get();
+    SK_COMPILE_ASSERT(offsetof(SkMatrix, fMat)      == offsetof(PODMatrix, matrix),   BadfMat);
+    SK_COMPILE_ASSERT(offsetof(SkMatrix, fTypeMask) == offsetof(PODMatrix, typemask), BadfTypeMask);
+
+    static const PODMatrix identity = { {SK_Scalar1, 0, 0,
+                                         0, SK_Scalar1, 0,
+                                         0, 0, SK_Scalar1 },
+                                       kIdentity_Mask | kRectStaysRect_Mask};
+    SkASSERT(identity.asSkMatrix().isIdentity());
+    return identity.asSkMatrix();
 }
 
 const SkMatrix& SkMatrix::InvalidMatrix() {
-    SK_DECLARE_STATIC_LAZY_PTR(SkMatrix, invalid, create_invalid);
-    return *invalid.get();
+    SK_COMPILE_ASSERT(offsetof(SkMatrix, fMat)      == offsetof(PODMatrix, matrix),   BadfMat);
+    SK_COMPILE_ASSERT(offsetof(SkMatrix, fTypeMask) == offsetof(PODMatrix, typemask), BadfTypeMask);
+
+    static const PODMatrix invalid =
+        { {SK_ScalarMax, SK_ScalarMax, SK_ScalarMax,
+           SK_ScalarMax, SK_ScalarMax, SK_ScalarMax,
+           SK_ScalarMax, SK_ScalarMax, SK_ScalarMax },
+         kTranslate_Mask | kScale_Mask | kAffine_Mask | kPerspective_Mask };
+    return invalid.asSkMatrix();
 }
 
 ///////////////////////////////////////////////////////////////////////////////