1 files changed, 61 insertions, 0 deletions
diff --git a/layout/painting/MatrixStack.h b/layout/painting/MatrixStack.h
new file mode 100644
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+++ b/layout/painting/MatrixStack.h
@@ -0,0 +1,61 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZILLA_PAINTING_MATRIXSTACK_H
+#define MOZILLA_PAINTING_MATRIXSTACK_H
+
+#include "nsTArray.h"
+#include "mozilla/gfx/MatrixFwd.h"
+
+namespace mozilla {
+
+/**
+ * MatrixStack stores a stack of matrices and keeps track of the accumulated
+ * transform matrix.
+ */
+template <typename T>
+class MatrixStack {
+ public:
+  MatrixStack() = default;
+
+  ~MatrixStack() { MOZ_ASSERT(mMatrices.IsEmpty()); }
+
+  /**
+   * Returns the current accumulated transform matrix.
+   */
+  const T& CurrentMatrix() const { return mCurrentMatrix; }
+
+  /**
+   * Returns true if any matrices are currently pushed to the stack.
+   */
+  bool HasTransform() const { return mMatrices.Length() > 0; }
+
+  /**
+   * Pushes the given |aMatrix| to the stack.
+   */
+  void Push(const T& aMatrix) {
+    mMatrices.AppendElement(mCurrentMatrix);
+    mCurrentMatrix = aMatrix * mCurrentMatrix;
+  }
+
+  /**
+   * Pops the most recently added matrix from the stack.
+   */
+  void Pop() {
+    MOZ_ASSERT(mMatrices.Length() > 0);
+    mCurrentMatrix = mMatrices.PopLastElement();
+  }
+
+ private:
+  T mCurrentMatrix;
+  AutoTArray<T, 2> mMatrices;
+};
+
+typedef MatrixStack<gfx::Matrix4x4Flagged> MatrixStack4x4;
+
+}  // namespace mozilla
+
+#endif /* MOZILLA_PAINTING_MATRIXSTACK_H */