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Bug 1823215 - Extract ElementOrArray<T> from CanvasRenderingContext2D into gfxUtils.h so it can also be used elsewhere in gfx/thebes. r=gfx-reviewers,lsalzman
Differential Revision: https://phabricator.services.mozilla.com/D172938
This commit is contained in:
Jonathan Kew
parent
dfac3c918a
commit
ce6caaeacf
@ -24,6 +24,7 @@
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#include "FilterDescription.h"
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#include "gfx2DGlue.h"
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#include "gfxFontConstants.h"
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#include "gfxUtils.h"
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#include "nsICanvasRenderingContextInternal.h"
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#include "nsColor.h"
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#include "nsIFrame.h"
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@ -78,106 +79,6 @@ struct DOMMatrix2DInit;
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class CanvasRenderingContext2D : public nsICanvasRenderingContextInternal,
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public nsWrapperCache,
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public BasicRenderingContext2D {
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// Container for either a single element of type T, or an nsTArray<T>.
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// Provides a minimal subset of nsTArray's API, just enough to support use
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// by ContextState for the clipsAndTransforms list.
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// Using this instead of a simple nsTArray avoids an extra allocation in the
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// common case where no more than one element is ever added to the list.
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// Unlike an AutoTArray<..., 1>, this class is memmovable and therefore can
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// be used in ContextState without breaking its movability.
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template <typename T>
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class ElementOrArray {
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union {
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T mElement;
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nsTArray<T> mArray;
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};
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enum class Tag : uint8_t {
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Element,
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Array,
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} mTag;
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public:
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// Construct as an empty array.
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ElementOrArray() : mTag(Tag::Array) { new (&mArray) nsTArray<T>(); }
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// For now, don't support copy/move.
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ElementOrArray(const ElementOrArray&) = delete;
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ElementOrArray(ElementOrArray&&) = delete;
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ElementOrArray& operator=(const ElementOrArray&) = delete;
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ElementOrArray& operator=(ElementOrArray&&) = delete;
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// Destroy the appropriate variant.
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~ElementOrArray() {
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switch (mTag) {
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case Tag::Element:
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mElement.~T();
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break;
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case Tag::Array:
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mArray.~nsTArray();
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break;
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}
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}
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size_t Length() const { return mTag == Tag::Element ? 1 : mArray.Length(); }
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T* AppendElement(const T& aElement) {
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switch (mTag) {
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case Tag::Element: {
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// Move the existing element into an array, then append the new one.
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T temp = std::move(mElement);
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mElement.~T();
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mTag = Tag::Array;
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new (&mArray) nsTArray<T>();
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mArray.AppendElement(std::move(temp));
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return mArray.AppendElement(aElement);
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}
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case Tag::Array: {
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// If currently empty, just store the element directly.
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if (mArray.IsEmpty()) {
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mArray.~nsTArray();
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mTag = Tag::Element;
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new (&mElement) T(aElement);
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return &mElement;
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}
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// Otherwise, append it to the array.
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return mArray.AppendElement(aElement);
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}
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default:
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MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE("invalid tag");
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}
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}
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const T& LastElement() const {
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return mTag == Tag::Element ? mElement : mArray.LastElement();
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}
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T& LastElement() {
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return mTag == Tag::Element ? mElement : mArray.LastElement();
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}
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bool IsEmpty() const {
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return mTag == Tag::Element ? false : mArray.IsEmpty();
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}
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// Simple iterators to support range-for loops.
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const T* begin() const {
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return mTag == Tag::Array ? mArray.IsEmpty() ? nullptr : &*mArray.begin()
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: &mElement;
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}
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T* begin() {
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return mTag == Tag::Array ? mArray.IsEmpty() ? nullptr : &*mArray.begin()
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: &mElement;
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}
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const T* end() const {
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return mTag == Tag::Array ? begin() + mArray.Length() : &mElement + 1;
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}
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T* end() {
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return mTag == Tag::Array ? begin() + mArray.Length() : &mElement + 1;
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}
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};
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protected:
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virtual ~CanvasRenderingContext2D();
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@ -417,6 +417,106 @@ class gfxUtils {
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namespace mozilla {
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// Container for either a single element of type T, or an nsTArray<T>.
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// Provides a minimal subset of nsTArray's API, just enough to support use
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// by ContextState for the clipsAndTransforms list.
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// Using this instead of a simple nsTArray avoids an extra allocation in the
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// common case where no more than one element is ever added to the list.
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// Unlike an AutoTArray<..., 1>, this class is memmovable and therefore can
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// be used in ContextState without breaking its movability.
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template <typename T>
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class ElementOrArray {
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union {
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T mElement;
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nsTArray<T> mArray;
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};
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enum class Tag : uint8_t {
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Element,
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Array,
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} mTag;
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public:
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// Construct as an empty array.
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ElementOrArray() : mTag(Tag::Array) { new (&mArray) nsTArray<T>(); }
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// For now, don't support copy/move.
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ElementOrArray(const ElementOrArray&) = delete;
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ElementOrArray(ElementOrArray&&) = delete;
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ElementOrArray& operator=(const ElementOrArray&) = delete;
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ElementOrArray& operator=(ElementOrArray&&) = delete;
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// Destroy the appropriate variant.
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~ElementOrArray() {
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switch (mTag) {
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case Tag::Element:
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mElement.~T();
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break;
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case Tag::Array:
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mArray.~nsTArray();
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break;
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}
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}
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size_t Length() const { return mTag == Tag::Element ? 1 : mArray.Length(); }
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T* AppendElement(const T& aElement) {
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switch (mTag) {
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case Tag::Element: {
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// Move the existing element into an array, then append the new one.
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T temp = std::move(mElement);
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mElement.~T();
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mTag = Tag::Array;
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new (&mArray) nsTArray<T>();
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mArray.AppendElement(std::move(temp));
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return mArray.AppendElement(aElement);
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}
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case Tag::Array: {
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// If currently empty, just store the element directly.
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if (mArray.IsEmpty()) {
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mArray.~nsTArray();
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mTag = Tag::Element;
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new (&mElement) T(aElement);
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return &mElement;
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}
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// Otherwise, append it to the array.
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return mArray.AppendElement(aElement);
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}
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default:
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MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE("invalid tag");
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}
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}
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const T& LastElement() const {
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return mTag == Tag::Element ? mElement : mArray.LastElement();
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}
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T& LastElement() {
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return mTag == Tag::Element ? mElement : mArray.LastElement();
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}
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bool IsEmpty() const {
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return mTag == Tag::Element ? false : mArray.IsEmpty();
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}
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// Simple iterators to support range-for loops.
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const T* begin() const {
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return mTag == Tag::Array ? mArray.IsEmpty() ? nullptr : &*mArray.begin()
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: &mElement;
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}
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T* begin() {
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return mTag == Tag::Array ? mArray.IsEmpty() ? nullptr : &*mArray.begin()
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: &mElement;
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}
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const T* end() const {
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return mTag == Tag::Array ? begin() + mArray.Length() : &mElement + 1;
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}
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T* end() {
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return mTag == Tag::Array ? begin() + mArray.Length() : &mElement + 1;
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}
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};
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struct StyleAbsoluteColor;
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namespace gfx {
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