gecko-dev/dom/canvas/WebGLObjectModel.h

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C++

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* 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 WEBGLOBJECTMODEL_H_
#define WEBGLOBJECTMODEL_H_
#include "nsCycleCollectionNoteChild.h"
#include "nsICanvasRenderingContextInternal.h"
#include "WebGLTypes.h"
namespace mozilla {
class WebGLBuffer;
class WebGLContext;
/* Each WebGL object class WebGLFoo wants to:
* - inherit WebGLRefCountedObject<WebGLFoo>
* - implement a Delete() method
* - have its destructor call DeleteOnce()
*
* This base class provides two features to WebGL object types:
* 1. support for OpenGL object reference counting
* 2. support for OpenGL deletion statuses
*
***** 1. OpenGL object reference counting *****
*
* WebGL objects such as WebGLTexture's really have two different refcounts:
* the XPCOM refcount, that is directly exposed to JavaScript, and the OpenGL
* refcount.
*
* For example, when in JavaScript one does: var newname = existingTexture;
* that increments the XPCOM refcount, but doesn't affect the OpenGL refcount.
* When one attaches the texture to a framebuffer object, that does increment
* its OpenGL refcount (and also its XPCOM refcount, to prevent the regular
* XPCOM refcounting mechanism from destroying objects prematurely).
*
* The actual OpenGL refcount is opaque to us (it's internal to the OpenGL
* implementation) but is affects the WebGL semantics that we have to implement:
* for example, a WebGLTexture that is attached to a WebGLFramebuffer must not
* be actually deleted, even if deleteTexture has been called on it, and even
* if JavaScript doesn't have references to it anymore. We can't just rely on
* OpenGL to keep alive the underlying OpenGL texture for us, for a variety of
* reasons, most importantly: we'd need to know when OpenGL objects are actually
* deleted, and OpenGL doesn't notify us about that, so we would have to query
* status very often with glIsXxx calls which isn't practical.
*
* This means that we have to keep track of the OpenGL refcount ourselves,
* in addition to the XPCOM refcount.
*
* This class implements such a refcount, see the mWebGLRefCnt
* member. In order to avoid name clashes (with regular XPCOM refcounting)
* in the derived class, we prefix members with 'WebGL', whence the names
* WebGLAddRef, WebGLRelease, etc.
*
* In practice, WebGLAddRef and WebGLRelease are only called from the
* WebGLRefPtr class.
*
***** 2. OpenGL deletion statuses *****
*
* In OpenGL, an object can go through 3 different deletion statuses during its
* lifetime, which correspond to the 3 enum values for DeletionStatus in this class:
* - the Default status, which it has from its creation to when the
* suitable glDeleteXxx function is called on it;
* - the DeleteRequested status, which is has from when the suitable glDeleteXxx
* function is called on it to when it is no longer referenced by other OpenGL
* objects. For example, a texture that is attached to a non-current FBO
* will enter that status when glDeleteTexture is called on it. For objects
* with that status, GL_DELETE_STATUS queries return true, but glIsXxx
* functions still return true.
* - the Deleted status, which is the status of objects on which the
* suitable glDeleteXxx function has been called, and that are not referenced
* by other OpenGL objects.
*
* This state is stored in the mDeletionStatus member of this class.
*
* When the GL refcount hits zero, if the status is DeleteRequested then we call
* the Delete() method on the derived class and the status becomes Deleted. This is
* what the MaybeDelete() function does.
*
* The DeleteOnce() function implemented here is a helper to ensure that we don't
* call Delete() twice on the same object. Since the derived class' destructor
* needs to call DeleteOnce() which calls Delete(), we can't allow either to be
* virtual. Strictly speaking, we could let them be virtual if the derived class
* were final, but that would be impossible to enforce and would lead to strange
* bugs if it were subclassed.
*
* This WebGLRefCountedObject class takes the Derived type
* as template parameter, as a means to allow DeleteOnce to call Delete()
* on the Derived class, without either method being virtual. This is a common
* C++ pattern known as the "curiously recursive template pattern (CRTP)".
*/
template<typename Derived>
class WebGLRefCountedObject
{
public:
enum DeletionStatus { Default, DeleteRequested, Deleted };
WebGLRefCountedObject()
: mDeletionStatus(Default)
{ }
~WebGLRefCountedObject() {
MOZ_ASSERT(mWebGLRefCnt == 0, "destroying WebGL object still referenced by other WebGL objects");
MOZ_ASSERT(mDeletionStatus == Deleted, "Derived class destructor must call DeleteOnce()");
}
// called by WebGLRefPtr
void WebGLAddRef() {
++mWebGLRefCnt;
}
// called by WebGLRefPtr
void WebGLRelease() {
MOZ_ASSERT(mWebGLRefCnt > 0, "releasing WebGL object with WebGL refcnt already zero");
--mWebGLRefCnt;
MaybeDelete();
}
// this is the function that WebGL.deleteXxx() functions want to call
void RequestDelete() {
if (mDeletionStatus == Default)
mDeletionStatus = DeleteRequested;
MaybeDelete();
}
bool IsDeleted() const {
return mDeletionStatus == Deleted;
}
bool IsDeleteRequested() const {
return mDeletionStatus != Default;
}
void DeleteOnce() {
if (mDeletionStatus != Deleted) {
static_cast<Derived*>(this)->Delete();
mDeletionStatus = Deleted;
}
}
private:
void MaybeDelete() {
if (mWebGLRefCnt == 0 &&
mDeletionStatus == DeleteRequested)
{
DeleteOnce();
}
}
protected:
nsAutoRefCnt mWebGLRefCnt;
DeletionStatus mDeletionStatus;
};
/* This WebGLRefPtr class is meant to be used for references between WebGL objects.
* For example, a WebGLProgram holds WebGLRefPtr's to the WebGLShader's attached
* to it.
*
* Why the need for a separate refptr class? The only special thing that WebGLRefPtr
* does is that it increments and decrements the WebGL refcount of
* WebGLRefCountedObject's, in addition to incrementing and decrementing the
* usual XPCOM refcount.
*
* This means that by using a WebGLRefPtr instead of a nsRefPtr, you ensure that
* the WebGL refcount is incremented, which means that the object will be kept
* alive by this reference even if the matching webgl.deleteXxx() function is
* called on it.
*/
template<typename T>
class WebGLRefPtr
{
public:
WebGLRefPtr()
: mRawPtr(0)
{ }
WebGLRefPtr(const WebGLRefPtr<T>& aSmartPtr)
: mRawPtr(aSmartPtr.mRawPtr)
{
AddRefOnPtr(mRawPtr);
}
explicit WebGLRefPtr(T* aRawPtr)
: mRawPtr(aRawPtr)
{
AddRefOnPtr(mRawPtr);
}
~WebGLRefPtr() {
ReleasePtr(mRawPtr);
}
WebGLRefPtr<T>&
operator=(const WebGLRefPtr<T>& rhs)
{
assign_with_AddRef(rhs.mRawPtr);
return *this;
}
WebGLRefPtr<T>&
operator=(T* rhs)
{
assign_with_AddRef(rhs);
return *this;
}
T* get() const {
return static_cast<T*>(mRawPtr);
}
operator T*() const {
return get();
}
T* operator->() const {
MOZ_ASSERT(mRawPtr != 0, "You can't dereference a nullptr WebGLRefPtr with operator->()!");
return get();
}
T& operator*() const {
MOZ_ASSERT(mRawPtr != 0, "You can't dereference a nullptr WebGLRefPtr with operator*()!");
return *get();
}
private:
static void AddRefOnPtr(T* rawPtr) {
if (rawPtr) {
rawPtr->WebGLAddRef();
rawPtr->AddRef();
}
}
static void ReleasePtr(T* rawPtr) {
if (rawPtr) {
rawPtr->WebGLRelease(); // must be done first before Release(), as Release() might actually destroy the object
rawPtr->Release();
}
}
void assign_with_AddRef(T* rawPtr) {
AddRefOnPtr(rawPtr);
assign_assuming_AddRef(rawPtr);
}
void assign_assuming_AddRef(T* newPtr) {
T* oldPtr = mRawPtr;
mRawPtr = newPtr;
ReleasePtr(oldPtr);
}
protected:
T *mRawPtr;
};
// This class is a mixin for objects that are tied to a specific
// context (which is to say, all of them). They provide initialization
// as well as comparison with the current context.
class WebGLContextBoundObject
{
public:
explicit WebGLContextBoundObject(WebGLContext* context);
bool IsCompatibleWithContext(WebGLContext *other);
WebGLContext *Context() const { return mContext; }
protected:
WebGLContext *mContext;
uint32_t mContextGeneration;
};
// this class is a mixin for GL objects that have dimensions
// that we need to track.
class WebGLRectangleObject
{
public:
WebGLRectangleObject()
: mWidth(0), mHeight(0) { }
WebGLRectangleObject(GLsizei width, GLsizei height)
: mWidth(width), mHeight(height) { }
GLsizei Width() const { return mWidth; }
void width(GLsizei value) { mWidth = value; }
GLsizei Height() const { return mHeight; }
void height(GLsizei value) { mHeight = value; }
void setDimensions(GLsizei width, GLsizei height) {
mWidth = width;
mHeight = height;
}
void setDimensions(WebGLRectangleObject *rect) {
if (rect) {
mWidth = rect->Width();
mHeight = rect->Height();
} else {
mWidth = 0;
mHeight = 0;
}
}
bool HasSameDimensionsAs(const WebGLRectangleObject& other) const {
return Width() == other.Width() && Height() == other.Height();
}
protected:
GLsizei mWidth;
GLsizei mHeight;
};
}// namespace mozilla
template <typename T>
inline void
ImplCycleCollectionUnlink(mozilla::WebGLRefPtr<T>& aField)
{
aField = nullptr;
}
template <typename T>
inline void
ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
mozilla::WebGLRefPtr<T>& aField,
const char* aName,
uint32_t aFlags = 0)
{
CycleCollectionNoteChild(aCallback, aField.get(), aName, aFlags);
}
#endif