Enable access to the VAO resolvers through QOpenGLContextPrivate

This is a commit in preparation for an upcoming change in QtQuick.
We want to store the resolved functions for managing VAOs somewhere;
the "least worst" choice is next to the all other function resolvers,
which are in QOpenGLContext(Private).

To avoid moving the VAO resolvers themselves, leave a hook in
QOGLCPrivate, similar to e.g. the texture function resolvers. The hook
gets populated when the VAO resolvers for a given context are
requested.

This removes memory management burden from the users of those functions
(again, just like other function resolvers), and makes the
initialization of the functions automatic.

Change-Id: I0eba30a85bf8ad82946a5d68e91009d8b4bd91cf
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

2 files changed, 48 insertions, 35 deletions

diff --git a/src/opengl/qopenglvertexarrayobject.cpp b/src/opengl/qopenglvertexarrayobject.cpp
index 44a0640567..63e37727f9 100644
--- a/src/opengl/qopenglvertexarrayobject.cpp
+++ b/src/opengl/qopenglvertexarrayobject.cpp
@@ -49,6 +49,7 @@
 #include <QtOpenGL/qopenglfunctions_3_0.h>
 #include <QtOpenGL/qopenglfunctions_3_2_core.h>
 
+#include <private/qopenglcontext_p.h>
 #include <private/qopenglextensions_p.h>
 #include <private/qopenglvertexarrayobject_p.h>
 
@@ -57,9 +58,28 @@ QT_BEGIN_NAMESPACE
 class QOpenGLFunctions_3_0;
 class QOpenGLFunctions_3_2_Core;
 
-void qtInitializeVertexArrayObjectHelper(QOpenGLVertexArrayObjectHelper *helper, QOpenGLContext *context)
+static void vertexArrayObjectHelperDestroyCallback(QOpenGLVertexArrayObjectHelper *vaoHelper)
+{
+    delete vaoHelper;
+}
+
+QOpenGLVertexArrayObjectHelper *QOpenGLVertexArrayObjectHelper::vertexArrayObjectHelperForContext(QOpenGLContext *context)
+{
+    Q_ASSERT(context);
+
+    auto contextPrivate = QOpenGLContextPrivate::get(context);
+    auto &vaoHelper = contextPrivate->vaoHelper;
+
+    if (!vaoHelper) {
+        vaoHelper = new QOpenGLVertexArrayObjectHelper(context);
+        contextPrivate->vaoHelperDestroyCallback = &vertexArrayObjectHelperDestroyCallback;
+    }
+
+    return vaoHelper;
+}
+
+void QOpenGLVertexArrayObjectHelper::initializeFromContext(QOpenGLContext *context)
 {
-    Q_ASSERT(helper);
     Q_ASSERT(context);
 
     bool tryARB = true;
@@ -67,32 +87,32 @@ void qtInitializeVertexArrayObjectHelper(QOpenGLVertexArrayObjectHelper *helper,
     if (context->isOpenGLES()) {
         if (context->format().majorVersion() >= 3) {
             QOpenGLExtraFunctionsPrivate *extra = static_cast<QOpenGLExtensions *>(context->extraFunctions())->d();
-            helper->GenVertexArrays = extra->f.GenVertexArrays;
-            helper->DeleteVertexArrays = extra->f.DeleteVertexArrays;
-            helper->BindVertexArray = extra->f.BindVertexArray;
-            helper->IsVertexArray = extra->f.IsVertexArray;
+            GenVertexArrays = extra->f.GenVertexArrays;
+            DeleteVertexArrays = extra->f.DeleteVertexArrays;
+            BindVertexArray = extra->f.BindVertexArray;
+            IsVertexArray = extra->f.IsVertexArray;
             tryARB = false;
         } else if (context->hasExtension(QByteArrayLiteral("GL_OES_vertex_array_object"))) {
-            helper->GenVertexArrays = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_GenVertexArrays_t>(context->getProcAddress("glGenVertexArraysOES"));
-            helper->DeleteVertexArrays = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_DeleteVertexArrays_t>(context->getProcAddress("glDeleteVertexArraysOES"));
-            helper->BindVertexArray = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_BindVertexArray_t>(context->getProcAddress("glBindVertexArrayOES"));
-            helper->IsVertexArray = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_IsVertexArray_t>(context->getProcAddress("glIsVertexArrayOES"));
+            GenVertexArrays = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_GenVertexArrays_t>(context->getProcAddress("glGenVertexArraysOES"));
+            DeleteVertexArrays = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_DeleteVertexArrays_t>(context->getProcAddress("glDeleteVertexArraysOES"));
+            BindVertexArray = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_BindVertexArray_t>(context->getProcAddress("glBindVertexArrayOES"));
+            IsVertexArray = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_IsVertexArray_t>(context->getProcAddress("glIsVertexArrayOES"));
             tryARB = false;
         }
     } else if (context->hasExtension(QByteArrayLiteral("GL_APPLE_vertex_array_object")) &&
                !context->hasExtension(QByteArrayLiteral("GL_ARB_vertex_array_object"))) {
-        helper->GenVertexArrays = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_GenVertexArrays_t>(context->getProcAddress("glGenVertexArraysAPPLE"));
-        helper->DeleteVertexArrays = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_DeleteVertexArrays_t>(context->getProcAddress("glDeleteVertexArraysAPPLE"));
-        helper->BindVertexArray = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_BindVertexArray_t>(context->getProcAddress("glBindVertexArrayAPPLE"));
-        helper->IsVertexArray = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_IsVertexArray_t>(context->getProcAddress("glIsVertexArrayAPPLE"));
+        GenVertexArrays = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_GenVertexArrays_t>(context->getProcAddress("glGenVertexArraysAPPLE"));
+        DeleteVertexArrays = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_DeleteVertexArrays_t>(context->getProcAddress("glDeleteVertexArraysAPPLE"));
+        BindVertexArray = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_BindVertexArray_t>(context->getProcAddress("glBindVertexArrayAPPLE"));
+        IsVertexArray = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_IsVertexArray_t>(context->getProcAddress("glIsVertexArrayAPPLE"));
         tryARB = false;
     }
 
     if (tryARB && context->hasExtension(QByteArrayLiteral("GL_ARB_vertex_array_object"))) {
-        helper->GenVertexArrays = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_GenVertexArrays_t>(context->getProcAddress("glGenVertexArrays"));
-        helper->DeleteVertexArrays = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_DeleteVertexArrays_t>(context->getProcAddress("glDeleteVertexArrays"));
-        helper->BindVertexArray = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_BindVertexArray_t>(context->getProcAddress("glBindVertexArray"));
-        helper->IsVertexArray = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_IsVertexArray_t>(context->getProcAddress("glIsVertexArray"));
+        GenVertexArrays = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_GenVertexArrays_t>(context->getProcAddress("glGenVertexArrays"));
+        DeleteVertexArrays = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_DeleteVertexArrays_t>(context->getProcAddress("glDeleteVertexArrays"));
+        BindVertexArray = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_BindVertexArray_t>(context->getProcAddress("glBindVertexArray"));
+        IsVertexArray = reinterpret_cast<QOpenGLVertexArrayObjectHelper::qt_IsVertexArray_t>(context->getProcAddress("glIsVertexArray"));
     }
 }
 
@@ -107,12 +127,6 @@ public:
     {
     }
 
-    ~QOpenGLVertexArrayObjectPrivate()
-    {
-        if (vaoFuncsType == ARB || vaoFuncsType == APPLE || vaoFuncsType == OES)
-            delete vaoFuncs.helper;
-    }
-
     bool create();
     void destroy();
     void bind();
@@ -167,7 +181,7 @@ bool QOpenGLVertexArrayObjectPrivate::create()
 
     if (ctx->isOpenGLES()) {
         if (ctx->format().majorVersion() >= 3 || ctx->hasExtension(QByteArrayLiteral("GL_OES_vertex_array_object"))) {
-            vaoFuncs.helper = new QOpenGLVertexArrayObjectHelper(ctx);
+            vaoFuncs.helper = QOpenGLVertexArrayObjectHelper::vertexArrayObjectHelperForContext(ctx);
             vaoFuncsType = OES;
             vaoFuncs.helper->glGenVertexArrays(1, &vao);
         }
@@ -187,11 +201,11 @@ bool QOpenGLVertexArrayObjectPrivate::create()
         } else
 #endif
         if (ctx->hasExtension(QByteArrayLiteral("GL_ARB_vertex_array_object"))) {
-            vaoFuncs.helper = new QOpenGLVertexArrayObjectHelper(ctx);
+            vaoFuncs.helper = QOpenGLVertexArrayObjectHelper::vertexArrayObjectHelperForContext(ctx);
             vaoFuncsType = ARB;
             vaoFuncs.helper->glGenVertexArrays(1, &vao);
         } else if (ctx->hasExtension(QByteArrayLiteral("GL_APPLE_vertex_array_object"))) {
-            vaoFuncs.helper = new QOpenGLVertexArrayObjectHelper(ctx);
+            vaoFuncs.helper = QOpenGLVertexArrayObjectHelper::vertexArrayObjectHelperForContext(ctx);
             vaoFuncsType = APPLE;
             vaoFuncs.helper->glGenVertexArrays(1, &vao);
         }
diff --git a/src/opengl/qopenglvertexarrayobject_p.h b/src/opengl/qopenglvertexarrayobject_p.h
index 0d0fca4d81..bd50d86073 100644
--- a/src/opengl/qopenglvertexarrayobject_p.h
+++ b/src/opengl/qopenglvertexarrayobject_p.h
@@ -57,25 +57,27 @@
 
 QT_BEGIN_NAMESPACE
 
-class QOpenGLVertexArrayObjectHelper;
 class QOpenGLContext;
 
-void Q_OPENGL_EXPORT qtInitializeVertexArrayObjectHelper(QOpenGLVertexArrayObjectHelper *helper, QOpenGLContext *context);
-
 class QOpenGLVertexArrayObjectHelper
 {
     Q_DISABLE_COPY(QOpenGLVertexArrayObjectHelper)
 
-public:
+private:
     explicit inline QOpenGLVertexArrayObjectHelper(QOpenGLContext *context)
         : GenVertexArrays(nullptr)
         , DeleteVertexArrays(nullptr)
         , BindVertexArray(nullptr)
         , IsVertexArray(nullptr)
     {
-        qtInitializeVertexArrayObjectHelper(this, context);
+        initializeFromContext(context);
     }
 
+    void Q_OPENGL_EXPORT initializeFromContext(QOpenGLContext *context);
+
+public:
+    static Q_OPENGL_EXPORT QOpenGLVertexArrayObjectHelper *vertexArrayObjectHelperForContext(QOpenGLContext *context);
+
     inline bool isValid() const
     {
         return GenVertexArrays && DeleteVertexArrays && BindVertexArray && IsVertexArray;
@@ -101,9 +103,6 @@ public:
         return IsVertexArray(array);
     }
 
-private:
-    friend void Q_OPENGL_EXPORT qtInitializeVertexArrayObjectHelper(QOpenGLVertexArrayObjectHelper *helper, QOpenGLContext *context);
-
     // Function signatures are equivalent between desktop core, ARB, APPLE, ES 3 and ES 2 extensions
     typedef void (QOPENGLF_APIENTRYP qt_GenVertexArrays_t)(GLsizei n, GLuint *arrays);
     typedef void (QOPENGLF_APIENTRYP qt_DeleteVertexArrays_t)(GLsizei n, const GLuint *arrays);