Added explicit threading API to QtOpenGL.

Since QtOpenGL/QGLContext is implemented in terms of
QtGui/QOpenGLContext which has stricter requirements about how it's
supposed to be used, we need to apply these requirements to QGLContext
as well.

This change adds QGLContext::moveToThread(QThread *) and documents it as
a necessity for making a context current on another thread.

Also introduces QGLPixelbuffer::context() to access the QGLContext of a
pixelbuffer, and made QGLWidget::context() return a non-const
QGLContext, since there's no good reason why it shouldn't, and it leads
to less const_cast clutter.

We could have introduced a backdoor in QOpenGLContext instead, making it
loosen its requirements, but that would have made it harder / impossible
to fully support threaded OpenGL in all the platforms.

Task-number: QTBUG-22560
Change-Id: Ibb6f65f342e7c963e80cc42ab5664c5f1cab30b0
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>

8 files changed, 84 insertions, 25 deletions

diff --git a/src/opengl/qgl.cpp b/src/opengl/qgl.cpp
index c94c8f550e..583ecb69a8 100644
--- a/src/opengl/qgl.cpp
+++ b/src/opengl/qgl.cpp
@@ -3127,6 +3127,19 @@ void QGLContextPrivate::setCurrentContext(QGLContext *context)
 }
 
 /*!
+    Moves the QGLContext to the given \a thread.
+
+    Enables calling swapBuffers() and makeCurrent() on the context in
+    the given thread.
+*/
+void QGLContext::moveToThread(QThread *thread)
+{
+    Q_D(QGLContext);
+    if (d->guiGlContext)
+        d->guiGlContext->moveToThread(thread);
+}
+
+/*!
     \fn bool QGLContext::chooseContext(const QGLContext* shareContext = 0)
 
     This semi-internal function is called by create(). It creates a
@@ -3195,16 +3208,18 @@ void QGLContextPrivate::setCurrentContext(QGLContext *context)
 
     In some very rare cases the underlying call may fail. If this
     occurs an error message is output to stderr.
+
+    If you call this from a thread other than the main UI thread,
+    make sure you've first pushed the context to the relevant thread
+    from the UI thread using moveToThread().
 */
 
 
 /*!
     \fn void QGLContext::swapBuffers() const
 
-    Swaps the screen contents with an off-screen buffer. Only works if
-    the context is in double buffer mode.
-
-    \sa QGLFormat::setDoubleBuffer()
+    Call this to finish a frame of OpenGL rendering, and make sure to
+    call makeCurrent() again before you begin a new frame.
 */
 
 
@@ -3362,13 +3377,18 @@ void QGLContextPrivate::setCurrentContext(QGLContext *context)
     1. Call doneCurrent() in the main thread when the rendering is
     finished.
 
-    2. Notify the swapping thread that it can grab the context.
+    2. Call QGLContext::moveToThread(swapThread) to transfer ownership
+    of the context to the swapping thread.
 
-    3. Make the rendering context current in the swapping thread with
+    3. Notify the swapping thread that it can grab the context.
+
+    4. Make the rendering context current in the swapping thread with
     makeCurrent() and then call swapBuffers().
 
-    4. Call doneCurrent() in the swapping thread and notify the main
-    thread that swapping is done.
+    5. Call doneCurrent() in the swapping thread.
+
+    6. Call QGLContext::moveToThread(qApp->thread()) and notify the
+    main thread that swapping is done.
 
     Doing this will free up the main thread so that it can continue
     with, for example, handling UI events or network requests. Even if
@@ -3400,7 +3420,10 @@ void QGLContextPrivate::setCurrentContext(QGLContext *context)
     QGLWidgets can only be created in the main GUI thread. This means
     a call to doneCurrent() is necessary to release the GL context
     from the main thread, before the widget can be drawn into by
-    another thread. Also, the main GUI thread will dispatch resize and
+    another thread. You then need to call QGLContext::moveToThread()
+    to transfer ownership of the context to the thread in which you
+    want to make it current.
+    Also, the main GUI thread will dispatch resize and
     paint events to a QGLWidget when the widget is resized, or parts
     of it becomes exposed or needs redrawing. It is therefore
     necessary to handle those events because the default
@@ -3749,7 +3772,7 @@ void QGLWidget::setFormat(const QGLFormat &format)
 
 
 /*!
-    \fn const QGLContext *QGLWidget::context() const
+    \fn QGLContext *QGLWidget::context() const
 
     Returns the context of this widget.
 
@@ -4483,7 +4506,7 @@ QGLFormat QGLWidget::format() const
     return d->glcx->format();
 }
 
-const QGLContext *QGLWidget::context() const
+QGLContext *QGLWidget::context() const
 {
     Q_D(const QGLWidget);
     return d->glcx;
diff --git a/src/opengl/qgl.h b/src/opengl/qgl.h
index ab2fd8d203..1d21b42cd5 100644
--- a/src/opengl/qgl.h
+++ b/src/opengl/qgl.h
@@ -281,6 +281,8 @@ public:
     QGLFormat requestedFormat() const;
     void setFormat(const QGLFormat& format);
 
+    void moveToThread(QThread *thread);
+
     virtual void makeCurrent();
     virtual void doneCurrent();
 
@@ -413,7 +415,7 @@ public:
     QGLFormat format() const;
     void setFormat(const QGLFormat& format);
 
-    const QGLContext* context() const;
+    QGLContext* context() const;
     void setContext(QGLContext* context, const QGLContext* shareContext = 0,
                     bool deleteOldContext = true);
 
diff --git a/src/opengl/qgl_p.h b/src/opengl/qgl_p.h
index df099ea281..904f3c1a3e 100644
--- a/src/opengl/qgl_p.h
+++ b/src/opengl/qgl_p.h
@@ -380,19 +380,18 @@ class Q_OPENGL_EXPORT QGLTextureDestroyer : public QObject
     Q_OBJECT
 public:
     QGLTextureDestroyer() : QObject() {
-        qRegisterMetaType<GLuint>();
-        connect(this, SIGNAL(freeTexture(QGLContext *, QPlatformPixmap *, GLuint)),
-                this, SLOT(freeTexture_slot(QGLContext *, QPlatformPixmap *, GLuint)));
+        connect(this, SIGNAL(freeTexture(QGLContext *, QPlatformPixmap *, quint32)),
+                this, SLOT(freeTexture_slot(QGLContext *, QPlatformPixmap *, quint32)));
     }
     void emitFreeTexture(QGLContext *context, QPlatformPixmap *boundPixmap, GLuint id) {
         emit freeTexture(context, boundPixmap, id);
     }
 
 Q_SIGNALS:
-    void freeTexture(QGLContext *context, QPlatformPixmap *boundPixmap, GLuint id);
+    void freeTexture(QGLContext *context, QPlatformPixmap *boundPixmap, quint32 id);
 
 private slots:
-    void freeTexture_slot(QGLContext *context, QPlatformPixmap *boundPixmap, GLuint id) {
+    void freeTexture_slot(QGLContext *context, QPlatformPixmap *boundPixmap, quint32 id) {
         Q_UNUSED(boundPixmap);
         QGLShareContextScope scope(context);
         glDeleteTextures(1, &id);
diff --git a/src/opengl/qgl_qpa.cpp b/src/opengl/qgl_qpa.cpp
index f52beceaae..ba07f6121c 100644
--- a/src/opengl/qgl_qpa.cpp
+++ b/src/opengl/qgl_qpa.cpp
@@ -186,9 +186,14 @@ void QGLContext::reset()
     d->initDone = false;
     QGLContextGroup::removeShare(this);
     if (d->guiGlContext) {
-        if (d->ownContext)
-            delete d->guiGlContext;
-        else
+        if (QOpenGLContext::currentContext() == d->guiGlContext)
+            doneCurrent();
+        if (d->ownContext) {
+            if (d->guiGlContext->thread() == QThread::currentThread())
+                delete d->guiGlContext;
+            else
+                d->guiGlContext->deleteLater();
+        } else
             d->guiGlContext->setQGLContextHandle(0,0);
         d->guiGlContext = 0;
     }
diff --git a/src/opengl/qglpaintdevice.cpp b/src/opengl/qglpaintdevice.cpp
index 5aa125f816..e870e45e15 100644
--- a/src/opengl/qglpaintdevice.cpp
+++ b/src/opengl/qglpaintdevice.cpp
@@ -43,6 +43,7 @@
 #include <private/qgl_p.h>
 #include <private/qglpixelbuffer_p.h>
 #include <private/qglframebufferobject_p.h>
+#include <qopenglfunctions.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -90,7 +91,7 @@ void QGLPaintDevice::beginPaint()
 
     if (m_previousFBO != m_thisFBO) {
         ctx->d_ptr->current_fbo = m_thisFBO;
-        glBindFramebuffer(GL_FRAMEBUFFER, m_thisFBO);
+        ctx->contextHandle()->functions()->glBindFramebuffer(GL_FRAMEBUFFER, m_thisFBO);
     }
 
     // Set the default fbo for the context to m_thisFBO so that
@@ -108,7 +109,7 @@ void QGLPaintDevice::ensureActiveTarget()
 
     if (ctx->d_ptr->current_fbo != m_thisFBO) {
         ctx->d_ptr->current_fbo = m_thisFBO;
-        glBindFramebuffer(GL_FRAMEBUFFER, m_thisFBO);
+        ctx->contextHandle()->functions()->glBindFramebuffer(GL_FRAMEBUFFER, m_thisFBO);
     }
 
     ctx->d_ptr->default_fbo = m_thisFBO;
@@ -120,7 +121,7 @@ void QGLPaintDevice::endPaint()
     QGLContext *ctx = context();
     if (m_previousFBO != ctx->d_func()->current_fbo) {
         ctx->d_ptr->current_fbo = m_previousFBO;
-        glBindFramebuffer(GL_FRAMEBUFFER, m_previousFBO);
+        ctx->contextHandle()->functions()->glBindFramebuffer(GL_FRAMEBUFFER, m_previousFBO);
     }
 
     ctx->d_ptr->default_fbo = 0;
diff --git a/src/opengl/qglpixelbuffer.cpp b/src/opengl/qglpixelbuffer.cpp
index a5e748a1e7..dd13ef24eb 100644
--- a/src/opengl/qglpixelbuffer.cpp
+++ b/src/opengl/qglpixelbuffer.cpp
@@ -100,6 +100,7 @@
 
 #include "gl2paintengineex/qpaintengineex_opengl2_p.h"
 
+#include <qglframebufferobject.h>
 #include <qglpixelbuffer.h>
 #include <private/qglpixelbuffer_p.h>
 #include <private/qfont_p.h>
@@ -115,11 +116,23 @@ QGLContext* QGLPBufferGLPaintDevice::context() const
     return pbuf->d_func()->qctx;
 }
 
-void QGLPBufferGLPaintDevice::endPaint() {
+void QGLPBufferGLPaintDevice::beginPaint()
+{
+    pbuf->makeCurrent();
+    QGLPaintDevice::beginPaint();
+}
+
+void QGLPBufferGLPaintDevice::endPaint()
+{
     glFlush();
     QGLPaintDevice::endPaint();
 }
 
+void QGLPBufferGLPaintDevice::setFbo(GLuint fbo)
+{
+    m_thisFBO = fbo;
+}
+
 void QGLPBufferGLPaintDevice::setPBuffer(QGLPixelBuffer* pb)
 {
     pbuf = pb;
@@ -221,6 +234,7 @@ bool QGLPixelBuffer::makeCurrent()
             format.setSamples(d->req_format.samples());
         d->fbo = new QOpenGLFramebufferObject(d->req_size, format);
         d->fbo->bind();
+        d->glDevice.setFbo(d->fbo->handle());
         glViewport(0, 0, d->req_size.width(), d->req_size.height());
     }
     return true;
@@ -242,6 +256,15 @@ bool QGLPixelBuffer::doneCurrent()
 }
 
 /*!
+    Returns the context of this pixelbuffer.
+*/
+QGLContext *QGLPixelBuffer::context() const
+{
+    Q_D(const QGLPixelBuffer);
+    return d->qctx;
+}
+
+/*!
     \fn GLuint QGLPixelBuffer::generateDynamicTexture() const
 
     Generates and binds a 2D GL texture that is the same size as the
@@ -366,6 +389,8 @@ QImage QGLPixelBuffer::toImage() const
         return QImage();
 
     const_cast<QGLPixelBuffer *>(this)->makeCurrent();
+    if (d->fbo)
+        d->fbo->bind();
     return qt_gl_read_framebuffer(d->req_size, d->format.alpha(), true);
 }
 
@@ -615,7 +640,7 @@ GLuint QGLPixelBuffer::generateDynamicTexture() const
 
 bool QGLPixelBuffer::hasOpenGLPbuffers()
 {
-    return QOpenGLFramebufferObject::hasOpenGLFramebufferObjects();
+    return QGLFramebufferObject::hasOpenGLFramebufferObjects();
 }
 
 QT_END_NAMESPACE
diff --git a/src/opengl/qglpixelbuffer.h b/src/opengl/qglpixelbuffer.h
index 58cd470d3d..f597a48695 100644
--- a/src/opengl/qglpixelbuffer.h
+++ b/src/opengl/qglpixelbuffer.h
@@ -66,6 +66,8 @@ public:
     bool makeCurrent();
     bool doneCurrent();
 
+    QGLContext *context() const;
+
     GLuint generateDynamicTexture() const;
     bool bindToDynamicTexture(GLuint texture);
     void releaseFromDynamicTexture();
diff --git a/src/opengl/qglpixelbuffer_p.h b/src/opengl/qglpixelbuffer_p.h
index fd20cee07a..caa2e2f7d1 100644
--- a/src/opengl/qglpixelbuffer_p.h
+++ b/src/opengl/qglpixelbuffer_p.h
@@ -68,8 +68,10 @@ public:
     virtual QPaintEngine* paintEngine() const {return pbuf->paintEngine();}
     virtual QSize size() const {return pbuf->size();}
     virtual QGLContext* context() const;
+    virtual void beginPaint();
     virtual void endPaint();
     void setPBuffer(QGLPixelBuffer* pb);
+    void setFbo(GLuint fbo);
 private:
     QGLPixelBuffer* pbuf;
 };