Added QGLPixelBuffer implementation using framebuffer objects.

Instead of having QGLPixelBuffer be a unusable stub implementation we
deprecate it and implement it in terms of QOpenGLFramebufferObject.
Framebuffer objects are anyway the recommended replacement for
pixelbuffers in modern OpenGL, as the context switching overhead is
avoided.

Change-Id: Ia220c358ee92813e87981d297c51d84525010322
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>

9 files changed, 124 insertions, 106 deletions

diff --git a/dist/changes-5.0.0 b/dist/changes-5.0.0
index 16ba1c3453..5f2781c1b6 100644
--- a/dist/changes-5.0.0
+++ b/dist/changes-5.0.0
@@ -570,6 +570,10 @@ QtOpenGL
   now have equivalents in QtGui, along with the naming change QGL -> QOpenGL.
   The classes in QtOpenGL that have equivalents in QtGui can now be considered
   deprecated.
+* QGLPixelBuffer is now deprecated and implemented in terms of a hidden
+  QGLWidget and a QOpenGLFramebufferObject. It is recommended that applications
+  using QGLPixelBuffer for offscreen rendering to a texture switch to using
+  QOpenGLFramebufferObject directly instead, for improved performance.
 
 QtScript
 --------
diff --git a/examples/opengl/pbuffers/main.cpp b/examples/opengl/pbuffers/main.cpp
index 6ae4542ca6..58d25245a1 100644
--- a/examples/opengl/pbuffers/main.cpp
+++ b/examples/opengl/pbuffers/main.cpp
@@ -49,14 +49,16 @@ int main(int argc, char **argv)
     Q_INIT_RESOURCE(pbuffers);
 
     QApplication a(argc, argv);
+    GLWidget widget(0);
+    widget.resize(640, 480);
+    widget.makeCurrent();
+
     if (!QGLFormat::hasOpenGL() || !QGLPixelBuffer::hasOpenGLPbuffers()) {
 	QMessageBox::information(0, "OpenGL pbuffers",
 				 "This system does not support OpenGL/pbuffers.");
         return -1;
     }
 
-    GLWidget widget(0);
-    widget.resize(640, 480);
     widget.show();
     return a.exec();
 }
diff --git a/examples/opengl/pbuffers2/glwidget.cpp b/examples/opengl/pbuffers2/glwidget.cpp
index 1fcfdcb533..d8dbe9854c 100644
--- a/examples/opengl/pbuffers2/glwidget.cpp
+++ b/examples/opengl/pbuffers2/glwidget.cpp
@@ -144,8 +144,6 @@ void GLWidget::draw()
     pbuffer_painter.end();
     glFlush();
 
-    // rendering directly to a texture is not supported on X11 and
-    // some Windows implementations, unfortunately
     if (!hasDynamicTextureUpdate)
         pbuffer->updateDynamicTexture(dynamicTexture);
 
diff --git a/examples/opengl/pbuffers2/main.cpp b/examples/opengl/pbuffers2/main.cpp
index eb956d472e..29ddec9bb9 100644
--- a/examples/opengl/pbuffers2/main.cpp
+++ b/examples/opengl/pbuffers2/main.cpp
@@ -47,14 +47,14 @@ int main(int argc, char **argv)
     Q_INIT_RESOURCE(pbuffers2);
 
     QApplication a(argc, argv);
+    GLWidget widget(0);
+    widget.resize(640, 480);
+    widget.makeCurrent();
     if (!QGLFormat::hasOpenGL() || !QGLPixelBuffer::hasOpenGLPbuffers()) {
 	QMessageBox::information(0, "OpenGL pbuffers 2",
 				 "This system does not support OpenGL/pbuffers.");
         return -1;
     }
-
-    GLWidget widget(0);
-    widget.resize(640, 480);
     widget.show();
     return a.exec();
 }
diff --git a/src/gui/kernel/qopenglcontext.h b/src/gui/kernel/qopenglcontext.h
index 7dfffde4a0..9ce76a9117 100644
--- a/src/gui/kernel/qopenglcontext.h
+++ b/src/gui/kernel/qopenglcontext.h
@@ -137,6 +137,7 @@ Q_SIGNALS:
 
 private:
     friend class QGLContext;
+    friend class QGLPixelBuffer;
     friend class QOpenGLContextResourceBase;
     friend class QOpenGLPaintDevice;
     friend class QOpenGLGlyphTexture;
diff --git a/src/opengl/opengl.pro b/src/opengl/opengl.pro
index 1d4abca64e..2adb2e09ce 100644
--- a/src/opengl/opengl.pro
+++ b/src/opengl/opengl.pro
@@ -61,7 +61,6 @@ SOURCES +=  qglshaderprogram.cpp \
             gl2paintengineex/qglcustomshaderstage.cpp \
             gl2paintengineex/qtextureglyphcache_gl.cpp
 
-SOURCES +=  qgl_qpa.cpp \
-            qglpixelbuffer_stub.cpp
+SOURCES +=  qgl_qpa.cpp
 
 INCLUDEPATH += ../3rdparty/harfbuzz/src
diff --git a/src/opengl/qglpixelbuffer.cpp b/src/opengl/qglpixelbuffer.cpp
index d9480c4994..135f2edd01 100644
--- a/src/opengl/qglpixelbuffer.cpp
+++ b/src/opengl/qglpixelbuffer.cpp
@@ -92,7 +92,10 @@
     \sa {opengl/pbuffers}{Pbuffers Example}
 */
 
+#include <private/qopenglextensions_p.h>
+
 #include <QtCore/qglobal.h>
+#include <QtGui/qopenglframebufferobject.h>
 
 #include "gl2paintengineex/qpaintengineex_opengl2_p.h"
 
@@ -129,16 +132,7 @@ void QGLPixelBufferPrivate::common_init(const QSize &size, const QGLFormat &form
         req_format = format;
         req_shareWidget = shareWidget;
         invalid = false;
-        qctx = new QGLContext(format);
-        qctx->d_func()->sharing = (shareWidget != 0);
-        if (shareWidget != 0 && shareWidget->d_func()->glcx) {
-            QGLContextGroup::addShare(qctx, shareWidget->d_func()->glcx);
-            shareWidget->d_func()->glcx->d_func()->sharing = true;
-        }
-
         glDevice.setPBuffer(q);
-        qctx->d_func()->paintDevice = q;
-        qctx->d_func()->valid = true;
     }
 }
 
@@ -198,7 +192,6 @@ QGLPixelBuffer::~QGLPixelBuffer()
     if (current != d->qctx)
         makeCurrent();
     d->cleanup();
-    delete d->qctx;
     if (current && current != d->qctx)
         current->makeCurrent();
 }
@@ -217,6 +210,17 @@ bool QGLPixelBuffer::makeCurrent()
     if (d->invalid)
         return false;
     d->qctx->makeCurrent();
+    if (!d->fbo) {
+        QOpenGLFramebufferObjectFormat format;
+        if (d->req_format.stencil())
+            format.setAttachment(QOpenGLFramebufferObject::CombinedDepthStencil);
+        else if (d->req_format.depth())
+            format.setAttachment(QOpenGLFramebufferObject::Depth);
+        if (d->req_format.sampleBuffers())
+            format.setSamples(d->req_format.samples());
+        d->fbo = new QOpenGLFramebufferObject(d->req_size, format);
+        d->fbo->bind();
+    }
     return true;
 }
 
@@ -306,14 +310,39 @@ bool QGLPixelBuffer::doneCurrent()
 void QGLPixelBuffer::updateDynamicTexture(GLuint texture_id) const
 {
     Q_D(const QGLPixelBuffer);
-    if (d->invalid)
+    if (d->invalid || !d->fbo)
+        return;
+
+    QOpenGLContext *ctx = QOpenGLContext::currentContext();
+    if (!ctx)
         return;
+
+#undef glBindFramebuffer
+
+#ifndef GL_READ_FRAMEBUFFER
+#define GL_READ_FRAMEBUFFER 0x8CA8
+#endif
+
+#ifndef GL_DRAW_FRAMEBUFFER
+#define GL_DRAW_FRAMEBUFFER 0x8CA9
+#endif
+
+    QOpenGLExtensions extensions(ctx);
+
+    if (d->blit_fbo) {
+        QOpenGLFramebufferObject::blitFramebuffer(d->blit_fbo, d->fbo);
+        extensions.glBindFramebuffer(GL_READ_FRAMEBUFFER, d->blit_fbo->handle());
+    }
+
     glBindTexture(GL_TEXTURE_2D, texture_id);
 #ifndef QT_OPENGL_ES
     glCopyTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, 0, 0, d->req_size.width(), d->req_size.height(), 0);
 #else
     glCopyTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 0, 0, d->req_size.width(), d->req_size.height(), 0);
 #endif
+
+    if (d->blit_fbo)
+        extensions.glBindFramebuffer(GL_READ_FRAMEBUFFER, ctx->d_func()->current_fbo);
 }
 
 /*!
@@ -521,4 +550,70 @@ QGLFormat QGLPixelBuffer::format() const
     \internal
 */
 
+bool QGLPixelBufferPrivate::init(const QSize &, const QGLFormat &f, QGLWidget *shareWidget)
+{
+    widget = new QGLWidget(f, 0, shareWidget);
+    widget->resize(1, 1);
+    qctx = const_cast<QGLContext *>(widget->context());
+    return widget->isValid();
+}
+
+bool QGLPixelBufferPrivate::cleanup()
+{
+    delete fbo;
+    fbo = 0;
+    delete blit_fbo;
+    blit_fbo = 0;
+    delete widget;
+    widget = 0;
+    return true;
+}
+
+bool QGLPixelBuffer::bindToDynamicTexture(GLuint texture_id)
+{
+    Q_UNUSED(texture_id);
+    return false;
+}
+
+void QGLPixelBuffer::releaseFromDynamicTexture()
+{
+}
+
+GLuint QGLPixelBuffer::generateDynamicTexture() const
+{
+    Q_D(const QGLPixelBuffer);
+    if (!d->fbo)
+        return 0;
+
+    if (d->fbo->format().samples() > 0
+        && QOpenGLExtensions(QOpenGLContext::currentContext())
+           .hasOpenGLExtension(QOpenGLExtensions::FramebufferBlit))
+    {
+        if (!d->blit_fbo)
+            const_cast<QOpenGLFramebufferObject *&>(d->blit_fbo) = new QOpenGLFramebufferObject(d->req_size);
+    } else {
+        return d->fbo->texture();
+    }
+
+    GLuint texture;
+
+    glGenTextures(1, &texture);
+    glBindTexture(GL_TEXTURE_2D, texture);
+
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, d->req_size.width(), d->req_size.height(), 0,
+            GL_RGBA, GL_UNSIGNED_BYTE, 0);
+
+    return texture;
+}
+
+bool QGLPixelBuffer::hasOpenGLPbuffers()
+{
+    return QOpenGLFramebufferObject::hasOpenGLFramebufferObjects();
+}
+
 QT_END_NAMESPACE
diff --git a/src/opengl/qglpixelbuffer_p.h b/src/opengl/qglpixelbuffer_p.h
index 6e8d6d7301..fd20cee07a 100644
--- a/src/opengl/qglpixelbuffer_p.h
+++ b/src/opengl/qglpixelbuffer_p.h
@@ -60,7 +60,7 @@
 QT_BEGIN_NAMESPACE
 
 class QEglContext;
-
+class QOpenGLFramebufferObject;
 
 class QGLPBufferGLPaintDevice : public QGLPaintDevice
 {
@@ -77,7 +77,7 @@ private:
 class QGLPixelBufferPrivate {
     Q_DECLARE_PUBLIC(QGLPixelBuffer)
 public:
-    QGLPixelBufferPrivate(QGLPixelBuffer *q) : q_ptr(q), invalid(true), qctx(0), pbuf(0), ctx(0)
+    QGLPixelBufferPrivate(QGLPixelBuffer *q) : q_ptr(q), invalid(true), qctx(0), widget(0), fbo(0), blit_fbo(0), pbuf(0), ctx(0)
     {
     }
     bool init(const QSize &size, const QGLFormat &f, QGLWidget *shareWidget);
@@ -88,6 +88,9 @@ public:
     bool invalid;
     QGLContext *qctx;
     QGLPBufferGLPaintDevice glDevice;
+    QGLWidget *widget;
+    QOpenGLFramebufferObject *fbo;
+    QOpenGLFramebufferObject *blit_fbo;
     QGLFormat format;
 
     QGLFormat req_format;
diff --git a/src/opengl/qglpixelbuffer_stub.cpp b/src/opengl/qglpixelbuffer_stub.cpp
deleted file mode 100644
index 528e48e9b6..0000000000
--- a/src/opengl/qglpixelbuffer_stub.cpp
+++ /dev/null
@@ -1,84 +0,0 @@
-/****************************************************************************
-**
-** Copyright (C) 2012 Digia Plc and/or its subsidiary(-ies).
-** Contact: http://www.qt-project.org/legal
-**
-** This file is part of the QtOpenGL module of the Qt Toolkit.
-**
-** $QT_BEGIN_LICENSE:LGPL$
-** Commercial License Usage
-** Licensees holding valid commercial Qt licenses may use this file in
-** accordance with the commercial license agreement provided with the
-** Software or, alternatively, in accordance with the terms contained in
-** a written agreement between you and Digia.  For licensing terms and
-** conditions see http://qt.digia.com/licensing.  For further information
-** use the contact form at http://qt.digia.com/contact-us.
-**
-** GNU Lesser General Public License Usage
-** Alternatively, this file may be used under the terms of the GNU Lesser
-** General Public License version 2.1 as published by the Free Software
-** Foundation and appearing in the file LICENSE.LGPL included in the
-** packaging of this file.  Please review the following information to
-** ensure the GNU Lesser General Public License version 2.1 requirements
-** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
-**
-** In addition, as a special exception, Digia gives you certain additional
-** rights.  These rights are described in the Digia Qt LGPL Exception
-** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
-**
-** GNU General Public License Usage
-** Alternatively, this file may be used under the terms of the GNU
-** General Public License version 3.0 as published by the Free Software
-** Foundation and appearing in the file LICENSE.GPL included in the
-** packaging of this file.  Please review the following information to
-** ensure the GNU General Public License version 3.0 requirements will be
-** met: http://www.gnu.org/copyleft/gpl.html.
-**
-**
-** $QT_END_LICENSE$
-**
-****************************************************************************/
-
-#include <qdebug.h>
-#include "qglpixelbuffer.h"
-#include "qglpixelbuffer_p.h"
-
-#include <qimage.h>
-#include <private/qgl_p.h>
-
-QT_BEGIN_NAMESPACE
-
-bool QGLPixelBufferPrivate::init(const QSize &size, const QGLFormat &f, QGLWidget *shareWidget)
-{
-    Q_UNUSED(size);
-    Q_UNUSED(f);
-    Q_UNUSED(shareWidget);
-    return false;
-}
-
-bool QGLPixelBufferPrivate::cleanup()
-{
-    return false;
-}
-
-bool QGLPixelBuffer::bindToDynamicTexture(GLuint texture_id)
-{
-    Q_UNUSED(texture_id);
-    return false;
-}
-
-void QGLPixelBuffer::releaseFromDynamicTexture()
-{
-}
-
-GLuint QGLPixelBuffer::generateDynamicTexture() const
-{
-    return 0;
-}
-
-bool QGLPixelBuffer::hasOpenGLPbuffers()
-{
-    return false;
-}
-
-QT_END_NAMESPACE