Cache the current QOpenGLFramebufferObject

This doesn't cover FBOs bound directly with glBindFramebuffer(),
but it's perfect to create a fast path for code we know uses QOGLFBO,
thus avoiding expensive glGetIntegerv() driver calls.

The use case is to use this in QSG24BitTextMaskShader::activate(), where
we need to check if the current FBO is sRGB capable.

Change-Id: I434eeeb7e6a3d16be9327315536ad7280245085d
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>

2 files changed, 11 insertions, 1 deletions

diff --git a/src/gui/kernel/qopenglcontext_p.h b/src/gui/kernel/qopenglcontext_p.h
index 4a746bf12b..7c8c698a7d 100644
--- a/src/gui/kernel/qopenglcontext_p.h
+++ b/src/gui/kernel/qopenglcontext_p.h
@@ -61,6 +61,7 @@ QT_BEGIN_NAMESPACE
 
 class QOpenGLFunctions;
 class QOpenGLContext;
+class QOpenGLFramebufferObject;
 class QOpenGLMultiGroupSharedResource;
 
 class Q_GUI_EXPORT QOpenGLSharedResource
@@ -204,6 +205,7 @@ public:
         , workaround_missingPrecisionQualifiers(false)
         , active_engine(0)
         , qgl_current_fbo_invalid(false)
+        , qgl_current_fbo(Q_NULLPTR)
         , defaultFboRedirect(0)
     {
         requestedFormat = QSurfaceFormat::defaultFormat();
@@ -242,6 +244,11 @@ public:
 
     bool qgl_current_fbo_invalid;
 
+    // Set and unset in QOpenGLFramebufferObject::bind()/unbind().
+    // (Only meaningful for QOGLFBO since an FBO might be bound by other means)
+    // Saves us from querying the driver for the current FBO in most paths.
+    QOpenGLFramebufferObject *qgl_current_fbo;
+
     QVariant nativeHandle;
     GLuint defaultFboRedirect;
 
diff --git a/src/gui/opengl/qopenglframebufferobject.cpp b/src/gui/opengl/qopenglframebufferobject.cpp
index 6fc18b1d01..1ee90a0827 100644
--- a/src/gui/opengl/qopenglframebufferobject.cpp
+++ b/src/gui/opengl/qopenglframebufferobject.cpp
@@ -1068,6 +1068,7 @@ bool QOpenGLFramebufferObject::bind()
     d->funcs.glBindFramebuffer(GL_FRAMEBUFFER, d->fbo());
 
     QOpenGLContextPrivate::get(current)->qgl_current_fbo_invalid = true;
+    QOpenGLContextPrivate::get(current)->qgl_current_fbo = this;
 
     if (d->format.samples() == 0) {
         // Create new textures to replace the ones stolen via takeTexture().
@@ -1107,7 +1108,9 @@ bool QOpenGLFramebufferObject::release()
     if (current) {
         d->funcs.glBindFramebuffer(GL_FRAMEBUFFER, current->defaultFramebufferObject());
 
-        QOpenGLContextPrivate::get(current)->qgl_current_fbo_invalid = true;
+        QOpenGLContextPrivate *contextPrv = QOpenGLContextPrivate::get(current);
+        contextPrv->qgl_current_fbo_invalid = true;
+        contextPrv->qgl_current_fbo = Q_NULLPTR;
     }
 
     return true;