Observe GL context loss in ShaderEffectItem

Recreate the shader program as required when the GL context
changes. Also delete the shader program when the ShaderEffectItem
is deactivated, to save graphics memory.

Previously, this was done only for Symbian platforms, and in a
suboptimal fashion. This patch implements the behaviour for all
platforms in a more optimal manner.

Task-number: QTBUG-28136
Change-Id: I8281e77f7285ea0046bdf092ab827cae3b00a6d2
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Reviewed-by: Alan Alpert <aalpert@rim.com>

2 files changed, 7 insertions, 34 deletions

diff --git a/src/imports/shaders/shadereffectitem.cpp b/src/imports/shaders/shadereffectitem.cpp
index 85a4076a..7d4ca497 100644
--- a/src/imports/shaders/shadereffectitem.cpp
+++ b/src/imports/shaders/shadereffectitem.cpp
@@ -218,21 +218,15 @@ ShaderEffectItem::ShaderEffectItem(QDeclarativeItem *parent)
     , m_hasShaderPrograms(false)
     , m_mirrored(false)
     , m_defaultVertexShader(true)
-    , m_contextObserver(0)
 {
     setFlag(QGraphicsItem::ItemHasNoContents, false);
     connect(this, SIGNAL(visibleChanged()), this, SLOT(handleVisibilityChange()));
     m_active = isVisible();
-
-#ifndef OBSERVE_GL_CONTEXT_LOSS
-    m_program = new QGLShaderProgram(this);
-#endif
 }
 
 ShaderEffectItem::~ShaderEffectItem()
 {
     reset();
-    delete m_contextObserver;
 }
 
 
@@ -412,30 +406,15 @@ void ShaderEffectItem::renderEffect(QPainter *painter, const QMatrix4x4 &matrix)
     if (!painter || !painter->device())
         return;
 
-#ifdef OBSERVE_GL_CONTEXT_LOSS
-    QGLContext *context = const_cast <QGLContext*> (QGLContext::currentContext());
-    if (!m_program || !m_contextObserver || !m_contextObserver->isValid()) {
-        // Context has changed, re-create QGLShaderProgram
-        if (context) {
-            delete m_program;
-            m_program = 0;
-
-            delete m_contextObserver;
-            m_contextObserver = 0;
-
+    if (!m_program || !m_program->programId()) {
+        // Deleted due to deactivation, to save GPU memory,
+        // or invalidated due to GL context change.
+        delete m_program;
+        if (QGLContext::currentContext())
             m_program = new QGLShaderProgram(this);
-            m_contextObserver = new QGLFramebufferObject(QSize(2,2));
-
-            if (!m_contextObserver || !m_program) {
-                delete m_program;
-                m_program = 0;
-                delete m_contextObserver;
-                m_contextObserver = 0;
-                qWarning() << "ShaderEffectItem::renderEffect - Creating QGLShaderProgram or QGLFrameBufferObject failed!";
-            }
-        }
+        if (!m_program)
+            qWarning() << "ShaderEffectItem::renderEffect - Creating QGLShaderProgram failed!";
     }
-#endif
 
     if (!m_program)
         return;
@@ -682,14 +661,10 @@ void ShaderEffectItem::setActive(bool enable)
     }
 
     // QGLShaderProgram is deleted when not active (to minimize GPU memory usage).
-#ifdef OBSERVE_GL_CONTEXT_LOSS
     if (!m_active && m_program) {
         delete m_program;
         m_program = 0;
-        delete m_contextObserver;
-        m_contextObserver = 0;
     }
-#endif
 
     emit activeChanged();
     markDirty();
diff --git a/src/imports/shaders/shadereffectitem.h b/src/imports/shaders/shadereffectitem.h
index ea390625..29dd799b 100644
--- a/src/imports/shaders/shadereffectitem.h
+++ b/src/imports/shaders/shadereffectitem.h
@@ -146,8 +146,6 @@ private:
     bool m_hasShaderPrograms : 1;
     bool m_mirrored : 1;
     bool m_defaultVertexShader : 1;
-
-    QGLFramebufferObject* m_contextObserver;
 };
 
 QT_END_HEADER