From 95bf7ebfcd7892d1f03bf34f1d2e9dc0fe9a4297 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marko=20A=2E=20Niemel=C3=A4?= <marko.a.niemela@nokia.com>
Date: Thu, 5 May 2011 10:32:43 +0300
Subject: Fix to avoid depth test when possible

---
 src/shadereffectitem.cpp | 22 +++++++++++++++-------
 src/shadereffectitem.h   |  1 +
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/src/shadereffectitem.cpp b/src/shadereffectitem.cpp
index 64b59bd..4d09327 100644
--- a/src/shadereffectitem.cpp
+++ b/src/shadereffectitem.cpp
@@ -211,6 +211,7 @@ ShaderEffectItem::ShaderEffectItem(QDeclarativeItem *parent)
     , m_checkedViewportUpdateMode(false)
     , m_checkedOpenGL(false)
     , m_mirrored(false)
+    , m_defaultVertexShader(true)
 {
     setFlag(QGraphicsItem::ItemHasNoContents, false);
     connect(this, SIGNAL(visibleChanged()), this, SLOT(handleVisibilityChange()));
@@ -288,6 +289,7 @@ void ShaderEffectItem::setVertexShader(const QString &code)
         return;
 
     m_vertex_code = code;
+    m_defaultVertexShader = false;
     if (isComponentComplete()) {
         reset();
         updateProperties();
@@ -423,16 +425,22 @@ void ShaderEffectItem::renderEffect(QPainter *painter, const QMatrix4x4 &matrix)
 
     bindGeometry();
 
-    glEnable(GL_DEPTH_TEST);
-    glDepthFunc(GL_GREATER);
-    glDepthMask(true);
+    // Optimization, disable depth test when we know we don't need it.
+    if (m_defaultVertexShader) {
+        glDepthMask(false);
+        glDisable(GL_DEPTH_TEST);
+    } else {
+        glEnable(GL_DEPTH_TEST);
+        glDepthFunc(GL_GREATER);
+        glDepthMask(true);
 #if defined(QT_OPENGL_ES)
-    glClearDepthf(0);
+        glClearDepthf(0);
 #else
-    glClearDepth(0);
+        glClearDepth(0);
 #endif
-    glClearColor(0, 0, 0, 0);
-    glClear(GL_DEPTH_BUFFER_BIT);
+        glClearColor(0, 0, 0, 0);
+        glClear(GL_DEPTH_BUFFER_BIT);
+    }
 
     if (m_blending){
         glEnable(GL_BLEND);
diff --git a/src/shadereffectitem.h b/src/shadereffectitem.h
index d1f9fd4..83fbaea 100644
--- a/src/shadereffectitem.h
+++ b/src/shadereffectitem.h
@@ -140,6 +140,7 @@ private:
     bool m_checkedViewportUpdateMode : 1;
     bool m_checkedOpenGL : 1;
     bool m_mirrored : 1;
+    bool m_defaultVertexShader : 1;
 };
 
 QT_END_HEADER
-- 
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