From fc54bdfe8995a1298c0350f3b003b1ebc071a14c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Gr=C3=A4=C3=9Flin?= <kde@martin-graesslin.com>
Date: Sun, 6 Feb 2011 09:27:30 +0100
Subject: [PATCH] Unbind shader before copying pixels to back buffer.

This solves the regression with NVIDIA drivers resulting in a black screen.
Apparently NVIDIA does not support glXCopySubBuffer and the copying of pixels
fails with a shader bound.

So unbinding the shader before copying the pixels and rebinding the shader
afterwards resolves the issue.

This allows to remove the temporary hack to make NVIDIA work, again.
---
 lib/kwinglutils.cpp  |  5 -----
 scene_opengl_glx.cpp | 11 +++++++++++
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/lib/kwinglutils.cpp b/lib/kwinglutils.cpp
index 49b94167a6..a01d1788a6 100644
--- a/lib/kwinglutils.cpp
+++ b/lib/kwinglutils.cpp
@@ -1183,11 +1183,6 @@ GLShader *ShaderManager::loadShaderFromCode(const QByteArray &vertexSource, cons
 
 void ShaderManager::initShaders()
 {
-    // HACK: the generic shaders fail with NVIDIA's blob
-    // temporarily disable them to force kwin on GL 1.x profile
-    if (GLPlatform::instance()->driver() == Driver_NVidia) {
-        return;
-    }
     m_orthoShader = new GLShader(":/resources/scene-vertex.glsl", ":/resources/scene-fragment.glsl");
     if (m_orthoShader->isValid()) {
         pushShader(SimpleShader, true);
diff --git a/scene_opengl_glx.cpp b/scene_opengl_glx.cpp
index 4e89664f56..edff792ab8 100644
--- a/scene_opengl_glx.cpp
+++ b/scene_opengl_glx.cpp
@@ -587,6 +587,13 @@ void SceneOpenGL::flushBuffer(int mask, QRegion damage)
                     glXCopySubBuffer(display(), glxbuffer, r.x(), y, r.width(), r.height());
                 }
             } else {
+                // if a shader is bound, copy pixels results in a black screen
+                // therefore unbind the shader and restore after copying the pixels
+                GLint shader = 0;
+                if (ShaderManager::instance()->isShaderBound()) {
+                   glGetIntegerv(GL_CURRENT_PROGRAM, &shader);
+                   glUseProgram(0);
+                }
                 // no idea why glScissor() is used, but Compiz has it and it doesn't seem to hurt
                 glEnable(GL_SCISSOR_TEST);
                 glDrawBuffer(GL_FRONT);
@@ -608,6 +615,10 @@ void SceneOpenGL::flushBuffer(int mask, QRegion damage)
                 glBitmap(0, 0, 0, 0, -xpos, -ypos, NULL);   // move position back to 0,0
                 glDrawBuffer(GL_BACK);
                 glDisable(GL_SCISSOR_TEST);
+                // rebind previously bound shader
+                if (ShaderManager::instance()->isShaderBound()) {
+                   glUseProgram(shader);
+                }
             }
         } else {
             waitSync();