From 9cb666f469ce41747ae5b433ad998ad0c57c7687 Mon Sep 17 00:00:00 2001
From: David Edmundson <kde@davidedmundson.co.uk>
Date: Mon, 6 Mar 2017 00:39:41 +0000
Subject: [PATCH] Restore the backend set viewport when popping the final
 render target

Summary:
The backend is responsible for setting the viewport, the GLRenderTarget
should save and restore the viewport actually set by the backend.

Test Plan:
Ran Blur effect which uses this method, under scaling the viewport "restored"
differed from the one set by the backend.

Reviewers: #plasma

Subscribers: plasma-devel, kwin, #kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D4952
---
 libkwineffects/kwinglutils.cpp | 8 +++++---
 libkwineffects/kwinglutils.h   | 1 +
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/libkwineffects/kwinglutils.cpp b/libkwineffects/kwinglutils.cpp
index b7514e1490..cbf2a74842 100644
--- a/libkwineffects/kwinglutils.cpp
+++ b/libkwineffects/kwinglutils.cpp
@@ -1038,6 +1038,7 @@ QStack<GLRenderTarget*> GLRenderTarget::s_renderTargets = QStack<GLRenderTarget*
 QSize GLRenderTarget::s_virtualScreenSize;
 QRect GLRenderTarget::s_virtualScreenGeometry;
 qreal GLRenderTarget::s_virtualScreenScale = 1.0;
+GLint GLRenderTarget::s_virtualScreenViewport[4];
 
 void GLRenderTarget::initStatic()
 {
@@ -1074,6 +1075,9 @@ bool GLRenderTarget::blitSupported()
 
 void GLRenderTarget::pushRenderTarget(GLRenderTarget* target)
 {
+    if (s_renderTargets.isEmpty()) {
+        glGetIntegerv(GL_VIEWPORT, s_virtualScreenViewport);
+    }
     target->enable();
     s_renderTargets.push(target);
 }
@@ -1086,10 +1090,8 @@ GLRenderTarget* GLRenderTarget::popRenderTarget()
     if (!s_renderTargets.isEmpty()) {
         s_renderTargets.top()->enable();
     } else {
-        glViewport (-s_virtualScreenGeometry.x(), s_virtualScreenGeometry.height() - s_virtualScreenSize.height() - s_virtualScreenGeometry.y(),
-                           s_virtualScreenSize.width(), s_virtualScreenSize.height());
+        glViewport (s_virtualScreenViewport[0], s_virtualScreenViewport[1], s_virtualScreenViewport[2], s_virtualScreenViewport[3]);
     }
-
     return ret;
 }
 
diff --git a/libkwineffects/kwinglutils.h b/libkwineffects/kwinglutils.h
index 9d1935544e..da2bedfc7f 100644
--- a/libkwineffects/kwinglutils.h
+++ b/libkwineffects/kwinglutils.h
@@ -534,6 +534,7 @@ private:
     static QSize s_virtualScreenSize;
     static QRect s_virtualScreenGeometry;
     static qreal s_virtualScreenScale;
+    static GLint s_virtualScreenViewport[4];
 
     GLTexture mTexture;
     bool mValid;