From e22d9d957b12fa84d552c8787df4426b22d4d0fe Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Fl=C3=B6ser?= <mgraesslin@kde.org>
Date: Tue, 23 Jan 2018 20:27:16 +0100
Subject: [PATCH] Enable blending if a subsurface has an alpha channel

Summary:
While investigating BUG 387313 I noticed that blending might be disabled
for subsurfaces. Blending was disabled before rendering the subsurfaces
and it is not checked whether the surfaces have an alpha channel or not.

This change addresses this problem by disabling blending after all
subsurfaces have been rendered and enabling blending if a subsurface has
an alpha channel.

Unfortunately this does not fix the investigated bug.

Reviewers: #kwin, #plasma

Subscribers: plasma-devel, kwin

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D10060
---
 plugins/scenes/opengl/scene_opengl.cpp | 8 +++++---
 plugins/scenes/opengl/scene_opengl.h   | 3 +++
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/plugins/scenes/opengl/scene_opengl.cpp b/plugins/scenes/opengl/scene_opengl.cpp
index 9a02c26ee0..d225b8e660 100644
--- a/plugins/scenes/opengl/scene_opengl.cpp
+++ b/plugins/scenes/opengl/scene_opengl.cpp
@@ -47,6 +47,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "decorations/decoratedclient.h"
 #include <logging.h>
 
+#include <KWayland/Server/buffer_interface.h>
 #include <KWayland/Server/subcompositor_interface.h>
 #include <KWayland/Server/surface_interface.h>
 
@@ -1358,7 +1359,7 @@ QMatrix4x4 SceneOpenGL2Window::modelViewProjectionMatrix(int mask, const WindowP
     return scene->projectionMatrix() * mvMatrix;
 }
 
-static void renderSubSurface(GLShader *shader, const QMatrix4x4 &mvp, const QMatrix4x4 &windowMatrix, OpenGLWindowPixmap *pixmap, const QRegion &region, bool hardwareClipping)
+void SceneOpenGL2Window::renderSubSurface(GLShader *shader, const QMatrix4x4 &mvp, const QMatrix4x4 &windowMatrix, OpenGLWindowPixmap *pixmap, const QRegion &region, bool hardwareClipping)
 {
     QMatrix4x4 newWindowMatrix = windowMatrix;
     newWindowMatrix.translate(pixmap->subSurface()->position().x(), pixmap->subSurface()->position().y());
@@ -1369,6 +1370,7 @@ static void renderSubSurface(GLShader *shader, const QMatrix4x4 &mvp, const QMat
     }
 
     if (!pixmap->texture()->isNull()) {
+        setBlendEnabled(pixmap->buffer() && pixmap->buffer()->hasAlphaChannel());
         // render this texture
         shader->setUniform(GLShader::ModelViewProjectionMatrix, mvp * newWindowMatrix);
         auto texture = pixmap->texture();
@@ -1515,8 +1517,6 @@ void SceneOpenGL2Window::performPaint(int mask, QRegion region, WindowPaintData
 
     vbo->unbindArrays();
 
-    setBlendEnabled(false);
-
     // render sub-surfaces
     auto wp = windowPixmap<OpenGLWindowPixmap>();
     const auto &children = wp ? wp->children() : QVector<WindowPixmap*>();
@@ -1528,6 +1528,8 @@ void SceneOpenGL2Window::performPaint(int mask, QRegion region, WindowPaintData
         renderSubSurface(shader, modelViewProjection, windowMatrix, static_cast<OpenGLWindowPixmap*>(pixmap), region, m_hardwareClipping);
     }
 
+    setBlendEnabled(false);
+
     if (!data.shader)
         ShaderManager::instance()->popShader();
 
diff --git a/plugins/scenes/opengl/scene_opengl.h b/plugins/scenes/opengl/scene_opengl.h
index 6643dc3537..6453d3b57c 100644
--- a/plugins/scenes/opengl/scene_opengl.h
+++ b/plugins/scenes/opengl/scene_opengl.h
@@ -173,6 +173,8 @@ protected:
     bool m_hardwareClipping;
 };
 
+class OpenGLWindowPixmap;
+
 class SceneOpenGL2Window : public SceneOpenGL::Window
 {
 public:
@@ -209,6 +211,7 @@ protected:
     virtual void performPaint(int mask, QRegion region, WindowPaintData data);
 
 private:
+    void renderSubSurface(GLShader *shader, const QMatrix4x4 &mvp, const QMatrix4x4 &windowMatrix, OpenGLWindowPixmap *pixmap, const QRegion &region, bool hardwareClipping);
     /**
      * Whether prepareStates enabled blending and restore states should disable again.
      **/