glxconvenience: Add a QT_XCB_FORCE_SOFTWARE_OPENGL environment variable.

The QT_XCB_FORCE_SOFTWARE_OPENGL environment variable is equivalent to
LIBGL_ALWAYS_SOFTWARE for Qt 5 applications only. This is most useful
with drivers that only support OpenGL 1. We need OpenGL 2, but the user
probably doesn't want LIBGL_ALWAYS_SOFTWARE in OpenGL 1 apps.

Together with
http://pkgs.fedoraproject.org/cgit/qt5-qtbase.git/tree/10-qt5-check-opengl2.sh
which goes into /etc/X11/xinit/xinitrc.d, it makes QML 2 just work on
old hardware that supports only OpenGL 1.x in hardware. The scriptlet
checks the glxinfo output for the OpenGL version and sets
QT_XCB_FORCE_SOFTWARE_OPENGL if the major version is < 2. (The scriptlet
requires xorg-x11-xinit and glx-utils.)

Tested on a Radeon 9200 SE (RV280) that supports only OpenGL 1.3 in
hardware.

Change-Id: Ief80d283820d6336052b8f390a0030ba9b687492
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/src/platformsupport/glxconvenience/qglxconvenience.cpp b/src/platformsupport/glxconvenience/qglxconvenience.cpp
index 11d9377db7..4630b12a57 100644
--- a/src/platformsupport/glxconvenience/qglxconvenience.cpp
+++ b/src/platformsupport/glxconvenience/qglxconvenience.cpp
@@ -39,6 +39,10 @@
 **
 ****************************************************************************/
 
+// We have to include this before the X11 headers dragged in by
+// qglxconvenience_p.h.
+#include <QtCore/QByteArray>
+
 #include "qglxconvenience_p.h"
 
 #include <QtCore/QVector>
@@ -116,6 +120,27 @@ QVector<int> qglx_buildSpec(const QSurfaceFormat &format, int drawableBit)
 
 GLXFBConfig qglx_findConfig(Display *display, int screen , const QSurfaceFormat &format, int drawableBit)
 {
+    // Allow forcing LIBGL_ALWAYS_SOFTWARE for Qt 5 applications only.
+    // This is most useful with drivers that only support OpenGL 1.
+    // We need OpenGL 2, but the user probably doesn't want
+    // LIBGL_ALWAYS_SOFTWARE in OpenGL 1 apps.
+    static bool checkedForceSoftwareOpenGL = false;
+    static bool forceSoftwareOpenGL = false;
+    if (!checkedForceSoftwareOpenGL) {
+        // If LIBGL_ALWAYS_SOFTWARE is already set, don't mess with it.
+        // We want to unset LIBGL_ALWAYS_SOFTWARE at the end so it does not
+        // get inherited by other processes, of course only if it wasn't
+        // already set before.
+        if (!qEnvironmentVariableIsEmpty("QT_XCB_FORCE_SOFTWARE_OPENGL")
+            && !qEnvironmentVariableIsSet("LIBGL_ALWAYS_SOFTWARE"))
+            forceSoftwareOpenGL = true;
+
+        checkedForceSoftwareOpenGL = true;
+    }
+
+    if (forceSoftwareOpenGL)
+        qputenv("LIBGL_ALWAYS_SOFTWARE", QByteArrayLiteral("1"));
+
     bool reduced = true;
     GLXFBConfig chosenConfig = 0;
     QSurfaceFormat reducedFormat = format;
@@ -159,6 +184,10 @@ GLXFBConfig qglx_findConfig(Display *display, int screen , const QSurfaceFormat
             reducedFormat = qglx_reduceSurfaceFormat(reducedFormat,&reduced);
     }
 
+    // unset LIBGL_ALWAYS_SOFTWARE now so other processes don't inherit it
+    if (forceSoftwareOpenGL)
+        qunsetenv("LIBGL_ALWAYS_SOFTWARE");
+
     return chosenConfig;
 }