X11: Better support non-32bit visuals

This patch improves support for non-32bit screen configurations on X. The
patch mostly touches the xcb platform plugin but the changes to the glx
convenience functions do affect e.g. the offscreen plugin as well.

Since QWindow instances are now by default of type RasterGL instead of
Raster the majority of all windows are in fact instances of QXcbGlxWindow.
This means that the eventual QSurfaceFormat that we use is chosen based on
the available OpenGL configurations. Here the GLX config resolution code
did not do a very good job in trying to find the closest match relative to
the requested QSurfaceFormat, instead preferring higher bit depths.

This is an issue since many configurations support 32-bit windows even
if the screen itself has a root window with depth 16. In particular,
servers supporting both GLX and Render are very likely to have such
visuals. Particularly affected are remote X connections - even if the
application itself makes no use of OpenGL at all!

The changes introduced by this patch are as follows:
 1. Improve the GLX visual selection logic
 2. Improve the xcb visual selection logic
 3. Remove duplicated visual lookup for OpenGL-enabled windows
 4. Configure the default QSurfaceFormat to match the primary screen depth

Change-Id: Id1c176359e63a4581410e20350db5ac2c083e1cf
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>

5 files changed, 9 insertions, 12 deletions

diff --git a/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.cpp b/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.cpp
index 4290ec54fc..5580f81a7a 100644
--- a/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.cpp
+++ b/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.cpp
@@ -715,8 +715,8 @@ bool QGLXContext::supportsThreading()
 
 QGLXPbuffer::QGLXPbuffer(QOffscreenSurface *offscreenSurface)
     : QPlatformOffscreenSurface(offscreenSurface)
-    , m_format(offscreenSurface->requestedFormat())
     , m_screen(static_cast<QXcbScreen *>(offscreenSurface->screen()->handle()))
+    , m_format(m_screen->surfaceFormatFor(offscreenSurface->requestedFormat()))
     , m_pbuffer(0)
 {
     GLXFBConfig config = qglx_findConfig(DISPLAY_FROM_XCB(m_screen), m_screen->screenNumber(), m_format);
diff --git a/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.h b/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.h
index f00d96e6d5..bf1f1b324b 100644
--- a/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.h
+++ b/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.h
@@ -106,8 +106,8 @@ public:
     GLXPbuffer pbuffer() const { return m_pbuffer; }
 
 private:
-    QSurfaceFormat m_format;
     QXcbScreen *m_screen;
+    QSurfaceFormat m_format;
     GLXPbuffer m_pbuffer;
 };
 
diff --git a/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxintegration.cpp b/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxintegration.cpp
index a3668df59a..d536121521 100644
--- a/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxintegration.cpp
+++ b/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxintegration.cpp
@@ -189,7 +189,7 @@ QXcbWindow *QXcbGlxIntegration::createWindow(QWindow *window) const
 QPlatformOpenGLContext *QXcbGlxIntegration::createPlatformOpenGLContext(QOpenGLContext *context) const
 {
     QXcbScreen *screen = static_cast<QXcbScreen *>(context->screen()->handle());
-    QGLXContext *platformContext = new QGLXContext(screen, context->format(),
+    QGLXContext *platformContext = new QGLXContext(screen, screen->surfaceFormatFor(context->format()),
                                                    context->shareHandle(), context->nativeHandle());
     context->setNativeHandle(platformContext->nativeHandle());
     return platformContext;
diff --git a/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxwindow.cpp b/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxwindow.cpp
index 36503f4a7c..8ae83b8084 100644
--- a/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxwindow.cpp
+++ b/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxwindow.cpp
@@ -53,17 +53,15 @@ QXcbGlxWindow::~QXcbGlxWindow()
 {
 }
 
-void QXcbGlxWindow::resolveFormat()
-{
-    m_format = window()->requestedFormat(); //qglx_findVisualInfo sets the resovled format
-}
-
-void *QXcbGlxWindow::createVisual()
+const xcb_visualtype_t *QXcbGlxWindow::createVisual()
 {
     QXcbScreen *scr = xcbScreen();
     if (!scr)
         return Q_NULLPTR;
-    return qglx_findVisualInfo(DISPLAY_FROM_XCB(scr), scr->screenNumber(), &m_format);
+    XVisualInfo *visualInfo = qglx_findVisualInfo(DISPLAY_FROM_XCB(scr), scr->screenNumber(), &m_format);
+    const xcb_visualtype_t *xcb_visualtype = scr->visualForId(visualInfo->visualid);
+    XFree(visualInfo);
+    return xcb_visualtype;
 }
 
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxwindow.h b/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxwindow.h
index 1954f972f1..9519245130 100644
--- a/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxwindow.h
+++ b/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qxcbglxwindow.h
@@ -52,8 +52,7 @@ public:
     ~QXcbGlxWindow();
 
 protected:
-    void resolveFormat() Q_DECL_OVERRIDE;
-    void *createVisual() Q_DECL_OVERRIDE;
+    const xcb_visualtype_t *createVisual() Q_DECL_OVERRIDE;
 };
 
 QT_END_NAMESPACE