XCB: Correctly report the created OpenGL context version and profile

This commit fixes the xcb qpa plugin such that it now correctly reports
the version and profile of the created OpenGL context in the
QOpenGLSurfaceFormat. To do this we have to create a temporary X window
so that we can make our new context current.

We also handle the buggy nVidia drivers which incorrectly report 0 for
the GL_CONTEXT_PROFILE_MASK query.

The reduced format is also copied back from qglx_findVisualInfo.

Change-Id: I6f34fe1c6130aebbb6b40c36df4acc216069d2b1
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>

1 files changed, 69 insertions, 8 deletions

diff --git a/src/plugins/platforms/xcb/qglxintegration.cpp b/src/plugins/platforms/xcb/qglxintegration.cpp
index d1a21c9c4f..089bca8a63 100644
--- a/src/plugins/platforms/xcb/qglxintegration.cpp
+++ b/src/plugins/platforms/xcb/qglxintegration.cpp
@@ -74,7 +74,6 @@ typedef GLXContext (*glXCreateContextAttribsARBProc)(Display*, GLXFBConfig, GLXC
 #define GLX_CONTEXT_PROFILE_MASK_ARB 0x9126
 #endif
 
-
 QGLXContext::QGLXContext(QXcbScreen *screen, const QSurfaceFormat &format, QPlatformOpenGLContext *share)
     : QPlatformOpenGLContext()
     , m_screen(screen)
@@ -86,18 +85,22 @@ QGLXContext::QGLXContext(QXcbScreen *screen, const QSurfaceFormat &format, QPlat
         m_shareContext = static_cast<const QGLXContext*>(share)->glxContext();
 
     GLXFBConfig config = qglx_findConfig(DISPLAY_FROM_XCB(screen),screen->screenNumber(),format);
+    XVisualInfo *visualInfo = 0;
+    Window window = 0; // Temporary window used to query OpenGL context
 
     if (config) {
         // Resolve entry point for glXCreateContextAttribsARB
         glXCreateContextAttribsARBProc glXCreateContextAttribsARB = 0;
         glXCreateContextAttribsARB = (glXCreateContextAttribsARBProc) glXGetProcAddress((const GLubyte*)"glXCreateContextAttribsARB");
 
+        // Use glXCreateContextAttribsARB if is available
         if (glXCreateContextAttribsARB != 0) {
 
             QVector<int> contextAttributes;
             contextAttributes << GLX_CONTEXT_MAJOR_VERSION_ARB << m_format.majorVersion()
                               << GLX_CONTEXT_MINOR_VERSION_ARB << m_format.minorVersion();
 
+            // If asking for OpenGL 3.2 or newer we should also specify a profile
             if (m_format.majorVersion() > 3 || (m_format.majorVersion() == 3 && m_format.minorVersion() > 1)) {
                 if (m_format.profile() == QSurfaceFormat::CoreProfile) {
                     contextAttributes << GLX_CONTEXT_FLAGS_ARB << GLX_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB
@@ -129,14 +132,17 @@ QGLXContext::QGLXContext(QXcbScreen *screen, const QSurfaceFormat &format, QPlat
             }
         }
 
-        if (m_context) {
+        // Get the basic surface format details
+        if (m_context)
             m_format = qglx_surfaceFormatFromGLXFBConfig(DISPLAY_FROM_XCB(screen), config, m_context);
-            m_format.setMajorVersion(format.majorVersion());
-            m_format.setMinorVersion(format.minorVersion());
-            m_format.setProfile(format.profile());
-        }
+
+        // Used for creating the temporary window
+        visualInfo = glXGetVisualFromFBConfig(DISPLAY_FROM_XCB(screen), config);
+        if (!visualInfo)
+            qFatal("Could not initialize GLX");
     } else {
-        XVisualInfo *visualInfo = qglx_findVisualInfo(DISPLAY_FROM_XCB(m_screen), screen->screenNumber(), &m_format);
+        // Note that m_format gets updated with the used surface format
+        visualInfo = qglx_findVisualInfo(DISPLAY_FROM_XCB(screen), screen->screenNumber(), &m_format);
         if (!visualInfo)
             qFatal("Could not initialize GLX");
         m_context = glXCreateContext(DISPLAY_FROM_XCB(screen), visualInfo, m_shareContext, true);
@@ -145,8 +151,63 @@ QGLXContext::QGLXContext(QXcbScreen *screen, const QSurfaceFormat &format, QPlat
             m_shareContext = 0;
             m_context = glXCreateContext(DISPLAY_FROM_XCB(screen), visualInfo, 0, true);
         }
-        XFree(visualInfo);
     }
+
+    // Create a temporary window so that we can make the new context current
+    Colormap cmap = XCreateColormap(DISPLAY_FROM_XCB(screen), screen->root(), visualInfo->visual, AllocNone);
+    XSetWindowAttributes a;
+    a.background_pixel = WhitePixel(DISPLAY_FROM_XCB(screen), screen->screenNumber());
+    a.border_pixel = BlackPixel(DISPLAY_FROM_XCB(screen), screen->screenNumber());
+    a.colormap = cmap;
+
+    window = XCreateWindow(DISPLAY_FROM_XCB(screen), screen->root(),
+                           0, 0, 100, 100,
+                           0, visualInfo->depth, InputOutput, visualInfo->visual,
+                           CWBackPixel|CWBorderPixel|CWColormap, &a);
+
+    XFree(visualInfo);
+
+    // Query the OpenGL version and profile
+    if (m_context && window) {
+        glXMakeCurrent(DISPLAY_FROM_XCB(screen), window, m_context);
+
+        int major = 0, minor = 0;
+        QString versionString(QLatin1String(reinterpret_cast<const char*>(glGetString(GL_VERSION))));
+        if (parseOpenGLVersion(versionString, major, minor)) {
+            m_format.setMajorVersion(major);
+            m_format.setMinorVersion(minor);
+        }
+
+        // If we have OpenGL 3.2 or newer we also need to query the profile in use
+        if (m_format.majorVersion() > 3 || (m_format.majorVersion() == 3 && m_format.minorVersion() > 1)) {
+            // nVidia drivers have a bug where querying GL_CONTEXT_PROFILE_MASK always returns 0.
+            // In this case let's assume that we got the profile that we asked for since nvidia implements
+            // both Core and Compatibility profiles
+            if (versionString.contains(QStringLiteral("NVIDIA"))) {
+                m_format.setProfile(format.profile());
+            } else {
+                GLint profileMask;
+                glGetIntegerv(GL_CONTEXT_PROFILE_MASK, &profileMask);
+                switch (profileMask) {
+                case GLX_CONTEXT_CORE_PROFILE_BIT_ARB:
+                    m_format.setProfile(QSurfaceFormat::CoreProfile);
+                    break;
+
+                case GLX_CONTEXT_COMPATIBILITY_PROFILE_BIT_ARB:
+                default:
+                    m_format.setProfile(QSurfaceFormat::CompatibilityProfile);
+                }
+            }
+        } else {
+            m_format.setProfile(QSurfaceFormat::NoProfile);
+        }
+
+        // Make our context non-current
+        glXMakeCurrent(DISPLAY_FROM_XCB(screen), 0, 0);
+    }
+
+    // Destroy our temporary window
+    XDestroyWindow(DISPLAY_FROM_XCB(screen), window);
 }
 
 QGLXContext::~QGLXContext()