xcb: prevent crash with pixmap cursors on XRender-less X servers

We were using xcb_render_* APIs without checking if the server even
supports this extension. Attempting to use an extension which is
not present will always result in a crash. This patch adds the required
guards and refactors how we detect presence of XRender extension.

Also instead of falling back to some odd-looking bitmapped version
just leave the current cursor unchanged. That is how we did it in
Qt4 AFAICT.

Task-number: QTBUG-66935
Change-Id: I4f27f1d65a77563ec34f3e0e94492c9236d7f9a6
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

1 files changed, 9 insertions, 1 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.h b/src/plugins/platforms/xcb/qxcbconnection.h
index ced5208c81..d9321d94d0 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.h
+++ b/src/plugins/platforms/xcb/qxcbconnection.h
@@ -478,7 +478,13 @@ public:
     bool hasXRandr() const { return has_randr_extension; }
     bool hasInputShape() const { return has_input_shape; }
     bool hasXKB() const { return has_xkb; }
-    bool hasXRender() const { return has_render_extension; }
+    bool hasXRender(int major = -1, int minor = -1) const
+    {
+        if (has_render_extension && major != -1 && minor != -1)
+            return m_xrenderVersion >= qMakePair(major, minor);
+
+        return has_render_extension;
+    }
     bool hasXInput2() const { return m_xi2Enabled; }
     bool hasShm() const { return has_shm; }
     bool hasShmFd() const { return has_shm_fd; }
@@ -707,6 +713,8 @@ private:
     bool has_shm = false;
     bool has_shm_fd = false;
 
+    QPair<int, int> m_xrenderVersion;
+
     Qt::MouseButtons m_buttonState = 0;
     Qt::MouseButton m_button = Qt::NoButton;