xcb: Reduce number of created colormaps

Create a colormap per visual, not per window.

Pick-to: 5.15
Change-Id: I97d94618f159b4beaffd4a1afe0611233ced6676
Reviewed-by: Liang Qi <liang.qi@qt.io>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 19 insertions, 0 deletions

diff --git a/src/plugins/platforms/xcb/qxcbscreen.cpp b/src/plugins/platforms/xcb/qxcbscreen.cpp
index 82e256657c..e65418b077 100644
--- a/src/plugins/platforms/xcb/qxcbscreen.cpp
+++ b/src/plugins/platforms/xcb/qxcbscreen.cpp
@@ -131,6 +131,9 @@ QXcbVirtualDesktop::QXcbVirtualDesktop(QXcbConnection *connection, xcb_screen_t
 QXcbVirtualDesktop::~QXcbVirtualDesktop()
 {
     delete m_xSettings;
+
+    for (auto cmap : qAsConst(m_visualColormaps))
+        xcb_free_colormap(xcb_connection(), cmap);
 }
 
 QDpi QXcbVirtualDesktop::dpi() const
@@ -493,6 +496,22 @@ quint8 QXcbVirtualDesktop::depthOfVisual(xcb_visualid_t visualid) const
     return *it;
 }
 
+xcb_colormap_t QXcbVirtualDesktop::colormapForVisual(xcb_visualid_t visualid) const
+{
+    auto it = m_visualColormaps.constFind(visualid);
+    if (it != m_visualColormaps.constEnd())
+        return *it;
+
+    auto cmap = xcb_generate_id(xcb_connection());
+    xcb_create_colormap(xcb_connection(),
+                        XCB_COLORMAP_ALLOC_NONE,
+                        cmap,
+                        screen()->root,
+                        visualid);
+    m_visualColormaps.insert(visualid, cmap);
+    return cmap;
+}
+
 QXcbScreen::QXcbScreen(QXcbConnection *connection, QXcbVirtualDesktop *virtualDesktop,
                        xcb_randr_output_t outputId, xcb_randr_get_output_info_reply_t *output)
     : QXcbObject(connection)