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>

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)

src/plugins/platforms/xcb/qxcbscreen.h

@@ -107,6 +107,7 @@ public:
     const xcb_visualtype_t *visualForFormat(const QSurfaceFormat &format) const;
     const xcb_visualtype_t *visualForId(xcb_visualid_t) const;
     quint8 depthOfVisual(xcb_visualid_t) const;
+    xcb_colormap_t colormapForVisual(xcb_visualid_t) const;
 
 private:
     QRect getWorkArea() const;
@@ -133,6 +134,7 @@ private:
     QString m_windowManagerName;
     QMap<xcb_visualid_t, xcb_visualtype_t> m_visuals;
     QMap<xcb_visualid_t, quint8> m_visualDepths;
+    mutable QMap<xcb_visualid_t, xcb_colormap_t> m_visualColormaps;
     uint16_t m_rotation = 0;
 };
 
@@ -190,6 +192,7 @@ public:
 
     const xcb_visualtype_t *visualForFormat(const QSurfaceFormat &format) const { return m_virtualDesktop->visualForFormat(format); }
     const xcb_visualtype_t *visualForId(xcb_visualid_t visualid) const;
+    xcb_colormap_t colormapForVisual(xcb_visualid_t visualid) const { return m_virtualDesktop->colormapForVisual(visualid); }
     quint8 depthOfVisual(xcb_visualid_t visualid) const { return m_virtualDesktop->depthOfVisual(visualid); }
 
     QString name() const override { return m_outputName; }

src/plugins/platforms/xcb/qxcbwindow.cpp

@@ -363,14 +363,9 @@ void QXcbWindow::create()
         return result;
     };
 
+    xcb_colormap_t cmap = XCB_COLORMAP_NONE;
     if ((window()->supportsOpenGL() && haveOpenGL()) || m_format.hasAlpha()) {
-        m_cmap = xcb_generate_id(xcb_connection());
-        xcb_create_colormap(xcb_connection(),
-                            XCB_COLORMAP_ALLOC_NONE,
-                            m_cmap,
-                            xcb_parent_id,
-                            m_visualId);
-
+        cmap = platformScreen->colormapForVisual(m_visualId);
         mask |= XCB_CW_COLORMAP;
     }
 
@@ -381,7 +376,7 @@ void QXcbWindow::create()
         type == Qt::Popup || type == Qt::ToolTip || (window()->flags() & Qt::BypassWindowManagerHint),
         type == Qt::Popup || type == Qt::Tool || type == Qt::SplashScreen || type == Qt::ToolTip || type == Qt::Drawer,
         defaultEventMask,
-        m_cmap
+        cmap
     };
 
     m_window = xcb_generate_id(xcb_connection());
@@ -552,9 +547,7 @@ void QXcbWindow::destroy()
         xcb_destroy_window(xcb_connection(), m_window);
         m_window = 0;
     }
-    if (m_cmap) {
-        xcb_free_colormap(xcb_connection(), m_cmap);
-    }
+
     m_mapped = false;
 
     if (m_pendingSyncRequest)

src/plugins/platforms/xcb/qxcbwindow.h

@@ -233,7 +233,6 @@ protected:
                                 quint8 mode, quint8 detail, xcb_timestamp_t timestamp);
 
     xcb_window_t m_window = 0;
-    xcb_colormap_t m_cmap = 0;
 
     uint m_depth = 0;
     QImage::Format m_imageFormat = QImage::Format_ARGB32_Premultiplied;