avoid repeated SkSurface recreating because of X11 being asynchronous

Sometimes VCL and X11 (and thus Skia) will have a different idea
about what the size of a window is. Check for the mismatch and avoid
recreating if it wouldn't do anything.

Change-Id: Icf3ebba9589cc6f12612e5f280840346cb0edaeb

4 files changed, 29 insertions, 9 deletions

diff --git a/vcl/inc/skia/gdiimpl.hxx b/vcl/inc/skia/gdiimpl.hxx
index 8225e76d27ff..04f96cb7bd11 100644
--- a/vcl/inc/skia/gdiimpl.hxx
+++ b/vcl/inc/skia/gdiimpl.hxx
@@ -208,6 +208,8 @@ protected:
     void checkSurface();
     void recreateSurface();
     void destroySurface();
+    // Reimplemented for X11.
+    virtual bool avoidRecreateByResize() const { return false; }
 
     void privateDrawAlphaRect(long nX, long nY, long nWidth, long nHeight, double nTransparency,
                               bool blockAA = false);
diff --git a/vcl/inc/skia/x11/gdiimpl.hxx b/vcl/inc/skia/x11/gdiimpl.hxx
index 1c40aa6b2c28..1dc5064e6667 100644
--- a/vcl/inc/skia/x11/gdiimpl.hxx
+++ b/vcl/inc/skia/x11/gdiimpl.hxx
@@ -37,6 +37,7 @@ public:
 protected:
     virtual void createSurface() override;
     virtual void performFlush() override;
+    virtual bool avoidRecreateByResize() const override;
 
 private:
     std::unique_ptr<sk_app::WindowContext> mWindowContext;
diff --git a/vcl/skia/gdiimpl.cxx b/vcl/skia/gdiimpl.cxx
index 6215317b18ee..776e44216c45 100644
--- a/vcl/skia/gdiimpl.cxx
+++ b/vcl/skia/gdiimpl.cxx
@@ -267,11 +267,14 @@ void SkiaSalGraphicsImpl::checkSurface()
     }
     else if (GetWidth() != mSurface->width() || GetHeight() != mSurface->height())
     {
-        Size oldSize(mSurface->width(), mSurface->height());
-        recreateSurface();
-        SAL_INFO("vcl.skia", "recreate(" << this << "): old " << oldSize << " new "
-                                         << Size(mSurface->width(), mSurface->height())
-                                         << " requested " << Size(GetWidth(), GetHeight()));
+        if (!avoidRecreateByResize())
+        {
+            Size oldSize(mSurface->width(), mSurface->height());
+            recreateSurface();
+            SAL_INFO("vcl.skia", "recreate(" << this << "): old " << oldSize << " new "
+                                             << Size(mSurface->width(), mSurface->height())
+                                             << " requested " << Size(GetWidth(), GetHeight()));
+        }
     }
 }
 
diff --git a/vcl/skia/x11/gdiimpl.cxx b/vcl/skia/x11/gdiimpl.cxx
index 72fc311f7aaa..e349074e70e1 100644
--- a/vcl/skia/x11/gdiimpl.cxx
+++ b/vcl/skia/x11/gdiimpl.cxx
@@ -73,10 +73,6 @@ void X11SkiaSalGraphicsImpl::createSurface()
     assert(winInfo.fDisplay && winInfo.fWindow != None);
     winInfo.fFBConfig = nullptr; // not used
     winInfo.fVisualInfo = const_cast<SalVisual*>(&mX11Parent.GetVisual());
-    // TODO Vulkan does not use these dimensions, instead it uses dimensions of the actual
-    // drawable, which may lead to repeated createSurface() calls from checkSurface()
-    // if the window is being resized and VCL already knows the new size but Vulkan doesn't.
-    // Avoid this somehow.
     winInfo.fWidth = GetWidth();
     winInfo.fHeight = GetHeight();
     switch (renderMethodToUse())
@@ -100,6 +96,24 @@ void X11SkiaSalGraphicsImpl::createSurface()
 #endif
 }
 
+bool X11SkiaSalGraphicsImpl::avoidRecreateByResize() const
+{
+    if (!mSurface)
+        return false;
+    // Skia's WindowContext uses actual dimensions of the X window, which due to X11 being
+    // asynchronous may be temporarily different from what VCL thinks are the dimensions.
+    // That can lead to us repeatedly calling recreateSurface() because of "incorrect"
+    // size, and we otherwise need to check for size changes, because VCL does not inform us.
+    // Avoid the problem here by checking the size of the X window and bail out if Skia
+    // would just return the same size as it is now.
+    Window r;
+    int x, y;
+    unsigned int w, h, border, depth;
+    XGetGeometry(mX11Parent.GetXDisplay(), mX11Parent.GetDrawable(), &r, &x, &y, &w, &h, &border,
+                 &depth);
+    return mSurface->width() == int(w) && mSurface->height() == int(h);
+}
+
 void X11SkiaSalGraphicsImpl::DeInit()
 {
     SkiaSalGraphicsImpl::DeInit();