Move HWND render target creation to WM_CREATE.

Author: xStrom

CHANGELOG.md

@@ -102,6 +102,7 @@ This means that druid no longer requires cairo on macOS and uses Core Graphics i
 - GTK: Support file filters in open/save dialogs. ([#903] by [@jneem])
 - GTK: Support DPI values other than 96. ([#904] by [@xStrom])
 - Windows: Removed flashes of white background at the edge of the window when resizing. ([#915] by [@xStrom])
+- Windows: Reduced chance of white flash when opening a new window. ([#916] by [@xStrom])
 - X11: Support key and mouse button state. ([#920] by [@jneem])
 - Routing `LifeCycle::FocusChanged` to descendant widgets. ([#925] by [@yrns])
 - Built-in open and save menu items now show the correct label and submit the right commands. ([#930] by [@finnerale])
@@ -201,6 +202,7 @@ This means that druid no longer requires cairo on macOS and uses Core Graphics i
 [#905]: https://github.com/xi-editor/druid/pull/905
 [#909]: https://github.com/xi-editor/druid/pull/909
 [#915]: https://github.com/xi-editor/druid/pull/915
+[#916]: https://github.com/xi-editor/druid/pull/916
 [#917]: https://github.com/xi-editor/druid/pull/917
 [#920]: https://github.com/xi-editor/druid/pull/920
 [#924]: https://github.com/xi-editor/druid/pull/924

druid-shell/src/platform/windows/window.rs

@@ -422,22 +422,27 @@ impl WndProc for MyWndProc {
         //println!("wndproc msg: {}", msg);
         match msg {
             WM_CREATE => {
-                let dcomp_state = unsafe {
-                    create_dcomp_state(self.present_strategy, hwnd).unwrap_or_else(|e| {
-                        warn!("Creating swapchain failed, falling back to hwnd: {:?}", e);
-                        None
-                    })
-                };
-
-                self.state.borrow_mut().as_mut().unwrap().dcomp_state = dcomp_state;
                 if let Some(state) = self.handle.borrow().state.upgrade() {
                     state.hwnd.set(hwnd);
                 }
-                let handle = self.handle.borrow().to_owned();
                 if let Some(state) = self.state.borrow_mut().as_mut() {
+                    let dcomp_state = unsafe {
+                        create_dcomp_state(self.present_strategy, hwnd).unwrap_or_else(|e| {
+                            warn!("Creating swapchain failed, falling back to hwnd: {:?}", e);
+                            None
+                        })
+                    };
+                    if dcomp_state.is_none() {
+                        unsafe {
+                            let rt = paint::create_render_target(&self.d2d_factory, hwnd);
+                            state.render_target = rt.ok();
+                        }
+                    }
+                    state.dcomp_state = dcomp_state;
+
+                    let handle = self.handle.borrow().to_owned();
                     state.handler.connect(&handle.into());
                 }
-
                 Some(0)
             }
             WM_ERASEBKGND => Some(0),