WinForms - Form minimise set browser size to 0,0

When the form is minimized set the browser window size to 0x0 to reduce resource usage.

https://github.com/chromiumembedded/cef/blob/c7701b8a6168f105f2c2d6b239ce3958da3e3f13/tests/cefclient/browser/browser_window_std_win.cc#L89

Issue #2922

Author: amaitland

CefSharp.WinForms/ChromiumWebBrowser.cs

@@ -660,7 +660,7 @@ protected override void OnHandleCreated(EventArgs e)
                 // NOTE: Had to move the code out of this function otherwise the designer would crash
                 CreateBrowser();
 
-                ResizeBrowser();
+                ResizeBrowser(Width, Height);
             }
 
             base.OnHandleCreated(e);
@@ -771,7 +771,7 @@ void IWebBrowserInternal.OnAfterBrowserCreated(IBrowser browser)
                 });
             }
 
-            ResizeBrowser();
+            ResizeBrowser(Width, Height);
 
             //If Load was called after the call to CreateBrowser we'll call Load
             //on the MainFrame
@@ -985,21 +985,38 @@ protected override void OnSizeChanged(EventArgs e)
 
             if (!designMode && initialized)
             {
-                ResizeBrowser();
+                ResizeBrowser(Width, Height);
             }
         }
 
         /// <summary>
         /// Resizes the browser.
         /// </summary>
-        private void ResizeBrowser()
+        private void ResizeBrowser(int width, int height)
         {
             if (IsBrowserInitialized)
             {
-                managedCefBrowserAdapter.Resize(Width, Height);
+                managedCefBrowserAdapter.Resize(width, height);
             }
         }
 
+        /// <summary>
+        /// When minimized set the browser window size to 0x0 to reduce resource usage.
+        /// https://github.com/chromiumembedded/cef/blob/c7701b8a6168f105f2c2d6b239ce3958da3e3f13/tests/cefclient/browser/browser_window_std_win.cc#L87
+        /// </summary>
+        internal void HideInternal()
+        {
+            ResizeBrowser(0, 0);
+        }
+
+        /// <summary>
+        /// Show the browser (called after previous minimised)
+        /// </summary>
+        internal void ShowInternal()
+        {
+            ResizeBrowser(Width, Height);
+        }
+
         /// <summary>
         /// Raises the <see cref="E:System.Windows.Forms.Control.GotFocus" /> event.
         /// </summary>

CefSharp.WinForms/Internals/ParentFormMessageInterceptor.cs

@@ -28,6 +28,13 @@ internal class ParentFormMessageInterceptor : NativeWindow, IDisposable
         /// </summary>
         private Rectangle movingRectangle;
 
+        /// <summary>
+        /// Store the previous window state, used to determine if the
+        /// Windows was previously <see cref="FormWindowState.Minimized"/>
+        /// and resume rendering
+        /// </summary>
+        private FormWindowState previousWindowState;
+
         /// <summary>
         /// Gets or sets the browser.
         /// </summary>
@@ -83,12 +90,17 @@ private void ParentParentChanged(object sender, EventArgs e)
                 {
                     oldForm.HandleCreated -= OnHandleCreated;
                     oldForm.HandleDestroyed -= OnHandleDestroyed;
+                    oldForm.Resize -= OnResize;
                 }
                 ParentForm = newForm;
                 if (newForm != null)
                 {
                     newForm.HandleCreated += OnHandleCreated;
                     newForm.HandleDestroyed += OnHandleDestroyed;
+                    newForm.Resize += OnResize;
+
+                    previousWindowState = newForm.WindowState;
+
                     // If newForm's Handle has been created already,
                     // our event listener won't be called, so call it now.
                     if (newForm.IsHandleCreated)
@@ -99,6 +111,37 @@ private void ParentParentChanged(object sender, EventArgs e)
             }
         }
 
+        private void OnResize(object sender, EventArgs e)
+        {
+            var form = (Form)sender;
+
+            if (previousWindowState == form.WindowState)
+            {
+                return;
+            }
+
+            switch (form.WindowState)
+            {
+                case FormWindowState.Normal:
+                case FormWindowState.Maximized:
+                {
+                    if (previousWindowState == FormWindowState.Minimized)
+                    {
+                        Browser?.ShowInternal();
+                    }
+                    break;
+                }
+                case FormWindowState.Minimized:
+                {
+                    Browser?.HideInternal();
+
+                    break;
+                }
+            }
+
+            previousWindowState = form.WindowState;
+        }
+
         /// <summary>
         /// Handles the <see cref="E:HandleCreated" /> event.
         /// </summary>
@@ -266,6 +309,7 @@ protected virtual void Dispose(bool disposing)
                 {
                     ParentForm.HandleCreated -= OnHandleCreated;
                     ParentForm.HandleDestroyed -= OnHandleDestroyed;
+                    ParentForm.Resize -= OnResize;
                     ParentForm = null;
                 }