fix bug - popup windows show hiding logic

CursorLang.Agent/Interop/WindowNative.cs

@@ -13,7 +13,6 @@ internal static class WindowNative
     internal delegate IntPtr WindowProc(IntPtr hWnd, uint message, IntPtr wParam, IntPtr lParam);
 
     internal const int WS_POPUP = unchecked((int)0x80000000);
-    internal const int WS_DISABLED = 0x08000000;
 
     internal const int WS_EX_LAYERED = 0x00080000;
     internal const int WS_EX_TOOLWINDOW = 0x00000080;
@@ -25,19 +24,14 @@ internal static class WindowNative
     internal const int SW_SHOWNOACTIVATE = 4;
 
     internal const uint WM_DESTROY = 0x0002;
-    internal const uint WM_PAINT = 0x000F;
     internal const uint WM_CLOSE = 0x0010;
     internal const uint WM_QUIT = 0x0012;
     internal const uint WM_NULL = 0x0000;
-    internal const uint WM_DISPLAYCHANGE = 0x007E;
-    internal const uint WM_DPICHANGED = 0x02E0;
     internal const uint WM_ENDSESSION = 0x0016;
 
     /// <summary>WM_APP and up belong to the application; the tray takes WM_APP + 1.</summary>
     internal const uint WM_APP = 0x8000;
 
-    private const uint LWA_ALPHA = 0x00000002;
-
     /// <summary>
     /// Registers a window class. A class already there is not an error: the name is
     /// unique per window kind, and a second agent in the same process would meet its
@@ -80,9 +74,55 @@ internal static class WindowNative
         return window;
     }
 
-    /// <summary>The whole opacity of a layered window, 0 to 255.</summary>
-    internal static void SetAlpha(IntPtr window, byte alpha) =>
-        SetLayeredWindowAttributes(window, 0, alpha, LWA_ALPHA);
+    /// <summary>
+    /// Puts a finished picture into a layered window, together with where it goes and
+    /// how see-through it is.
+    /// </summary>
+    /// <remarks>
+    /// One call replaces moving the window, resizing it, painting it and setting its
+    /// opacity, and it works while the window is still hidden. That is the point: the
+    /// content is ready before anyone can see the window, so it can never be shown
+    /// holding the picture of the previous time.
+    /// </remarks>
+    internal static bool SetContent(
+        IntPtr window, PopupWindowNative.Point at, Size size, IntPtr sourceDc, byte alpha)
+    {
+        var source = new PopupWindowNative.Point { X = 0, Y = 0 };
+        var blend = new BlendFunction
+        {
+            BlendOp = AC_SRC_OVER,
+            SourceConstantAlpha = alpha,
+            AlphaFormat = AC_SRC_ALPHA,
+        };
+
+        return UpdateLayeredWindow(
+            window, IntPtr.Zero, ref at, ref size, sourceDc, ref source, 0, ref blend, ULW_ALPHA);
+    }
+
+    private const byte AC_SRC_OVER = 0;
+    private const byte AC_SRC_ALPHA = 1;
+    private const uint ULW_ALPHA = 0x00000002;
+
+    [StructLayout(LayoutKind.Sequential)]
+    private struct BlendFunction
+    {
+        public byte BlendOp;
+        public byte BlendFlags;
+        public byte SourceConstantAlpha;
+        public byte AlphaFormat;
+    }
+
+    [StructLayout(LayoutKind.Sequential)]
+    internal struct Size
+    {
+        public int Width;
+        public int Height;
+    }
+
+    [DllImport("user32.dll", SetLastError = true)]
+    private static extern bool UpdateLayeredWindow(IntPtr hWnd, IntPtr hdcDst,
+        ref PopupWindowNative.Point pptDst, ref Size psize, IntPtr hdcSrc,
+        ref PopupWindowNative.Point pptSrc, uint crKey, ref BlendFunction pblend, uint dwFlags);
 
     [DllImport("user32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
     private static extern ushort RegisterClassEx(ref WindowClass lpwcx);
@@ -104,27 +144,12 @@ internal static class WindowNative
     [DllImport("user32.dll")]
     internal static extern bool IsWindowVisible(IntPtr hWnd);
 
-    [DllImport("user32.dll")]
-    internal static extern bool InvalidateRect(IntPtr hWnd, IntPtr lpRect, bool bErase);
-
-    [DllImport("user32.dll")]
-    internal static extern bool UpdateWindow(IntPtr hWnd);
-
-    [DllImport("user32.dll")]
-    internal static extern bool SetWindowRgn(IntPtr hWnd, IntPtr hRgn, bool bRedraw);
-
-    [DllImport("user32.dll")]
-    internal static extern bool GetClientRect(IntPtr hWnd, out PopupWindowNative.Rect lpRect);
-
     [DllImport("user32.dll", CharSet = CharSet.Unicode, EntryPoint = "PostMessageW")]
     internal static extern bool PostMessage(IntPtr hWnd, uint message, IntPtr wParam, IntPtr lParam);
 
     [DllImport("user32.dll")]
     internal static extern void PostQuitMessage(int nExitCode);
 
-    [DllImport("user32.dll")]
-    private static extern bool SetLayeredWindowAttributes(IntPtr hWnd, uint crKey, byte bAlpha, uint dwFlags);
-
     [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
     private static extern IntPtr GetModuleHandle(string? lpModuleName);