From 5499f35ecaf6426d5140956afecfad63a50715d6 Mon Sep 17 00:00:00 2001
From: Finn Lindig <Lindig@swms.de>
Date: Tue, 10 Jun 2025 17:44:21 +0200
Subject: [PATCH] Fix viewport bug (#7 #5)

---
 OpenTKAvalonia/BaseTkOpenGlControl.cs | 32 +++++++++++++++++++--------
 1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/OpenTKAvalonia/BaseTkOpenGlControl.cs b/OpenTKAvalonia/BaseTkOpenGlControl.cs
index be1782f..7b3fea2 100644
--- a/OpenTKAvalonia/BaseTkOpenGlControl.cs
+++ b/OpenTKAvalonia/BaseTkOpenGlControl.cs
@@ -1,4 +1,6 @@
-using Avalonia;
+using System.Runtime.InteropServices;
+using Avalonia;
+using Avalonia.Controls;
 using Avalonia.Input;
 using Avalonia.OpenGL;
 using Avalonia.OpenGL.Controls;
@@ -24,7 +26,7 @@ public abstract class BaseTkOpenGlControl : OpenGlControlBase, ICustomHitTest
     /// </summary>
     protected virtual void OpenTkRender()
     {
-        
+
     }
 
     /// <summary>
@@ -34,7 +36,7 @@ protected virtual void OpenTkRender()
     /// </summary>
     protected virtual void OpenTkInit()
     {
-        
+
     }
 
     /// <summary>
@@ -45,16 +47,17 @@ protected virtual void OpenTkInit()
     /// </summary>
     protected virtual void OpenTkTeardown()
     {
-        
+
     }
 
     protected sealed override void OnOpenGlRender(GlInterface gl, int fb)
     {
         //Update last key states
         KeyboardState.OnFrame();
-        
+
         //Set up the aspect ratio so shapes aren't stretched.
-        GL.Viewport(0, 0, (int) Bounds.Width, (int) Bounds.Height);
+        var (w, h) = GetPlatformSpecificBounds();
+        GL.Viewport(0, 0, w, h);
 
         //Tell our subclass to render
         if (Bounds.Width != 0 && Bounds.Height != 0)
@@ -66,6 +69,17 @@ protected sealed override void OnOpenGlRender(GlInterface gl, int fb)
         Dispatcher.UIThread.Post(RequestNextFrameRendering, DispatcherPriority.Background);
     }
 
+    private static readonly bool OnLinux = RuntimeInformation.IsOSPlatform(OSPlatform.Linux);
+
+    private double? _renderScaling = null;
+    private double RenderScaling => (_renderScaling ??= TopLevel.GetTopLevel(this)?.RenderScaling)
+                                 ?? throw new PlatformNotSupportedException("Could not obtain TopLevel");
+    private (int width, int height) GetPlatformSpecificBounds()
+        => OnLinux
+            ? ((int)Bounds.Width, (int)Bounds.Height)
+            : (Math.Max(1, (int)(Bounds.Width * RenderScaling)),
+                Math.Max(1, (int)(Bounds.Height * RenderScaling)));
+
 
     protected sealed override void OnOpenGlInit(GlInterface gl)
     {
@@ -87,15 +101,15 @@ protected override void OnKeyDown(KeyEventArgs e)
     {
         if (!IsEffectivelyVisible)
             return;
-        
+
         KeyboardState.SetKey(e.Key, true);
     }
-    
+
     protected override void OnKeyUp(KeyEventArgs e)
     {
         if (!IsEffectivelyVisible)
             return;
-        
+
         KeyboardState.SetKey(e.Key, false);
     }