Fix HiDPI scaling on XWayland (#88)

src/XIVLauncher.Core/Program.cs

@@ -255,8 +255,21 @@ private static void Main(string[] args)
 #endif
 
         // Create window, GraphicsDevice, and all resources necessary for the demo.
+        Sdl2Native.SDL_Init(SDLInitFlags.Video);
+
+        float dpiScale = 1f;
+
+        if (Environment.GetEnvironmentVariable("XDG_SESSION_TYPE") == "wayland"
+            && SdlHelpers.GetCurrentVideoDriver() == "x11")
+        {
+            dpiScale = SdlHelpers.GetDisplayDpiScale().Y;
+        }
+
+        var windowWidth = (int) Math.Round(1280 * dpiScale);
+        var windowHeight = (int) Math.Round(800 * dpiScale);
+
         VeldridStartup.CreateWindowAndGraphicsDevice(
-            new WindowCreateInfo(50, 50, 1280, 800, WindowState.Normal, $"XIVLauncher {version}"),
+            new WindowCreateInfo(50, 50, windowWidth, windowHeight, WindowState.Normal, $"XIVLauncher {version}"),
             new GraphicsDeviceOptions(false, null, true, ResourceBindingModel.Improved, true, true),
             out window,
             out gd);
@@ -270,7 +283,7 @@ private static void Main(string[] args)
         cl = gd.ResourceFactory.CreateCommandList();
         Log.Debug("Veldrid OK!");
 
-        bindings = new ImGuiBindings(gd, gd.MainSwapchain.Framebuffer.OutputDescription, window.Width, window.Height, storage.GetFile("launcherUI.ini"), Config.FontPxSize ?? 21.0f);
+        bindings = new ImGuiBindings(gd, gd.MainSwapchain.Framebuffer.OutputDescription, window.Width, window.Height, storage.GetFile("launcherUI.ini"), (Config.FontPxSize ?? 21.0f) * dpiScale);
         Log.Debug("ImGui OK!");
 
         StyleModelV1.DalamudStandard.Apply();

src/XIVLauncher.Core/SdlHelpers.cs

@@ -0,0 +1,53 @@
+using System.Numerics;
+using System.Runtime.InteropServices;
+using System.Text;
+using Serilog;
+using Veldrid.Sdl2;
+
+namespace XIVLauncher.Core;
+
+public static unsafe partial class SdlHelpers
+{
+    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
+    private delegate byte* SDL_GetCurrentVideoDriver_t();
+    private static SDL_GetCurrentVideoDriver_t s_sdl_getCurrentVideoDriver =
+        Sdl2Native.LoadFunction<SDL_GetCurrentVideoDriver_t>("SDL_GetCurrentVideoDriver");
+    private static byte* SDL_GetCurrentVideoDriver() => s_sdl_getCurrentVideoDriver();
+
+    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
+    private delegate int SDL_GetDisplayDPI_t(int displayIndex, float* ddpi, float* hdpi, float* vdpi);
+    private static SDL_GetDisplayDPI_t s_sdl_getDisplayDPI =
+        Sdl2Native.LoadFunction<SDL_GetDisplayDPI_t>("SDL_GetDisplayDPI");
+    private static int SDL_GetDisplayDPI(int displayIndex, float* ddpi, float* hdpi, float* vdpi)
+        => s_sdl_getDisplayDPI(displayIndex, ddpi, hdpi, vdpi);
+
+    private static unsafe string GetString(byte* stringStart)
+    {
+        int characters = 0;
+        while (stringStart[characters] != 0)
+        {
+            characters++;
+        }
+
+        return Encoding.UTF8.GetString(stringStart, characters);
+    }
+
+    public static string GetCurrentVideoDriver()
+    {
+        return GetString(SDL_GetCurrentVideoDriver());
+    }
+
+    public static Vector2 GetDisplayDpiScale()
+    {
+        float ddpi, hdpi, vdpi;
+
+        if (SDL_GetDisplayDPI(0, &ddpi, &hdpi, &vdpi) < 0)
+        {
+            Log.Warning("Cannot determine display DPI scale, defaulting to 1.0: {0}",
+                GetString(Sdl2Native.SDL_GetError()));
+            return new Vector2(1.0f, 1.0f);
+        }
+
+        return new Vector2(hdpi / 96, vdpi / 96);
+    }
+}