clean up TEXTURE_WHITE initialization & thumbnail geometry

Program.cs

@@ -198,10 +198,10 @@ public class UiGeometry {
   public UiGeometry(Vector2i windowSize) {
     WindowSize = windowSize;
 
-    int thumbnailHeight = 150;
+    int numThumbnails = 12;
+    int thumbnailHeight = WindowSize.Y / numThumbnails;
     int thumbnailWidth = (int) 1.0 * thumbnailHeight * activeCamera.Resolution.X / activeCamera.Resolution.Y;
-    int numBoxes = 10; // FIXME
-    for (int i = 0; i < numBoxes; i++) {
+    for (int i = 0; i < numThumbnails; i++) {
       Box2i box = Util.makeBox(WindowSize.X - thumbnailWidth, i * thumbnailHeight, thumbnailWidth, thumbnailHeight);
       ThumbnailBoxes.Add(box);
     }
@@ -219,8 +219,7 @@ public static class Util {
 public class Game : GameWindow {
   public Game(GameWindowSettings gwSettings, NativeWindowSettings nwSettings) : base(gwSettings, nwSettings) { }
 
-  private static Image<Rgba32> white1x1 = new(1, 1, new Rgba32(255, 255, 255));
-  private static Texture TEXTURE_WHITE = new Texture(white1x1);
+  private static Texture TEXTURE_WHITE = new Texture(new Image<Rgba32>(1, 1, new Rgba32(255, 255, 255)));
 
   UiGeometry geometry = new();