clean up photo / letterbox centering code

Program.cs

@@ -328,12 +328,13 @@ public class Game : GameWindow {
     Texture active = textures[textureIndex];
 
     // FIXME: make a function for scaling & centering one box on another.
-    double scaleX = 1.0 * geometry.PhotoBox.Size.X / active.Size.X;
-    double scaleY = 1.0 * geometry.PhotoBox.Size.Y / active.Size.Y;
-    double scale = Math.Min(scaleX, scaleY);
-    int renderWidth = (int) (active.Size.X * scale);
-    int renderHeight = (int) (active.Size.Y * scale);
-    Box2i photoBox = Util.makeBox((int) geometry.PhotoBox.Center.X - renderWidth / 2, (int) geometry.PhotoBox.Center.Y - renderHeight / 2, renderWidth, renderHeight);
+    float scaleX = 1f * geometry.PhotoBox.Size.X / active.Size.X;
+    float scaleY = 1f * geometry.PhotoBox.Size.Y / active.Size.Y;
+    float scale = Math.Min(scaleX, scaleY);
+
+    Vector2i renderSize = (Vector2i) (((Vector2) active.Size) * scale);
+    Vector2i center = (Vector2i) geometry.PhotoBox.Center;
+    Box2i photoBox = Util.makeBox(center.X - renderSize.X / 2, center.Y - renderSize.Y / 2, renderSize.X, renderSize.Y);
     DrawTexture(active, photoBox); 
     for (int i = 0; i < textures.Count; i++) {
       Box2i box = geometry.ThumbnailBoxes[i];