Respect sprite X and Y offsets

This makes menus display more correctly, and also fixes trees and other
objects on the main map, although it messes up bounds clipping (sigh).

internal/conv/object.go

@@ -11,8 +11,10 @@ import (
 //   * Width & height now stored using int
 //   * Colour data is now 32-bit rather than using a palette
 type Sprite struct {
-	Width  int
-	Height int
+	XOffset int
+	YOffset int
+	Width   int
+	Height  int
 
 	Image *ebiten.Image
 }
@@ -39,14 +41,18 @@ func ConvertObject(rawObj *data.Object, name string) (*Object, error) {
 	}
 
 	for i, rawSpr := range rawObj.Sprites {
-		w := int(rawSpr.Width)
-		h := int(rawSpr.Height)
 		ebitenImage, err := ebiten.NewImageFromImage(rawSpr.ToImage(), ebiten.FilterDefault)
 		if err != nil {
 			return nil, err
 		}
 
-		out.Sprites[i] = &Sprite{Width: w, Height: h, Image: ebitenImage}
+		out.Sprites[i] = &Sprite{
+			XOffset: int(rawSpr.XOffset),
+			YOffset: int(rawSpr.YOffset),
+			Width:   int(rawSpr.Width),
+			Height:  int(rawSpr.Height),
+			Image:   ebitenImage,
+		}
 	}
 
 	return out, nil