Fix 2d software skinning with scaled polys

In some situations where polygons were scaled, existing software skinning was producing incorrect results.

The transform inverse needed to use an affine inverse rather than a cheaper inverse to account for this scaling.

drivers/gles_common/rasterizer_canvas_batcher.h

@@ -1625,13 +1625,16 @@ PREAMBLE(bool)::_software_skin_poly(RasterizerCanvas::Item::CommandPolygon *p_po
 
 	if (num_verts && (p_poly->bones.size() == num_verts * 4) && (p_poly->weights.size() == p_poly->bones.size())) {
 
+		const Transform2D &item_transform = p_item->xform;
+		Transform2D item_transform_inv = item_transform.affine_inverse();
+
 		for (int n = 0; n < num_verts; n++) {
 			const Vector2 &src_pos = p_poly->points[n];
 			Vector2 &dst_pos = pTemps[n];
 
 			// there can be an offset on the polygon at rigging time, this has to be accounted for
 			// note it may be possible that this could be concatenated with the bone transforms to save extra transforms - not sure yet
-			Vector2 src_pos_back_transformed = p_item->xform.xform(src_pos);
+			Vector2 src_pos_back_transformed = item_transform.xform(src_pos);
 
 			float total_weight = 0.0f;
 
@@ -1661,7 +1664,7 @@ PREAMBLE(bool)::_software_skin_poly(RasterizerCanvas::Item::CommandPolygon *p_po
 				dst_pos /= total_weight;
 
 				// retransform back from the poly offset space
-				dst_pos = p_item->xform.xform_inv(dst_pos);
+				dst_pos = item_transform_inv.xform(dst_pos);
 			}
 		}