In lv_draw_sw_mask_rect.c there are two implementations of this function depeding on LV_DRAW_SW_COMPLEX value, but LV_DRAW_SW_COMPLEX == 0 variant has additional argument const lv_areat_t coords. And ...

But the order of parameters passed into constructor of Windows::Foundation::Rect is wrong, the order are supposed to be (left, top, height, width), but the parameters passed in are (height, width, ...