What the heck, this compensation code works
(got to it through trial and error, check it with different resolutions):
draw_vec.x /= screen_size.x / fullscreen_image_pan[0].size_x; //size_x/size_y are both 450
draw_vec.y /= screen_size.x / fullscreen_image_pan[0].size_y; //but screen reso are e.g. 1000x600
draw_vec.x += fullscreen_image_pan[0].pos_x;
draw_vec.y += fullscreen_image_pan[0].pos_y * (screen_size.x/screen_size.y);
Note that for draw_vec.y I am using screen_size
.x too.
We make a strange team, haha.
Info: this VIEW is not isometric, aspect is default (/ not touched), VIEW is top down, panel has same aspect as screen reso I think.