integer inaccuracy when zooming

[Arttale]

I can see what you did with the zoom being limited to a max of 2.
the issue with the decreased inaccuracy at higher zoom is that point(0,0) is limited to integers and will automatically cast to integers even if you pass a float into it.

here's my fix
variables:

local image_pos = { x = 0.0, y = 0.0 }
local image_origin = { x = 0.0, y = 0.0 }

mouse move adjustment so that the fix doesn't cause issues:

onmousemove=function(ev)
			if mouse_drag then
				local mouse = Point(ev.x, ev.y)
				local dpos = {
					x = (mouse.x - mouse_origin.x) * inv_scale_factor,
					y = (mouse.y - mouse_origin.y) * inv_scale_factor
				}
				image_pos = {
					x = image_origin.x - dpos.x,
					y = image_origin.y - dpos.y
				}
				--dlg:repaint()
			end