Writting map editor from scratch tutorial (With Allegro)

[User137]

No, you don't need 2 offset variables, ViewPointX already does that. If you wanted to also draw a tool panel (instead of using IDE components) on the left side, and always draw the entire map more to right, then you would use OffsetX. But then it would be
GridXPosition := ((Mouse.X + ViewPointX - ToolPanelWidth) div GridCellWidth);