The original Transport Tycoon predated DirectX and ran on DOS. Later games like RollerCoaster Tycoon had basically the same UI and were also almost entirely wri

The original Transport Tycoon predated DirectX and ran on DOS. Later games like RollerCoaster Tycoon had basically the same UI and were also almost entirely written in assembly (despite now running on Windows rather than DOS), so it's clear that Sawyer pretty much did write a graphics library in assembly.