# S3 ViRGE builds draw 15-bit pixels: their 16-bit surfaces are 5-5-5

## Symptoms

In a stand-in for the S3D Toolkit, the chip's triangles come out in the wrong colours against
the game's software-drawn pixels, or the reverse.

## Cause

The ViRGE's 3D engine draws 8-, 15- or 24-bit pixels, never 5-6-5: the S3D Toolkit's surface
formats are `S3DTK_VIDEORGB8` (0), `RGB15` (4) and `RGB24` (8). POD's S3 build describes its
16-bit draw surfaces as `RGB15` (*measured*: `sfFormat` 4 in the `S3DTK_SURFACE` it passes),
so on the real card its DirectDraw surfaces were 5-5-5 (*inferred*).

## Evidence

A probe `S3DTKW.dll` dumping the `S3DTK_SURFACE` set as `S3DTK_DRAWSURFACE`:
`{linear address, 640, 480, 4}`.

## What to do

Draw the chip's pixels in the format the game names (`sfFormat`), and make the DirectDraw
surfaces report the same masks (`0x7c00`, `0x3e0`, `0x1f`). POD's software renderer reads the
surface's pixel format and follows it, so both halves agree (`wrappers/ddraw`:
`DDRAW_PIXELS=555`).