Classic Elite ships wireframe
In Classic Elite the ship geometries are limited to convex hulls to aid in rendering the wire-frame graphics as quickly as possible with hidden line removal. Each vertex is usually associated with 4 faces, each edge joining 2 vertices is associated with 2 faces. The maximum number of faces is 14, as is the case for the asteroid model. Face 15 is reserved to indicate a vertex is always visible regardless of the objection's orientation, e.g. more than 4 faces meet at that vertex. The (time consuming) 3D projection calculations for that vertex should always be performed, if the vertex is close enough to the player, else if the face is not visible then further tests are done to see if any visible face is associated with that vertex. An edge is only rendered if both faces associated with it are visible.
Ship data file format
An initial header of 20 bytes is followed by the vertex data, in groups of 6 bytes, then the edge data in groups of 4 bytes, and finally the face normal data in groups of 4 bytes.
| Byte (in Hex) | Ship header information (example ship) |
|---|---|
| 03 | hi nibble is cargo type if scooped (0 is not scoopable). lo nibble is max pieces of debris if destroyed. |
| E9 | lo byte of ship area for target hit decision |
| 07 | hi byte of ship area for target hit decision |
| 86 | lo byte of offset to edge data. |
| F2 | lo byte of offset to face data. |
| 5D | maximum size of heap reserved for processed line plotting data (1+4*max visible edges) |
| 00 | vertex id for laser gun (*4), used for firing laser lines |
| 1A | number of vertices(*4 + 6), used for explosion dust origin(s) |
| 72 | number of vertices*6, used for vertex loop counter |
| 1B | number of edges |
| 2C | lo byte of bounty (in units of 0.1 Cr) if awarded |
| 01 | hi byte of bounty (in units of 0.1 Cr) if awarded |
| 28 | number of faces*4, used for face loop counter |
| 1E | distance away when wireframe rendering replaced by large dot |
| A0 | Maximum ship energy |
| 1E | Maximum ship speed |
| 00 | hi byte of offset to edge data. |
| 00 | hi byte of offset to face data. |
| 01 | Scale factor for ship size when calculating whether face normal is visible |
| 22 | Laser firepower*8 plus maximum number (7) of missiles. |
Each vertex has 6 bytes of data.
| Byte X | ! Byte Z | Byte S | Byte F1 | Byte F2 | ||||
|---|---|---|---|---|---|
| 00 | 0E | 6C | 5F | 01 | 59 |
| ... |
Source code for the BBC tape and TUBE versions of BBC Elite can be found at Ian Bell's web site and were used to disassemble and interpret the Disk version described here.
