Payback Status Report:

We wrote status reports during the development of almost all the other versions of Payback but we haven't so far for the GP2X. To address this glaring omission, We've put together this report to give you an insight into what's new in the GP2X version of the game - and there's a lot!

New And Improved
The GP2X version of the game is based on the GBA code as this is the most bug free and up-to-date - and is also helpfully already very optimised for the ARM processor. Of course, the GP2X's extra CPU power allowed the game to be improved dramatically. The main new features in the GP2X version are:

Completely reworked front end and HUD.
HDR rendering and tone mapping, including extremely high quality precalculated lighting.
Almost all dialogue is now recorded speech.
A new "Challenge" game mode.
Lots of new songs on the soundtrack.
New vehicle models.
Higher resolution and framerate.
Lots of bug fixes and gameplay tweaks.
Lighting
By far the biggest change here was the switch to a vastly more sophisticated lighting algorithm. Each surface is assigned a unique HDR floating point lightmap (this means there are around 40,000 unique lightmaps per city), creating almost 1GB of lighting data per city. These lightmaps are calculated using a very high quality radiosity algorithm. This involves simulating the path of 77 billion photons per city (almost a trillion for all 11 cities). Despite the code being very optimised, this process still takes over 10 hours per city on a 2.4GHz PC. This tool also allows you to view the city from any angle using the new lighting data, as shown in the grabs below:

All this data is then reduced to around 2MB so it can easily be loaded into memory by the GP2X. This 500:1 compression ratio is achieved using a JPEG-style Discrete Cosine Transform and removing duplicate lightmaps or those that can never be seen from an overhead viewpoint. As you move around the city on the GP2X, these lightmaps are decompressed and combined with the real-time lighting (which is done using gouraud shading). Once this final lightmap has been calculated, it is then combined with the texture maps and rendered to the screen. (The combined textures are cached so none of this significantly effects performance.)