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Old 19 June 2017, 02:12   #35
touyats
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Join Date: Feb 2016
Location: Trieste
Posts: 11
Both the blitter and copper are indeed very similar to the old ones that we know. Some of the differences are below:

The copper has a real "jump" instruction that support a 1-level subroutine call, instead of triggering a jump writing to a register like in the classic chipset. Hombre's copper is line-syncronized, but not pixel synchronized (you can't wait for a specific horizontal position). I am not sure why, possibly it's due to the pipelined/asynchronous architecture (like AAA) with the pixel clock/"byteplane" fetching clocked differently and split from the rest (blitter/copper/etc), so one side of the system can't really tell at which point in the line the raster is at.

Hombre's blitter is similar to the original one, and probably the very same 32 bit blitter that AAA had. It can fill areas, draw lines, do gourad shading (that is, linearly interpolate color over a line), and texture mapping (it reads the source channel not by the carthesian axes but by u,v mapping).

As it was alfready said, there is no hardware coordinate transformation pipeline so all the 3D transformation steps would have be done by the built-in Risc PA processor. IIRC there is not even a hardware Z-buffer or support to blit with a Z buffer (am I remembering right?).

The playfield hardware has up to 4 "byteplanes" (8-bit values) fetched at the same time. These 4 byteplanes can be combined to give a 24 bit 8:8:8 RGB color playfield (3 byteplanes needed), a 16 bit 5:5:5 RGB color playfield (2 byteplanes needed) or a 8 bit CLUT color playfield (1 byteplane needed). Up to 4 playfield so defined can be layered on top of each other, staying within the limit of the total of 4 byteplanes fetched (for example: you can have one 24 bit playfield with a 8 bit CLUT overlay ).

All in all, Hombre seems like the new AAA functionalities (the new blitter, a new copper, the "hybrid" modes) with a RISC PA processor packaged together (whereas AAA was basically the new features on top a ECS compatible implementation of the old blitter, copper and playfield logic).

Would it have competed with the Playstation? Dunno.

Personally, I think it was a good design albeit still perhaps late. It's somewhat a "along-the-usual-lines" design too - at least if you compare it to AAA - and indeed I must say I find the Atari Jaguar's Tom & Jerry design more revolutionary.

Last edited by touyats; 19 June 2017 at 02:18.
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