Mendel - how big are those black squares?
What I'm suggesting is that a tile, which is 16x16 pixels in size, is assigned to a single quad. Throughout the lifetime of rendering the frame, only that quad will write pixels there.
The squares can only be black because they've been written by a single quad (though I'm at a loss to explain why only the sky shows the fault! - could it be a fog unit fault in the quad?).
The actual quad-tile assignment ordering isn't material to this discussion. What is material is that regardless of the number of graphics cards rendering a frame, it's possible to identify precisely which quad (and therefore
which graphics card) will draw every tile. This doesn't change from frame to frame. It's what enables super-tiling (which I propose uses the same tile organisation scheme as single-card tiling) to operate independently on both graphics cards.
When both graphics cards come to the same triangle (let's say it covers 7 tiles for the sake of argument) the setup engine in each graphics card knows
which of its tiles the triangle falls upon, so it will only issue the triangle to those tiles' owning quads. Similarly the setup engine knows that certain tiles are off-limits, so it will never try to issue a triangle to those tiles. The other graphics card will handle those tiles.
If it makes you happy, here's a revised 7-quad tiling, with that 7-tile triangle - note the X800 Pro owns 4 of the tiles
So the setup engine on the X800 Pro issues the triangle to four tiles:
- Red 1
- Orange 1
- Yellow 1
- Red 2
And the X800XT's setup engine issues the triangle to these three tiles:
- Green 1
- Blue 1
- Violet 1
This is clearly a pathological case where the X800 Pro is doing much more work for this triangle than the X800XT. That's how the cookie crumbled...
An odd number of quads is an awkward-looking tiling however you order it. You've got a similarly awkward tiling in a single X800 Pro
Obviously multi-card tiling is neatest when you've got two identical cards...
Jawed
