[PATCH 2/5] d3d9: Add depth clamp tests.

[Stefan Dösinger]

Am 26.01.2010 um 19:23 schrieb Henri Verbeet:

> On 26 January 2010 18:56, Stefan Dösinger <stefandoesinger at gmx.at> wrote:
>> It would be interesting to see how D3DCMP_GREATER behaves with clipping off. Does the clamping occur before the depth test, or after the test but before writing the values into the depth buffer. (ie, is 3.0 > 1.0 or is 3.0 == 1.0)
>> 
> It's not completely trivial to reliably test that due to precision
> differences between the vertex data and the depth buffer
Why? I'd expect that if you first draw something with depth clamping enabled with z=2(so it ends up at 1.0) then it really ends up at 1.0 and not 0.999998. If the Z buffer is cleared without drawing anything I'd expect it to contain an exact 1.0 as well. If there are precision problems in either situation I think the card/driver would be pretty broken.

> ARB_depth_buffer_float doesn't describe interactions with
> ARB_depth_clamp, which might imply we'll have to disable depth
> clamping for floating point depth buffers, but I doubt floating point
> depth buffers are particularly useful without shaders anyway.
Did you try depth clamping with shaders? Wrt vertex shaders I don't really expect surprises on either side, and wrt pixel shaders there are at least no surprises on the GL side(since we have that replacement pipeline and are using shaders anyway)