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Direct3D9 GPU Hacks

I've been trying to catch up what hacks GPU vendors have exposed in Direct3D9, and turns out there's a lot of them!

If you know more hacks or more details, please let me know! (mail or comment on my blog post).

Most hacks are exposed as custom ("FOURCC") formats. So to check for that, you do

CheckDeviceFormat

. Here's the list (Usage column codes: DS=DepthStencil, RT=RenderTarget; Resource column codes: tex=texture, surf=surface). More green = more hardware support.

Format	Usage	Resource	Description	NVIDIA GeForce	ATI Radeon	Intel
Shadow mapping
D3DFMT_D16	DS	tex	Sample depth buffer directly as shadow map.	3+	HD 2xxx+	?
D3DFMT_D24X8	DS	tex	3+	HD 2xxx+	?
Depth Buffer As Texture
DF16	DS	tex	Read depth buffer as texture.	9500+	?
DF24	DS	tex	X1300+	?
INTZ	DS	tex	8+	HD 4xxx+	?
RAWZ	DS	tex	6 & 7	?
Anti-Aliasing related
RESZ	RT	surf	Resolve MSAA'd depth stencil surface into non-MSAA'd depth texture.	HD 4xxx+	?
ATOC	surf	Transparency anti-aliasing.	7+	?
SSAA	surf	7+	?
All ATI SM2.0+ hardware	9500+	?
n/a	Coverage Sampled Anti-Aliasing[6]	8+	?
Texturing
ATI1	tex	ATI1n & ATI2n texture compression formats.	8+	X1300+	?
ATI2	tex	6+	9500+	?
DF24	DS	tex	Fetch 4: when sampling 1 channel texture, return four touched texel values[1]. Check for DF24 support.	X1300+	?
Misc
NULL	RT	surf	Dummy render target surface that does not consume video memory.	6+	HD 4xxx+	?
NVDB	surf	Depth Bounds Test.	6+	?
R2VB	surf	Render into vertex buffer.	6 & 7	9500+	?
INST	surf	Geometry Instancing on pre-SM3.0 hardware.	9500+	?

Native Shadow Mapping

Native support for shadow map sampling & filtering was introduced ages ago by NVIDIA. Turns out ATI also implemented the same feature for it's DX10 level cards. Yay!

The usage is quite simple; just create a texture with regular depth/stencil format and render into it. When reading from the texture, one extra component in texture coordiantes will be the depth to compare with. Compared & filtered result will be returned.

Also useful:

• Creating NULL color surface to keep D3D runtime happy and save on video memory.

Depth Buffer as Texture

For some rendering schemes (anything with "deferred") or some effects (SSAO, depth of field, volumetric fog, ...) having access to a depth buffer is needed. If native depth buffer can be read as a texture, this saves both memory and a rendering pass or extra output for MRTs.

Depending on hardware, this can be achieved via INTZ, RAWZ, DF16 or DF24 formats:

• INTZ is for recent hardawre from both NVIDIA and ATI. According to ATI [1], it also allows using stencil buffer while rendering. Also allows reading from depth texture while it's still being used for depth testing (but not depth writing). Not sure if those capabilities apply to NVIDIA.
• RAWZ is for GeForce 6 & 7 series only. Depth is specially encoded into four channels of returned value.
• DF16 and DF24 is for ATI cards, including older cards that don't support INTZ.

Also useful when using depth textures:

• Creating NULL color surface to keep D3D runtime happy and save on video memory.
• RESZ allows resolving multisampled depth surfaces into non-multisampled depth textures (result will be sample zero for each pixel).

Depth Bounds Test

Direct equivalent of GL_EXT_depth_bounds_test OpenGL extension. See [3] for more information.

Transparency Anti-Aliasing

NVIDIA exposes two controls: transparency multisampling (ATOC) and transparency supersampling (SSAA) [5]. ATI says that all Radeons since 9500 support "alpha to coverage" [1].

Render Into Vertex Buffer

Similar to "stream out" or "memexport" in other APIs/platforms. See [2] for more information. Apparently some NVIDIA GPUs (or drivers?) support this as well.

Geometry Instancing

Instancing is supported on all Shader Model 3.0 hardware by Direct3D 9.0c, so there's no extra hacks necessary there. ATI has exposed a capability to enable instancing on their Shader Model 2.0 hardware as well. Check for "INST" support, and do dev->SetRenderState (D3DRS_POINTSIZE, kFourccINST); at startup to enable instancing.

I can't find any document on instancing from AMD now. Other references: [7] and [8].

References

All this information gathered mostly from:

1. Advanced DX9 Capabilities for ATI Radeon Cards (pdf)
2. ATI R2VB Programming (pdf)
3. NVIDIA GPU Programming Guide (pdf)
4. ATI Tesselation
5. NVIDIA Transparency AA
6. NVIDIA Coverage Sampled AA
7. Humus' Instancing Demo
8. Arseny's article on particles

Changelog

• 2009 11 21: Added instancing on SM2.0 hardware.
• 2009 11 20: Added Fetch-4, CSAA.
• 2009 11 20: Initial version.