GeForce 4 MX 420 question

AFAIK the GF4MX is based on a GF2 (NV15 core) chipset, so OpenGL is indeed supported (I did a lot of OpenGL programming on my GF2 GTS back then).

The only problem is that the card is probably not supported in the latest drivers. IIRC there are currently two legacy driver series. The latest legacy driver series has still support for the GeforceFX (NV35 core) series, at least on linux it's driver version 173.14.x. All newer drivers have dropped FX support.

The same is true for your MX card. But the support was dropped longer ago. So you should google for the first legacy driver series. That one should still include the support for this card.

I only have the unix driver series link around:
What's a legacy driver?

At least according to this the card is supported through 96.x series.

EDIT: Looks like it's the 93.x series on Win32:
http://www.nvidia.com/object/winxp_2k_93.71_2.html

Jam it back in, in the dark.

Well, it depends how you define "pixel shader". IIRC the NV15 supports the NV_register_combiners extensions and therefore has some limited pixelshading caps (emphasis on limited).

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Hmm? I don't know why you're always referring to the CPU?

Pixelshading is done entirely inside the GPU (the graphics card), the only thing that you can offload to the CPU is the TnL (transform and lighting) step.

It's correct that the NV15 series does have vertex shader support. Still it's very limited when comparing it to like the new shader model 4.0 in DX10. Plus the vertex processing engine inside the NV15 is kinda slow when driving the card with a recent processor.

You should also keep in mind that the NV15 was designed around the DirectX 7.0 specs. ps1.4 programs however were supported later in DirectX 8 though. And this pixelshader version was the first that was widely used by application. IIRC the NV15 didn't support this though (in hardware of course, but you can really try rendering this in software since it's just awfully slow).

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OK, I see what you mean. However you've got it a bit wrong.

The Doom 3 (id tech 3) engine has multiple renderpaths. For example there is an ARB2 renderpath which uses the now common ARB_vertex_program and ARB_fragment_program extensions. Then there is a NV30 path which was specifically written for the NV30 hardware in mind. It uses a mix of ARB and NV proprietary extensions and has some modifications to the shader assembler code, so the GPU performs better (the NV30 is some very moody beast and you have to be very careful with the shadercode to get good performance out of it).

Plus there is a ARB, NV10, NV20 and R200 path. The NV10 path is used for Geforce 1 and 2 series hardware, since it only uses register combiner stuff. The NV20 path is used for Geforce3 series hardware and makes use of the NV_texture_shader extension.

To make some things clear: When one speaks of "pixelshaders" you usually mean the Direct3D pixelshaders introduced in D3D8. The OpenGL equivalent to these are exposed through ARB_fragment_program (this extension went core in OpenGL 2.0 I think).

The NV15 core doesn't support ARB_fp though. It only has the NV_register_combiners extension, that's the only way to reprogram the fragment pipeline if you don't want to use the fixed-function pipeline.

Coming back to Doom3: Try setting the renderpath to ARB2 on a Geforce2 Ultra and you will see that it won't work (r_renderer is the cvar if you really want to try it). Doom3 will always use the NV10 renderpath when it is run on such a GPU. Sure, you can just set all gfx settings to max, but you won't get the same render quality as with a GPU that supports the ARB2 renderpath (ARB2 provides the best render quality since it always uses fp32 values for calculation, this is also the reason for the NV30 renderpath - the NV30 supports fp32 but slows down a lot when only using fp32 and not fp16).

So you probably saw Doom 3 on the system you mentioned in your post. But surely not all effects the id tech 4 engine is capable of were enabled (since this is only the case with ARB2).
You have to differentiate between effect that can be enabled in the graphics configuration menu and the effects the engine is capable of.

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