Pixel Shader

The name sais it all. Pixel Shaders are a instruction set to manipulate pixel data. With those functions you can program shaders for effects like Bumpmapping or reflections. This means that developers are not limited by fixed functions on the chip anymore. They now can create their very own, totaly new functions - fully accelerated by the 3D chip!

Here comes the first difference between GeForce 3 and Smartshader alias DX 8.1. The adress operations are now included in the pixel shaders. The programming language was altered for that. Smartshader pixel shader effects can use up to 22 instructions (6 texture sampling / 8 texture adressing / 8 color blending). In DirectX 8 (GeForce 3) there are only 12 (4 texture sampling / 8 color blending). In addition, Smartshader can use up to 6 textures instead of 4. See the table below.

Examples for the use of Pixel Shaders:

Left: Multiple bumpmaps at the same time (watch the spot in the middle). The right image shows a procedual marble texture

3 colored light sources manipulate the textures of this object

Per Pixel Phong Shading

You must understand that the benefit of Pixel- and Vertex Shaders are not only the look of an effect. You can also create similar effects with enormous effort by calculating this stuff on the CPU. But this is very slow. The point is that those new shaders allow game developers to create their own effects - fully accelerated in high performance by the 3D card!

Summary

Many people expected that RADEON 2 will be a very strong performer on the level of NVIDIA“s GeForce 3 - or above. Through the new extensions in the Pixel Shader part it now has a small technology advantage - on the paper. We“ll have to wait and see if the new instructions really make a difference. There are only very few games and demos out yet which use Pixel- and Vertex Shader functions. But Smartshader looks promising and don“t forget ATI“s Truform technology (to enhance the look of 3D objects in existing games) which will be also implemented in the new ATI 3D chip.

Updates:

• The Pixel Shader version numbers in the comparsion table were wrong. Smartshader is version v1.4, NVIDIA“s GF3 is version v1.1

• You can download the Vertex Shader Shadow demo that is shown in this Article on the ATI deveolpers site: RADEON Shadow Shader Demo. It does also run on a GF3!

Links: ATI Homepage

Lars "Borsti" Weinand - Editor In Chief - RIVA Station 2001

Copyright: 16.07.2001 -   RIVA Station 2001 - Lars Weinand
No Copy without Permission!

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