question about vertex shader

[virtual]

hi

i am new in DX vertex shader , from my reading i understand that Vertex Shader control the rendering pipline ( transformation , lighting )

whats the major deference between a program work with VS and other with fixed function pipline ?

dose VS capable for things that FFP could not ?

[chronozphere]

A vertex shader allows you to "program" the vertex behaviour of your graphics. You could apply some formula's to achieve specific effects (like a waving surface, your own vertex lighting etc).. FFP doesn't provide this kind of flexibility.

[virtual]

thats true

but waving surface without VS is possible too !

[NecroDOME]

The big difference is that you can for example add extra texture coordinates, calculate normals etc in the vertex shader so you don't have to calculate them in your program, saving bandwidth so your vertex structure can be smaller.
But mostly you will end up using a vertex shader that also can be done in the FFPL.
But it simply gives you more flexibility.

[User137]

Doesn't the big difference come to using pixel-shader?

[NecroDOME]

Mostly yes.

[virtual]

thnx

i've seen alot of great demo scene using vertex shader and the effects were amazing ,

do you think is it possible to produce a high quality effect without VS ?

[NecroDOME]

Yes, but I think it would be slower.

[tpascal]

There is only one thing i dislike About vertex shaders (well, when you are going to use one for first time)...you dont have one working by default; >:( i mean, with the fixed pipeline you already have working functions to apply multiple textures with several blend options, vertex world/view transformations, per vertex lighting with matyerials settings, etc...the basic stuff you need to render thousand triangles textured and lightened; but if you say "humm, i would like to add a wave effect...i am going to write a shader for that..." forget it, beside the wave effect you also have to code your self in the shader any function you was using from the fixed pipeline, you cant combine boths, when you switch to shaders, you have to code everithing needed for render a vertex: transformations, textures, blending effects, colors, lighting maths, etc. :'(

Beside that, once you have one basic vertex shader coded and working for doing basic stuff, then you will want to do everithing in shaders, :yes: and none in cpu, ::)

[Brainer]

Don't forget about CUDA. ;)

[NecroDOME]

@tpascal: if you try XNA you have a vertex and pixel shader that work at start :), just tried it a few days ago.

This is what XNA gives you as vertex shader:


VertexShaderOutput VertexShaderFunction(VertexShaderInput input)
{
VertexShaderOutput output;

float4 worldPosition = mul(input.Position, World);
float4 viewPosition = mul(worldPosition, View);
output.Position = mul(viewPosition, Projection);

// TODO: add your vertex shader code here.

return output;
}

[JSoftware]

There is only one thing i dislike About vertex shaders (well, when you are going to use one for first time)...you dont have one working by default; >:( i mean, with the fixed pipeline you already have working functions to apply multiple textures with several blend options, vertex world/view transformations, per vertex lighting with matyerials settings, etc...the basic stuff you need to render thousand triangles textured and lightened; but if you say "humm, i would like to add a wave effect...i am going to write a shader for that..." forget it, beside the wave effect you also have to code your self in the shader any function you was using from the fixed pipeline, you cant combine boths, when you switch to shaders, you have to code everithing needed for render a vertex: transformations, textures, blending effects, colors, lighting maths, etc. :'(

Beside that, once you have one basic vertex shader coded and working for doing basic stuff, then you will want to do everithing in shaders, :yes: and none in cpu, ::)




I'm actually pretty sure there's an instruction which can make it do that(in GLSL)

[NecroDOME]

Not sure, but I recall reading something about it... at microsoft site... (in HLSL)