Hi I've been googling for a couple of hours and also looking through my HLSL books, but haven't found the answer to this question: How do I pass the X, Y and Z floats of a vertex into the vertex shader from 2 different streams? I've got a vertex buffer containing floats which are the heights of my heightmap (y) and I've got a vertex buffer containing floats which are the x and z positions of the terrain. I can't see anything that allows you to pass a float and 2 floats into the vertex shader. My decl looks like this: D3DVERTEXELEMENT9 declTerrainXYZ[] = { {0, 0, D3DDECLTYPE_FLOAT1, D3DDECLMETHOD_DEFAULT, D3DDECLUSAGE_POSITION, 0}, {1, 0, D3DDECLTYPE_FLOAT2, D3DDECLMETHOD_DEFAULT, D3DDECLUSAGE_POSITION, 1}, D3DDECL_END() }; I'm pretty sure this is wrong for a start as D3DDECLUSAGE_POSITION would signify a POSITION which is a 3 float vector - not what I want to pass in. Does anyone know how this is done? Or can point me in the direction of a tutorial? Thanks in advance

I'm not sure if 2 positions would work like that. I seem to remember there being some other meaning already applied to a second position. You can however pass it in as anything else. Texcoords make good generic inputs.

In your shader you would list 2 inputs

float2 posxz : POSITION;
float posy : TEXCOORD0;

In your shader code you'd just combine them to make your full position vector.

float4 pos = float4(IN.posxz.x, IN.posy, IN.posxz.y, 1);

At this point you just start using the new "pos" instead of IN.position wherever you're transforming and using your position information.

If you want to test if 2 positions work, just change the semantic on posy to POSITION1

Thanks for the quick responses guys.

Ok, so I get the vertex shader part, but I'm still getting errors with my declaration. It is basically saying, if I want to use D3DDECLUSAGE_POSITION, I must supply a FLOAT3. I can't see any other D3DDECLUSAGE that uses FLOAT1 as a type.

Could you possibly suggest a suitable vertex declaration? I have two streams, in the first is just a list of floats and in the second, a list of two floats (although both appear identical, the second stream is just twice as big as the first).

Also, my CreateVertexBuffer call insists I supply an FVF (DWORD) for the 3rd parameter - how do I tell it that it's just one float and not something like D3DFVF_XYZ, etc.

Thanks again

I'm now using this vertex declaration:



DirectX gives me the following debug error:

"Declaration can't map to fixed function FVF because position field is missing. Usage: D3DDECLUSAGE_POSITION, with usage index 0 is required for fixed function."

And my shader looks like this:



I'm a bit confused as to why it's saying it needs a position field when I haven't specified one anywhere.

Any help, greatly appreciated

Hi all

It appears that you can't actually do what I'm trying to do. My first vertex buffer creation (for the y values) specifies 0 (zero) for the FVF parameter (in CreateVertexBuffer) with a sizeof(float). This contains all the y value floats (e.g. y,y,y,y,y,y....

The second vertex buffer creation (for the xz values) specifies 0 (zero) for the FVF parameter (in CreateVertexBuffer) and a sizeof(float) * 2. This stream contains all the x and z value floats sequentially (e.g. x,z,x,z,x,z...)

I cannot use this type of declaration:



The reason I can't is because the D3D runtime complains that FLOAT1 is being used for a POSITION usage type, both of these declarations (if using a usage of POSITION) require FLOAT3. If I use FLOAT3 for stream 0 and stream 1, won't it mean that for each vertex of my triangle, 3 floats from each stream will be passed to the vertex shader?

Is there something I can specify in the SetStreamSource call to say that although I want to pass in a FLOAT3 to the shader from this stream, I only want to pass one float (for stream 0) from my vertex stream in, say, the x float part of that FLOAT3 component?

Can anyone help? I'm tearing my hair out over this.

Thanks