I thought I'd start a new post as my previous one got a bit confusing. I've hunted high and low on the net and still can't find a way to do what I'm trying to do. Here's what I'm using and trying to do: DirectX 9, vs_3_0, c++ I have a vertex buffer full of single floats (y values) and one full of single float pairs (x and z values). The second buffer, having pairs of floats is twice as big as the first. I'd like to combine these two buffers as input into the vertex shader in order to create the position vector. This is essentially to save memory for my terrain which has an overall size of 4096x4096 with about 5 levels of detail. Could someone please show me how the vertex declaration should look for this setup? I've tried loads of different configurations and DirectX complains at most of them. If I use D3DDECLUSAGE_POSITION, it complains that the D3DDECLTYPE_ should be a FLOAT3 which won't work in my case. If I don't use D3DDECLUSAGE_POSITION for the usage (e.g. using something like D3DDECLUSAGE_TEXCOORD), it complains with this 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" This is confusing for a start, because I thought I was trying to use the programmable pipleline - both my vertex buffers are created with zero as the FVF parameter specifying them to be NON-FVF buffers. If I were to use D3DDECLUSAGE_POSITION and D3DDECLTYPE_FLOAT3, is there some way that, for each vertex, I can some how only pass in one float for the first stream and 2 floats for the second stream? I don't mind if I get two FLOAT3s into my vertex shader like this: first stream input: FLOAT3 - x = <actual correct y value> y = 0 z = 0 second stream input: FLOAT3 - x = <actual correct x value> y = <actual correct z value> z = 0 I can then just extract the floats out and create a new vector in the vertex shader. I'm 100% sure I've heard of this being done before, but I can't seem to find a way to do it. If anyone can shed any more light, I'd be eternally grateful - I've been banging my head about this for over a week now. I did have a couple of useful replies about this before, but they didn't work. Thanks in advance [Edited by - RobMaddison on July 31, 2008 2:38:38 PM]

Thanks for the quick responses guys.

Quote:
Off the top of my head (don't have my old code to hand) the trick was creating two streams, one with a <D3DDECLUSAGE_POSITION, usage=0, size=float> and a <D3DDECLUSAGE_POSITION, usage=1, size=float2> and then the declaration in the VS can be something like:

Jack, that doesn't quite work in my configuration as when using POSITION as a usage, it requires a size of FLOAT3. Here is my exact usage at the moment:



When I call the DrawIndexPrimitive method using this declaration, I get

"Declaration can't map to fixed function FVF because position must use D3DDECLTYPE_FLOAT3". Here is the very simple shader fx file I'm using:



Here is the code to draw the primitives:



Tim, if I specify FLOAT3 for both elements and use usagetypes of POSITION, it doesn't error, but how would I specify that my first FLOAT3 is only (x, y, 0) and the second is only (x, 0 ,0)?

Thanks guys, I'd really love to get to the bottom of this.

Hi Tim

Thanks for spotting the error in the SetStreamSource line, although that was a typo as my code is on my dev machine.

I see what you're saying about putting FLOAT3's (or vectors) into the vertex buffer, but the whole point of this exercise for me is to cut down on memory by reusing the x and z coordinates of each terrain patch as they are regular grids. The heights are individual and need to be stored in a buffer on their own. If I store 3 float vectors in the buffer, then I may as well store the x and z too in the unused parts. This would take up too much memory though, as my terrain at the highest LOD level is made up of 4096 65x65 patches.

Using the method I'm aiming at, the y values for the entire terrain would take up:

65x65 (verts) = 4225 total verts per patch
4225 x 4 bytes (y value float) = 16,900 bytes
16,900 x 4096 (patches) = 69.2mb

the x and z coordinates would only need to be stored for one patch - when drawing, they'll just be translated to the correct positon.

This is a totally acceptable amount of memory for what I need, but if I have to add the x and z into the mix, my vertex buffer(s) grow to over 200mb which I can't afford. Does that help to explain what I'm trying to achieve better?

Thanks

Hi Jack

I tried using TEXCOORD instead of position and yes, it complains that it should have a POSITION:

"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"

(I had also changed the shader file to use TEXCOORD0 and TEXCOORD1 as the inputs).

It would appear to me that my engine somehow things I'm tryin to use the fixed function pipeline. Is there a way to tell which I'm using? I'm currently using the DXUT libraries just to get things up and running. If there's a "SetDeviceToUseFVF" or something similar I can just do a search for it in my code.

Thanks again for your input, it is much appreciated.

Tim

I believe you might be onto something here. If I put the FLOAT3 POSITION value first, that satisfies DX's need for it and my repeated xz values can just have a dummy 0 value added for the y - I can then hopefully make the second stream just use TEXCOORD with FLOAT1.

I'll let you know how I get on, thanks.

Rob