HLSL - Global variables are unchanged in Geometry Shader (DirectX11) - geometry

Question

My program receives input consists of line segments and expand the lines to cylinder-like object (like the PipeGS project in DX SDK sample browser).
I added an array of radius scaling parameter for the pipes, and modify them procedurally, but the radii of pipes just didn't change.
I'm pretty sure the scaling parameters are updated every frame because I set them as the pixel value. When I modify them, the pipes change color while their radii keep unchanged.
So I am wondering if there's any limitation of using global variables in GS and I didn't find it on the internet. (or just wrong keywords I used)
The shader code is like
cbuffer {
.....
float scaleParam[10];
.....
}
// Pass 1
VS_1 { // pass through }
// Tessellation stages
// Hull shader, domain shader and patch constant function
GS_1 {
pipeRadius = MaxRadius * scaleParam[PipeID];
....
// calculate pipe positions base on line-segments and pipeRadius
....
OutputStream.Append ( ... );
}
// Pixel shader is disabled in the first pass
// Pass 2
VS_2 { // pass through }
// Tessellation stages
// Hull shader, domain shader and patch constant function
// Transform the vertices and normals to world coordinate in DS
// No geometry shader in the second pass
PS_2
{
return float4( scaleParam[0], scaleParam[1], scaleParam[2], 0.0f );
}
Edit:
I shrinked the problem.
There are 2 passes in my program, in the first pass I calculate the line-segment expanding in Geometry Shader and stream-out.
In the second pass, the program receives pipe position from the first pass, tessellate the pipes and apply displacement mapping on them so they can be more detailed.
I can change the surface tessellation factor and pixel color which are in the second pass and see the result on screen immediately.
When I modify the scaleParam, the pipes change color while their radii keep unchanged. It means I did change the scaleParam and pass them into shader correctly but something's wrong in the first pass.
Second edit:
I modified shader code above and post some code of the cpp file here.
In the cpp file:
void DrawScene()
{
// Update view matrix, TessFactor, scaleParam etc.
....
....
// Bind stream-output buffer
ID3D11Buffer* bufferArray[1] = {mStreamOutBuffer};
md3dImmediateContext->SOSetTargets(1, bufferArray, 0);
// Two pass rendering
D3DX11_TECHNIQUE_DESC techDesc;
mTech->GetDesc( &techDesc );
for(UINT p = 0; p < techDesc.Passes; ++p)
{
mTech->GetPassByIndex(p)->Apply(0, md3dImmediateContext);
// First pass
if (p==0)
{
md3dImmediateContext->IASetVertexBuffers(0, 1,
&mVertexBuffer, &stride, &offset);
md3dImmediateContext->Draw(mVertexCount,0);
// unbind stream-output buffer
bufferArray[0] = NULL;
md3dImmediateContext->SOSetTargets( 1, bufferArray, 0 );
}
// Second pass
else
{
md3dImmediateContext->IASetVertexBuffers(0, 1,
&mStreamOutBuffer, &stride, &offset);
md3dImmediateContext->DrawAuto();
}
}
HR(mSwapChain->Present(0, 0));
}

Answer 1

Check if you are using a float4 position, the w value of vector is a scale for final position in scene, example:
float4 pos0 = float4(5, 5, 5, 1);
// is equals that:
float4 pos1 = float4(10, 10, 10, 2);
To correct scale a position you must changue only the .xyz value of vector position.

Answer 2

I solved this problem by rebuilding Vertex buffer and Stream-output buffer everytime after I modified the parameters, but I still don't know what exactly causes this problem.