# DX11 Geometry shader issue (linestrip)

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Hi all,

I've managed to get a geometry shader working, with a vertex as input, outputting a cube in a trianglestream

As a next step/ practice, I've tried to change my code/ approach to achieve the following (book exercise):

- input: linestrip of vertices

- output: a cylinder going upwards, from the viewpoint of the linestrip

(people who worked through Luna's d3d11 book might recognize the exercise)

I think I did what I should, but I don't get any visible results.

The vertices going into the vtx buffer look OK (debugged).

Any idea what I'm doing wrong?

struct GeoOut
{
float4 PosH    : SV_POSITION;
float3 PosW    : POSITION;
float3 NormalW : NORMAL;
float2 Tex     : TEXCOORD;
};

// geometry shader for linestrip as input (cylinder, exercise 1)
[maxvertexcount(7)]
void GSStrip(line VertexOut gin[2], inout LineStream<GeoOut> stream)
{
float4 v[2];
float4 b[1];

v[0] = float4(gin[0].CenterW.xyz, 1.0f);
v[1] = float4(gin[1].CenterW.xyz, 1.0f);

const float StripWidth = 0.5f;

float2 dir = normalize(v[1].xy - v[0].xy);
float4 off = float4(-dir.y, dir.x, 0, 0);

GeoOut gout;

// only to prevent not completely initialized (UV's and normals not needed)
gout.Tex = float2(0.0f, 1.0f);
gout.NormalW = float3(1.0f, 0.0f, 0.0f);

// 2 vertices at a time to create 2 triangles out of the quad (between non existing top/ bottom caps)
gout.PosW	=    (v[0]-off*5).xyz;
gout.PosH	= mul(v[0]-off*5, gViewProj);
stream.Append(gout);

gout.PosW	=    (v[0]+off*5).xyz;
gout.PosH	= mul(v[0]+off*5, gViewProj);
stream.Append(gout);

gout.PosW	=    (v[1]-off*5).xyz;
gout.PosH	= mul(v[1]-off*5, gViewProj);
stream.Append(gout);

stream.RestartStrip();

gout.PosW	=    (v[0]-off*5).xyz;
gout.PosH	= mul(v[0]-off*5, gViewProj);
stream.Append(gout);

gout.PosW	=    (v[1]-off*5).xyz;
gout.PosH	= mul(v[1]-off*5, gViewProj);
stream.Append(gout);

stream.RestartStrip();

gout.PosW	=    (v[0]+off*5).xyz;
gout.PosH	= mul(v[0]+off*5, gViewProj);
stream.Append(gout);

gout.PosW	=    (v[1]+off*5).xyz;
gout.PosH	= mul(v[1]+off*5, gViewProj);
stream.Append(gout);
}

// the application code (relevant parts)

{
md3dImmediateContext->ClearRenderTargetView(mRenderTargetView, reinterpret_cast<const float*>(&Colors::Silver));
md3dImmediateContext->ClearDepthStencilView(mDepthStencilView, D3D11_CLEAR_DEPTH|D3D11_CLEAR_STENCIL, 1.0f, 0);

float blendFactor[] = {0.0f, 0.0f, 0.0f, 0.0f};

XMMATRIX viewProj = view*proj;

// draw cube and/or circle
//DrawCube(viewProj);
DrawCircle(viewProj);

HR(mSwapChain->Present(0, 0));
}

{
Effects::mTreeSpriteFX->SetDirLights(mDirLights);
Effects::mTreeSpriteFX->SetEyePosW(mEyePosW);
Effects::mTreeSpriteFX->SetFogColor(Colors::Silver);
Effects::mTreeSpriteFX->SetFogStart(15.0f);
Effects::mTreeSpriteFX->SetFogRange(175.0f);
Effects::mTreeSpriteFX->SetViewProj(viewProj);
Effects::mTreeSpriteFX->SetMaterial(mBoxMat);
Effects::mTreeSpriteFX->SetDiffuseMap( mCircleMapSRV);

md3dImmediateContext->IASetPrimitiveTopology(D3D11_PRIMITIVE_TOPOLOGY_LINESTRIP);
md3dImmediateContext->IASetInputLayout(InputLayouts::mTreePointSprite);

UINT stride = sizeof(Vertex::TreePointSprite);
UINT offset = 0;

ID3DX11EffectTechnique* circleTech = Effects::mTreeSpriteFX->mLight3Tech;
switch(mRenderOptions)
{
case RenderOptions::Lighting:
circleTech = Effects::mTreeSpriteFX->mLight3Tech;
break;

case RenderOptions::Textures:
circleTech = Effects::mTreeSpriteFX->mLight3TexAlphaClipTech;
break;

case RenderOptions::TexturesAndFog:
circleTech = Effects::mTreeSpriteFX->mLight3TexAlphaClipFogTech;
break;
}

D3DX11_TECHNIQUE_DESC techDesc;
circleTech->GetDesc(&techDesc);
for(UINT p=0;p<techDesc.Passes;++p)
{
md3dImmediateContext->IASetVertexBuffers(0, 1, &mCircleVtxBuffer, &stride, &offset);

circleTech->GetPassByIndex(p)->Apply(0, md3dImmediateContext);
md3dImmediateContext->Draw(NUM_VERTS, 0);
}
}

{
const UINT numSlices = 32;

const UINT numCircleVerts = 33;
float dTheta = 2.0f * XM_PI/numSlices;

Vertex::TreePointSprite vertices[numCircleVerts];

for(UINT i=0;i<numCircleVerts;++i)
{
float x = 5*cosf(i*dTheta);
float z = 5*sinf(i*dTheta);

vertices[i].Pos    = XMFLOAT3(x, 0.0f, z);
}

D3D11_BUFFER_DESC vbd;
vbd.Usage = D3D11_USAGE_IMMUTABLE;
vbd.ByteWidth = sizeof(Vertex::TreePointSprite) * numCircleVerts;
vbd.BindFlags = D3D11_BIND_VERTEX_BUFFER;
vbd.CPUAccessFlags = 0;
vbd.MiscFlags = 0;
D3D11_SUBRESOURCE_DATA vinitData;
vinitData.pSysMem = vertices;
HR(md3dDevice->CreateBuffer(&vbd, &vinitData, &mCircleVtxBuffer));
}

Edited by cozzie

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I've read that thread first and tried to figure it out like mentioned there, but that didn't solve it );

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I think that when you've done a RestartStrip() you need to supply 3+ vertices before next RestartStrip(), or you'll be outputting 2 vertices which won't form a triangle..?

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Clear, so that makes the solution in the link above incorrect or incomplete.

I'll dig into it to align the theory with the code. Not sure how yet, any suggestions are welcome (stil quite new to GS's, besides my cube experiment)

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