Direct3D11 renders only lines, and in weird order

Question

I have reduced a previous rending problem to a core where I am stuck.

I have a vertex buffer, consisting of 4 vertices, arranged in a plane (labeled 0 to 3 ):

1.  .2

0.  .3

and an according index buffer {0,1,2,3,0} .

Now, when I render with D3D11_PRIMITIVE_TOPOLOGY_LINESTRIP , I achieve the expected image:

  __ 
 |  |
 |__|

However, when I render with D3D11_PRIMITIVE_TOPOLOGY_TRIANGLESTRIP the result is:

 | /|
 |/ |

Note that no filling of triangles is performed.

Even more confusing, when using D3D11_PRIMITIVE_TOPOLOGY_TRIANGLELIST the result is:

 |
 |

If I change the index buffer to {0,1,2,0,2,3} it renders:

 | /
 |/

That is, just one pixel line between the first two vertices are being drawn.

I have reduced my shaders to the most primitive examples:

Vertex shader:

struct VertexInputType
{
    float4 position : POSITION;
};
struct PixelInputType
{
    float4 position : SV_POSITION;
};
PixelInputType VertexShader(VertexInputType input)
{
    PixelInputType output;
    input.position.w = 1.0f;
    output.position = input.position;
    return output;
}

Pixel shader:

struct PixelInputType
{
    float4 position : SV_POSITION;
};
float4 PixelShader(PixelInputType input) : SV_TARGET
{
    float4 color;
    color.r = 0;
    color.g = 0;
    color.b = 0;
    color.a = 1;
    return color;
}

As vertices I'm using DirectX::XMFLOAT3 :

D3D11_INPUT_ELEMENT_DESC polygon_layout[1];
polygon_layout[0].SemanticName = "POSITION";
polygon_layout[0].SemanticIndex = 0;
polygon_layout[0].Format = DXGI_FORMAT_R32G32B32_FLOAT;
polygon_layout[0].InputSlot = 0;
polygon_layout[0].AlignedByteOffset = 0;
polygon_layout[0].InputSlotClass = D3D11_INPUT_PER_VERTEX_DATA;
polygon_layout[0].InstanceDataStepRate = 0;
d3d11_device->CreateInputLayout(polygon_layout, 1, compiled_vshader_buffer->GetBufferPointer(), compiled_vshader_buffer->GetBufferSize(), &input_layout);


D3D11_BUFFER_DESC vertex_buffer_desc;
vertex_buffer_desc.Usage = D3D11_USAGE_DEFAULT;
vertex_buffer_desc.ByteWidth = sizeof(DirectX::XMFLOAT3) * 4;
vertex_buffer_desc.BindFlags = D3D11_BIND_VERTEX_BUFFER;
vertex_buffer_desc.CPUAccessFlags = 0;
vertex_buffer_desc.MiscFlags = 0;
vertex_buffer_desc.StructureByteStride = 0;
DirectX::XMFLOAT3 vertices[4];
vertices[0].x = -0.5;    vertices[0].y = -0.5;    vertices[0].z = 0;
vertices[1].x = -0.5;    vertices[1].y =  0.5;    vertices[1].z = 0;
vertices[2].x =  0.5;    vertices[2].y =  0.5;    vertices[2].z = 0;
vertices[3].x =  0.5;    vertices[3].y = -0.5;    vertices[3].z = 0; 
D3D11_SUBRESOURCE_DATA vertex_buffer_data;
vertex_buffer_data.pSysMem = vertices;
vertex_buffer_data.SysMemPitch = 0;
vertex_buffer_data.SysMemSlicePitch = 0;
hr = d3d11_device->CreateBuffer(&vertex_buffer_desc, &vertex_buffer_data, &vertex_buffer);

D3D11_BUFFER_DESC index_buffer_desc;
index_buffer_desc.Usage = D3D11_USAGE_DEFAULT;
index_buffer_desc.ByteWidth = sizeof(int32_t) *  6;
index_buffer_desc.BindFlags = D3D11_BIND_INDEX_BUFFER;
index_buffer_desc.CPUAccessFlags = 0;
index_buffer_desc.MiscFlags = 0;
index_buffer_desc.StructureByteStride = 0;
int32_t indices[6];
indices[0] = 0;
indices[1] = 1;
indices[2] = 2;
indices[3] = 2;
indices[4] = 3;
indices[5] = 0;
D3D11_SUBRESOURCE_DATA index_buffer_data;
index_buffer_data.pSysMem = indices;
index_buffer_data.SysMemPitch = 0;
index_buffer_data.SysMemSlicePitch = 0;
hr = d3d11_device->CreateBuffer(&index_buffer_desc, &index_buffer_data, &index_buffer);

// during rendering I set:
unsigned int stride = sizeof(DirectX::XMFLOAT3);
unsigned int offset = 0;
d3d11_context->IASetVertexBuffers(0, 1, &vertex_buffer, &stride, &offset);
d3d11_context->IASetIndexBuffer(index_buffer, DXGI_FORMAT_R32_UINT, 0);
d3d11_context->IASetPrimitiveTopology(D3D11_PRIMITIVE_TOPOLOGY_TRIANGLELIST);
d3d11_context->RSSetState(rasterizer_state);
d3d11_context->IASetInputLayout(input_layout);
d3d11_context->VSSetShader(vertex_shader, NULL, 0);
d3d11_context->PSSetShader(pixel_shader,  NULL, 0);
// and render with:
d3d11_context->DrawIndexed(6, 0, 0);

When I look at the shaders with the ID3D11ShaderReflection::GetGSInputPrimitive() , I receive D3D_PRIMITIVE_UNDEFINED for both the vertex shader and pixel shader.

I am setting the rasterizer stage with D3D11_FILL_SOLID and D3D11_CULL_NONE .

Is there any setting or state in the D3D11 context that could explain such a behavior? I'm happy for any ideas where to look. Thanks in advance!

Answer 1

Firstly, triangle strip draws exactly what you'd expect - a sequence of triangles. Each index into the triangle index array is combined with the two previous indices to create a triangle.

I'd suggest that as your Triangle List is not divisible by 3 DirectX may be rendering incorrectly (remember that as this is a high-capacity system it skips checks and balances where it can to promote speed).

Try to draw your expected results on paper after reviewing the logic behind each of the draw modes - list, strip, fan etc to be sure that you are using the correct vertex ordering and drawmode.

Good luck!

Answer 2

It turns out that the code was not the problem. Somewhere prior something was changed in the Direct3D state.

Calling context->ClearState(); solved the issue.