Draw multiple objects in D3D12 - c++

Question

I am tinkering with DirectX 12 and have hit a wall while trying to draw a "checker board." I have search the net quite a bit, so any help/pointers will be appreciated.
In D3D11 the working code is as follows.
auto context = m_deviceResources->GetD3DDeviceContext();
for (int i = -10; i < 10; i++)
{
for (int j = -10; j < 10; j++)
{
// perform translation
XMStoreFloat4x4(&m_constantBufferData.model, XMMatrixTranspose(XMMatrixTranslation(i, j, 0.0f)));
context->UpdateSubresource(
m_constantBuffer.Get(),
0,
NULL,
&m_constantBufferData,
0,
0
);
// shaders, etc...
// draw the square
context->DrawIndexed(
m_indexCount,
0,
0
);
}
}
In D3D12, I have tried doing the same thing, but it appears to be performing the translation globally, as all square are in the same location.
bool Sample3DSceneRenderer::Render()
{
if (!m_loadingComplete)
{
return false;
}
DX::ThrowIfFailed(m_deviceResources->GetCommandAllocator()->Reset());
DX::ThrowIfFailed(m_commandList->Reset(m_deviceResources->GetCommandAllocator(), m_pipelineState.Get()));
PIXBeginEvent(m_commandList.Get(), 0, L"Draw the objects");
{
m_commandList->SetGraphicsRootSignature(m_rootSignature.Get());
ID3D12DescriptorHeap* ppHeaps[] = { m_cbvHeap.Get() };
m_commandList->SetDescriptorHeaps(_countof(ppHeaps), ppHeaps);
CD3DX12_GPU_DESCRIPTOR_HANDLE gpuHandle(m_cbvHeap->GetGPUDescriptorHandleForHeapStart(), m_deviceResources->GetCurrentFrameIndex(), m_cbvDescriptorSize);
m_commandList->SetGraphicsRootDescriptorTable(0, gpuHandle);
D3D12_VIEWPORT viewport = m_deviceResources->GetScreenViewport();
m_commandList->RSSetViewports(1, &viewport);
m_commandList->RSSetScissorRects(1, &m_scissorRect);
CD3DX12_RESOURCE_BARRIER renderTargetResourceBarrier =
CD3DX12_RESOURCE_BARRIER::Transition(m_deviceResources->GetRenderTarget(), D3D12_RESOURCE_STATE_PRESENT, D3D12_RESOURCE_STATE_RENDER_TARGET);
m_commandList->ResourceBarrier(1, &renderTargetResourceBarrier);
D3D12_CPU_DESCRIPTOR_HANDLE renderTargetView = m_deviceResources->GetRenderTargetView();
D3D12_CPU_DESCRIPTOR_HANDLE depthStencilView = m_deviceResources->GetDepthStencilView();
m_commandList->ClearRenderTargetView(renderTargetView, m_colors.Get_background(), 0, nullptr);
m_commandList->ClearDepthStencilView(depthStencilView, D3D12_CLEAR_FLAG_DEPTH, 1.0f, 0, 0, nullptr);
m_commandList->OMSetRenderTargets(1, &renderTargetView, false, &depthStencilView);
m_commandList->IASetPrimitiveTopology(D3D_PRIMITIVE_TOPOLOGY_TRIANGLELIST);
m_commandList->IASetVertexBuffers(0, 1, &m_vertexBufferView);
m_commandList->IASetIndexBuffer(&m_indexBufferView);
for (float i = -10.0f; i < 10.0f; i++)
{
for (float j = -10.0f; j < 10.0f; j++)
{
// as far as I know, this is how I should perform the translation
XMStoreFloat4x4(&m_constantBufferData.model, XMMatrixTranspose(XMMatrixTranslation(i, j, 0.0f)));
UINT8* destination = m_mappedConstantBuffer + (m_deviceResources->GetCurrentFrameIndex() * c_alignedConstantBufferSize);
memcpy(destination, &m_constantBufferData, sizeof(m_constantBufferData));
m_commandList->DrawIndexedInstanced(6, 1, 0, 0, 0);
}
}
CD3DX12_RESOURCE_BARRIER presentResourceBarrier =
CD3DX12_RESOURCE_BARRIER::Transition(m_deviceResources->GetRenderTarget(), D3D12_RESOURCE_STATE_RENDER_TARGET, D3D12_RESOURCE_STATE_PRESENT);
m_commandList->ResourceBarrier(1, &presentResourceBarrier);
}
PIXEndEvent(m_commandList.Get());
DX::ThrowIfFailed(m_commandList->Close());
ID3D12CommandList* ppCommandLists[] = { m_commandList.Get() };
m_deviceResources->GetCommandQueue()->ExecuteCommandLists(_countof(ppCommandLists), ppCommandLists);
return true;
}
Thank you,
Chelsey

Answer 1

You're just writing your translation matrix to the same piece of memory for every copy of the model. Since the GPU hasn't even begun drawing the first model by the time you've finished writing the translation matrix for the last one, the only place any of these models are going to draw is at the place of the last translation matrix written.
You need to write each matrix to a separate, distinct location in memory and ensure they're not overwritten by anything else until the GPU has finished drawing the models.
The act of calling DrawIndexedInstanced does not immediately instruct the GPU to draw anything, it merely adds a command to a command list to draw the object at some time in the future. If you're not familiar with the asynchronous nature of Graphics APIs and GPU execution you should probably read up a bit more on how it works.