(DirectX 11) Dynamic Vertex/Index Buffers implementation with constant scene content changes - c++

Question

Been delving into un-managed DirectX 11 for the first time (bear with me) and there's an issue that, although asked several times over the forums still leaves me with questions.
I am developing as app in which objects are added to the scene over time. On each render loop I want to collect all vertices in the scene and render them reusing a single vertex and index buffer for performance and best practice. My question is regarding the usage of dynamic vertex and index buffers. I haven't been able to fully understand their correct usage when scene content changes.
vertexBufferDescription.Usage = D3D11_USAGE_DYNAMIC;
vertexBufferDescription.BindFlags = D3D11_BIND_VERTEX_BUFFER;
vertexBufferDescription.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE;
vertexBufferDescription.MiscFlags = 0;
vertexBufferDescription.StructureByteStride = 0;
Should I create the buffers when the scene is initialized and somehow update their content in every frame? If so, what ByteSize should I set in the buffer description? And what do I initialize it with?
Or, should I create it the first time the scene is rendered (frame 1) using the current vertex count as its size? If so, when I add another object to the scene, don't I need to recreate the buffer and changing the buffer description's ByteWidth to the new vertex count? If my scene keeps updating its vertices on each frame, the usage of a single dynamic buffer would loose its purpose this way...
I've been testing initializing the buffer on the first time the scene is rendered, and from there on, using Map/Unmap on each frame. I start by filling in a vector list with all the scene objects and then update the resource like so:
void Scene::Render()
{
(...)
std::vector<VERTEX> totalVertices;
std::vector<int> totalIndices;
int totalVertexCount = 0;
int totalIndexCount = 0;
for (shapeIterator = models.begin(); shapeIterator != models.end(); ++shapeIterator)
{
Model* currentModel = (*shapeIterator);
// totalVertices gets filled here...
}
// At this point totalVertices and totalIndices have all scene data
if (isVertexBufferSet)
{
// This is where it copies the new vertices to the buffer.
// but it's causing flickering in the entire screen...
D3D11_MAPPED_SUBRESOURCE resource;
context->Map(vertexBuffer, 0, D3D11_MAP_WRITE_DISCARD, 0, &resource);
memcpy(resource.pData, &totalVertices[0], sizeof(totalVertices));
context->Unmap(vertexBuffer, 0);
}
else
{
// This is run in the first frame. But what if new vertices are added to the scene?
vertexBufferDescription.ByteWidth = sizeof(VERTEX) * totalVertexCount;
UINT stride = sizeof(VERTEX);
UINT offset = 0;
D3D11_SUBRESOURCE_DATA resourceData;
ZeroMemory(&resourceData, sizeof(resourceData));
resourceData.pSysMem = &totalVertices[0];
device->CreateBuffer(&vertexBufferDescription, &resourceData, &vertexBuffer);
context->IASetVertexBuffers(0, 1, &vertexBuffer, &stride, &offset);
isVertexBufferSet = true;
}
In the end of the render loop, while keeping track of the buffer position of the vertices for each object, I finally invoke Draw():
context->Draw(objectVertexCount, currentVertexOffset);
}
My current implementation is causing my whole scene to flicker. But no memory leaks. Wonder if it has anything to do with the way I am using the Map/Unmap API?
Also, in this scenario, when would it be ideal to invoke buffer->Release()?
Tips or code sample would be great! Thanks in advance!

Answer 1

At the memcpy into the vertex buffer you do the following:
memcpy(resource.pData, &totalVertices[0], sizeof(totalVertices));
sizeof( totalVertices ) is just asking for the size of a std::vector< VERTEX > which is not what you want.
Try the following code:
memcpy(resource.pData, &totalVertices[0], sizeof( VERTEX ) * totalVertices.size() );
Also you don't appear to calling IASetVertexBuffers when isVertexBufferSet is true. Make sure you do so.