DirectX particle system. ConstantBuffer
- by Liuka
I'm new in DirectX and I'm making a 2D game.
I want to use a particle system to simulate a 3D starfield, so each star has to set its own constant buffer for the vertexshader es. to set it's world matrix.
So if i have 500 stars (that move every frame) i need to call 500 times VSsetconstantbuffer, and map/unmap each buffer.
with 500 stars i have an average of 220 fps and that's quite good.
My bottelneck is Vs/PsSetconstantbuffer.
If i dont call this function i have 400 fps(obliviously nothing is display, since i dont set the position of the stars).
So is there a method to speed up the render of the particle system??
Ps.
I'm using intel integrate graphic (hd 2000-3000). with a nvidia (or amd) gpu will i have the same bottleneck??
If, for example, i dont call setshaderresource i have 10-20 fps more (for 500 objcets), that is not 180.Why does SetConstantBuffer take so long??
LPVOID VSdataPtr = VSmappedResource.pData;
memcpy(VSdataPtr, VSdata, CszVSdata);
context->Unmap(VertexBuffer, 0);
result = context->Map(PixelBuffer, 0, D3D11_MAP_WRITE_DISCARD, 0, &PSmappedResource);
if (FAILED(result))
{
outputResult.OutputErrorMessage(TITLE, L"Cannot map the PixelBuffer", &result, OUTPUT_ERROR_FILE);
return;
}
LPVOID PSdataPtr = PSmappedResource.pData;
memcpy(PSdataPtr, PSdata, CszPSdata);
context->Unmap(PixelBuffer, 0);
context->VSSetConstantBuffers(0, 1, &VertexBuffer);
context->PSSetConstantBuffers(0, 1, &PixelBuffer);
this update and set the buffer.
It's part of the render method of a sprite class that contains a the vertex buffer and the texture to apply to the quads(it's a 2d game) too.
I have an array of 500 stars (sprite setup with a star texture).
Every frame:
clear back buffer;
draw the array of stars;
present the backbuffer;
draw also call the function update( which calculate the position of the sprite on screen based on a "camera class")
Ok, create a vertex buffer with the vertices of each quads(stars) seems to be good, since the stars don't change their "virtual" position; so....
In a particle system (where particles move) it's better to have all the object in only one vertices array, rather then an array of different sprite/object in order to update all the vertices' position with a single setbuffer call.
In this case i have to use a dynamic vertex buffer with the vertices positions like this:
verticesForQuad={{ XMFLOAT3((float)halfDImensions.x-1+pos.x, (float)halfDImensions.y-1+pos.y, 1.0f), XMFLOAT2(1.0f, 0.0f) },
{ XMFLOAT3((float)halfDImensions.x-1+pos.x, -(float)halfDImensions.y-1+pos.y, 1.0f), XMFLOAT2(1.0f, 1.0f) },
{ XMFLOAT3(-(float)halfDImensions.x-1+pos.x, (float)halfDImensions.y-1.pos.y, 1.0f), XMFLOAT2(0.0f, 0.0f) },
{ XMFLOAT3(-(float)halfDImensions.x-1.pos.x, -(float)halfDImensions.y-1+pos.y, 1.0f), XMFLOAT2(0.0f, 1.0f) },
....other quads}
where halfDimensions is the halfsize in pixel of a texture and pos the virtual position of a star.
than create an array of verticesForQuad and create the vertex buffer
ZeroMemory(&vertexDesc, sizeof(vertexDesc));
vertexDesc.Usage = D3D11_USAGE_DEFAULT;
vertexDesc.BindFlags = D3D11_BIND_VERTEX_BUFFER;
vertexDesc.ByteWidth = sizeof(VertexType)* 4*numStars;
ZeroMemory(&resourceData, sizeof(resourceData));
resourceData.pSysMem = verticesForQuad;
result = device->CreateBuffer(&vertexDesc, &resourceData, &CvertexBuffer);
and
call each frame Context->IASetVertexBuffers(0, 1, &CvertexBuffer, &stride, &offset);
But if i want to add and remove obj i have to recreate the buffer each time, havent i??
There is a faster way? I think i can create a vertex buffer with a max size (es. 10000 objs) and when i update it set only the 250 position (for 250 onjs for example) and pass this number as the vertexCount to the draw function (numObjs*4), or i'm worng
