Vertex and Index Buffer Locking

noodleBowl · 2013-10-22T08:43:12

I was cleaning up my dynamic vertex and index buffer code, when I started wondering something Am I locking these buffers right? This is a little hard to explain for me so please let me know what does not make sense currently I just lock the entire buffer like this: vBuffer->Lock(0, 0, (void**) &vertices, bufferLockFlag); iBuffer->Lock(0, 0, (void**) &indices, bufferLockFlag); But since these are dynamic buffers wouldnt I want to be locking like this? vBuffer->Lock(vertexDataAmountUsed, vertexBufferSize - vertexDataAmountUsed, (void**) &vertices, bufferLockFlag); iBuffer->Lock(indexDataAmountUsed, indexBufferSize - indexDataAmountUsed, (void**) &indices, bufferLockFlag); For example lets say we are: - Drawing quads - Each quad has 4 vertices and 6 indices, since we are using a index buffer - That each quad has a vertex data size of 10 - That each quad has a index data size of 2 - That our vertex buffer can hold 3 quads before it is "full" - Meaning that our buffers sizes are: vertexBufferSize: 'Vertex Data size per quad' * 'number of quads the buffer can hold' = 10 * 3 = 30 indexBufferSize: 'Index Data size per quad' * 'number of quads the buffer can hold' = 2 * 3 = 6 - That we are starting with fresh empty buffers vertexDataAmountUsed = 0; indexDataAmountUsed = 0; We lock the buffers like so vBuffer->Lock(vertexDataAmountUsed, vertexBufferSize - vertexDataAmountUsed, (void**) &vertices, bufferLockFlag); iBuffer->Lock(indexDataAmountUsed, indexBufferSize - indexDataAmountUsed, (void**) &indices, bufferLockFlag); Meaning that we are locking the entire buffer for both the index and vertex buffers because: - vertexDataAmountUsed and indexDataAmountUsed is 0. This tells the lock call to use a 0 offset for the lock (First param in the lock calls) - We are locking the entire buffers worth for both buffers, based on the amount of data to lock (Second param in the lock calls) vertexBufferSize - vertexDataAmountUsed = 30 - 0 = 30 indexBufferSize - indexDataAmountUsed = 6 - 0 = 6 So down the line, lets say we do not need a fresh buffer. That we still have room left. Lets say there are 2 quads worth of data in for each buffer meaning: vertexDataAmountUsed = 'Vertex data per quad' * 2 = 10 * 2 = 20 indexDataAmountUsed = 'Index data per quad' * 2 = 2 * 2 = 4 So this means we can hold one more quad before we have to use the DISCARD flag to get a fresh buffer Meaning that when we lock again using vBuffer->Lock(vertexDataAmountUsed, vertexBufferSize - vertexDataAmountUsed, (void**) &vertices, bufferLockFlag); iBuffer->Lock(indexDataAmountUsed, indexBufferSize - indexDataAmountUsed, (void**) &indices, bufferLockFlag); We are locking like so: - We are starting the lock at the 20 data amount offset mark for the vertex buffer (First param in the vertex buffer lock) - We are starting the lock at 4 data amount offset mark for the index buffer (First param in the index buffer lock) - For the vertex buffer we are only locking what we have left available (Second param in the vertex buffer lock). In this case: vertexBufferSize - vertexDataAmountUsed = 30 - 20 = 10 - For the index buffer we are only locking what we have left available (Second param in the vertex buffer lock). In this case: indexBufferSize - indexDataAmountUsed = 6 - 4 = 2 Meaning that only the remaining data quad spot left in the buffers was locked Now, what am I really asking? Well, I want to know if what I just described above is correct? Is that how I should be locking dynamic vertex and index buffers? That I can say vertexBufferSize - vertexDataAmountUsed to lock my whole buffer assuming it matches my max vertex buffer size? I know if you use 0, 0 in the first and second param it locks the whole thing, but can this be used as an alternative? Or should I just stick with locking the entire thing?

Graphics and GPU Programming Programming

Started by noodleBowl October 20, 2013 06:08 PM

9 comments, last by 21st Century Moose 10 years, 6 months ago

21st Century Moose

13,459

October 22, 2013 08:43 AM

No, even in DX9 you can save 50% of the bandwidth.

But bandwidth isn't the primary bottleneck with either text rendering or particles; the bottleneck is fillrate and ROP. Even with OpenGL's immediate mode there's next to no performance difference.

Direct3D has need of instancing, but we do not. We have plenty of glVertexAttrib calls.

Vertex and Index Buffer Locking

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Vertex and Index Buffer Locking

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