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Fastest way to upload streaming points, and removing occasionally


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#1 Ender1618   Members   -  Reputation: 242

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Posted 16 August 2013 - 08:39 PM

So i have a system (using OpenGL 4.x) where i am receiving a stream of points (potentially with color and/or normal), from an external source. And I need to draw these points as GL_POINTS, running custom switchable shaders for coloring (color could be procedurally generated, or come from vertex color or normal direction).

 

The stream consists of receiving a group of points (with or without normal or color) of an arbitrary count (typical from 1k to 70k points) at a fairly regular interval, I need to add these points to my current points and draw all the points so far received points.

 

I am guaranteed that my vertex type will not change, I am told at the beginning of the streaming which to expect, so i am either using an interleaved vertex with: pos+normal+color, pos+normal, pos+color, or just pos.

 

My current solution is to allocate interleaved vertex VBOs (with surrounding VAOs) of the appropriate vertex type at a config file specified max vertex count (allocated with the DYNAMIC hint).

 

As new points come in i fill up my current non filled VBO via glBufferSubData. I keep a count (activePoints) of how many vertices the current frontier VBO has in it so far, and use glBufferSubData to fill in a range starting with activePoints, if my current update group has more vertices than can fit in my frontier buffer (since i limit the vertex count per VBO), then i allocate a new VBO and fill the range starting at 0 and ending with the number of points left in my update group (not added to the last buffer), if I still have points left I do this again and again. It is rare that an update group straddles more than 2 buffers.

 

When rendering i render all my VBOs (-1) with a glDrawArrays(m_DrawMode,0,numVertices), where numVertices is equal to max buffer allowed size, and my frontier buffer with a glDrawArrays(m_DrawMode,startElem,numElems) to account for it not being completely filled with valid vertices.

 

Of course at some point I will have more points than I can draw interactively, so i have an LRU mechanism that deallocates the oldest (according to the LRU alg) sets of VBOs as needed.

 

Is there a more optimal method for doing this? Buffer orphaning? Streaming hint? Map vs SubData? Something else?

 

The second issue is that i am now asked to removed points (at irregular intervals), ranging from 10 to 2000 at a time. But these points are irregularly spaced within the order I received them initially. I can find out what offsets in which buffers they currently exit in, but its more of a scattering than a range. I have been "removing them" by finding their offsets into the right buffers and one by one calling glBufferSubData with a range of 1 (its rare that they are beside each other in a buffer), and changing there pos to be somewhere far off where they will never be seen. Eventually i guess buffers should be deleted from these remove request adding up, but I don't currently do that.

 

What would be a better way to handle that?


Edited by Ender1618, 16 August 2013 - 08:54 PM.


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