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trs79

opinions on buffer usage/draw calls for a scrolling album art program

6 posts in this topic

Hello,

 

I'm planning on creating a program whereby a list of album names is retrieved via http. Once the names are received, I plan to do the following:

  1. Create a static VBO, with one quad for each album name. Each quad shares part of a texture atlas, so I can use a single draw call
  2. There will be additional http requests for album art images
  3. Display a loading indicator until image arrives, then lock part of dynamic texture atlas and write image data
  4. There will be a scissor clipping rectangle that will hide the quads not yet shown
  5. User can scroll list up and down

 

Questions:

  1. I'm using GLES, is there a better way to handle the asynchronous incoming images then to use a dynamic texture with locking overhead?
  2. Instead of one VBO for a single draw call, I could issue a separate draw call for each quad, not sure if this would be much slower? I think it would be easier because I could simply draw each quad with either album art texture or progress texture until image comes in

 

Thanks for any help, please see image below

 

 

IsongListApp.gif

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Seems over optimized to me. I'd do a draw call for each album, unless there are thousands visible at the same time.

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i would probably just download an image into a buffer in ram, when the transfer was complete, copy it to a NON-DYNAMIC texture. then use sprites to draw. no locks, no vertex  buffers, none of that BS. after all, you're just showing bitmaps.

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Hopefully anyone else who posts here will have advice on how to optimize texture data uploads.

 

It appears to me that you should not be the least bit concerned about VBO performance or optimization.  Even the weakest GPU's that I've tested can handle way more than what you are describing by a long shot, so far as models are concerned. The image data is another matter, I think that all of your performance concerns should be focused on your images not the quads, the quads can all be the same VBO anyways, just assign the particular image before making the draw call to the same VBO. 

 

Maybe PBO's will be useful to you.  They don't have much performance benefit for static textures but for situations where things are changing a lot there can be a 2x-3x increase in transfer speed to the GPU.

 

The following is an example on how to swap between two PBO's to help eliminate stalling, it's kind of like double buffering.

http://www.songho.ca/opengl/gl_pbo.html

 

The following is some data collected by nVidia engineers on PBO performance using various texture formats.  Don't expect these results to be consistent across all GPU manufacturers. 

 

http://http.download.nvidia.com/developer/Papers/2005/Fast_Texture_Transfers/Fast_Texture_Transfers.pdf

 

You will, however, gain some insight into what factors can influence performance in these matters.  Look at the chart that has timing measurements for different texture formats.  Specifically, for nVidia, using BGRA can be more than 3x faster than using RGBA, but this is for nVidia.  You cannot expect these same results for ATI or PowerVR or Mali, etc....

 

This idea in it's essence will hold true, test all formats on your preferred platform and you are bound to find one that works best for the device that you are targeting.

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Thanks for the responses everyone.

 

@froop:

Yeah, I think over-optimization is to blame here, I hate it when that happens.  A draw call for each album seems like the way to go

 

@Norman Barrows:

Thanks for the tip about sprites, I had forgotten about those. So it sound sounds like you're also saying to use a draw call per album, but using point sprites instead of quads?

 

@marcClintDion:

PBO's sound interesting, but unfortunately they don't seem to be supported in GLES 2 that I'm targeting. I wish they were though, sounds like that would be the best way to update the textures

Edited by trs79
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@marcClintDion: PBO's sound interesting, but unfortunately they don't seem to be supported in GLES 2 that I'm targeting.

 

Oh how embarrassing, I have no interest in them, I never bothered to check if they are supported before recommending them.  Oh well, live and learn.

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Oh, no worries! Too many api's and combinations of extensions to keep track of :)
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