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Setting a dynamic index buffer

Started by Valor Knight Jan 22, 2006 at 11:12 PM 4 replies 850+ views

Original Post

Jan 22, 2006 at 11:12 PM

RESOLVED I was currently using a dynamic index buffer, or so I though, until today when I was adding in degeneative triangles to my terrain, and noticed, much to my dismay that my index buffer broke: http://photobucket.com/albums/c305/biohaz1/?action=view&current=INDEXBUFFERISFed.gif I have no idea on what happened, but using the settings I had, I was getting triangles every direction if I did not use the entire buffer (I do not remember if I was working on the lod with the dynamic flag or not, so I may have triggered it when I was trying to clean up my code). Now this is the current working buffer, with the defunct one commented out.


if(FAILED(_pDevice->CreateIndexBuffer(numindicesperpatch * sizeof(WORD),
/*D3DUSAGE_DYNAMIC | D3DUSAGE_WRITEONLY*/0, D3DFMT_INDEX16,
D3DPOOL_MANAGED/*DEFAULT*/, &_vecpIndexBuffers[patchindex], 0)))

How would I do one dynamically correctly? Does the Index buffer need the DYMANIC flag or is it just for the vertex buffer? Thanks EDIT: Broke up the long line of code - it was messing up the way your post was displayed. [Edited by - Valor Knight on January 29, 2006 4:09:01 PM]

jollyjeffers

Jan 23, 2006 at 5:29 AM

Technically speaking you don't REQUIRE the dynamic flag - but performance can really suck if you don't use it. It's basically a hint to the runtime/driver so that it can place the resource somewhere that it's easy to change.

What is your code for locking/updating the buffer? It is possible to trip-up using those - particularly if you have nooverwrite/discard flags specified. Some older hardware tends to have odd behaviour with various combinations of these flags.

Also, that mess of triangles - do they actually correspond to locations of vertices in any way? I've had that sort of "noise" created when I mis-match the format/alignment/stride of data - causing the GPU to address the wrong data with the wrong semantic..

hth
Jack

jamesw

Jan 23, 2006 at 11:07 AM

If you're not using the entire buffer remember to only render the number of primitives you are using in your call to DrawPrimitive().

Valor Knight

Jan 23, 2006 at 4:07 PM

This is my buffer creation / locking

if(FAILED(_pDevice->CreateIndexBuffer(numindicesperpatch * sizeof(WORD), D3DUSAGE_WRITEONLY, D3DFMT_INDEX16, D3DPOOL_MANAGED, &_vecpIndexBuffers[patchindex], 0)))..//LockWORD *indices = 0;_vecpIndexBuffers[patch]->Lock(0, 0, (void**)&indices, D3DLOCK_DISCARD);

Do I need the D3DUSAGE_DYNAMIC flag? If so, what is the correct pool setting?

Quote:
Original post by jollyjeffers
Also, that mess of triangles - do they actually correspond to locations of vertices in any way? I've had that sort of "noise" created when I mis-match the format/alignment/stride of data - causing the GPU to address the wrong data with the wrong semantic..

I guess it could have, but not anything that I was drawing ( I was only drawing one patch of land). It was doing that if I used an empty index buffer as well, so it must have been memory thing, I dont think I had the pool correct for dynamic.
_________________________

I am only calling DrawIndexedPrimitive with the correct number of triangles, But in the past it did not matter (at least for the extra triangles showing up - now that I think about it, it was before I added DYNAMIC flag)

jamesw

Jan 29, 2006 at 3:20 PM

If you lock the buffer every frame then yes, you should use the dynamic flag. Here's some relevant docs:

Quote:
index buffers and vertex buffers cannot be created using D3DPOOL_MANAGED together with D3DUSAGE_DYNAMIC.

For dynamic textures, it is sometimes desirable to use a pair of video memory and system memory textures, allocating the video memory using D3DPOOL_DEFAULT and the system memory using D3DPOOL_SYSTEMMEM. You can lock and modify the bits of the system memory texture using a locking method. Then you can update the video memory texture using UpdateTexture.

If that seems like too much trouble, you can just use a D3DPOOL_DEFAULT version and lock that. Also I found this:

Quote:
The D3DLOCK_DISCARD and D3DLOCK_NOOVERWRITE flags are valid only on buffers created with D3DUSAGE_DYNAMIC.

That may very well be the source of your problem when using the managed buffer.

Valor Knight

Jan 29, 2006 at 4:08 PM

Thanks, I figured it out a while ago and works fine now (I was telling it too many triangles to draw).

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