CreateVertexBuffer() memory allocation

Graphics and GPU Programming Programming

Started by quant November 15, 2003 09:05 AM

6 comments, last by quant 20 years, 5 months ago

100

Author

November 15, 2003 09:05 AM

When i create and lock a vertex buffer, how would i assign values to the memory allocated? Are the vertex objects already contructed? or would i have to use placement new to construct the objects. For example


pdevice->CreateVertexBuffer(8*sizeof(vertextype), D3DUSAGE_SOFTWAREPROCESSING, CUSTOM_VERTEX, D3DPOOL_SYSTEMMEM, &pbuf);

pbuf->Lock(0, sizeof(vertextype), &pmem, 0);

for( int j = 0; j < 8; ++j )
pmem[j].x = 1;

is that valid? or would i have to use placement new


vertextype* pvert = new(pmem) vertextype;
pvert->x = 1;

[edited by - quant on November 15, 2003 10:14:57 AM]

-keyboard

Painless

126

November 15, 2003 10:10 AM

Creating the vertex buffer only allocates memory. Usually, you''ll just want to keep your vertex structures/classes simple enough that it doesn''t matter whether the constructor''s been called or not (so you could just use the first method and overwrite what was in the memory before). Remember, the destructors for the vertices will never be called, so you''ll have to keep things pretty simple anyways. The placement new will probably work, though, if that''s what you want to use.

wasd

171

November 15, 2003 01:03 PM

What you''d normally do (well, I would anyway) is one of two things. Either:

1) Have an array of vertex data set up already and just memcpy the data into the buffer after it''s been locked, e.g.:

pdevice->CreateVertexBuffer(8*sizeof(vertextype), D3DUSAGE_SOFTWAREPROCESSING, CUSTOM_VERTEX, D3DPOOL_SYSTEMMEM, &pbuf);
pbuf->Lock(0, sizeof(vertextype), &pmem, 0);
memcpy(pmem, vertArray, 8 * sizeof(vertextype);

OR

2) Cast your pmem pointer e.g.:

vertextype * pmem;
pdevice->CreateVertexBuffer(8*sizeof(vertextype), D3DUSAGE_SOFTWAREPROCESSING, CUSTOM_VERTEX, D3DPOOL_SYSTEMMEM, &pbuf);
pbuf->Lock(0, sizeof(vertextype), (void**)&pmem, 0);
for(int j = 0; j < 8; j++)
{
pmem[j].x = 1;
etc....
}

---------------------------------------

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hoopjones

122

November 15, 2003 01:06 PM

You don''t have to use new. The CreateVertexBuffer function returns to you the address of some allocated memory, so you should use that memory. Then you just go through your vertex structure and fill in the data. I''m not sure why you would use new in this situation...

quant

100

Author

November 15, 2003 02:25 PM

Thanks for the replys.

quote:
Original post by hoopjones
I'm not sure why you would use new in this situation...

C++ normally deals with objects that have been constructed using a constructor, and the only way to construct an object in a particular area of memory is by using placement new.

But i guess that because the vertex structure only contains basic data types, a constructor isnt needed.

[edited by - quant on November 15, 2003 3:26:03 PM]

-keyboard

hoopjones

122

November 16, 2003 04:44 AM

Yes, but new is giving you memory from the heap, not the AGP accessible memory that CreateVertexBuffer gives you, which is why you would want to use CreateVertexBuffer in the first place.

Anonymous

November 16, 2003 04:50 AM

quote:Original post by hoopjones
Yes, but new is giving you memory from the heap, not the AGP accessible memory that CreateVertexBuffer gives you, which is why you would want to use CreateVertexBuffer in the first place.

Placement new doesnt give you memory anywhere, it simply constructs an object in the memory location you pass to it.

hoopjones

122

November 16, 2003 05:41 AM

quote:Original post by Anonymous Poster
quote:Original post by hoopjones
Yes, but new is giving you memory from the heap, not the AGP accessible memory that CreateVertexBuffer gives you, which is why you would want to use CreateVertexBuffer in the first place.

Placement new doesnt give you memory anywhere, it simply constructs an object in the memory location you pass to it.

I never knew about "placement new", thanks for mentioning it!

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