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OpenGl

Started by programering Feb 24, 2003 at 9:03 AM 23 replies 1k views

Original Post

Feb 24, 2003 at 9:03 AM

Glu? Glaux? Why is they called that? What''s the difference between vertex arrays and vertex buffers? Is vertex the same as node and point? void build_render_tree(); void sort_render_tree(); Why do some textured 3d games runs so slow? Is it a too large for(;

loop? Anton Karlsson Klingis Entertainment Games with silly humor

Yann L

219

Yann L

Feb 24, 2003 at 10:09 AM

quote:

What''s the difference between vertex arrays and vertex buffers?

None, both are representations of the same concept. Vertex arrays are OpenGL, vertex buffers are Direct3D. Semantics are different, but they are functionally the same.

quote:

Is vertex the same as node and point?

No. A vertex represents a point, but can optionally contain additional information about that point, besides the 3D position: colour, normal, texture coordinate, weighting factors, etc...

programering

Author

programering

Feb 25, 2003 at 1:59 AM

What''s semantics?

Anton Karlsson
Klingis Entertainment
Games with silly humor

OrangyTang

333

OrangyTang

Feb 25, 2003 at 3:45 AM

Languages are typically described in terms of syntax and semantics, syntax being the structure and how the program is described, and semantics being the meaning and how the program actually works/behaves.

Further reading.

neurokaotix

Feb 25, 2003 at 4:14 AM

What are back propagations?

Galileo430

Feb 25, 2003 at 9:43 PM

Actually Vertex Buffers / Vertex Arrays (D3D/OGL) are slightly diffrent.

The OGL implementation of Vertex Arrays keeps the data in RAM hand has to feed the coords to the card via the CPU. Vertex buffers in (D3D) use DMA (Direct Memory Access) to grab the coords from RAM.

You can get OpenGL to do this with ATI''s ATI_vertex_array_object extension and nVidia''s NV_vertex_array_range extension.

Trivial issues really.

Yann L

219

Yann L

Feb 25, 2003 at 10:31 PM

quote:

The OGL implementation of Vertex Arrays keeps the data in RAM hand has to feed the coords to the card via the CPU

Nope. OpenGL vertex arrays are also DMA''ed to the 3D card, this is done behind the scenes by the driver. You can use VAR/VAO to control that process manually, and store data directly in VRAM (which is not possible to do for standard vertex arrays, as the client/server model of VAs restrict that).

programering

Author

programering

Feb 26, 2003 at 2:27 AM

What''s VAR/VAO, VRAM and VA?

Anton Karlsson
Klingis Entertainment
Games with silly humor

davepermen

160

davepermen

Feb 26, 2003 at 2:33 AM

what is google?

"take a look around" - limp bizkit
www.google.com

OrangyTang

333

OrangyTang

Feb 26, 2003 at 4:10 AM

quote:
Original post by programering
What''s VAR/VAO, VRAM and VA?

VAR/VAO = vertex array extensions by nVidia/Ati for finer control over where vertex buffers are stored.

vRAM = video ram/graphics card memory. Local to the actual graphics card.

VA = vertex array (standard GL feature).

Slightly off-topic, when on earth is the ARB_VERTEX_OBJECT (or whatever the thing is going to be called) going to turn up

Yann L

219

Yann L

Feb 26, 2003 at 3:38 PM

quote:

Slightly off-topic, when on earth is the ARB_VERTEX_OBJECT (or whatever the thing is going to be called) going to turn up

Now that''s an excellent question. The last news were from the december ARB notes, ARB_buffer_object was supposed to be voted by january...

programering

Author

programering

Mar 17, 2003 at 6:24 AM

What does ARB stands for?

Anton Karlsson
Klingis Entertainment
Games with silly humor

mentat

Mar 17, 2003 at 7:03 AM

OpenGL Architecture Review Board.. They take care of standardization of new stuff in OpenGL, extensions, versions..

siaspete

Mar 17, 2003 at 7:16 AM

programering, you should use Google before asking questions.

Helpful links:
How To Ask Questions The Smart Way | Google can help with your question | Search MSDN for help with standard C or Windows functions

krazywest

Mar 17, 2003 at 1:42 PM

quote:
Original post by siaspete
Helpful links:
How To Ask Questions The Smart Way | Google can help with your question | Search MSDN for help with standard C or Windows functions

Your link to smart questions don''t work....

Mar 17, 2003 at 5:09 PM

Yann, JC in his feb 8 2003 plan file writes:

"The newly-ratified ARB_vertex_buffer_object extension will probably let me do the same thing for NV_vertex_array_range and ATI_vertex_array_object."

The one thing gl needs are better doc format something like msdn. As 1.4 docs are now they read like a novel and is hard to find info in timely manner. Extension docs? I''m not even going to go there

D3d9 docs need to be streamlined, there''s too much redundant info. Someone needs to take 1.4 gl specs, pullout all the topic overviews and create a link list out of them. Then a section on use should accompany each topic along with a reference section for functions used in that topic. Very much like msdn win32 docs which I find very quick to read.

Ready4Dis

Mar 17, 2003 at 5:19 PM

quote:
Original post by Yann L
None, both are representations of the same concept. Vertex arrays are OpenGL, vertex buffers are Direct3D. Semantics are different, but they are functionally the same.

Incorrect Yann L. A vertex array, can aslo be an array of vertices in order. A triangle vertex array is a vertex array that contains x1,y1,z1, x2,y2,z2, x3,y3,z3 sets in it, and can be drawn without an Index Buffer. A vertex buffer is not in order, and has to be indexed using the Index Buffer for drawing. A vertex array cam be drawn without the index buffer. Although similar, they are not the same, and there ARE vertex buffers in opengl, not just vertex arrays, although people often refer to them as vertex arrays, because they do hold vertices in an array (so it is "technically" correct to say it''s a vertex array).

Yann L

219

Yann L

Mar 17, 2003 at 5:35 PM

It's not only "technically" correct, it's the official denomination. A vertex array is an array containing vertices - this is totally independent on the way they are accessed. Might it be in sequential order, or might it be indexed, it still is a vertex array. Array == Buffer, there is no conceptual difference behind those names, they are just that: different names. The OP asked about the difference between VBs and VAs. There is none. Both are structures that contain vertex data in user-definable order. He did not ask about index buffers.

And BTW, unless you are drawing points, you should avoid non-indexed vertex arrays like the plague.

JD: yeah, great news about the new extension. And I agree on the OGL docs, they'd really need some better indexing system.

[edited by - Yann L on March 17, 2003 6:40:27 PM]

Ready4Dis

Mar 17, 2003 at 5:40 PM

I''m just saying, that the term Vertex Buffer isn''t used to mean an array in order, while Vertex Array is used that way. And, in opengl, it is also reffered to as a vertex buffer, so it''s not a Direct 3d only thing.

Myopic Rhino

452

Myopic Rhino

Mar 17, 2003 at 6:19 PM

quote:
Original post by Ready4Dis
I'm just saying, that the term Vertex Buffer isn't used to mean an array in order, while Vertex Array is used that way.

And that point really isn't relevant. You're just nitpicking. Fundamentally - and especially as far as the OP is concerned - they are the same thing. The fact that their usage sematics are slightly different doesn't change the fact that are both essentially pools of vertices allowing for increased efficiency.

This is a good example of why so many people find 3D graphics intimidating. From a beginner's perspective, a statement that vertex buffers and arrays are functionally equivalent is sufficient. Getting into the details of how they are different is only going to expose them to concepts and terms they aren't ready for yet.

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