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Rendering only visible objects

Started by cozzie Oct 14, 2004 at 6:14 AM 3 replies 750+ views

Original Post

Oct 14, 2004 at 6:14 AM

Hi all. I'm writing my first OpenGL 3d engine at the moment, and I have a question about rendering objects. A couple of years ago I coded a crappy 3d engine using Watcom C++, I remember that I needed to write some code that made sure that objects outside the viewingspace, wouldn't be rendered. This resulted in a nice fps improval. Can someone tell me if openGL does this for you, when you use it correctly (GLulookat, modelview matrices etc.)? Thank you for the help. [Edited by - cozzie on October 14, 2004 7:39:30 AM]

dawidjoubert

Oct 14, 2004 at 6:29 AM

OpenGL Does its own Frustum Culling BUT, You can do it faster and more effecient since you dont have to pass 1 million polies down the pipeline.

Frustum Culling is Easy in concept!

Create Bounding Boxes for the entire world which in turn is subdivided into 8 more boxes and so on.

Then By simple culling the boxes you will be clipping the correct polies also.

Bottom Line:When Passing Small amounts of polies(100-400) you dont need to clip when talking 6000 like in a typical quake map it will realy speed up things!

NOTE:If you implement your octree properly the real speed up comes when you only check collision with a couple of polies instead of 6000 each frame!!

Regards Dawid,
go to gametutorials.com and check for frustum culling!

cozzie

Oct 14, 2004 at 7:25 AM

hi,
thanks for the answer, it sounds really clear to me.
Since I'm new on this forum, can you tell me where I can select on which forum (for example: OpenGL) I can post my topic.

Krohm

Oct 14, 2004 at 8:55 AM

Quote:
Original post by cozzie
can you tell me where I can select on which forum (for example: OpenGL) I can post my topic.

OpenGL.org has math & algorithms forum specifically for that. This forum is also pretty good.

FluxCapacitor

Oct 14, 2004 at 3:57 PM

Check out the Frustum Culling tutorial at GameTutorials:

http://www.gametutorials.com/Tutorials/opengl/OpenGL_Pg5.htm
(scroll down)

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