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OpenGL Display Lists in Opengl, the anti-optimization at high poly counts?

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I''ve written a small LWO importer for OpenGL that basically loads the object into a rotating scene. Then to test out how much of an increase display lists are on the TNT2 chipset I ran a series of tests with ''brute force'' rendering and then display list rendering. Much to my dismay the display list actually got a worse framerate than the non display list version at high poly counts (~9000) and showed no gain when the poly count was low (~150). What gives, I thought that display lists couldnt hurt the performance. Makes me wonder if commercial products use display lists extensively and if so how much performance im loosing

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In my project I tried using a display list for my 5000-or-so-triangle object since it uses 3 passes. I didn''t get any noticeable performance gain or hit, actually. Are you sure you''re not accidentally building the list for each rendering pass or something? I can''t imagine why the performance would *drop* so significantly.

Can anyone out there say when display lists will actually do something significant?

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Im using a single pass render... no textures no G.Lighting, just flat poly''s to test if the geometry imported ok.

I benchmarked using a really primitive method that involved counting the number of succesful calls to display() and outputing that number every second (reseting it to zero at that point). with this the fps was around 260 for the display listed high poly count and 300 for the non-type, that In my mind is a noticable hit. If you are HW accelling with a TNT2U i guess Im doing something terribly wrong otherwise It might just be the chipset implementation

-menasius

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you don''t have any transform matrices in the display list code, do you? if so, this''ll slow it down. display lists are only for rigid bodies, not if you''re going to do some subobject animation, like filling in a variable for a vertex.

a2k

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Nope no transformations ... I do however have a for loop because the geometry has an undefined number of polys (until runtime ) so it loops through all the vertices

-menasius

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No transforms here, either. The only major question I have, then, is whether or not it''s correct to have glBegin/glEnd within glNewList/glEndList or not. I *do*, and I can''t recall why I''d done that other than that it got things working. I''m using a regular TNT. To say the least, this problem is strange. I wonder if any Direct3D people are having similar issues.

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When you are using display lists it is best if you only use one per object. When you say "loop through all the vertices", are you creating a seperate display list for each polygon? If you are you will find that the overhead per display list will drop your performance notably. If you aren''t then it is probably a driver issue, because display lists should be faster in most cases.

PreManDrake

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no no no Im not that idiotic... The loop looks like this

start the list...
loop through vertices of triangles..
end list

so its one list with a bunch of vertices in it and a glBegin and glEnd (although I''ve tried it without)



-menasius

"Quitters never win...
winners never quit...
but those who never win and never quit, are idiots"

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Guest Anonymous Poster
Try using GL_COMPILE or GL_COMPILE_AND_EXECUTE to decrease render times for display list. These calls optimize the list before display and stores it in video memory(I believe). Also make sure you only call display() when absolutely necessary.

--Cauldron the Ancient

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Guest Anonymous Poster
If I am not wrong, display list puts geometry and/or transformations into the video card that supports T&L.
I experienced steady speed increment by the dispaly list with a T&L supported board.

If the video board does not support T&L, display list may not have any advantage. When the memory allocation for the geometry/transformation is bad (jumping around?), you may suffer from speed delay.

HRS

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I am using GL_COMPILE... what is the difference between GL_COMPILE and GL_COMPILE_AND_EXECUTE?

-menasius

"Quitters never win...
winners never quit...
but those who never win and never quit, are idiots"

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also it doesnt make sense that it would loose so much for simply compiling one list and displaying it once as opposed to just placing the glBegin...glEnd block in as is. If nothing else the methods should yield the same performance, thats what I gathered from the documentation on the web and in books about them.

-menasius

"Quitters never win...
winners never quit...
but those who never win and never quit, are idiots"

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Hi menasius,

The difference between GL_COMPILE and GL_COMPILE_AND_EXECUTE is that with compile & execute, OpenGL commands are executed as they are encountered (i.e. it will draw to the screen, or whatever) as well as compiled (GL_COMPILE just compiles them to a display list).

I find your situation pretty damn weird to say the least. As you seem to know, all a display list does is capture all commands called in it, along with vertex data values etc at that moment in time, and store them in an efficient manner for fast output. BTW, it is completely valid to perform tranformations within a display list, and can even be more efficient than doing them outside, as only the resultant matrix of transformations is saved in the list (i.e. it doesn''t do the calculations each time it is called).

Methinks I''ll be going home to check this out with my terrain engine (which uses display lists) on my TNT2 now... just as soon as I fix my installation of Win2k


-------------
squirrels are a remarkable source of protein...

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actually, i meant transformations with variables in them. that's what i should say, with passing variables through. doesn't that slow it down?

supposing you had glvertex(xvar, yvar, zvar). this wouldn't be fast in a display list. right?

sorry if this has nothing to do with your code, menasius, since you don't even have transformations, and less likely any variables passed through.

(oh, and if i'm totally wrong about the variable-passing thing totally, i'd like to know, cuz then, i'd use it in my game. i have the perfect application for it.)

a2k

Edited by - a2k on 4/10/00 1:40:55 AM

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