Hi,
While optimizing my game to run on different gfx cards, I have noticed a really weird performance drop when I plugged into my rig nVidia TNT1 8 MB card. After switching off almost everything I was left off only with floor that is being rendered like NonIndexed triangle List from one Vertex Buffer. Without floor, the fps is 150, with floor (264 triangles) it falls down to 75 fps.
After experimenting with different triangle counts I found the threshold: It is triangle Number 36. If there are just 36 or less triangles, fps is 150 fps, if there are 37 or more, the fps falls to 75 fps - what is also strange is that it is actually the half!
It shouldn`t be a fillrate problem since the fact whether i set the camera to show all 36 triangles or just half of them doesn`t change the fps at all (even not for 0.1 fps). But when I add the 37th, it falls to 75 fps (from 150) - i.e. exactly down to half.
Here is the render code:
fm_pd3dDevice->SetStreamSource( 0, BigFloorVB_Handle, sizeof(FLOORCUSTOMVERTEX) );
fm_pd3dDevice->SetVertexShader( D3DFVF_FLOORCUSTOMVERTEX );
int rows = 4;
int cols = 4;
CGrid * G = &Grid [0];
for (int cRow = 0; cRow < rows; cRow++)
fm_pd3dDevice->DrawPrimitive( D3DPT_TRIANGLELIST, cRow*G->Dimension_Columns*2*3, cols*2);
fm_pd3dDevice->DrawPrimitive( D3DPT_TRIANGLELIST, rows*G->Dimension_Columns*2*3, 2*2+1);
As you can see, there are no state changes between DrawPrimitive calls. Vertex Buffer for floor is locked just once during startup with following flags: D3DUSAGE_WRITEONLY, D3DFVF_FLOORCUSTOMVERTEX, D3DPOOL_DEFAULT and never locked again during rendering.
Also please note that whether I draw the triangles with one call to DrawPrimitive (it is in current version, since it is faster to send ~200 triangles to render than to play with their visibility) or with several of them (which is just for debug purposes of course), it doesn`t simply make any difference. I also can`t do it in Windowed mode (which would help in debugging - but unfortunately DirectX Debug Window didn`t show anything when rendering that last triangle
), it shows only in FullScreen Mode.
I will of course use Indexed triangle lists (or strips in case of floor) in final build. But what on Earth causes that halving ?
And I just noticed that this 150 fps is exactly my monitor refresh rate. Why does it ignore my DirectX settings of VSync (off) in Display Properties and aTuner ? I haven`t noticed any variable for window creation related to VSync. (Though I`m gonna search these boards for Refresh stuff - it gets asked a lot I think.)
BTW, the rig is : AMD XP2100, 256 MB, gfx (TNT1-GF2MX, GF2GTS,GF3,GF4MX), Debug DX 8.1, Dets 30.00
EDIT : If I render 1600 additional triangles of my low-poly characters, the fps stays still at those magic 75 fps (as is the fps with only 37 floor triangles).
EDIT2: I plugged GF2MX this time to see what is the situation there. She can naturally render much higher amount of tris with no problems at all (compared to TNT1). Now GF2MX renders whole floor at full 150 fps (gotta search the docs for those presentation parameters - thanks Anon
). What is however strange is that it stops at round fps : Either 150.0, or 75.0 or 50.0 fps.
There is obviously some correlation between fps and VSync not depending on amount of tris - because I get here those 75.0 fps whether I render 10.000 tris or 4.000 tris per frame (it changes from one floor quad walking onto another) - still on GF2MX. Drivers seem to play it their way here not caring for 10k or 5k polys ...
Any idea is appreciated...
VladR
Avenger game
[edited by - VladR on May 26, 2003 4:59:44 PM]
. I wonder what it shall be like with TNT1 (shall try this evening, but now I gotta go sleep since I`m getting up in few hours to daily work).
