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Triangles, how many is too many?

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Hey there, I''ve hacked up a very simple terrain loading program in OpenGL. It just takes a 257x257 grid and forces triangles onto the points and shades the triangles according to the height of each of the 3 vertices. Okay, so I get like 3.5 FPS here, and I am running with about 132,098 triangles (yeah, 132K). So, I take it that I am getting bad performance because I am outputting so many triangles, or is it because I am not outputting the triangles in a very friendly manney (I just run through the points, and draw triangles, 2 loops, nothing fancy). I bet I could get it to like 6 FPS with just better coding, but is it mostly due to the enormous amount of triangles? PS - How many triangles are displayed in an average frame in popular games now? Is there a way to see this? Thanks!

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Your numbers suggest a setup rate of ~460k triangles per second ( 132ktpf * 3.5fps ). This may not be the answer you are looking for but here is some data that might interest you. I can render 129x129 grid heightfields w/o textures or lights ( ie. testing my LOD setup approach ) and I can get about 9.5 million triangles per second at 640x480 @ 32BPP 60HZ ( w/o VSYNC ) on a PIII 666 and a GeForce 256 SDR running DirectX 7 on Win98se. That equates to ~150k triangles / frame at 60 fps. I have a few suggestions that could vastly improve your performance.

1) Use vertex buffers.
2) Use tri strips if possible. ( Best throughput )
3) Minimize number of API calls
4) Optimize for the HWs vertex cache.

Best of luck,
himh

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Neat, thanks. I''m gonna try some more stuff tonight, I think that I just did some really hackish coding... Seems like I should get better FPS even though 130k is a lot of triangles. I am currently just doing:


// Render the map as triangles, shaded based on height.
void renderTriangles()
{
int numTriangles = 0;

glColor3f(1.0, 1.0, 1.0);

int x = 0, z = 0;

while(z < TERRAIN_HEIGHT)
{
for(x = 0; x < TERRAIN_WIDTH; x++)
{
glBegin(GL_TRIANGLES);
float temp = (float) heightMap[z][x] / 255.0;
glColor3f(temp + 0.2, temp + 0.2, temp + 0.2);

glVertex3f(MAP_SCALE * x, HEIGHT_SCALE * heightMap[z][x], MAP_SCALE * z);

temp = (float) heightMap[z+1][x] / 255.0;
glColor3f(temp + 0.2, temp + 0.2, temp + 0.2);

glVertex3f(MAP_SCALE * x, HEIGHT_SCALE * heightMap[z+1][x], MAP_SCALE * (z+1));

temp = (float) heightMap[z][x+1] / 255.0;
glColor3f(temp + 0.2, temp + 0.2, temp + 0.2);

glVertex3f(MAP_SCALE * (x+1), HEIGHT_SCALE * heightMap[z][x+1], MAP_SCALE * z);
glEnd();

numTriangles++;

glBegin(GL_TRIANGLES);
temp = (float) heightMap[z][x+1] / 255.0;
glColor3f(temp + 0.2, temp + 0.2, temp + 0.2);

glVertex3f(MAP_SCALE * (x+1), HEIGHT_SCALE * heightMap[z][x+1], MAP_SCALE * z);

temp = (float) heightMap[z+1][x] / 255.0;
glColor3f(temp + 0.2, temp + 0.2, temp + 0.2);

glVertex3f(MAP_SCALE * x, HEIGHT_SCALE * heightMap[z+1][x], MAP_SCALE * (z+1));

temp = (float) heightMap[z+1][x+1] / 255.0;
glColor3f(temp + 0.2, temp + 0.2, temp + 0.2);

glVertex3f(MAP_SCALE * (x+1), HEIGHT_SCALE * heightMap[z+1][x+1], MAP_SCALE * (z+1));
glEnd();

numTriangles++;
}

z++;
}

cout << endl;
cout << "Number of Triangles: " << numTriangles;
}

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OH! And before calling say, t.renderTriangles(), I was calling camera.use() which I defined as the following:


// Use this Eye for viewing.
void use()
{
glRotatef(-pitch, 1.0, 0.0, 0.0);
glRotatef(heading + 180, 0.0, 1.0, 0.0);
glTranslatef(-x, -y, -z);

reportEye();
}


That is done with no culling at all, and I suppose it would end up transformind all 130K triangles... Thanks guys, I really appreciate the help. Any more pointers would be gr8!

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"PS - How many triangles are displayed in an average frame in popular games now? Is there a way to see this?"

quake3/UT do about 10000 a frame

hints
cull triangles from your scene (quadtree or octree)
- speedup of 2-10x
use tri strips
- speedup of 2x

u prolly want to precalulate all this beforehand
(MAP_SCALE * (x+1), HEIGHT_SCALE * heightMap[z][x+1], MAP_SCALE * z);
-speedup bugger all


http://members.xoom.com/myBollux

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