Triangles calculation in DebugHud

Hi,
How triangles are counted in DebugHud? I see that I have counted about 8 times more than it is in models. What could be the reason for this surplus?

More info, plz. Shadows, viewports, text, anything.
E.g. screenshot of Uhro window.

I found same problem some time ago. DebugHud always add its text triangles to summary triangles count. It adds about 10000 triangles if DebugHud is in DEBUGHUD_SHOW_ALL mode.

Sorry to reply this old post.
I am having the same question.

I have two terrains, each is constructed by a 65*65 heightmap.
So for each terrain, I expect 64 * 64 * 2 = 8192 triangles. Total would be ~16,000 triangles.
But I am seeing 61,559 triangles instead, about 4 times more!

Attached two screenshots.

Overview

image2062×1554 874 KB

Zoom In (you can count the size manually)

image2058×1552 1.37 MB

It looks to me that you have 64 x 64 quads per height map, so 128 x 128 triangles x 2. That puts you at ~33k. The rest is apparently taken up by the HUD text and logo.

Correct me if I am wrong, but 1 quad = 2 triangles, so 64 x 64 quads = 64 * 64 * 2 = 8192 triangles. Two terrains make it into ~16k. I think you double counted it.
Even by your calculation, the logo and HUD is making up the rest ~30k triangles which does not make any sense to me?

I did a simple test, just rotate the camera to the background and no terrain showing.
The base count of triangles ~11k.
This agrees with @ KonstantTom’s result

image2062×1558 248 KB

My bad. I misread your post and didn’t see that you multiplied by 2 before doubling (and yeah, if counting the triangles across, my formula should have been 128 x 64 x 2 = ~16K).

So, I did a test with an empty scene and got ~12k tris. Then I threw a model in and got 97k tris. However, that model in Blender is only 28k Tris… So, it looks like something is wrong. I never questioned it before

That’s interesting.
So basically for my case,
the display triangles / real triagnels = (62k - 12k) / 16k ~ 3 times;
For your case,
the display triangles / real triagnels = (97k - 12k) / 28k ~ 3 times;

A quick guess would be the calculation counted vertices instead of triangles.

But I took a quick look at the source code, could not find anything suspicious. For example, in D3D11Graphics.cpp or OGLGraphics.cpp, we can get the primitiveCount number.

static void GetD3DPrimitiveType(unsigned elementCount, PrimitiveType type, unsigned& primitiveCount,
    D3D_PRIMITIVE_TOPOLOGY& d3dPrimitiveType)
{
    switch (type)
    {
    case TRIANGLE_LIST:
        primitiveCount = elementCount / 3;
        d3dPrimitiveType = D3D_PRIMITIVE_TOPOLOGY_TRIANGLELIST;
        break;

    ...
    }
}

Anyway, I believe it should be just a mis-count somewhere, not mistakenly rendering more triangles than we need. So it should not impact the performance.

Note that in forward rendering, each per-pixel light will re-render the affected geometry. If you have an unlit scene there should be just a single pass.

For shadowed lights, there will be also shadow map pass, which renders even more triangles.

Ah! That explains it!
I do have 3 lights in the scene.
When I leave only one light there, the total triangle count is ~28k, exactly 16k + base 12k.

image2046×1556 490 KB

Thanks so much for pointing this out ! Lasse!
I am still learning all those computer graphics rendering techniques. I am writing a custom terrain class to dynamically create/destroy patches for a super large world.