CODEWITHSUNDEEP
opengl3dgpu
user2464424
user2464424

Reputation: 1616

Performance of GL_POINTS on modern hardware

Is there any difference in performance between drawing a scene with full triangles (GL_TRIANGLES) instead of just drawing their vertices (GL_POINTS), on modern hardware?

Where GL_POINTS is initialized like this:

glPointSize(1.0);
glDisable(GL_POINT_SMOOTH);

I have a somewhat low-end graphics card (9600gt) and drawing vertices-only can bring a 2x fps increase on certain sceneries. Not sure if it applies too on more recent gpus.

Upvotes: 4

Views: 2760

Answers (2)

user2464424
user2464424

Reputation: 1616

No, if the number of triangles is similar to the number of their shared vertices (considering the glDrawElements rendering command being used) in both modes the geometry-wise part of the rendering pipeline will be evaluated at roughly the same speed. The only benefit you can get from drawing GL_POINTS relies solely on the percentage of empty screen space you get from not drawing faces, thus only at fragment shader level.

Upvotes: 2

SigTerm
SigTerm

Reputation: 26409

2x fps increase on

You lose 98% of picture and get only 2x fps increase. That's not impressive. If you take into account that you should be able to easily render 300..500 fps on any decent hardware (with vsync disabled and minor optimizations), that's probably not worth it.

Is there any difference in performance between drawing a scene with full triangles (GL_TRIANGLES) instead of just drawing their vertices (GL_POINTS), on modern hardware?

Well, if your scene has a LOT of alpha-blending and very "heavy" pixel shaders, then, obviously, displaying scene as point cloud will speed things up, because there's less pixels to fill.

On other hand, this kind of "optimization" will be completely useless for any practical task. I mean, if you're using blending and shaders, you probably wouldn't want to display your scene as pointlist in the first place, unless you're doing some kind of debug render (using glPolygonMode), and in case of debug render, you'll probably turn shaders off (because shaded/lit point will be hard to see) and disable lighting.

Even if you're using point sprites as particles or something, I'd stick with triangles - they give more control and do not have maximum size limit (compared to point sprites).

I can display more objects?

If you want more objects, you should probably try to optimzie things elsewhere first. If you stop trying to draw invisible objects (outside of field of view, etc), that'll be a start that can improve performance.

you have a mesh which is very far away from the camera. 1 million triangles and you know it is always in view. At this density ratio, triangles can't be bigger than a pixel,

When triangles are smaller than a pixel, and there are many of them, your mesh start looking like garbage and turns into pixelated mess of points. It will be ugly. Roughly same effect as when you disable mippimapping and texture filters and then render checkboard pattern. Using points instead of triangles might even aggravate effect.

: If you have 1mil triangle mesh that is always visible, you already need different kind of optimization. Reduce number of triangles (level of detail, dynamic tesselation or some solution that can simplify geometry on the fly), use bump mapping(maybe parallax mapping) to simulate extra geometry details that aren't even here, or even turn it into static background or a sprite. That'll work much better. Trying to render it using points will simply make it look ugly.

Upvotes: 4

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