Face culling all faces that cannot be seen

Question

I'm working on a simple 3d game using the Processing Java environment. I want to optimise my code so I can draw many many 'objects' (the world is made up of many different shaped objects that live inside the volume of a cube) without the framerate dropping. How can I detect which faces cannot be seen and stop drawing them? I have tried this code:

pgl = (PJOGL) beginPGL();  
gl = pgl.gl.getGL2ES2();
gl.glEnable(GL.GL_CULL_FACE);
gl.glCullFace(GL.GL_BACK);

which does do backface culling but it is not all that I want. I want to stop rendering any face that the camera cannot see, i.e. inside faces etc.

The code used to draw the objects (just a simple cube for testing) is as follows:

    noFill();
    noStroke();
    noSmooth();
    push();
    lights();
    translate(this.x * this.size, this.y * this.size, this.z * this.size);
    beginShape(QUADS);
    texture(this.texture_image);
    vertex(-this.size / 2, -this.size / 2, this.size / 2, 0, 0);
    vertex( this.size / 2, -this.size / 2, this.size / 2, this.size / 2, 0);
    vertex( this.size / 2, this.size / 2, this.size / 2, this.size / 2, this.size / 2);
    vertex(-this.size / 2, this.size / 2, this.size / 2, 0, this.size / 2);

    // -Z "back" face
    vertex( this.size / 2, -this.size / 2, -this.size / 2, 0, 0);
    vertex(-this.size / 2, -this.size / 2, -this.size / 2, this.size / 2, 0);
    vertex(-this.size / 2, this.size / 2, -this.size / 2, this.size / 2, this.size / 2);
    vertex( this.size / 2, this.size / 2, -this.size / 2, 0, this.size / 2);

    // +Y "bottom" face
    vertex(-this.size / 2, this.size / 2, this.size / 2, 0, 0);
    vertex( this.size / 2, this.size / 2, this.size / 2, this.size / 2, 0);
    vertex( this.size / 2, this.size / 2, -this.size / 2, this.size / 2, this.size / 2);
    vertex(-this.size / 2, this.size / 2, -this.size / 2, 0, this.size / 2);

    // -Y "top" face
    vertex(-this.size / 2, -this.size / 2, -this.size / 2, 0, 0);
    vertex( this.size / 2, -this.size / 2, -this.size / 2, this.size / 2, 0);
    vertex( this.size / 2, -this.size / 2, this.size / 2, this.size / 2, this.size / 2);
    vertex(-this.size / 2, -this.size / 2, this.size / 2, 0, this.size / 2);

    // +X "right" face
    vertex( this.size / 2, -this.size / 2, this.size / 2, 0, 0);
    vertex( this.size / 2, -this.size / 2, -this.size / 2, this.size / 2, 0);
    vertex( this.size / 2, this.size / 2, -this.size / 2, this.size / 2, this.size / 2);
    vertex( this.size / 2, this.size / 2, this.size / 2, 0, this.size / 2);

    // -X "left" face
    vertex(-this.size / 2, -this.size / 2, -this.size / 2, 0, 0);
    vertex(-this.size / 2, -this.size / 2, this.size / 2, this.size / 2, 0);
    vertex(-this.size / 2, this.size / 2, this.size / 2, this.size / 2, this.size / 2);
    vertex(-this.size / 2, this.size / 2, -this.size / 2, 0, this.size / 2);

    endShape();
    pop();

Sorry for the long code.

Thanks in advance.

In what specific way does the code you've shown fail to work? It looks like pretty typical back face culling. — DMGregory, Apr 16 '19 at 09:37
@DMGregory It works for back face culling but I want to stop rendering anything that the camera cannot see. I understand that this is a difficult task but was wondering if Processing/OGL had any inbuilt features to help with it. — Jachdich, Apr 16 '19 at 09:40
Are you talking about frustum culling? Occlusion culling? Or something else? What is an "inside face" if it's not already handled by back face culling? — DMGregory, Apr 16 '19 at 09:42
@DMGregory I have not heard of Occlusion or frustum culling, I'll look into it. By 'inside faces' I mean that if I have a 3x3x3 cube of the cubes, I don't want to render the inside one (although it needs to be there for other reasons) — Jachdich, Apr 16 '19 at 09:46
Ohhh, you're building your objects out of cube-shaped voxels? The usual solution there is to group them into chunks, pre-processed to contain only outside faces. When you say "it needs to be there for other reasons" that sounds like a detail you should explain in your question. It's unclear why a face that's not drawn needs to be submitted to the GPU at all. Maybe you're using a different definition of "be there" meaning something other than "included in the vertex buffer used for drawing"? — DMGregory, Apr 16 '19 at 09:59
@DMGregory (sorry for inactivity) that is pretty much what I meant, thank you. I'll check out that link — Jachdich, Apr 16 '19 at 11:17

score 0 · Answer 1 · answered Apr 16 '19 at 10:01

It not always beneficial to cull absolutely everything, not even in voxel games. Loading new geometry or dealing with faces as separate objects can really cost a lot of computational power, especially given how 3 of those sides gets culled by backface culling automatically 100% of the time.

What you could do instead is to render only what's roughly in front of the player and rendering everything starting from the players position and going outward. That way the blocks will obstruct everything coming after them and depth culling will kick in reducing the time spent in the fragment shader to close to zero.

You can combine that with instanced rendering (and possibly geometry buffers) and you'll get a pretty fast system

Face culling all faces that cannot be seen

1 Answers1