Plane Clipping

[Shadoh]

I've scoured the site, and can't find how to implement Plane Clipping, I need this to create water reflections. It's simple to implement via OpenGL, infact the commands are below, can it please be wrapped in Leadwerks?

 

A quick side-question, can we actually call OpenGL commands ourself?

 

double plane[4] = {0.0, 1.0, 0.0, 0.0}; //water at y=0
glEnable(GL_CLIP_PLANE0);
glClipPlane(GL_CLIP_PLANE0, plane);
RenderScene();
glDisable(GL_CLIP_PLANE0);

[Shadoh]

I just had a stroke of genius

 

What I'll do as a temporary solution is render the scene ONLY with the water plane, then when I render the reflection camera I'll remove any pixels with less depth than the plane.

 

Pretty crappy work-around, but at-least it'll let me get a screenshot up

[shadmar]

Yes you can use discard like that, but then you need to change all object shader in use (the ones that are supposed to be clipped), which makes water making with plane reflection difficult for general easy usage.

[Shadoh]

gah, Yes, just found that out the hard way lol, after several hours getting my shader right, I realised that I can't get the pixel behind the bit that gets masked out lol... back to the drawing-board.

[Shadoh]

Just FYI here's what I have so far, the map is LakeTumbleson. And has over 200,000 trees. I can't easily remove the glitchy spots in the water where the sky is cutting out the reflection, that is until PlaneClipping is added.

 

As you can see it's very much a W.I.P and me and my team-mate are keeping the game quiet until we're sure we're going to finish it, this is mainly just a test to see what we can do at this stage.

 

EDIT: Yes, there are trees in the water, the tree generation system still needs some fine tuning lol

[Josh]

Plane clipping is part of the fixed-function pipeline that was removed in OpenGL 4. It can be done in a shader, though, as discussed.

[Shadoh]

Thanks for the reply, I know you must be a busy guy. I found it, now just to figure out how to access the terrain shader.

 

Here's the post on OpenGL.org that helped me for anyone else out there needing to find out how to do this.

[shadmar]

I did something like this in 3.0 for the model shaders

 

vertex:

out vec3 clip_pos;
..
clip_pos = (entitymatrix*vec4(vertex_position, 1.0)).xyz;

 

frag:

in vec3 clip_pos;
uniform float water_height;
..
if (clip_pos.y < water_height) discard;

 

The thing is that you have to change all shaders that are in play or has the chance of being clipped, so making clipped workshop items etc will be a nightmare.