Clip planes and shader materials

[Rusty Rooster]

Hi, I noticed that my custom clip planes, which work as expected when rendering EMT_SOLID and other engine default materials, don’t work anymore when using a material created from addHighLevelShaderMaterialFromFiles(). Nothing gets clipped.

Any idea what the issue might be?

I’m running opengl, can’t test it on D3D. Irrlicht Trunk although not the most up to date. Also verified that it’s not an issue with render targets.

[CuteAlien]

It uses glClipPlane which indeed only seems to be for the fixed function pipeline.
I found this discussion, maybe it helps: https://community.khronos.org/t/glclipp ... /108078/19

I haven't worked with those yet myself, so I would also have to experiment first.

If you only need depth clipping (probably not, but just in case...), you can use real planes. Like following code I used in some navigation node to clip the back half of circles away:

Code: Select all

// Create plane for clipping
const f32 clipSize = (TORUS_MAJOR_RADIUS+TORUS_MINOR_RADIUS)*2.1f;
scene::IMesh * clipMesh = SceneManager->getGeometryCreator()->createPlaneMesh(core::dimension2df(clipSize,clipSize));
if ( clipMesh )
{
	core::matrix4 m;
	m.setRotationDegrees(core::vector3df(-90.f, 0.f, 0.f) );
	meshManip->transform(clipMesh, m);

	// fully transparent but fills the z-buffer
	video::SMaterial& clipMaterial = clipMesh->getMeshBuffer(0)->getMaterial();
	clipMaterial.Lighting = false;
#if 1	// disable to see how the clip-plane looks like
	clipMaterial.MaterialType = video::EMT_TRANSPARENT_VERTEX_ALPHA;
	clipMaterial.ZWriteEnable = video::EZW_ON;
	meshManip->setVertexColorAlpha(clipMesh, 0);
#endif

	ClipNode = SceneManager->addMeshSceneNode(clipMesh, this, 0);
	clipMesh->drop();

        // Selector as the clipped away parts also have selectors which are now invisible and shouldn't be hit
	scene::ITriangleSelector* s = SceneManager->createTriangleSelector(clipMesh, ClipNode);
	ClipNode->setTriangleSelector(s);
	s->drop();

	ClipNode->setVisible(false);	// should never render itself, as we have to ensure it's rendered before handles, so we render it's mesh manually in render()
}

Obvious downside is that you can't easily reset this (it just fills the z-buffer).

[Rusty Rooster]

Thanks CuteAlien. Indeed, when using shaders one has to feed any clipping information to the gpu via the vertex shader:

Code: Select all

vec4 plane0 = vec4(1,1,0,0);
gl_ClipDistance[0] = dot(plane0, mWorld * gl_Vertex);
//this clips in world coordinates

Then in the program just call enableClipPlane(0,true)