Applying clipping in the shader can be achieved with relative ease. By performing certain calculations, it is even possible to create a clipping area resembling a sphere, for instance. The simplest way to clip is at a plane perpendicular to the coordinate system. First, compute the world position of the pixel in the vertex shader:
worldPosition = modelMatrix * vec4( position, 1.0 );
In the fragment shader, prevent the rendering of the pixel if it exceeds your defined clipping limit:
if ( worldPosition.x > clippingLimitX ) {
discard;
}
However, this approach may result in leaving the mesh open along the clipping edge. To address this issue, utilize a stencil buffer. Reduce the stencil using a scene showing the backfaces and then increase it with a scene displaying the clipped front faces. Ensure that the materials used in these scenes are not visible by deactivating their color and depth write capabilities:
new THREE.ShaderMaterial( { colorWrite: false, depthWrite: false, ... } );
Employ the stencil to depict a plane positioned at the clipping planes' location. Subsequently, render the clipped front faces following the disabling of the stencil:
renderer.autoClear = false;
renderer.clear();
var gl = renderer.context;
renderer.state.setStencilTest( true );
renderer.state.setStencilFunc( gl.ALWAYS, 1, 0xff );
renderer.state.setStencilOp( gl.KEEP, gl.KEEP, gl.INCR );
renderer.render( backStencilScene, camera );
renderer.state.setStencilFunc( gl.ALWAYS, 1, 0xff );
renderer.state.setStencilOp( gl.KEEP, gl.KEEP, gl.DECR );
renderer.render( frontStencilScene, camera );
renderer.state.setStencilFunc( gl.EQUAL, 1, 0xff );
renderer.state.setStencilOp( gl.KEEP, gl.KEEP, gl.KEEP );
renderer.render( capsScene, camera );
renderer.state.setStencilTest( false );
renderer.render( scene, camera );
An interactive demo illustrating how to clip at multiple planes simultaneously can be found here:
The built-in three.js clipping planes were not employed in this demo since it necessitates rendering the stencil utilizing a shader to determine if a clipping plane is oriented towards or away from the camera, allowing for clipping only at planes facing the camera.