The WebGLRenderingContext.stencilOpSeparate() method of the WebGL API sets the front and/or back-facing stencil test actions.

The fail, zfail and zpass parameters accept all constants listed below.

face

A GLenum specifying whether the front and/or back stencil state is updated. The possible values are:

• gl.FRONT
• gl.BACK
• gl.FRONT_AND_BACK

fail

A GLenum specifying the function to use when the stencil test fails. The default value is gl.KEEP.

zfail

A GLenum specifying the function to use when the stencil test passes, but the depth test fails. The default value is gl.KEEP.

zpass

A GLenum specifying the function to use when both the stencil test and the depth test pass, or when the stencil test passes and there is no depth buffer or depth testing is disabled. The default value is gl.KEEP.

None (undefined).

gl.KEEP

Keeps the current value.

gl.ZERO

Sets the stencil buffer value to 0.

gl.REPLACE

Sets the stencil buffer value to the reference value as specified by WebGLRenderingContext.stencilFunc().

gl.INCR

Increments the current stencil buffer value. Clamps to the maximum representable unsigned value.

gl.INCR_WRAP

Increments the current stencil buffer value. Wraps stencil buffer value to zero when incrementing the maximum representable unsigned value.

gl.DECR

Decrements the current stencil buffer value. Clamps to 0.

gl.DECR_WRAP

Decrements the current stencil buffer value. Wraps stencil buffer value to the maximum representable unsigned value when decrementing a stencil buffer value of 0.

gl.INVERT

Inverts the current stencil buffer value bitwise.

The stencil testing is disabled by default. To enable or disable stencil testing, use the enable() and disable() methods with the argument gl.STENCIL_TEST.

gl.enable(gl.STENCIL_TEST);
gl.stencilOpSeparate(gl.FRONT, gl.INCR, gl.DECR, gl.INVERT);

To get the current information about stencil and depth pass or fail, query the following constants with getParameter().

gl.getParameter(gl.STENCIL_FAIL);
gl.getParameter(gl.STENCIL_PASS_DEPTH_PASS);
gl.getParameter(gl.STENCIL_PASS_DEPTH_FAIL);
gl.getParameter(gl.STENCIL_BACK_FAIL);
gl.getParameter(gl.STENCIL_BACK_PASS_DEPTH_PASS);
gl.getParameter(gl.STENCIL_BACK_PASS_DEPTH_FAIL);
gl.getParameter(gl.STENCIL_BITS);

• WebGLRenderingContext.stencilOp()
• WebGLRenderingContext.stencilFunc()
• WebGLRenderingContext.stencilFuncSeparate()
• WebGLRenderingContext.stencilMask()
• WebGLRenderingContext.stencilMaskSeparate()