The WebGLRenderingContext.stencilFunc() method of the WebGL API sets the front and back function and reference value for stencil testing.

Stenciling enables and disables drawing on a per-pixel basis. It is typically used in multipass rendering to achieve special effects.

func

A GLenum specifying the test function. The default function is gl.ALWAYS. The possible values are:

• gl.NEVER: Never pass.
• gl.LESS: Pass if (ref & mask) < (stencil & mask).
• gl.EQUAL: Pass if (ref & mask) = (stencil & mask).
• gl.LEQUAL: Pass if (ref & mask) <= (stencil & mask).
• gl.GREATER: Pass if (ref & mask) > (stencil & mask).
• gl.NOTEQUAL: Pass if (ref & mask) !== (stencil & mask).
• gl.GEQUAL: Pass if (ref & mask) >= (stencil & mask).
• gl.ALWAYS: Always pass.

ref

A GLint specifying the reference value for the stencil test. This value is clamped to the range 0 to 2^n - 1 where n is the number of bitplanes in the stencil buffer. The default value is 0.

mask

A GLuint specifying a bit-wise mask that is used to AND the reference value and the stored stencil value when the test is done. The default value is all 1.

None (undefined).

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.stencilFunc(gl.LESS, 0, 0b1110011);

To get the current stencil function, reference value, or other stencil information, query the following constants with getParameter().

gl.getParameter(gl.STENCIL_FUNC);
gl.getParameter(gl.STENCIL_VALUE_MASK);
gl.getParameter(gl.STENCIL_REF);
gl.getParameter(gl.STENCIL_BACK_FUNC);
gl.getParameter(gl.STENCIL_BACK_VALUE_MASK);
gl.getParameter(gl.STENCIL_BACK_REF);
gl.getParameter(gl.STENCIL_BITS);

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