glStencilMask

glStencilMask: man4/glStencilMask.xml

glStencilMask controls the writing of individual bits in the stencil planes. The least significant n bits of mask, where n is the number of bits in the stencil buffer, specify a mask. Where a 1 appears in the mask, it's possible to write to the corresponding bit in the stencil buffer. Where a 0 appears, the corresponding bit is write-protected. Initially, all bits are enabled for writing. There can be two separate mask writemasks; one affects back-facing polygons, and the other affects front-facing polygons as well as other non-polygon primitives. glStencilMask sets both front and back stencil writemasks to the same values. Use glStencilMaskSeparate to set front and back stencil writemasks to different values.

glStencilMask is the same as calling glStencilMaskSeparate with face set to GL_FRONT_AND_BACK.