HP Workstation zx2000 OpenGL 1.1 Reference for HP-UX 11.x - Page 407

S glStencilOp GL_INCR Increments the current stencil buffer value. Clamps to the maximum representable unsigned value. GL_DECR Decrements the current stencil buffer value. Clamps to 0. GL_INVERT Bitwise inverts the current stencil buffer value. Stencil buffer values are treated as unsigned integers. When incremented and decremented, values are clamped to 0 and 2n - 1, where n is the value returned by querying GL_STENCIL_BITS. The other two arguments to glStencilOp specify stencil buffer actions that depend on whether subsequent depth buffer tests succeed (zpass) or fail (zfail) (see glDepthFunc). The actions are specified using the same six symbolic constants as fail. Note that zfail is ignored when there is no depth buffer, or when the depth buffer is not enabled. In these cases, fail and zpass specify stencil action when the stencil test fails and passes, respectively. Notes Initially the stencil test is disabled. If there is no stencil buffer, no stencil modification can occur and it is as if the stencil tests always pass, regardless of any call to glStencilOp. Errors • GL_INVALID_ENUM is generated if fail, zfail, or zpass is any value other than the six defined constant values. • GL_INVALID_OPERATION is generated if glStencilOp is executed between the execution of glBegin and the corresponding execution of glEnd. Associated Gets glGet with argument GL_STENCIL_FAIL glGet with argument GL_STENCIL_PASS_DEPTH_PASS glGet with argument GL_STENCIL_PASS_DEPTH_FAIL glGet with argument GL_STENCIL_BITS glIsEnabled with argument GL_STENCIL_TEST See Also glAlphaFunc, glBlendFunc, glDepthFunc, glEnable, glLogicOp, glStencilFunc Chapter 17 407