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GLSTENCILFUNC() GLSTENCILFUNC() NAME glStencilFunc - set function and reference value for stencil testing delim $$ C SPECIFICATION void glStencilFunc( GLenum func, GLint ref, GLuint mask ) PARAMETERS func Specifies the test function. Eight tokens are valid: GL_NEVER, GL_LESS, GL_LEQUAL, GL_GREATER, GL_GEQUAL, GL_EQUAL, GL_NOTEQUAL, and GL_ALWAYS. The initial value is GL_ALWAYS. ref Specifies the reference value for the stencil test. ref is clamped to the range [0,$2 sup n - 1$], where $n$ is the number of bitplanes in the stencil buffer. The initial value is 0. mask Specifies a mask that is ANDed with both the reference value and the stored stencil value when the test is done. The initial value is all 1's. DESCRIPTION Stenciling, like depth-buffering, enables and disables drawing on a per-pixel basis. You draw into the stencil planes using GL drawing primitives, then render geometry and images, using the stencil planes to mask out portions of the screen. Stenciling is typically used in multipass rendering algorithms to achieve special effects, such as de- cals, outlining, and constructive solid geometry rendering. The stencil test conditionally eliminates a pixel based on the outcome of a comparison between the reference value and the value in the sten- cil buffer. To enable and disable the test, call glEnable and glDis- able with argument GL_STENCIL_TEST. To specify actions based on the outcome of the stencil test, call glStencilOp. func is a symbolic constant that determines the stencil comparison function. It accepts one of eight values, shown in the following list. ref is an integer reference value that is used in the stencil compari- son. It is clamped to the range [0,$2 sup n - 1$], where $n$ is the number of bitplanes in the stencil buffer. mask is bitwise ANDed with both the reference value and the stored stencil value, with the ANDed values participating in the comparison. If stencil represents the value stored in the corresponding stencil buffer location, the following list shows the effect of each comparison function that can be specified by func. Only if the comparison suc- ceeds is the pixel passed through to the next stage in the rasteriza- tion process (see glStencilOp). All tests treat stencil values as un- signed integers in the range [0,$2 sup n - 1$], where $n$ is the number of bitplanes in the stencil buffer. The following values are accepted by func: GL_NEVER Always fails. GL_LESS Passes if ( ref & mask ) < ( stencil & mask ). GL_LEQUAL Passes if ( ref & mask ) <= ( stencil & mask ). GL_GREATER Passes if ( ref & mask ) > ( stencil & mask ). GL_GEQUAL Passes if ( ref & mask ) >= ( stencil & mask ). GL_EQUAL Passes if ( ref & mask ) = ( stencil & mask ). GL_NOTEQUAL Passes if ( ref & mask ) != ( stencil & mask ). GL_ALWAYS Always passes. 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 test always passes. ERRORS GL_INVALID_ENUM is generated if func is not one of the eight accepted values. GL_INVALID_OPERATION is generated if glStencilFunc is executed between the execution of glBegin and the corresponding execution of glEnd. ASSOCIATED GETS glGet with argument GL_STENCIL_FUNC glGet with argument GL_STENCIL_VALUE_MASK glGet with argument GL_STENCIL_REF glGet with argument GL_STENCIL_BITS glIsEnabled with argument GL_STENCIL_TEST SEE ALSO glAlphaFunc, glBlendFunc, glDepthFunc, glEnable, glIsEnabled, glLogi- cOp, glStencilOp GLSTENCILFUNC()
NAME | C SPECIFICATION | PARAMETERS | DESCRIPTION | NOTES | ERRORS | ASSOCIATED GETS | SEE ALSO
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