glStencilDecrement

glStencilDecrement is a function in the OpenGL graphics API. It is used to modify the stencil buffer, which is a separate buffer in the graphics pipeline that can be used for various rendering effects. Specifically, glStencilDecrement decreases the value of stencil buffer pixels that pass a stencil test.

The stencil buffer is often used for masking, which allows for selective rendering. For example, it can be used to render only specific regions of the screen or to create effects like reflections or shadows. When glStencilDecrement is used, the stencil value for a pixel is decremented by a specified amount if the stencil test for that pixel passes.

The function has two parameters: a stencil reference value and a stencil mask. The stencil reference value is compared against the current stencil buffer values. The stencil mask is used to selectively enable or disable the modification of individual bits within the stencil buffer. If a bit in the stencil mask is set to 1, the corresponding bit in the stencil buffer can be modified. If it's 0, the bit remains unchanged.

The effect of glStencilDecrement is to reduce the stencil buffer's intensity in areas where rendering occurs and passes the stencil test. This can be useful in algorithms that involve drawing multiple overlapping shapes or layers, where you might want to "consume" stencil buffer values as you draw. This contrasts with glStencilIncrement, which increases the stencil buffer value.