// StencilExt operates like stencil but with access to change the stencil action,
// value, and keepvalues.
//
// action: How to modify any stencil values of pixels that are touched by what's
// drawn in the stencil function.
//
// value: The new stencil value to use for pixels if the "replace" stencil action
// is used. Has no effect with other stencil actions. Must be between 0 and 255.
//
// keepvalues: True to preserve old stencil values of pixels, false to re-set
// every pixel's stencil value to 0 before executing the stencil function. Clear
// will also re-set all stencil values.
func StencilExt(stencil_func func(), action StencilAction, value int32, keepvalues bool) {
gl_state.writingToStencil = true
if !keepvalues {
gl.Clear(gl.STENCIL_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
}
if gl_state.currentCanvas != nil {
gl_state.currentCanvas.checkCreateStencil()
}
gl.Enable(gl.STENCIL_TEST)
gl.ColorMask(false, false, false, false)
gl.StencilFunc(gl.ALWAYS, int(value), 0xFF)
gl.StencilOp(gl.KEEP, gl.KEEP, gl.Enum(action))
stencil_func()
gl_state.writingToStencil = false
SetColorMask(states.back().colorMask)
SetStencilTest(states.back().stencilCompare, states.back().stencilTestValue)
}
// SetColorMask will set a mask for each r, g, b, and alpha component.
func SetColorMask(mask ColorMask) {
gl.ColorMask(mask.r, mask.g, mask.b, mask.a)
states.back().colorMask = mask
}