lighttroupe/luz

module DrawingStencilBuffer
    def with_stencil_buffer
        return yield if GL.IsEnabled(GL::STENCIL_TEST)

        GL.Enable(GL::STENCIL_TEST)
        yield
        GL.Disable(GL::STENCIL_TEST)
    end

    def with_stencil_buffer_for_writing(options = {})
        $next_stencil_buffer_index ||= 0

        # Select stencil buffer
        with_stencil_buffer {
            GL.StencilMask(1 << $next_stencil_buffer_index)

            # Clear stencil buffer
            GL.ClearStencil(0)
            GL.Clear(GL::STENCIL_BUFFER_BIT)

            GL.StencilOp(GL::REPLACE, GL::REPLACE, GL::REPLACE)
            GL.StencilFunc(GL::ALWAYS, 0x00000001, 0x00000001)

            # Don't write to color buffer
            GL.ColorMask(false, false, false, false)
            GL.DepthMask(false)

            with_alpha_test(options[:alpha_cutoff] || 0.0) {
                $next_stencil_buffer_index += 1
                yield
                $next_stencil_buffer_index -= 1
            }

            GL.DepthMask(true)
            GL.ColorMask(true, true, true, true)
            GL.StencilMask(0x00000000)
        }
    end

    def with_stencil_buffer_filter
        $next_stencil_buffer_index ||= 0

        with_stencil_buffer {
            GL.StencilMask(1 << $next_stencil_buffer_index)
            GL.StencilFunc(GL::EQUAL, 0x00000001, 0x00000001)

            $next_stencil_buffer_index += 1
            yield
            $next_stencil_buffer_index -= 1

            GL.StencilMask(0x00000000)
        }
    end
end