Constant gl_utils::render::params::BLEND_FUNC_INVERT_COLOR

pub const BLEND_FUNC_INVERT_COLOR: Blend = glium::Blend{color:
                 glium::BlendingFunction::Addition{source:
                                                       glium::LinearBlendingFactor::OneMinusDestinationColor,
                                                   destination:
                                                       glium::LinearBlendingFactor::OneMinusSourceAlpha,},
             alpha: glium::BlendingFunction::Max,
             constant_value: (0.0, 0.0, 0.0, 0.0),}

Writing white source pixels will invert the destination pixel. Color channels in the texture should all be equal to the alpha channel (grayscale) so that 100% opaque regions are white and 100% transparent regions are black.