Method brightness_decrease

emu/src/cpu/hardware/lcd.rs:483–494

Brightness decrease (fade to black): result = color - color * evy / 16

(color: Color, evy: u8)

                let evy = self.registers.get_blend_brightness();
                Self::brightness_decrease(top_color, evy)
            }
            _ => top_color,
        }
    }

    /// Alpha blend two colors: result = (color1 * eva + color2 * evb) / 16
    fn alpha_blend(color1: Color, color2: Color, eva: u8, evb: u8) -> Color {
        let blend_component = |c1: u8, c2: u8| -> u8 {
            let result = (u16::from(c1) * u16::from(eva) + u16::from(c2) * u16::from(evb)) / 16;
            result.min(31) as u8
        };

        Color::from_rgb(
            blend_component(color1.red(), color2.red()),
            blend_component(color1.green(), color2.green()),