The Blender 2.66.1 texture painting "Normal" setting that @theluthier is speaking of around 10:42 in this video can be found in Blender 2.90 in the "Normal Falloff" panel:
The value set there determines how much the normal on a surface may deviate from your view direction in order to still receive paint. In other words it's the angle where the falloff begins with the color then becoming denser the more a surface point is pointing into your direction.