TrueType systems include a virtual machine that executes programs inside the font, processing the "hints" of the glyphs. These distort the control points which define the outline, with the intention that the rasterizer produce fewer undesirable features on the glyph. Each glyph's hinting program takes account of the size (in pixels) at which the glyph is to be displayed, as well as other less important factors of the display environment.