Contours
By the contours element the object surface display versus alpha component can be controlled in an active object . As the element's parameter a numeric parameter ranging between 0 and 1 is specified. Only those object surface portions are displayed the alpha component of which has a higher value than that of the parameter specified. The default setting of the contours is 0 , displaying the whole object. After setting to 1 no object portion is displayed. Usualy the contours element is set to approximately 0.5 . The contours are especially significant in connection with textures . Most frequently they are utilized with 2D objects as well as with static 2D objects . When drawing a texture, the object's surroundings are filled out with transparent color . This transparent color is black, its alpha component being 0. The alpha component of the other colors is 1. Thus it is secured that the texture portion having a transparent color will be suppressed (its alpha component being lower than the threshold level specified by the contours element). Only that picture portion having normal colors will be displayed. A texture can be smoothed by the smoothing of textures element. Such a texture contains also other alpha component values than 0 and 1. (This takes place on the contour transitions or on localities where color points and transparency points alternate).