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QRT Language Reference INTRODUCTION This document is a reference guide to the QRT command language. One section is devoted to each QRT command. All parameters to commands are listed. More information on QRT can be found in the User's Manual and Technical Reference Manual. The following table shows the syntax used in this document: TEXT MEANING EXAMPLE RANGE (x,y,z) floating pt vector (10, -20, 30.56) all (r,g,b) color value triple (0, .5, 1.00) 0 to 1 i an integer 12 0 to 127 n floating pt number -123.4 all p positive float 123.4 >0 string text string FOO_BAR ASCII Each section of this document contains one or more of the following sub-sections: Command Type : OPTIONAL or REQUIRED Parameters (required) : Lists required parameters Parameters (optional) : Lists optional parameters Optional Forms : Alternatives for parameter names. Ex: 'horiz' = 'horizon' means either can be used as a parameter name. Example : An example of the command (with all required parameters, but not necessarily all optional ones. Restrictions : Things not to do See also : Similar commands QRT has a free format input language, and parameters can be given in any order. QRT Misc. Setup Commands SKY: Command type: OPTIONAL The SKY command is used to specify the color of all rays that don't hit any other object. The sky is black by default. The sky color at the zenith (up), and horizon can be specified, and QRT will blend the colors in between as smoothly as possible. In addition, dithering can be specified. Parameters (optional): zenith = (r,g,b) : the color of the zenith horiz = (r,g,b) : the color at the horizon dither = i : dithering Optional forms: 'horiz' = 'horizon' Example: SKY ( horiz = (0, 0, .6), zenith = (0, 0, .4), dither = 5 ) See also : GROUND GROUND: Command type: OPTIONAL QRT does not have a specific ground command. Instead, use a large parallelogram with an optional pattern. PARALLELOGRAM ( loc = (-10000, 0, -10000), v1 = ( 20000, 0, 0), v2 = ( 0, 0, 20000), pattern = PATTERN_OF_CHOICE ) It is also possible to use a VERY large sphere for the ground, which moves the horizon closer to the observer. This is advisable when rendering tall, reflecting objects. See also : PARALLELOGRAM, SPHERE FOC_LENGTH: Command type: OPTIONAL This sets the focal length of QRT's "camera". The default is 50, but it can be changed with this command. As with 35mm photography, larger numbers result in a 'telephoto' effect, and smaller numbers will result in wide angle (and distorted) views. As of QRT 1.5, focal length is no longer resolution dependent. Example: FOC_LENGTH = 70 Restrictions: 0 < FOC_LENGTH FIRST_SCAN: Command type: OPTIONAL This command is obsolete with QRT version 1.5. Use the X_RES and Y_RES options to the DEFAULT() command. See also : DEFAULT LAST_SCAN: Command type: OPTIONAL This command is also obsolete with QRT 1.5. See also : DEFAULT FILE_NAME: Command type: REQUIRED This is used to set the output file for QRT, which will be read by the post processor. The file name will be mapped to upper case. Some restrictions may arise from file naming conventions on specific computers. Example: FILE_NAME = QRT_IMAGE.RAW OBSERVER: Command type: REQUIRED OBSERVER tells QRT where the observer is located, and his direction of view. The view direction is specified by giving the coordinates he should look at. In addition, the observer UP vector may be given. This is, by default, (0,1,0). Parameters (required): loc = (x,y,z) : location of observer lookat = (x,y,z) : point of interest Parameters (optional): up = (x,y,z) : up vector Optional forms: 'loc' = 'pos' = 'location' = 'position' Example: OBSERVER ( loc = (0, 0, 0), lookat = (100, 0, 0) ) Restrictions: The observer cannot look in the direction of the up vector. 'lookat' cannot be equal to 'loc'. 'up' must have non-zero length. LAMP: Command type: OPTIONAL Lamps are sources of light in QRT. They can be placed anywhere, and emit any color and intensity of light. The ambient light value is the color of the lamp. The distance parameter is the minimum distance from the lamp that objects will be illuminated at full intensity. Most objects should be farther from the lamp than this value, or else they will be washed out. The radius parameter is ignored by this version of QRT, but may eventually be used to implement penumbral shadows. Parameters (required): loc = (x,y,z) : location of object dist = p : distance of max illumination Parameters (optional): amb = (r,g,b) : ambient light radius = p : radius Optional forms: 'loc' = 'pos' = 'location' = 'position' Example: LAMP ( loc = (12,34,56), radius = 123.4, ) QRT Primitive Types SPHERE: Command type: OPTIONAL SPHERE creates a sphere with a given location, radius, and surface characteristics. Parameters (required): loc = (x,y,z) : location of object radius = p : radius Parameters (optional): name = string : name for object pattern = string : pattern name to attach remove = string : pattern to cut out amb = (r,g,b) : ambient light diff = (r,g,b) : diffuse reflection trans = (r,g,b) : transmission density = (r,g,b) : light attenuation mirror = (r,g,b) : mirror reflection fuzz = i : currently unused index = p : index of refraction dither = i : dithering sreflect = p : Phong specular refl. coeff. reflect = p : percent specular reflection Optional forms: 'loc' = 'pos' = 'location' = 'position' Example: SPHERE ( loc = (100, 100, 50.234), radius = 123.4, diff = (1.00, .20, .20) ) PARALLELOGRAM: Command type: OPTIONAL This command creates a parallelogram with a given location, shape, and surface characteristics. Two vectors define the shape of the parallelogram (they need not be orthogonal). Parameters (required): loc = (x,y,z) : location of object v1 = (x,y,z) : vector for side one v2 = (x,y,z) : vector for side two Parameters (optional): name = string : name for object pattern = string : pattern name to attach remove = string : pattern to cut out amb = (r,g,b) : ambient light diff = (r,g,b) : diffuse reflection trans = (r,g,b) : transmission density = (r,g,b) : light attenuation mirror = (r,g,b) : mirror reflection fuzz = i : currently unused index = p : index of refraction dither = i : dithering sreflect = p : Phong specular refl. coeff. reflect = p : percent specular reflection Optional forms: 'loc' = 'pos' = 'location' = 'position' 'vect1' = 'v1' 'vect2' = 'v2' Example: PARALLELOGRAM ( loc = (10, 20, 50), vect1 = (20, 0, 0), vect2 = ( 0, 0, 50), diff = (0, .90, .20) ) TRIANGLE: Command type: OPTIONAL The TRIANGLE command (similar to PARALLELOGRAM) creates a triangle shape. Two vectors define the sides of the triangle. Parameters (required): loc = (x,y,z) : location of object v1 = (x,y,z) : vector for side one v2 = (x,y,z) : vector for side two Parameters (optional): name = string : name for object pattern = string : pattern name to attach remove = string : pattern to cut out amb = (r,g,b) : ambient light diff = (r,g,b) : diffuse reflection trans = (r,g,b) : transmission density = (r,g,b) : light attenuation mirror = (r,g,b) : mirror reflection fuzz = i : currently unused index = p : index of refraction dither = i : dithering sreflect = p : Phong specular refl. coeff. reflect = p : percent specular reflection Optional forms: 'loc' = 'pos' = 'location' = 'position' 'vect1' = 'v1' 'vect2' = 'v2' Example: TRIANGLE ( loc = (52, 21, 50), vect1 = (10, 5, 0), vect2 = ( 0, 8, 20), diff = ( 0, 0, 0), mirror = ( 1, 1, 1) ); RING: Command type: OPTIONAL RING creates a ring (annulus), which is a circle with a smaller circle cut out of it. If the inner radius is zero, the ring will be a simple circle. Two vectors define the plane of the annulus, as with RING and PARALLELOGRAM. Parameters (required): loc = (x,y,z) : location of object v1 = (x,y,z) : vector one v2 = (x,y,z) : vector two rad_1 = p : inner radius rad_2 = p : outer radius Parameters (optional): name = string : name for object pattern = string : pattern name to attach remove = string : pattern to cut out amb = (r,g,b) : ambient light diff = (r,g,b) : diffuse reflection trans = (r,g,b) : transmission density = (r,g,b) : light attenuation mirror = (r,g,b) : mirror reflection fuzz = i : currently unused index = p : index of refraction dither = i : dithering sreflect = p : Phong specular refl. coeff. reflect = p : percent specular reflection Optional forms: 'loc' = 'pos' = 'location' = 'position' 'vect1' = 'v1' 'vect2' = 'v2' Example: RING ( loc = (52, 21, 50), v1 = (10, 5, 0), v2 = ( 0, 8, 20), rad_1 = 10, rad_2 = 20, ) Restrictions: 0 < rad_1 < rad_2 QUADRATIC: Command type: OPTIONAL This command creates a quadratic surface given by the equation: 2 2 2 a x + b y + c z = d The coefficients a,b,c and d can be specified. This primitive can be used to create cylinders, cones, oblong spheroids, etc. Several min and max parameters specify the maximum extents of the surface. Parameters (required): loc = (x,y,z) : location of object a = n b = n c = n d = n xmax = n xmin = n ymax = n ymin = n zmax = n zmin = n Parameters (optional): name = string : name for object pattern = string : pattern name to attach remove = string : pattern to cut out amb = (r,g,b) : ambient light diff = (r,g,b) : diffuse reflection trans = (r,g,b) : transmission density = (r,g,b) : light attenuation mirror = (r,g,b) : mirror reflection fuzz = i : currently unused index = p : index of refraction dither = i : dithering sreflect = p : Phong specular refl. coeff. reflect = p : percent specular reflection Optional forms: 'loc' = 'pos' = 'location' = 'position' Example: { ** vertical cylinder ** } QUADRATIC ( loc = (57, 21.2, 0), a = 1, b = 0, c = 1, d = 100 ); Restrictions: a != 0 or b != 0 or c != 0 Patterned Surfaces PATTERN: Command type: OPTIONAL This command creates a pattern definition which can be attached to any primitive object. A pattern is a two dimensional array than can be mapped to the surface of any primitive. Patterns must be defined before they are used. The PATTERN keyword serves two functions: to create a pattern definition, and to attach this definition to a primitive. The correct meaning is found by context: if the PATTERN keyword appears in a primitive definition followed by a name, it is assumed to refer to a predefined pattern. However, if PATTERN occurs outside any primitive definition, it is assumed to be a pattern definition. If all the pattern definitions are grouped at the top of the file, they will always be defined before they are used. A pattern is defined by giving it a size, a name, and one or more sub-pattern definitions. There are currently three types of sub-patterns: CIRCLE, RECTANGLE, and POLYGON. The sub-pattern list can be of any length (although long lists will slow the ray tracer), and can use several of each type of sub-pattern primitive. The X and Y size parameters specify the size of the pattern; the pattern will be repeated over the surface of an object each X or Y units in the indicated direction. These size units are arbitrary, since the pattern can be given a new size when attached to an object. In each sub-pattern, any object surface characteristics can be specified. If a given ray hits this sub-pattern, the surface will be colored as indicated. If it does not hit any sub pattern in the list, the objects default surface characteristics will be used. The example below defines a red-checkered pattern. The background color of the object to which this pattern is attached will determine the color of the other checker box in the pattern. Parameters (required): name = string : name for pattern x_size = p : x size of pattern y_size = p : y size of pattern Parameters (optional): CIRCLE = circle_defn : CIRCLE sub-pattern - see reference for CIRCLE RECTANGLE = rect_defn : RECTANGLE sub-pattern - see reference for RECTANGLE POLYGON = poly_defn : POLYGON sub-pattern - see reference for POLYGON. Example: PATTERN ( x_size = 16, y_size = 16, name = CHECK, RECTANGLE ( start_x = 0, start_y = 0, end_x = 8, end_y = 8, diff = (1.00, .20, .20); ) RECTANGLE ( start_x = 8, start_y = 8, end_x = 16, end_y = 16, diff = (1.00, .20, .20); ) ) This pattern can now be attached to an object as follows: SPHERE ( { ** sphere definition here ** } pattern = CHECK, xmult = .5, ymult = .5 ) Where the xmult and ymult parameters specify a new size for the pattern. Restrictions: At least one sub-pattern must appear. If two sub-patterns overlap in a region, the last one defined will be used in this region. See also : RECTANGLE, CIRCLE, PARALLELOGRAM RECTANGLE: Command type: OPTIONAL RECTANGLE is a type of sub-pattern. Parameters (required): start_x = p : start position for rectangle start_y = p end_x = p : end position for rectangle end_y = p Parameters (optional): amb = (r,g,b) : ambient light diff = (r,g,b) : diffuse reflection trans = (r,g,b) : transmission mirror = (r,g,b) : mirror reflection density = (r,g,b) : light attenuation fuzz = i : currently unused index = p : index of refraction dither = i : dithering sreflect = p : Phong specular refl. coeff. reflect = p : percent specular reflection Example: RECTANGLE ( start_x = 10, start_y = 12, end_x = 15, end_y = 15, diff = (1.00, .20, .20); ) Restrictions: RECTANGLE should be used only within a pattern definition. start_x < end_x start_y < end_y See also : PATTERN CIRCLE: Command type: OPTIONAL CIRCLE is a type of sub-pattern. Parameters (required): radius = p : radius Parameters (optional): amb = (r,g,b) : ambient light diff = (r,g,b) : diffuse reflection trans = (r,g,b) : transmission mirror = (r,g,b) : mirror reflection density = (r,g,b) : light attenuation fuzz = i : currently unused index = p : index of refraction dither = i : dithering sreflect = p : Phong specular refl. coeff. reflect = p : percent specular reflection Example: CIRCLE ( radius = 5, diff = (1.00, .20, .20); ) Restrictions: CIRCLE should be used only within a pattern definition. See also : PATTERN POLYGON: Command type: OPTIONAL POLYGON is a type of sub-pattern. Parameters (required): point = (x,y) : a point of the polygon. Any number of points can be defined, but at least four must be defined, with the last the same as the first. Parameters (optional): amb = (r,g,b) : ambient light diff = (r,g,b) : diffuse reflection trans = (r,g,b) : transmission mirror = (r,g,b) : mirror reflection density = (r,g,b) : light attenuation fuzz = i : currently unused index = p : index of refraction dither = i : dithering sreflect = p : Phong specular refl. coeff. reflect = p : percent specular reflection Example: POLYGON ( point = (0,0), { triangle pattern } point = (10, 0), point = (0, 10), point = (0,0) ) Restrictions: POLYGON should be used only within a pattern definition. The last point defined must be the same as the first. At least 4 points must appear, with the last the same as the first. See also : PATTERN Bounding Boxes BEGIN_BBOX: Command type: OPTIONAL The BEGIN_BBOX, END_BBOX commands form an enclosing bounding box around a group of objects (which may include other bounding boxes). An optional name must precede the bounding box begin statement. Bounding boxes cannot be given surface characteristics, since they are conceptual objects. Parameters (optional): name = string : name for box Example: name = SAMPLE_BBOX BEGIN_BBOX SPHERE (); { ** sphere here ** } TRIANGLE (); { ** triangle here ** } END_BBOX Restrictions: Must be paired with an END_BBOX statement. END_BBOX: Command type: OPTIONAL Companion command to BEGIN_BBOX. Example: name = SAMPLE_BBOX BEGIN_BBOX SPHERE (); { ** sphere here ** } TRIANGLE (); { ** triangle here ** } END_BBOX Restrictions: Must be paired with a BEGIN_BBOX statement. Instances BEGIN_INSTANCES: Command type: OPTIONAL Several primitives may be grouped into an 'instance', and this group can easily be placed in several locations. In addition, it can be resized. All instance definitions must be placed within the BEGIN_INSTANCES and END_INSTANCES statements; only one set of these statements is allowed. A group of objects must be placed in a BBOX, and this BBOX must be given a name. In the following example, three objects are defined: OBJECT_1, SUB_OBJECT_1, and OBJECT_2. Any inclusion of OBJECT_1 will implicitly include SUB_OBJECT_1, but not OBJECT_2. Any arbitrary object tree can be included. Referring to a node will include the sub-tree rooted at that node. Example: BEGIN_INSTANCES NAME = OBJECT_1 BEGIN_BBOX { ** some primitives here ** } NAME = SUB_OBJECT_1 BEGIN_BBOX { ** some more primitives here ** } END_BBOX END_BBOX NAME = OBJECT_2 BEGIN_BBOX { ** more primitives ** } END_BBOX END_INSTANCES Restrictions: There can be only one BEGIN_INSTANCES statement. There must be a matching END_INSTANCES statement. See also: END_INSTANCES, INSTANCE_OF END_INSTANCES: Command type : OPTIONAL This command specifies the end of the instance tree. Any primitive after the END_INSTANCES statement are actually displayed as part of the image. Restrictions: There can be only one END_INSTANCES statement. See Also: BEGIN_INSTANCES, INSTANCE_OF INSTANCE_OF: Command type: OPTIONAL After an instance tree is defined with the BEGIN_INSTANCES, END_INSTANCES command pair, parts of the tree can be referred to with the INSTANCE_OF statement. This actually puts the sub-tree in the image. You must specify the name of the root of the sub-tree. The original instance should be defined relative to (0,0,0), and the location parameter specifies where the new copy will go. Parameters (required): name = string : name of sub-tree loc = (x,y,z) : location for instance Parameters (optional): scale = (x,y,z) : scale factor Example: INSTANCE_OF ( name = OBJECT_1, loc = (100.23, 20.23, 45.678), scale = (.5, .5, .5) ) Optional forms: 'loc' = 'pos' = 'location' = 'position' Restrictions: All scale factor entries should be greater than zero. If the scale factor entries are unequal, some primitives in the instance will not be affected correctly. For example, a SPHERE will remain round if scaled by (1,2,3), not change to a QUADRATIC spheroid. See also : BEGIN_INSTANCES, END_INSTANCES Setting Defaults DEFAULT: Command type: OPTIONAL QRT sets certain defaults for the color attributes of a surface. The standard default is for a white, non reflective, non shiny, non transparent surface with a medium amount of dithering. These defaults can be changed with the DEFAULT command. More than one DEFAULT command can be included, in which case each one affects all primitives after it and before the next DEFAULT or the end of the file. In addition to new surface characteristics, the NO_SHADOW keyword instructs QRT not to compute shadow information for the scene. This can decrease image generation time at the expense of image quality. X and Y resolution and image aspect ratio can be set in the DEFAULT command. If they are set more than once, the values from the last DEFAULT command are taken. The aspect ratio for any monitor can be determined as follows: aspect ratio = (XR/XD)/(YR/YD) where: XR = X resolution of monitor XD = width of monitor in arbitrary units YR = Y resolution of monitor YD = height length of monitor in arbitrary units Parameters (optional): no_shadow : QRT will not compute shadow information threshold = p : QRT will stop tracing reflected or transmitted rays when they reach this percent of their original intensity. x_res = p : X image resolution. Any command line arguments override this parameter. x_res = p : Y image resolution. Any command line arguments override this parameter. aspect = p : image aspect ratio. This is computer and resolution dependent. amb = (r,g,b) : ambient light diff = (r,g,b) : diffuse reflection trans = (r,g,b) : transmission density = (r,g,b) : light attenuation mirror = (r,g,b) : mirror reflection fuzz = i : currently unused index = p : index of refraction dither = i : dithering sreflect = p : Phong specular refl. coeff. reflect = p : percent specular reflection Example: DEFAULT ( no_shadow, { * no shadowing * } diff = (1, 0, 0) { * default = red objects * } x_res = 1280, { ** BIG image ** } y_res = 1024, aspect = .89 );