CM30075 Software Guide
CM30075 – software guide
This is a rough guide to equally rough software – comprising a library of functions to help you build up a ray caster. The library files are divided into families.
Type help <filename> to get MATLAB help for any library file. For example
> help Cam_canonical
will print a description of the file to the MATLAB console. Not all files contain embedded help (this is part of the roughness).
The demo family: examples of code in use
demo_camera
demo_wirecam
The Brep family: deals with objects
Brep_cylinder – makes a cylinder
Brep_fprintf – writes a Brep object to a file
Brep_fscanf – reads a Brep object from a file
The Brep file format is first for give vertex points inside [], then to give triangles that index to these points, again inside [], and then colour data for each triangle, inside []. Note each colour has five entries. The first three are diffuse colour coefficients used in local lighting computation. The last two are used in global lighting; the first specifies the fraction of globally reflected light returned in the “parent ray” direction, the second is the same but for refracted light – both greater than zero but less than 1. Call the first a2 and the second a3, then [a1 a2 a3] = [1 a2 a3]/(1+a2+a3) gives the ratio of local light, globally reflected and globally refracted light in the parent ray direction. This is not a good physical model, but is easy to code and use.
Example: plane.brep
[-0.5 -0.5 0
0.5 -0.5 0
0.5 0.5 0
-0.5 0.5 0
]
[ 1 2 4
3 4 2
]
[
1 1 1 1 0
1 1 1 1 0
]
Brep_move – transforms a Brep object by a given transform
Brep_nrm _ computes the normals at each triangle for a moved Brep object
Brep_wireframe – renders a Brep object as a wireframe in 2D,
which assumes the object has been projected
Brep_wireframe3D – renders a Brep object as a wireframe in 3D
The Cam family: deals with cameras
Cam_canonical – makes a canonical camera
Cam_move – moves the camera by the give transform
Cam_flen_set – sets the focal length
CamObj_project – projects a Brep object using the given camera
Cam_project – projects points x to give y
Cam_visualise – makes a 3D visualisation of a camera
The Trns family: deals with transforms
Trns_scale – scale
Trns_shift – shift (displacement)
Trns_xrot - turn about x axis by given radians
Trns_yrot - same
Trns_zrot – same, all use a right-handed coordinate system
The scene family: deals with whole scenes
scene_fscanf – reads a scene file
The scene file has the following format
The number of objects
A list of each objects by name, followed by some transform (use the identity transform if you do wish to leave the object where it is defined)
The camera pixels counts and window width, both in the X direction first.
The ambient lighting coefficients and the direction of the point light.
Example. Shadwscene.dat
2
plane.brep
Trns_scale( [6 4 1])*Trns_xrot( 70*pi/180 )*Trns_shift( [0 -0.5 4] );
cube.brep
Trns_shift( [0 0 -0.5] )*Trns_zrot(pi*30/180)*Trns_xrot( 70*pi/180 )*Trns_shift( [0.4 -0.5 4] );
256 256 1 1
0.3 0.3 0.3
1 0.5 -0.5
Other files
Other files exist to support, it is assumed reading these is sufficient. Please contact the author if this is not so.