Messages from Usenet group comp.lang.idl-pvwave, compiled by Paulo Penteado
Question about polygons in object graphics
I am trying to convert some direct graphics 3-D rendering programs to object graphics, and I am very low on the object graphics learning curve. For simplicity in my education at this point I generate a set of triangles that form a 3-D surface mesh. The data consists of 3 lists of the x, y, and z-coordinates of each vertex, and a (4 x n_triangles) array 'tri' of indices that define the triangles. These are set up in the manner used by POLYSHADE, and I can successfully plot the surface, i.e. image3 = POLYSHADE(x, y, z, tri, /T3D) after setting up the 3-D transform, etc. The documentation for the IDLgrPolygon object gives the impression that it takes polygon data in the same format, i.e., surface = OBJ_NEW('IDLgrPolygon', x, y, z, POLYGONS = tri) However, when I try to render the surface, I get a blank (white) window. I have tried adding triangles one at a time omitting the POLYGONS keyword. This works only when I transpose the coordinate array from what the documentation indicates, which then renders an incorrect (black) triangle. The possible explanations that I have come up with for this behavior (in order of highest to lowest probability) are: 1. I'm doing something wrong. a. Colors all set to white? b. Vertices in wrong order? c. I don't have a clue what I'm doing and will never understand object graphics. 2. Documentation is incorrect. 3. There's a bug somewhere. Any help here would be greatly appreciated. I have tried a large number of possible permutations of parameters, etc. to no avail. I have not screamed in frustration yet, but I'm getting ready to. E-mail responses appreciated. Replace the AT in my e-mail address with the symbol of the same name. k-bowmanATtamu.edu Thanks, Ken Bowman