Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!husc6!cmcl2!nrl-cmf!ames!ptsfa!well!adh From: adh@well.UUCP (Allen D. Hastings) Newsgroups: comp.sys.amiga Subject: Re: Interchange program for Sculpt 3D and Videoscape3D Message-ID: <4443@well.UUCP> Date: Sat, 14-Nov-87 04:36:47 EST Article-I.D.: well.4443 Posted: Sat Nov 14 04:36:47 1987 Date-Received: Sun, 15-Nov-87 18:00:35 EST Sender: adh@well.UUCP Organization: Whole Earth 'Lectronic Link, Sausalito, CA Lines: 124 Summary: Corrections concerning VideoScape 3D This posting is a response to a message by John Foust in which he explains some of the difficulties he had writing a conversion program for VideoScape 3D and Sculpt 3D object description files. While he brought up several good points, he also made several misleading statements about VideoScape 3D. For example, he complains that non-planar polygons are allowed by VideoScape. Many polygons with more than three vertices are bound to be slightly nonplanar to some extent, simply because their coordinates are not specified with infinite precision. If perfect planarity is desired, one can always construct objects out of only triangles. The fact that VideoScape allows up to 250 vertices per polygon simply gives additional flexibility and convenience to the object designer. (It is also important to note that VideoScape allows less than three vertices per polygon for creating lines and points. To make a starfield in Sculpt 3D, each star would have to be represented by tiny triangle!) >As for the problems of object size relativism, I came up against that wall, >too. Niether program has a "meter", so all coordinates are relative to >each other. For each scene, you determine the standard unit meter size. While it is true that "one unit" in the coordinate system of any 3D program can be interpreted as any actual distance, in VideoScape the convention is that one unit corresponds to one metric meter (a convenient unit for floating point representations of common objects). This means that objects such as those included with the program and on future library disks can all be used together in the same scenes without having to worry about rescaling any of them. >VideoScape will allow any number of polygons (or surface details) at a >given set of vertices. The surface details will be rendered in the order >of their description in the GEO file. The polygons - hmm - who knows. >Sculpt does wacky things when you've got two very nearly coincident >polygons, too. They aren't rendered quite right. > >Allen exploits this in the HouseAndYard file. The windows are two surface >details, not one. First a black square, then a blue one. The black square >is rendered, then the blue one, at the same endpoints. *But the blue >window is still surrounded by a black border.* Why? Actually, in that case the blue window is drawn first and then a black outline polygon is drawn around the window ("outline only" is one of the rendering modes for a polygon). Both of these are examples of surface details, which are a useful feature of VideoScape and allow it to avoid the confusion that Sculpt 3D suffers when one polygon is inside another. >What about the way VideoScape clips polygons? It uses a very crude method. >It first checks the centroid of the polygon. If the centroid is not >visible in the viewing window, then the polygon is not drawn. This statement is obviously false. If it were true, then when the camera panned around a scene, polygons would be disappearing along one edge as their centers went off the screen (which clearly does not happen). VideoScape "culls" polygons (what John meant by the term "clips") only when all of their vertices are behind the camera, or when they are "back faces" and point away from the camera. The latter condition allows one to paint each side of the same polygon with a different color (a unique ability among Amiga 3D programs as far as I know). > ...In other words, a Sculpt Painting mode >picture of a VideoScape scene looks much nicer than VideoScape. (Sculpt >Painting mode can render your unicycle in about three or four minutes, >compared to about a minute for VideoScape.) A scene rendered by VideoScape will look nicer (and still be drawn much faster) than a scene rendered by Sculpt 3D's painting mode when there are lots of colors in the scene, because VideoScape can use dithering to create more subtle shading than exists in Sculpt's computed pallette (this is especially true when Extra Halfbrite mode is used in VideoScape 1.10). Also, knowing the pallette in advance allows the use of IFF foreground and background paintings (another unique feature among 3D programs so far). >To me, the ultimate proof that most people have trouble with VideoScape is >the dearth of user-created objects. I expected to see objects uploaded and >shared between users within weeks of VideoScape's release. None of the Amiga 3D programs have done too well in this regard, and the problem is not a lack of objects, but a shortage of people who want to give out their creations. However, there are lots of user-created objects out there (some of the ones I've seen are incredibly complex, and I don't just mean Leo's), and it's only a matter of time before they are available in greater abundance. I have several hundred VideoScape objects now, many of which I plan to distribute on a library disk (disks?) shortly. > ...Allen Hastings stopped creating objects on graph paper >months ago when his friend Stuart Ferguson wrote this object editing >program. I'm afraid that is completely untrue. I have found very efficient ways of creating complex objects quickly using the techniques explained in the VideoScape manual. To make the Psycho-like haunted house in Halloween 3D, for example, I simply traced a few basic parts from a book (like a wall with a window, a roof section, etc.) and then put them all together like toy building blocks with the OCT utility, resulting in a complex object with very little work. In fact, if one uses see-through graph paper, it is easier and more accurate to trace the outline of an object from a diagram in a book than it is to "eyeball" it with the mouse (and there are no jaggies on the paper). I should point out, however, that Stuart's graphic object editor, Modeler 3D, is simple to use and quite powerful, and I'm sure I'll use it a lot when it's completed. > ...The selection of colors is completely arbitrary, unless >you consider that it may be ported to the IBM... Port VideoScape to the IBM? That's heresy for an Amiga fanatic like me! Actually, the color codes follow a very logical system in binary: the one's digit represents blue, the two's digit represents green, the four's digit represents red, and the eight's digit represents intensity. More significant bits are used to select various modes such as dull, shiny, luminous, etc. VideoScape 1.10 also renders semi-transparent polygons and various "special effect" polygons for things like spotlight beams or atmospheric shadows. Colors can be mixed to get 121 different choices (not counting the different rendering modes), and the pallette can be set by the user to any of the Amiga's 4096 colors. I hope this message clears things up a bit. Since serious Amiga graphics nuts should have both Sculpt 3D and VideoScape, I wish John luck with his object translation program. Sorry if you had trouble writing it, but nobody said it was going to be easy! - Allen Hastings