CAD-3D Animation file format

                                 by Tom Hudson



         This document is intended to give interested persons the
         ability to generate or read the animation data files used by
         the CAD-3D solid-modeling program.  The animation files were
         created to be as compact as possible, while including all the
         information necessary to animate a wireframe or solid object
         quickly.

                                  The Files.

         Each CAD-3D animation file is resolution-specific to run in
         either monochrome or low-resolution mode.  The coordinates
         are set to the appropriate resolution at the time of writing
         to reduce processing done by the animation program.  The
         normal way to use a CAD-3D animation file is to read the
         entire file into a single RAM data structure and then use
         pointers to scan through the data, plotting the objects to
         the screen.

         The animation file structure is useful for other
         applications, as well.  Since the animation images are stored
         as "frames", each frame can be processed as an independent
         image, and output to a printer or plotter for later use.  The
         nice thing about this capability is that the user could
         record a number of images in the animation file and run them
         all off onto a printer in a single operation later, with the
         computer automatically advancing the paper after each image
         is printed.

         Each image in the animation file is termed a "frame".  Within
         each frame is a list of faces or line segments that is to be
         plotted to reconstruct the 3-D object.  For solid objects
         (with hidden faces removed), these faces are furnished in
         order from the farthest face to the nearest face and plotted
         in this order.  In this way, the subsequent face plots erase
         the faces that are behind the face being plotted.

         Each line segment or face in a frame is plotted until a
         "frame" flag is found, at which time the program advances to
         the next frame, sheet of paper, etc.

         The file is structured as follows:

         WORD -- Animation resolution (0 -- 16-color low-res or 2 --
         monochrome)

         WORD -- Animation mode (0 -- Wireframe, 1 -- Hidden, 2 --
         Solid, 3 -- Outlined)












         16 WORDS -- Color palette for the animation sequence

         The remainder of the file is a structure that gives data for
         the various triangular faces in the image.  The structure
         repeats until the count flag is <= 0.  If the flag is zero,
         there are no more faces to draw in the current frame, and you
         can show the frame just drawn.  The next group of faces
         should be plotted on another screen in memory.  When that
         frame is drawn, it is shown and plotting begins on the
         original screen.  This repeats until the flag is -1,
         indicating the end of the animation file.

         BYTE -- Count flag, has the following values:

             0: New frame.  Clear screen and reread the count flag.

                          -1: End of animation file.

                          >0: A normal face to draw.

         BYTE -- Face color and line segment flags.  Low nybble
         contains color to use for drawing the face in color modes or
         0-15 for shading level in monochrome.  High nybble contains
         the line segment draw flags.  Bit 6 tells whether the first
         line segment is drawn, bit 5 tells whether the second line
         segment is drawn, and bit 4 tells whether the third line
         segment is drawn.

         In animation modes 1, 2 and 3, there are two WORDs at this
         point, the polygon minimum Y and maximum Y values for using
         line A to plot the polygons.  The first is POLYMINY, the
         second is POLYMAXY.  These values let you avoid having to
         find the minimum and maximum Y values yourself.  These values
         are not needed in wireframe mode and are not present.

         Now come the Vertices for the object, stored as eight WORDS
         as follows:

                                   VERTEX1 X
                                   VERTEX1 Y
                                   VERTEX2 X
                                   VERTEX2 Y
                                   VERTEX3 X
                                   VERTEX3 Y
                                   VERTEX1 X
                                   VERTEX1 Y

         The first line segment is VERTEX1-VERTEX2, the second line
         segment is VERTEX2-VERTEX3, and the third line segment is
         VERTEX3-VERTEX1.

         For wireframe objects, the last two points are unnecessary,
         but for solid objects, you can simply point to the first
         value and execute the polygon fill operation.  The last two
         values close the polygon by joining the last point to the











         first.




























































ace are edges.

             Bits 0-3:  Color of the face.  COLOR 1 is 1-7 (where