========================================================================== ____ ___ / / / / // / / / PLANET GENERATOR / / / / / / / / / ____ / / / BY: Russell Leighton ____ / / / \ \ \ / / / December 1987 \ \ \ / / / \ \ \ / / / \ \ \ / / / \ \ \/ / / \ \ \/ / / \ \/ / / \ \/ / / \/_/_/ \/_/_/ ========================================================================== Any comments? I can be reached at the following address: Russell Leighton 845 W. Newgrove Lancaster, CA 93534 This program has been released to the public domain and can be freely distributed. I only ask to be given credit for the long hours spent. Please include this file with the program and if any parts are used I would be interested in knowing about it. ========================================================================== This is version 1.0 and is therefore somewhat lean on user interface. There may be updates to come. If you have any suggestions I welcome them. *Note: To quit, use the "QUIT" menu option. Simply put, this program will map any IFF picture around a sphere (hence forth referred to as a planet). The planet is then shaded based on the location and size of a light source. The mapping is done by equating constant latitude and longitude lines around the planet with constant horizontal and vertical lines on the map. The planet view is computed by applying a transformation based on inputted planet rotation angles. The result is displayed using HAM mode in lo-res interlaced resolution (320 x 400). The method used to shade the planet involves taking the cosine of the angle between the normal vector on the surface of the planet and the light source vector and multiplying each color component with the result. The actual color displayed is computed by attempting to get as close to the desired color as possible. This is accomplished in three steps. First a color is computed using the rules of HAM mode (see ROM Kernal manual). A difference factor is then computed and compared to the difference between the desired color and each color in the existing color palette (initially this color palette may be all black). If a color in the palette comes closer then that color is selected and the difference factor is again computed. If this difference exceeds a set maximum allowed difference then the desired color is added to the color palette (if room exists). In this manner the color palette is adaptive (you can override this feature by specifing the map color palette be used as the planet color palette). A color bar located in the screens title bar shows the planet color palette as it is updated. If the specified map is a HAM picture a further complexity develops. The program computes the map coordinates from the pixel location on the planet display. Therefore, the map coordinates will not progress in a linear fashion. For HAM pictures the RGB value at any location on the map is dependant on all preceding color values on a particular row and is not necessarily dependant on the last color value obtained from the map. Therefore, to obtain the correct RGB value for a location on the map all preceding color values must be taken into account. The overall effect is an increase in the amount of time required to generate the planet. The size of the light source has an effect on the "wrapping" of the lighted portion of the planet. If the light source is the same size as the planet then half the planet will be illuminated. If the light source is significantly larger than the planet (say 5 planet radii) then the planet will be illuminated around a noticably larger area. Likewise, if the light source is smaller than the planet the illumination will cover less than half. Both the planet rotation and the light source position are specified in terms of rotations about the three axes, x, y, and z. Counterclockwise rotation is positive and clockwise is negative. These angles can be specified in any order. The resulting rotations are very dependant on this order of input. I could try to explain how the transformation is accomplished, but I'm lazy so I recommend just trying some different angles to get a feel for how it works. I suggest using the same angles while changing the order. Currently this program can only be run from the CLI and takes the following form: planet [filename] [-r -px -py -pz -lx -ly -lz -s -f -h] The arguments are optional and may or may not require numerical input. A filename may be supplied for the planet map. This file must be an IFF picture (form ILBM) and may be in any mode or mixture of modes (LORES, HIRES, LACE, HAM). If no filename is given then the map is assumed to be planet.map (which must be present). The radius of the planet (argument -r) is specified in number of pixels. If the radius is not input it is assumed to be 180 pixels. The planet rotation angles (arguments -px, -py, -pz) are specified in degrees. If any of these angles are not specified they are assumed to be 0. Likewise, if the angles for the light source position (arguments -lx, -ly, -lz) are not input they are assumed to be 0. The radius of the light source (argument -s) is given in terms of the planet radius. A value of 1.0 indicates that the light source is the same size as the planet. This is the default value. If you require the color map of the planet be the same as the map include the -f argument. This option is useful for those occasions when successive planets are generated from the same map and they require the same color palette (this is required by some animation routines). This argument does not require a numerical input. If it is not included then the planet color palette is adaptive and will depend on the values specified for the other arguments. The maximum allowable difference can be specified with the -h argument. The hard upper limit for this value is 45 (the difference factor between white and black) and hard lower limit is 0 (somewhat rediculous since this would result in every computed color value failing the final test and being added to the palette). The default value for this argument is 6. An example follows: planet fractal.map -r 120 -pz 30 -py 20 -lx -30 -ly 45 -h 12 -s 2.0 -f If you need to be reminded of the optional arguments just type the following: planet ? I have had very good success with a variety of pictures ranging from paintings to digitized pictures. I hope that this program provides some insight into programming with graphics on the Amiga. A lot of time was spent trying to get HAM pictures to process properly and I feel that those parts of the program could be very useful.