No Fragments Archive 10: Diskmags

home *** CD-ROM | disk | FTP | other *** search

/ No Fragments Archive 10: Diskmags / nf_archive_10.iso / MAGS / ST_USER / 1990 / USERNV90.MSA / TEXT_STOS.DOC < prev next >

Wrap

Text File | 1990-05-24 | 11.0 KB | 247 lines

SPRITE PATH DEFINER This month's STOS feature is devoted to Phil Lawson's utility for creating sprite paths to include in your own mega-blasting arcade games. Well, I've promised it for long enough, so now here it is. If you recall the articles from a couple of months back, you'll remember we discovered how to control the sprites by using an array, holding the X and Y coordinates of every position the sprite goes though. The Sprite Path Definer, (SPD), does a similar thing, except the actual starting position is the only real coordinate present. All the rest are offsets from the previous position. For example: Start pos = 100,100 If next values are 2 and 4, the actual coordinates will be 102 and 104. If the next two were 4 and -3, the coordinates would be (102+4,104-3) 106 and 101. The reason for this small alteration in storing the sprite positions is that it drastically reduces the amount of space needed to save the data on disk. I'm not going to start explaining the workings of 16-bit arithmetic, so you'll just have to believe me on this one. Anyway, enough of the waffle, let's get down to business. The easiest way for you to understand what each option does is for me to explain them in turn, so here goes. MENU 1 ¯¯¯¯ ¯ LOAD - Loads a previously saved set of sprite paths SAVE - Once you've created the sprite paths, it would be a shame if you were not able to save them. UNUSED - There are two of these, mainly because I designed the screen and then couldn't think of anything else to include. No doubt you'll have your own ideas of what these should be used for, so I've left them for you to alter the program and do with them what you will. (STOS owners only). SET X and SET Y - Several options require one or two parameters to be set. For example, if you wished to copy only a section of a path to the end of another one, you would set the X and Y values to the start and finish number of the section to copy, and then use the COPY X/Y TO END option. Each of the nine paths has its own unique X and Y values, which are automatically displayed whenever you select a new path. To increase the number, position the pointer over the required option and press the right mouse button. To decrease it press the left button. Notice that under each of the nine paths, selected by clicking in one of the boxes, is a 3-digit number. This is the number of coordinates that each path currently contains. This will range from 0, (meaning empty), to 999. When trying to set the X and Y values, the numbers will whizz round pretty quickly. To allow a bit of "fine-tuning" to select a specific number, press the S key. To get things going at full speed again press F. RESET - This will reset everything to zero, including speed, x and y values and the contents of all the paths. Since selecting this by mistake would be very upsetting, especially after several hours work, both mouse buttons have to be pressed before the reset is performed. SELECT SPRITE - There's no point in defining paths if you cannot use your own sprites, therefore this option will allow you to choose one of the sprites currently stored in the sprite-bank. LOAD SPRITES - Quite obvious really. When the program is fully running, a lot of memory is taken up. Therefore try and keep the sprite banks to a minimum. One way of doing this is to create a second file containing only the main sprites you intend to use in the your game. LOAD BKGND .PI1 - Since most arcade games contain some form of terrain that the sprites are to pass over, it would be nice to make sure they're going where they're supposed to. This option will load a standard Degas PI1 picture, and can then be used to check on the movement of the sprite. LOAD BKGND .MBK - Exactly the same as the above option, except it will load a screen that has been compacted with the STOS accessory, COMPACT.ACB. If you're not intending to use the game in STOS, this option can be disabled. See STOS / OTHER. DELETE ONE PATH - Does just what it says. The current sprite path will be deleted. Take care though, once it's gone there's no way of getting it back again. To change the current path, position the pointer over one of the nine boxes at the top of the screen and press the left mouse button. The selected path number will be shown at the far right of the screen. DELETE ALL PATHS - Go on, try and guess what this one does. MENU 2 - Displays the second set of options available. BACKWARDS - If selected, the PLAY commands will result in the sprite going backwards. Can be used to give the illusion of two paths being defined by one set of data. Just have one type of sprite going forwards, and another going backwards. With a little work and thought, this can produce really amazing effects. FORWARDS - The normal way of moving a sprite. See BACKWARDS STOS / OTHER. Since the main program has been compiled, it follows that anyone can use it to define their own sprite paths. In this case, they may not have access to sprite banks and compressed picture screen. By selecting the other option they can turn off the STOS only options. PLAY - Use this option to check the movement of a sprite along a previously defined path. Before using, seek the PLAY OPTIONS in menu 2. PLAY & PLOT - Just like PLAY, except each point the sprite passes through is plotted on the screen. SPEED - To closely check what the sprite is doing, change the value of speed. As with SET X and SET Y, this is achieved with the left and right mouse buttons. The speed value can range from 0 (fast) to 100 (zzzzz). QUIT - Back to the desktop. As with RESET, this need both mouse buttons to be pressed at the same time. MENU 2 ¯¯¯¯ ¯ DELETE 1 to X - Deletes the whole of the current path from the first position to the Xth position. All the ones from X onwards are moved down to fill the gap. DELETE X to END - Deletes everything from the Xth position to the end of the current path. KEEP X - Y - Everything apart from the data between X and Y is deleted. PLAY OPTIONS UNTIL MOUSEKEY - Will play the whole path until a mousekey is pressed or the end of the path is reached. FROM X to Y - Plays between X and Y only. UNTIL X VALUE - Plays from the beginning, (or end if BACKWARDS is selected) until the X value is reached. With all these play options, once the sprite has finished moving, the current X and Y coordinates of the sprite are displayed, along with the position number. By setting the SET X and SET Y values to numbers slightly lower and higher respectively, you can now examine the area of the path around where the sprite was stopped. BACKGROUND OPTIONS BACKGROUND ON - If a background picture has been loaded, it will be displayed. BACKGROUND OFF - Surprise, surprise. This option will stop any loaded pictures from being displayed. MENU 1 - Takes you back to the first set of options. COPY OPTIONS 1 to X - Will copy the first X amount of data from the current path to the path you next click on, which will be totally overwritten by the new data X to Y - Copies the data between X and Y from the current path to the one you next click. This option will also overwrite the original data held in the selected path. X/Y to END - Copies the data between X and Y to the end of the next selected path. This option is best used to produce complicated paths by joining together many smaller ones. Your best chance of becoming famliar with SPD is to actually play around with it, but some extra information may be of use later on. 1) When saving the path data to a file, the following format is used: The first four bytes are 11, 22, 33 and 44. This is used to identify a sprite path file when loading it back into SPD. The next byte is how many positions are defined in this path. The next four bytes are the actual starting position of the sprite, in hi-lo order. For instance, if these were 01, 04, 00 and 95, the start position can be found by: x = (01 * 256) + 04 = 260 y = (00 * 256) + 95 = 95 The remainder is taken up with the offset values for each of the sprite positions defined within this path. Note, if an offset value is greater than 127, treat it as a negative number. The way to calculate negatives is: if num > 127 then num = 256 - num All the above information, apart from the 11,22,33 and 44, is repeated for the whole nine paths. If any of these is empty, the "how many" value will be zero. To start using the program, first load your sprites. Non-STOS users will have to make do with the three I've included as part of the program. These are 8 by 8, 16 by 16 and 32 by 32 pixels respectively. You will now have to select which sprite to use. After choosing the SELECT SPRITE option, pressing the right mouse button will display the next sprite in the bank, while pressing the left button will display the previous one. To select a particualr sprite, make sure it is shown on the screen and press the return key. To define the path, click once on the DEFINE PATH option and the screen will clear. If a background picture has been loaded, and not turned off, it will now be displayed. The mouse pointer now changes into the image of the selected sprite and can be moved around the screen. To define a point press the left mouse button. Note, you cannot define another point in the same place as the last one. The top of the screen will show the current X and Y coordinates of the sprite along with how many points have been defined. Since trying to define a previously defined path would result in the original data being lost, you will have to press both mouse buttons at the same time when selecting the DEFINE option if the current path already contains data. Since large numbers are treated as being negative, don't try to move the sprite in large jumps across the screen. Around 10 pixels is most a sprite should move from one place to another, otherwise it will seem "jerky". When you've finished defining the path, press the right mouse button. Nine paths may not seem like very many, but few games have more. If you do need some extra ones though, try creating small ones and joining them together with the COPY X/Y to END option. It would be a simple matter to separate these when you load them into the game. =========================================================================== If any STOS users require the original Basic program, to either study or adapt to their own specific needs, please send a cheque for £2.00 (to cover postage, packing, cost of blank disc and wear & tear on a worn & torn disc drive), to: PHIL LAWSON 7, Eaglescliffe Close New Marske Redcar Cleveland TS11 8BB Please, do not include any other correspondance for the STOS column, since this must be addressed to the magazine. (We've got to keep those editors busy).