"Undo" means "revoke an action". It's exactly this purpose we have Undo for. Suppose you'd like to try something you can't imagine the result of, or you'd like to test different parameters of a processing module: you have to save your data before. If the experiment failed, or else to set new parameters, you can retrieve them quickly and without loss. Like already mentioned under Temp, you need big RAM capacities for this feature which only can be achieved by RAM extensions. Therefore, Undo won't work on a basic C64. Also, Undo doesn't work on the VDC of a C128, for you need a RAM device for this function which only exists for REUs until now.
To activate Undo you change from whatever saver to the file requester (click on "Save" in the commands window), and there click unit RAM, as if you wanted to save a picture (which is indeed correct). If a REU is plugged in, you will be presented by two given file names: "Undo 4Bit" and "Undo Rendered". According to the picture memory you like to save, you may click the first name for the 32,000 bytes of the 4Bit memory, and the second name for the 9,500 bytes on the C64 screen (rendered by "Display" in "Screen Controls"). The RAM device will immediately react and keep your data.
"Undo Rendered" you will mainly need for picture masking (ldr.4Bit&Mask) and for trying different parameters. GoDot saves either the 8,000 bytes of the bitmap, the 1,000 bytes of the text RAM ($0400, hires colors), and 500 bytes color RAM (the lower 1,000 nibbles of the $D800 area, packed into bytes).
You load Undo like you load any picture. Even this activity works from almost any loader because it is performed by a RAM device.
Copyright © 1997, A. Dettke, Last Updated - 09/11/97