NU128479@NDSUVM1.BITNET (02/07/91)
In reference to the C-64 interlace mode (by the way I have never seen the demo) I currently use this "interlace" technique in programming the 64. It works by setting up two bitmap screens in different 16K blocks (the VIC II can only see 16K at a time) and flipping between them every 1/60th second using interrupts. I find this interlace works very good in games. It allows you to display a background picture (one bitmap) and then an "action" bitmap in which you move objects. It is quick because in the "action" bmap you can easily erase and redraw objects without worrying about messing up the background. The bitmap screens are interlaced with each one visible an alternate 1/60th second. Five different foreground colors (if both bmaps are in multi-color mode) can be used in each 8X8 pixel block. Some flickering occurs, but this can be reduced by using compatible (non-contrasting) foreground and background colors. Sprites can also be used at the same time, but sprite data and pointers must be located in both blocks. Sixteen sprites can be displayed using the same technique as the interlaced bmaps, but this is a different subject. PS: I don't mean to confuse anyone. Steve Harter