John Gresham wrote: > I think scrolling has been done in a mode 4 game on the SAM. > Defender has a scrolling landscape and looks to be mode 4. I > think it sometimes shifts the land at pixel-by-pixel > resolution when you move slowly.
The most you can move (using traditional "shift every byte" methods) in a single frame is about 1/4 of the screen (IIRC). Given that you need to move stuff around aswell, you'd probably only be able to scroll 2/3rds of the screen about every 15 frames (which should still be reasonably acceptable). Think of something like Blood Money or Wings Of Death, both for the Atari ST, where the screen moves quite slowly but the gameplay is still acceptable. > It looks like it's sometimes 2/3rds of the screen at times, > so I imagine Mode 4 scrolling can't be that slow??? Well things like Defender (I haven't seen the Sam version, but my memory of the game is of large blocks of single colour) cheat by only moving the edges. A bit like the old "Snake" game you get now on Nokia phones - since the mid-sections aren't moving you only need to draw the beginning and the end. My Big Scrolly Demo (on NVG, I believe) used this technique to draw a full-screen-height scrolltext. Cookie once showed me a demo of a neat routine that used screen switching to do 50fps parallax scrolling - very cool, since then all you need to do is draw the thing at the start of the level. Geoff ________________________________________________________________________ This email has been scanned for all viruses by the MessageLabs SkyScan service. For more information on a proactive anti-virus service working around the clock, around the globe, visit http://www.messagelabs.com ________________________________________________________________________
