Hi whoever you are, SAM Graphics,
Question 1, Derek Morgan sells a program (Pseudo Color) which allows 256 colour VGA screens to be seen on the SAM. The program was written by Dylan Hall from Australia and the result is rather bloody amazing! You do need an RGB output to be able to see the screens properly (monitor or TV RGB input work fine). What the program does is interlace three screens. Why three screens? Red, Green and Blue are extracted from the VGA picture leaving a screen with only the red component etc. By dithering the RGB screens you get a brilliant effect, ok it does flicker a little, but the general effect is awesome. And since the SAM is only swapping screens it costs no processor time whatsoever. Derek also has five or so demo disks filled with pictures grabbed using the pseudo color program. Pseudo Color contains a disk image for the PC which contains a number of shareware image processing programs (Alchemy, Piclab plus a screen thief) and a batch routine to make the whole thing work perfectly simple, I was impressed. Dylan asked me if I could improve the pics using lineinterrupts, but I wasn't sure what he meant until Robert van der Veeke came up with an idea involving setting the red green and blue per line allowing a full 16 levels per colour instead of the current 5 levels (5 red, 5 green, 5 blue + black), but the effect is more flicker. What Dylan was doing was constantly swapping screens in a machine code loop, I pointed out to him that this was rather pointless (the result was a shearing effect) and wrote a little basic program to simply DISPLAY the screens with a PAUSE 1 in between. The result is a stiller screen. Question 2. The format of the SAM screen is rather simple, check out the technical manual. With the above program it does all the conversion for you anyway (Alchemy handles dozens of screen formats). In brief though, here's mode 4. The SAM has 4 bits per pixel (16 colours). Each byte therefore is two pixels. The upper nibble is the left pixel, the lower nibble the right pixel. Each line therefore consists of 128 bytes (*2 = 256 pixels). Byte 128 is the first byte of the second line of the screen. This goes on for 192 lines. (192*128=24576=24k). To find the address of the screen being displayed use: LET VID=16384*(1+IN 252 BAND 31). Poke around in VID and things should become rather clear. Question 3. Never heard of any vector art programs on the SAM, maybe someone else has, personally I prefer bitmaps, would vector drawings be done justice when display is a relatively low resolution. And the kaleidescope definitely is a load of rubbish. That's all for now, keep cool till after school.... Solar Flare of Entropy ([EMAIL PROTECTED])
