As a further example, you can modify the sine curve program to display a semicircle. Here are the lines to type to make the changes:
50 FORX=0TO160:REM DO HALF THE SCREEN 55 Y1=100+SQR(160*X-X*X) 56 Y2=100-SQR(160*X-X*X) 60 FORY=Y1TOY2STEPY1-Y2 70 CH=INT(X/() 80 RO=INT(Y/X) 85 LNYAND7 90 BY=BASE+RO*320+8*CH+LN 100 BI=7-(XAND7) 110 POKEBY,PEEK(BY)OR(2^BI) 114 NEXTThis will create a semicircle in the HI-RES area of the screen.
|WARNING: BASIC variables can overlay your high-resolution screen. If you need more memory space you must move the bottom of BASIC above the high-resolution screen area. Or, you must move your high-resolution screen area. This problem will NOT occur in machine language. It ONLY happens when you're writing programs in BASIC.|
Like multi-color mode characters, multi-color bit map mode allows you to display up to four different colors in each 8 by 8 section of bit map. And as in multi-character mode, there is a sacrifice of horizontal resolution (from 320 dots to 160 dots).
Multi-color bit map mode uses an 8K section of memory for the bit map. You select your colors for multi-color bit map mode from (1) the background color register 0, (the screen background color), (2) the video matrix (the upper 4 bits give one possible color, the lower 4 bits an- other), and (3) color memory.
Multi-color bit mapped mode is turned ON by setting bit 5 of 53265 ($D011) and bit 4 at location 53270 ($D016) to a 1. The following POKE does this:
POKE 53265,PEEK(53625)OR 32: POKE 53270,PEEK(53270)OR 16
|This page has been created by Sami Rautiainen.|
|Read the small print.||Last updated May 12, 2002.|