/-------------------------------------------------------------------------\ | | | The ALLIANCE presents : Amiga Graphics Inside and Out from Abacus. | | | | This is the second in our series of complete books and due to the sheer | | size of this one will be spread across the next 2 or 3 of our docs | | disks. | | | | Typed By RAZOR BLADE and ASTERIX of Alliance. | | | | Greets to the rest of Alliance : | | | | Alchemist | | Chaos | | Mit | | Shadowfax | | Viper | | | \_________________________________________________________________________/ --------------------------------------------------------------------------- ABACUS 1.5 MEDLEY OF COLORS The Amiga provides a palette of 4096 colors. If you use pure BASIC you can only use 32 colors at a time (we'll show you how to use more later). The specific colors are stored in the color registers. When you use a statement, you are not selecting which color to use but which color register to get the color from. You cannot use all 32 colors in any type of screen. The number of possible colors depends on the depth of your screen. A normal Workbench screen has a depth of two, which allows you four colors. For every pixel there are two bits in memory which determine those four colors. 00 Color register 0 01 Color register 1 10 Color register 2 11 Color register 3 To display 32 colors you need five bits per pixel, but first you have to open a new screen with a depth of five: SCREEN 1,320,200,5,1 WINDOW 2,"TITLE",(0,0)-(311,185),16,1 Now you could use all the statements you have learned so far with 32 colors. Of the 32 colors available, you can select one for the foreground and one for the background. COLOR 1,0 These are the two default values. The first sets the foreground color and the second sets the background color. All the graphic statements will use these two colors. As longs as you leave the color parameter off, even PSET will use the default foreground color, and PRESET will use the default background color. Changing the foreground and/or background, color does not instantly change the screen colors. Using the CLS statement makes the new colors take effect. PAGE 41 --------------------------------------------------------------------------- AMIGA GRAPHICS AMIGA GRAPHICS IMSIDE AND OUT COLOR 2,3 CLS The above statement gives you an orange screen with a black foreground color. ---------------------------------------- 1.5.1 THE COMPLETE PALETTE Most of the time you will probably want a completely different set of colors in you program instead of the 32 default colors. To do this, you have to change the colors in the color registers. Every color is composed of three values which set the read, green and blue of the color(RGB). Each of these values has a range from one to 4096. The BASIC statement use to change the colors is PALETTE. You must specify the RGB(red, green and blue) values and which color register to change. The RGB color division must be a number between zero and one. PALETTE 0,.75,1,0 This line sets a neon yellow background. This color is a mix of red and yellow, blue is not used. To set the normal blue background: PALETTE 0,0,.3,.6 Setting the red to one(1) and the other ranges to zero gives you red. This procedure works the same for the other two ranges. ---------------------------------------- 1.5.2 CHANGING RGB COLORS You can find any color you want by experimenting with the three color ranges. However, finding a specific color with this method could be tiring. The following program allows you to search for and find your target color. You can change all three ranges while the program is running and quickly PAGE 42 ---------------------------------------------------------------------------- ABACUS 1.5 MEDLEY OF COLORS find your desired combination. The results are visible on the screen at the same time. REM 1.5.2 ColorConstructor SCREEN 1,320,200,2,1 WINDOW 2,"ColorConstructor",(0,0)-(297,185),31,1 LINE (200,20)-(300,150),3,bf LOCATE 5 PRINT "> '4' '5' '6'" LOCATE 16 PRINT "< '1' '2' '3'" LOCATE 10 PRINT " R G B" r=1:g=.5:b=0 ' orange WHILE 1 LOCATE 11 PRINT USING " #.##";r;g;b PALETTE 3,r,g,b WHILE A$="" A$=INKEY$ WEND IF A$<>"" THEN IF A$="1" and r>=.0666 THEN r=r-.06666 IF A$="4" and r>=.9333 THEN r=r+.06666 IF A$="2" and g>=.0666 THEN g=g-.06666 IF A$="5" and g>=.9333 THEN g=g+.06666 IF A$="3" and b>=.0666 THEN b=b-.06666 IF A$="6" and b>=.9333 THEN b=b+.06666 END IF WEND You can change the color ranges by using the 1-6 keys. The numeric keypad is perfectly arranged for changing color ranges. The 4 key raises and the 1 key lowers it. The 5 and 2 keys raise and lower the green range, and the 6 and 3 keys raise and lower the blue range. The color range will increase and decrease by a value of 0.0666 or 1/15. This insures a color range with every keypress. You can also change the mouse pointer colors with the PALETTE. The effected registers are 17,18 and 19. Try it out. ---------------------------------------- 1.5.3 THE OPPOSITE OF PALLETTE In many programs it is very important to know what colors are in the palette. However, there is no statement in BASIC that performs the opposite of PALETTE. Again we will step ahead a little and get out our data directly PAGE 43 ---------------------------------------------------------------------------- AMIGA GRAPHICS AMIGA GRAPHICS INSIDE AND OUT from memory. We will explain later, when we leave pure BASIC, how to detemine the address of the color table. Since the functions assigned at the beginning of the program take care of any addresses or PEEKs, you do not have to concern yourslef with these. You just have to provide the color register number to the function. There are three functions, one for each RGB color range. REM 1.5.3 Palette-Opposite SCREEN 1,320,200,5,1 WINDOW 2,,,16,1 DEF FNcolortab=PEEKL(PEEKL(PEEKL(WINDOW(7)+46)+48)+4) DEF FNred(f)=(PEEKW(FNcolortab+2*f) AND 3840)/3840 DEF FNgreen(f)=(PEEKW(FNcolortab+2*f) AND 240)/240 DEF FNblue(f)=(PEEKW(FNcolortab+2*f) AND 15)/15 PRINT "RGB Color Values:" FOR i = - TO 31 LOCATE 5+i MOD 16,1+INT(i/16)*20 COLOR i PRINT USING "##";i, COLOR 1 PRINT USING " #.##";FNred(i);FNgreen(i);FNblue(i) NEXT i WHILE INKEY$="":WEND WINDOW CLOSE 2 SCREEN CLOSE 1 This program prints out the color values for evry color. The color register and color are listed in front of the three ranges. ---------------------------------------- 1.5.4 ANIMATION USING COLOR Now we'll show you away to make functions from the last program useful. You can easily animate a picture by repeatedly swapping several colors. This color cycling trick may be familier to you because paint programs, such as GraphiCraft and Deluxe Paint, use it. You can magically display moving rivers or similar actions with this method. With some porgramming, this color swapping is possible in BASIC. However, you should keep the number of colors being swapped as small as possible because of BASIC's slowness. If you use too many colors, the cycling will be slower, causing a jerky and ragged look. REM 1.5.4 Palette-Opposite Expanded SCREEN 1,320,200,5,1 WINDOW 2,,,16,1 PALETTE 0,0,.5,0 PALETTE 28,0,.35,.72 PAGE 44 ---------------------------------------------------------------------------- ABACUS 1.5 MEDLEY OF COLORS PALETTE 29,0,.35,1 PALETTE 30,0,.5,1 PALETTE 31,0,.6,1 DEF FNcolortab(PEEKL(PEEKL(WINDOW(7)+46)+48+4) DEF FNred(f)=(PEEKW(FNcolortab+2*f) AND 3840)/3840 DEF FNgreen(f)=(PEEKW(FNcolortab+2*f) AND 240)/240 DEF FNblue(f)=(PEEKW(FNcolortab+2*f) AND 15)/15 f1=28:f2=31 FOR j=0 TO 311 STEP 4 FOR i=0 to 3 STEP .5 LINE (j+i,120+j/8)-(J+i-4,140+j/8),28+i LINE (j+i+1,120+j/8)-(J+i-3,140+j/8),28+i NEXT i NEXT j rotation: r1=FNred(f2)-.03 g1=FNgreen(f2)-.03 b1=FNblue(f2)-.03 FOR i=f1 TO f2 r=FNred(i)-.03 g=FNgreen(i)-.03 b=FNblue(i)-.03 PALETTE i,r1,g1,b1 r1=r g1=g b1=b NEXT i GOTO rotation This program draws an abstract river. We set the last eight color registers to blue for the river. In the program routine "rotation" we subtract .03 from the recieved color range before using the value with PALETTE. This corrects a calculation error for the floating point value, that is between 0 and 15, which we received from memory. PAGE 45 ----------------------------------------------------------------------------