/-------------------------------------------------------------------------\ | | | 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 it this one will be spread across the next 2 or 3 of our docs | | disks. | | | | Typed By RAZOR BLADE of Alliance. | | | | Greets to the rest of Alliance : | | | | Alchemist | | Asterisk | | Chaos | | Mit | | Shadowfax | | Viper | | | \_________________________________________________________________________/ ---------------------------------------------------------------------------- 3.6 THE RASTPORT. With this data block, we get even closer to the basic elements of Amiga graphics, the so called "graphic primitives". We'll leave intuition to go deeper into the Amiga system architecture. We'll now explore the graphic libraries. The RastPort, which contains the data that controls how a drawing takes place, manages a drawing plane. The starting address of the data block for an actual window is always in the variable WINDOW(8). This address can be read directly from the window data structure. PRINT WINDOW(8) PRINT PEEKL(WINDOW(7)+50) The RastPort structure is constructred as follows: Data Structure: RastPort/Graphics/100 Bytes. Offset Type Description. ------- ------- ------------------------------------------------------ +000 Long Pointer to the layer structure. +004 Long Pointer to the Bit-map structure. +008 Long Pointer to the AreaFill pattern. +012 Long Pointer to the TmpRas structure. +016 Long Pointer to the AreaInfo structure. +020 Long Pointer to the GelsInfo structure. +024 Byte Mask: Writemask for this raster. +025 Byte Foreground colour. +026 Byte Background colour. +027 Byte AreaFill outline colour. +028 Byte Drawing mode: JAM1 = 0 JAM2 = 1 COMPLEMENT = 2 INVERSVID = 4 +029 Byte AreaPtSz: 2^n Words for AreaFill pattern. +030 Byte Unused. +031 Byte Line draw pattern preshift. +032 Word various control bits. FIRST DOT = 1 : Draw first pixel? ONE DOT = 2 : one dot mode for lines. DBUFFER = 4 : Double buffered set. +034 Word LinePtrn: 16 bits for line pattern. +036 Word X coordinate of graphic cursor. PAGE 122 ---------------------------------------------------------------------------- +038 Word Y coordinate of graphic cursor. +040 ---- 8*1 byte minterms. +048 Word Cursor Width. +050 Word Cursor Height. +052 Long Pointer to character set. +056 Byte Character set mode (bold, italics etc...) +057 Byte textspecific flags. +058 Word Height of characterset. +060 Word Average character width. +062 Word Text height without underline. +064 Word Character spacing. +066 Long Pointer to user data. +070 Word Reserved (7x) +084 Long Reserved (2x) +092 Byte Reserved (8x) ------------------------------------------ 3.6.1 THE RASTPORT STRUCTURE. The following explains the RastPort structure by offset the same manner we did for windows and screens: OFFSET 0 : THE LAYER. The Amiga uses layers to keep each drawing plane separate from the other planes. These layers are actually the principle elements of each Intuition window. You might think layers are very complicated and, compared to windows, relatively useless. However, layers are important and a closer look (as seen in a later chapter) will prove that they are really a storehouse of graphic possibilities. OFFSET 4: THE BITMAP. You have already learned about the Bitmap, which is a pointer to the bit-map structure. With this pointer you have indirect access to the screen address through the RastPort: scr& = PEEKL(WINDOW(8)+4)-184 The bit-map is the intersection between the data structure and the RAM banks where the window and screen contents are stored. PAGE 123 ---------------------------------------------------------------------------- OFFSET 8 : POINTER TO THE AREAFILL PATTERN. You have seen how to fill areas with a single colour or with a pattern. If you use a pattern, then that pattern has to be stored somewhere in memory. This offset contains the address pointer to where the pattern is stored. We will provide more information and examples after the offset explanations. One of our subjects will show you how to use multi-colour patterns of up to 32 colours. OFFSET 12: THE TmpRas. TmpRas stands for Temporary Raster. This is a pointer to an area of free RAM used for certain operations. Whenever you use the fill commands like PAINT or LINE BF, this RAM is used as a temporary holding area for the entire object being filled. OFFSET 16: AREA INFO. This pointer is for a data structure used when drawing polygon shapes. There is not much use for this from BASIC, but we will discuss it later. OFFSET 20: GELSINFO. Gels are Graphic Elements, such as sprites and Bobs (Blitter Objects), and also the complete automatic Amiga animation system. Before this system can be activated the GelsInfo structure has to be defined. This structure contains some very important parameters. OFFSET 24: WRITEMASK. This variable allows individual bit-planes of the drawing plane to fade. The default value is normally 255. All bits are set which means that all available bit-planes are used. The POKE, POKE WINDOW(8) + 24,0 makes all bit-planes inactive and nothing more will be drawn on the screen. You can also select specific bit planes to be active or inactive. OFFSET 25,26 AND 27: DRAWING COLOUR. These registers determine the drawing colours. The first contains the number of the colour register for the drawing colour. The second has the background and the third the AreaOutlineMode. PAGE 124 ------------------------------------------------------------------------------ OFFSET 28: DRAWING MODE. The Amiga has four basic drawing modes that you can use. They are: JAM1 = 0 JAM2 = 1 COMPLEMENT = 2 INVERSEVID = 4 The normal drawing mode is JAM2. This means that the foreground colour is used to draw in the drawing plane and the rest will be in the background colour. THe following example will make this clear: (Enter these examples in Direct Mode!) LINE (0,0)-(100,100),2,bf LOCATE 1,1:PRINT "hello!" Thw white text appears on a blue background. A hole is made in the original black background. JAM 1 is different. The foreground colour is used to draw, but the background is not changed. LINE (0,0)-(100,100),2,bf POKE WINDOW(8)+28,0 LOCATE 1,1:PRINT "hello" POKE WINDOW(8)+28,1 COMPLEMENT complements the graphic with the background: Where ever a pixel is set, it will be erased and just the opposite for unset pixels: LINE (0,0)-(100,100),2,bf POKE WINDOW(8)+28,2 LINE(50,50)-(150,150),3,bf POKE WINDOW(8)+28,1 INVERSEVID inverts a graphicL background and foreground are exchanged. It looks like this: POKE WINDOW(8)+28,4 PRINT "Inverse!" POKE WINDOW(8)+28,1 These pokes work great in direct mode. However, they do not work in a program. Nothing will happen. The routine SetDrMd in the graphic library sets the desired mode safely and reliably. PAGE 125 ---------------------------------------------------------------------------- LIBRARY "graphic.library" CALL SetDrMd(WINDOW(8),mode%) mode% = 0 - 255 Various modes may be combined, only JAM1 and JAM2 work against each other. OFFSET 29: AreaPtSz. Whenever you work with patterns, you must specify how high the pattern will be. Patterns can only be defined using powers of two (1,2,4,8,....). This field stored the power of two. Using a special programming method, you can use this register to activate the mutli-colour pattern mode. This allows you to create patterns with up to 32 colours. ( There will be more on this in the next section). OFFSET 30,31 AND 32. FOR SYSTEM USE. OFFSET 34: LINE PATTERN. Patterns are not only for areas, but for lines also. The method is easy: 16 pixels in a row can be set or unset. The amiga then uses this Sample pattern to draw lines. Take the following line pattern for example: *****.*.*****.*. A dash dot dash dot line. First you determine the bit values of the line: bit& = 2^15+2^14+2^13+2^12+2^11+2^9+2^7+2^6+2^5+2^4+2^3+2^1 Now the value is stored to this register: POKEW WINDOW(8)+34,bit& A test: LINE (10,10)-(600,10) AS you can see it works. OFFSET 36 AND 38: COORDINATES OF THE GRAPHIC CURSOR. These two fields are extremely important. Text on the Amiga is nothing more than text shaded graphics. Because of this, text can be placed in any position on the screen. The following example demonstrates this: WHILE INKEY$ = "" x% = RND(1)*600 y% = RND(1)*160 POKEW WINDOW(8)+36,x% POKEW WINDOW(8)+38,y% PRINT "Commodore Amiga!" WEND PAGE 126 ---------------------------------------------------------------------------- OFFSET 40-51: MINTERMS, INTERNAL USAGE. OFFSET 52: THE CHARACTER SET. Just as in the screen structure this is a pointer to the currently active font. The character set determines what your text looks like. We will return to this subject later. OFFSET 56: ACTUAL TEXT STYLE. The Amiga can display a font in various forms on the screen: normal = 0 underlined = Bit 0 set. bold = Bit 1 set. italics = Bit 2 set. The last three modes can be combined to form different combinations. OFFSET 57: TEXT FLAGS, INTERNAL USAGE. OFFSET 58: TEXT HEIGHT. This field contains the height of the currently active font. This value is used to average the line height to calculate the correct line spacing. There is nothing to prevent you from setting you own line spacing. It can be even closer together than normal: POKEW WINDOW(8)+58,5 or further apart: POKEW WINDOW(8)+58,12 OFFSET 60: CHARACTER WIDTH. This register contains the average width of the font. Since the Amiga also supports proportional fonts (characters of different widths), you can set the average width in this register. PAGE 127 ---------------------------------------------------------------------------- OFFSET 62: TEXT HEIGHT WITHOUT UNDERLINE. OFFSET 64: CHARACTER SPACING. The following routine allows you to vary the spacing between individual characters. The default for this field is zero. Storing larger values here will spread the characters over a larger area as in the following example: text$ = "Hello World!" text%=LEN(text$) FOR loop% = 1 TO 40 POKEW WINDOW(8)+36,280-(loop%*text%*.5) '(centering) POKEW WINDOW(8)+38,90 POKEW WINDOW(8)+64,loop% PRINT text$ NEXT loop% FOR loop% = 39 TO 0 STEP -1 POKEW WINDOW(8)+36,280-(loop%*text%*.5) POKEW WINDOW(8)+38,90 POKEW WINDOW(8)+64,loop% PRINT text% NEXT loop% END OFFSET 66: USER DATA. This is a pointer to more data that can be linked to this structure. OFFSET 70 to END - Reserved Data Fields. PAGE 128 ----------------------------------------------------------------------------