The Graphics Interface module provides a simple and convenient way to access the color graphics and joystick functions of the Dragon Computer from &b09; programs. The module is a program written in assembly language and stored in a file called "GFX". It can be loaded into memory using the OS-9 "LOAD" command prior to or after called &b09;, or it will be automatically called by &b09; the first time it is referenced in a program if the "GFX" file is located in the execution ("CMDS") directory. "GFX" is called using the &b09; "RUN" statement. The first parameter passed is the name of the graphics function desired. Other parameters are used to pass coordinates, color modes, etc. The are two basic graphics modes: 4-color having 128 by 192 pixel resolution, and 2-color having 256 by 192 pixel resolution. The display is treated as a 256 by 192 point grid with coordinates 0,0 in the lower left-hand corner. X (horizontal) coordinates in either mode must be in the range of 0 to 255. An X-coordinate greater than 255 will cause a run-time error. Y coordinates (vertical) must be in the range of 0 to 191. A number greater than 191 will be replaced by 191. Some of the graphics functions require or optionally accept a color mode which controls the foreground color and color set. The mode and color codes are given in the table on the next page. Color Code Two Color Format Four Color Format Background Foreground Background Foreground Color Set 1 00 Black Black Green Green 01 Black Green Green Yellow 02 Green Blue 03 Green Red Color Set 2 04 Black Black Buff Buff 05 Black Buff Buff Cyan 06 Buff Magenta 07 Buff Orange Color Set 3* 08 Black Black 09 Black Dark Green 10 Black Med. Green 11 Black Light Green Color Set 4* 12 Black Black 13 Black Green 14 Black Red 15 Black Buff Color Sets 3 and 4 are not available on PAL video system (U.K. and European) models. MODE RUN GFX("Mode",format,color) MODE switches the screen from alphanumeric to graphics display mode, and selects the screen mode and color mode. "Format" determines between two-color (Format = 0), or four-color (Format = 1) graphics modes. "Color" is the initial color code that specifies the foreground color and color set. This command must be given before aby other graphics command is used. The first time MODE is called, it requests 6K bytres of memory from OS-9 for use as the graphics display memory. MODE will return an error if sufficient free memory is not available. An example: RUN GFX("Mode",1,3) selects four-color mode graphics is used, and the initial foreground color is red. MOVE RUN GFX("Move",x,y) MOVE positions the (invisible) graphics cursor to the specified location without changing the display. X and Y are the coordinates of the new position. Example: RUN GFX("Move",0,0) This example positions the cursor in the lower left-hand corner. COLOR RUN GFX("Color",color) COLOR changes the current foreground color (and possibly the color set). The current graphics mode and cursor position are not changed. For example: RUN GFX("Color",0) changes the foreground color to green in four-color format (or black in two-color format). POINT RUN GFX("Point",x,y) or RUN GFX("Point",x,y,color) POINT moves the graphics cursor to the specified X.Y coordinate and sets the pixel at that coordinate to the current foreground color. If the optional "Color" is specified, the current foreground color is set to the given "Color". For example: RUN GFX("Point",0,192,1) Point moves the cursor to the upper left-hand corner and changes the foreground color to green in two-color format, or it changes the color to yellow in the four-color format. CLEAR RUN GFX("Clear") or RUN GFX("Clear",color) CLEAR resets all points on the screen to the background color, or if the optional color is given presets the screen to that color. The current graphics cursor is reset to (0,0). LINE RUN GFX("Line",x2,y2) RUN GFX("Line",x2,y2,color) RUN GFX("Line",x1,y1,x2,y2) RUN GFX("Line",x1,y1,x2,y2,color) LINE draw lines in various ways. If one coordinate is given, the line will be drawn from the current graphics cursor position to the coordinates specified. If two sets of coordinates are given, they are used as the start and end points of the line. The line will be drawn in the current foreground color unless a new color is given as a parameter. After the line is drawn the graphics cursor will be positioned at x2,y2. For example RUN GFX("Line",0,0,0,192) draws a line from (0,0) to (0,192). RUN GFX("line",24,65,2) draws a blue line (4-color mode) to point 24,65. CIRCLE RUN GFX("Circle",radius) RUN GFX("Circle",radius,color) RUN GFX("Circle",x,y,radius) RUN GFX("Circle",x,y,radius,color) CIRCLE draws a circle of the given radius. The current graphics cursor position is assumed if no X,Y value is given. The current foreground color is assumed if the Color parameter is not used. The center of the circle must be on the screen. ALPHA RUN GFX("Alpha") Alpha is a quick convenient way of getting the screen back to alphanumeric mode. When graphics mode is entered again, the screen will show the previous unchanged graphics display. QUIT RUN GFX("Quit") QUIT switches the screen back to alpha mode and returns the 6K byte graphics display memory to OS-9. GLOC RUN GFX("Gloc",vdisp) GLOC returns the address of the video display RAM as an integer number. This address may be used in subsequent PEEK and POKE operations to access the video display directly. GLOC can be used to create special functions that are not available in the Graphics Module. GCOLR RUN GFX("Gcolr",color) RUN GFX("Gcolr",x,y,color) GCOLR is used to read the color of the pixel at the current graphics cursor position, or from the coordinates X,Y. The parameter "Color" may be an integer or a byte variable in which the color code is returned. JOYSTK RUN GFX("Joystk",stick,fire,x,y) JOYSTK returns the status of the specified joystick's Fire button, and returns the X,Y position of the joystick. The Fire button may be read as a BYTE, INTEGER, or a BOOLEAN value. Non-zero (TRUE) means the button was pressed. The X,Y values returned may be BYTE or INTEGER variables, and they will be in the range 0 to 63. The Stick parameter may be BYTE or INTEGER, and should be 0 for RIGHT, or 1 for LEFT, depending on whether the RIGHT or the LEFT joystick is to be tested. Example: RUN GRX("Joystk",1,leftfire,leftx,lefty) A Sample Graphics Program The program on the next page illustrates how the GFX module is called and used. It creates an analog clock on the graphics display. PROCEDURE clk 0000 (* Simple Clock Simulator *) 001C DIM time(4),last(4),xx(3),yy(3):INTEGER 0043 DIM x0,y0,radius,bkg:INTEGER 0056 DIM i,j,x1,y1,x2,y2:INTEGER 0071 DEG 0073 bkg=0 007A x0=128 0081 y0=96 0088 radius=95 008F RUN GFX("MODE",1,bkg+1) 00A5 RUN GFX("CLEAR") 00B2 RUN GFX("CIRCLE",x0,y0,radius) 00CF FOR i=0 to 89 STEP 6 00E4 x2=SIN(i)*radius 00F4 y2=COS(i)*radius 0104 x1=x2*.9 0115 y1=y2*.9 0126 j=MOD(i/30,3)+bkg+1 013B RUN GFX("LINE",x0+x1,y0+y1,x0+x2,y0+y2,j) 016C RUN GFX("LINE",x0-x1,y0-y1,x0-x2,y0-y2,j) 019D RUN GFX("LINE",x0+y1,y0-x1,x0+y2,y0-x2,j) 01CE RUN GFX("LINE",x0-y1,y0+x1,x0-y2,y0+x2,j) 01FF NEXT i 020A FOR i=1 TO 3 021A time(i)=0 0225 xx(i)=x0 0231 yy(i)=y0 023D NEXT i 0248 LOOP 024A time$=DATE$ 0250 last=time 0258 time(3)=VAL(MID$(time$,16,2))*6 026E time(2)=VAL(MID$(time$(13,2))*6 0284 time(1)=MOD(VAL(MID$(time$,10,2))*30+time/2)/12,360) 02A9 j=last(3) 02B3 FOR i=3 TO 1 STEP -1 02C9 IF i=3 OR j=0 OR ABS(time(i)-last(i+1))<6 OR ABS(time(i)-j)<6 THEN 0300 RUN GFX("LINE",x0,y0,xx(i),yy(i),bkg) 032B xx(i)=x0+SIN(time(i))*radius*(.3+i*.2) 035A yy(i)=y0+COS(time(i))*radius*(.3+i*.2) 0389 RUN GFX("LINE",x0,y0,xx(i),yy(i),bkg+i) 03B7 ENDIF 03B9 NEXT i 03C4 WHILE time$=DATE$ DO 03CF ENDWHILE 03D3 ENDLOOP