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Text File | 1996-01-28 | 12KB | 290 lines

Tutorial for writing Special icons for Megaboard ------------------------------------------------ ---------------- - Introduction - ---------------- This file explains in a step-by-step manner how to create a special icon that displays the current time, it will only be of interest to programmers, other users should refer to the "Guide" file for information on general use. For a full technical description of special icons see the ProgGuide file. Note: the icon defined here serves no practical use as it simply duplicates an icon already supplied with MegaBoard, but it is a good example of a typical special icon. ---------------------------------- - Part 1: Writing the definition - ---------------------------------- Open the !MegaBoard application directory, locate the file 'Cstm_Scrpt', and load it into a text editor. Now add the following command to the end of the file: Start_Icon This notifies MegaBoard that an icon definition begins here. The following lines must contain the commands descried in the 'ProgGuide' file i.e: Name: TutTime To specify the name of the icon Purpose: Display the current time Author: Your Name Version: 0.00 These will be displayed in the special info dialogue box. Width: 150 This sets the initial width of the icon to 150 OS units Height: 40 This sets the initial height of the icon to 150 OS units Worksize: 1024 Reserves 1024 bytes of workspace for the icon when it is created Update: Second Informs Megaboard that the icon requires updating every second Mouse_State: Off Keypress_State: Off Message_State: Off Menu_State: Off The icon does not respond to mouse clicks, keypresses or Wimp messages and does not have a menu associated with it. Start_Parameters Format: %z24:%mi:%se End_Parameters States that the icon has one user-definable parameter called "Format" with the default value "%z24:%mi:%se". End_Icon Terminates the icon definition. The icon definition should now look like this: Start_Icon Name: TutTime Purpose: Display the current time Author: Your Name Version: 0.00 Width: 150 Height: 40 Worksize: 1024 Mouse_State: Off Keypress_State: Off Message_State: Off Menu_State: Off End_Icon Now save the file and if it is not already running, run MegaBoard. The Special icon submenu should now contain an additional item, namely "TutTime". DO NOT CHOOSE THIS ITEM YET!!! ----------------------------------- - Part 2: Writing the code blocks - ----------------------------------- The BASIC file 'Skeleton' in this directory contains the source code of a "blank" special icon i.e. one that neither display anything nor responds to any events. Run this file, it will save the code file in the current directory. Open the directory !MegaBoard.Special and create a new diretory called "TutTime" (the same as the icon name) then locate the code file previously saved and copy it into this direcory. Now the icon's menu item in the 'Special icon' submenu can be chosen, but take care to note the location of the pointer when Menu was originally clicked or you will have difficulty locating the icon. An invisible icon will then be placed on MegaBoard, you can verify this by dragging Seelect or Adjust over the pointer position where menu was clicked, which should allow the icon represented by a 'rotating dash' box to to dragged around MegaBoard. In order for the icon to do something meaningful the relevant code blocks will have to be written. Load the "Skeleton" file into a BASIC editor A Code block in the skeleton file looks something like this: REM initialise EQUD init_end-P% MOV PC,R14 .init_end The file line after the REM inserts a word conatining the length of the block. Following this is the actual code, in this case it is simply a return instruction terminated by the label referred to in the EQUD. 1. Initialise ------------- In our example the initialisation code must simply copy the parameter string into the icon's own workspace, encoding is not necessary: .init MOV R7,#0 :REM set the offset to 0 .stringloop LDRB R6,[R5],#1 :REM load a character into R6 and REM increment R5 STRB R6,[R4,R7] :REM store the character in R4+R7 ADD R7,R7,#1 :REM increment R7 CMP R6,#32 :REM check if the character was a REM terminator BGE stringloop :REM if not then copy the next character MOV R6,#0 :REM replace the control terminator with STRB R6,[R4,R7] :REM a null. Next we have to read the curent time in a 5-byte format: ADD R1,R4,#256 :REM the 5 bytes are stored at workspace offset 256 MOV R0,#3 STR R0,[R1] MOV R0,#14 SWI"OS_Word" This 5-byte time information now needs to be converted ino a string: MOV R0,R1 :REM R0 points to the 5-byte time ADD R1,R0,#8 :REM R1 points to the buffer for the REM string at workspace offset 264 REM (i.e. 256+8) MOV R2,#240 :REM buffer size MOV R3,R4 :REM R3 points to the format string STMFD R13!,{R0-R3} :REM push these registers to the stack :REM because we need them later SWI "XOS_ConvertDateAndTime" :REM do not generate errors If OS_ConvertDateAndTime detected an error in the format string it will return with the V flag set this must now be checked for and handled. If an error occurred the time and format strings will be replaced with the word "ERROR". MOV R5,R0 :REM these registers will be needed if there was MOV R6,R1 :REM no error LDMFD R13!,{R0-R3} :REM pull the registers from the stack that were REM stored above. REM the following is only executed if there was an error LDRVS R2,error1 :REM load the first 4 bytes of the word "ERROR" REM into R2 STRVS R2,[R1] :REM replace both the format string and the time STRVS R2,[R3] :REM string with the word "ERROR" LDRVS R2,error2 :REM copy the second STRVS R2,[R1,#4] :REM 4 bytes STRVS R2,[R3,#4] :REM (actually only 2) SUBVC R1,R6,R5 :REM if there was no error set R1 to the length REM of the time string +1 MOVVS R1,#6 :REM if there was an error set R1 to the length REM of "ERROR" +1 i.e. 6 Finally BASIC's C% variable must be modifed to the width of the of the string in OS units. SUB R1,R1,#1 :REM subtract 1 from R1 to obtain the number REM of characters MOV R1,R1,LSL# 4 :REM multiply R1 by 16 (the width of system REM font text under the WIMP. STR R1,pointer_stuff-8 :REM use it as the new icon width MOV PC,R14 :REM return This code should be entered between the "EQUD init_end-P%" and the ".init_end" label. 2. Null ------- This entry point simply reads the current time then converts it to a string using the stored format string: .null ADD R1,R4,#256 :REM read the MOV R0,#3 :REM current time STR R0,[R1] :REM and store it MOV R0,#14 :REM at workspace SWI "OS_Word" :REM offset 256 MOV R0,R1 :REM and ADD R1,R0,#8 :REM convert MOV R2,#248 :REM it MOV R3,R4 :REM to SWI"OS_ConvertDateAndTime" :REM a string MOV PC,R14 :REM return to BASIC 3. Redraw --------- Here it is first necessary to move the cursor to [x_coord-icon_width/2,ycoord-icon_height/2+36]: SUB R3,R1,R3,LSR #1 :REM subtract half the icon height from the Y REM coordinate and store the result in R3 ADD R3,R3,#36 :REM add 36 to this value SUB R1,R0,R2,LSR #1 :REM subtract half the icon width from the X REM coordinate and store the result in R1 MOV R2,R3 :REM copy the calculated Y coordinate into R2 MOV R0,#68 :REM plot code 68 to move cursor SWI "OS_Plot" :REM execute the move Next the colour must be set to black: MOV R5,R4 :REM copy the workspace pointer to R5 as it is REM needed later MOV R0,#0 :REM the palette entry for black MOV R3,#0 :REM flags all 0 MOV R4,#0 :REM GCOL action 0 SWI "ColourTrans_SetGCOL" :REM set the colour 4. Finish --------- This entry point can be left empty, there is no finishing up necessary. 5. Save ------- The only string that needs saving is the unencoded format string but first the header "1: " must be output: MOV R1,R5 :REM copy the file handle to R1 ADR R2,header :REM point R2 at the header .save_loop1 LDRB R0,[R2],#1 :REM load a character CMP R0,#32 :REM check if it's a terminator SWIGE "OS_BPut" :REM if not ouput it to the file BGE save_loop1 :REM then get the next character Now we can output the format string: .save_loop2 LDRB R0,[R4],#1 :REM load a character and increment R4 CMP R0,#32 :REM check if it's a terminator MOVLT R0,#10 :REM if it is output a newline instead SWI "OS_BPut" :REM output the character BGE save_loop2 :REM if it was not a terminator then get REM the next character One parameter has been saved, so the ntry returns with a R0 set to 0 MOV R0,#1 MOV PC,R14 .header EQUS " 1: "+CHR$(0):ALIGN 5. Load ------- As only one parameter was saved, load will only be called once. All that has to be done is to copy that string to the icon's workspace: MOV R1,R4 :REM Copy R4 to R1 as it is needed later .load_loop LDRB R0,[R6],#1 :REM load the first character into R0 REM and increment R6 CMP R0,#32 :REM check if it's a terminator MOVLT R0,#0 :REM if it is replace it with a null STRB R0,[R1],#1 :REM store the character and increment REM R1 BGE load_loop :REM if it was not a termintor get the REM next character Immediately after this call redraw will be called, however there will not be a valid time string in the buffer for it to display, therefore one must be generated here, this is achieved by simply calling null. STMFD R13!,{R14} :REM push R14 as the BL instruction will corrupt it BL null :REM call null LDMFD R13!,{PC} :REM return to BASIC All other entry points can remain empty. Once these code segments have been entered into the skeleton file run it again and copy the created code file into the TutTime directory as described above. The special icon is now complete and can be placed on MegaBoard just like the ones provided with the package.