AppBasic Tutorial

Drawing using drawfiles

Create an application
Create an application which opens a window which has its auto-redraw flag deselected; see Example 2.3.a

Add an “Initial” event-handler
The following procedure sets aside a 100K block of memory (starting at address drawfile) where drawfiles can be stored. It also loads a drawfile, stored in the application's resources directory, into memory

DEF PROCDealWith_InitialEvent length=0 maxlength=100*1024 DIM drawfile maxlength PROCFile_Load("<BasicApp$Dir>.DrawFile",maxlength) ENDPROC

Add a “File” utility library
A drawfile, whose pathname is file$, can be loaded into memory by calling the utility procedures

DEF PROCFile_Load(file$,maxlength) IF FNFile_Length(file$)<=maxlength THEN SYS "OS_File",12,file$,drawfile TO ,,,,length : REM Loads file ELSE PROCUtils_Alert("File too big!") ENDIF ENDPROC DEF FNFile_Length(file$) LOCAL length SYS "OS_File",13,file$ TO ,,,,length =length

Add a “WindowRedraw” event-handler
The method PROCWindow_DrawfileRedraw method uses the RISCOS Draw module to render drawfiles:

DEF PROCDealWith_WindowRedraw(object,a%,b%,h%) IF length<>0 PROCWindow_DrawfileRedraw(drawfile,length,a%,b%) ENDPROC

draw/png

Worked solution