[Oberon] Static variable overflow (bug?)

[Hans Klaver]

Well, as you can see MyViewer doesn't do any dot-drawing. The only thing it does is declaring an array of 32 bit entities and creating an emty viewer. The viewer works fine apart from its menu remaining emty. This is what puzzles me.

Hans Klaver


> Chris Burrows wrote:
> 
> If I were you I would have started by looking at the newer graphics examples supplied with Project Oberon 2013 as a basis for porting the Fern example to the newer system. The bitmap in the original XYPlane code appears to have been used for dot-drawing optimisation that is no longer used (necessary?).
>  
> Recently I tried to implement XYplane.Mod from the book of Reiser & Wirth 'Programming in Oberon' for Project Oberon. Within Peter de Wachter's RISC emulator I ran into an overflow problem (leading to the remaining empty of the menu line of a viewer) that appears to be dependent on which disk image is used.
>  
> Otherwise my port works fine (produces the IFS fractal fern as expected). 
> For those interested I will post it to my github repository.
>  
> A minimal module that can reproduce this menu problem can be found below.
>  
> When starting the emulator in macOS as follows this problem occurs:
> $ ./risc --fullscreen DiskImage/Oberon-2019-01-21.dsk
>  
> But the problem does NOT occur when starting thus: 
> $ ./risc --fullscreen DiskImage/Oberon-2016-08-02.dsk
>  
> I do understand that there is a limit to the use of static variables within the PO version of Oberon, but I would not expect this limit to be reached this easily, and I would not expect it to appear in newer versions of the software and not in older.
>  
> Does anyone have a clue where to look for the cause of this happening?
>  
> Hans Klaver
>  
>  
>  
> ---------------------
>  
> MODULE MyViewer;  
> (* Test of the menu line of a viewer *)
>  
> IMPORT Display, Viewers, Oberon, MenuViewers, TextFrames;
>  
> CONST 
>    max = 16377;   (* If max >= 16367 the frame name disappears; If max >= 16377 the whole menu line disappears! *)
>    menu = "System.Close System.Copy System.Grow"; 
>  
> TYPE 
>    XYframe = POINTER TO XYframeDesc;
>    XYframeDesc = RECORD (Display.FrameDesc) END;
>  
> VAR bitmap: ARRAY max OF SET;  (* with this variable present the menu may remain empty! *)
>  
>  
> PROCEDURE Restore(F: XYframe);
> BEGIN 
>    Oberon.RemoveMarks(F.X, F.Y, F.W, F.H);
>    Display.ReplConst(Display.black, F.X, F.Y, F.W, F.H, Display.replace);  (* clear *)
> END Restore;
>  
>  
> PROCEDURE Handle(F: Display.Frame; VAR M: Display.FrameMsg);
>    VAR F1: XYframe;
> BEGIN  
>    CASE F OF XYframe:
>       CASE M OF 
>          Oberon.InputMsg:
>             IF M.id <http://m.id/> = Oberon.track THEN Oberon.DrawMouseArrow(M.X, M.Y) END |
>          Oberon.CopyMsg:
>                Oberon.RemoveMarks(F.X, F.Y, F.W, F.H); NEW(F1); F1^ := F^; M.F := F1 |
>          MenuViewers.ModifyMsg:
>             IF (M.Y # F.Y) OR (M.H # F.H) THEN F.Y := M.Y; F.H := M.H; Restore(F) END        
>       END
>    END
> END Handle;
>  
>  
> PROCEDURE Open*;
>    VAR F: XYframe;    V: Viewers.Viewer;   x, y: INTEGER;
> BEGIN
>    NEW(F);   F.handle := Handle; 
>    Oberon.AllocateUserViewer(Oberon.Par.vwr.X, x, y); 
>    V := MenuViewers.New(TextFrames.NewMenu("MyViewer", menu), F, TextFrames.menuH, x, y)
> END Open;
>  
> END MyViewer.
> --
> Oberon at lists.inf.ethz.ch <mailto:Oberon at lists.inf.ethz.ch> mailing list for ETH Oberon and related systems
> https://lists.inf.ethz.ch/mailman/listinfo/oberon <https://lists.inf.ethz.ch/mailman/listinfo/oberon>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.inf.ethz.ch/pipermail/oberon/attachments/20200224/9d11ba35/attachment.html>