[Oberon] SystemV - Viewer Scroll

[Tomas Kral]

On Fri, 15 Mar 2019 09:33:10 +0100
Jörg Straube <joerg.straube at iaeth.ch> wrote:

> Textframes knows lines and line breaks, Texts doesn‘t care.

Thank you, having re-read chapters on Texts and Frames.

Interesting, line brakes are kept in `Line' list that is built on the
fly when line is displayed `DisplayLine'.

Updating display is single pass and is fast. I also looked into
`LocateLine' these are all simple procs, I can understand so far.

Forward move seems favoured to backward in `Show' procedure, that I do not understand yet.

Unlike `Modify' proc that is called when a menu bar is moved up or down.

  PROCEDURE Modify* (F: Frame; id, dY, Y, H: INTEGER);
  BEGIN
    Mark(F, FALSE); RemoveMarks(F); SetChangeMark(F,  FALSE);
    IF id = MenuViewers.extend THEN
      IF dY > 0 THEN Display.CopyBlock(F.X, F.Y, F.W, F.H, F.X, F.Y + dY, 0); F.Y := F.Y + dY END;
      Extend(F, Y)
    ELSIF id = MenuViewers.reduce THEN
      Reduce(F, Y + dY);
      IF dY > 0 THEN Display.CopyBlock(F.X, F.Y, F.W, F.H, F.X, Y, 0); F.Y := Y END
    END;
    IF F.H > 0 THEN Mark(F, TRUE); SetChangeMark(F,  F.text.changed) END
  END Modify;

Modify above almost mimics scroll forward(extend) and backward(reduce), it also nicely shows the idea of `dY'.
Both directions using `CopyBlock'!

I wonder why `Show' does not follow similar pattern of Modify. I can see, howevber, that code is symetric, though.

Show()
  if pos < F.pos
    extend()
  elsif pos > F.pos
    CopyBlock()
    else
      extend()
End.

-- 
Tomas Kral <thomas.kral at email.cz>