Scrolling a BGRABitmap image

[atlatl]

I can't get an image to scroll. I calculate the location the image should move to in a scrollbarChange handler, then call image.draw(Canvas, x, y, true), and the image dosen't move.

Debugging the scrollbar handler shows the math is correct.

I must be missing some vital step.

Does anyone have an idea of what I'm missing?

[Tony Stone]

Depending on what you are doing I am pretty sure I used a scrollbox in the past and put a full size image in it.  Made it pretty automatic but this is probably not the best way.

[lainz]

Share your minimal code. Else who can help you?

[Dzandaa]

Hi,

@atlatl:

Here the minimal project I use as template to open, save and transform, Zoom and Scroll BGRABitmap:

You can use it as if or put in your template directory:

B->

[atlatl]

Thanks for the replys.

@Tony Stone:

"this is probably not the best way" - I'll take your word for it. 😊

@lainz:

Code: Pascal  [Select][+][-]

1. PROCEDURE TForm1.HScrollBarChange(Sender: TObject);
2.   BEGIN
3.     gImageLeft:= HScrollBar.Position * (-gImageSize Div gPortSize);
4.     IF gImageLeft < -(gImageSize - gPortSize) THEN gImageLeft:= -(gImageSize - gPortSize);
5.     gImage.draw(Canvas, gImageLeft, gImageRight, true)
6.   END;
7.  

It turns out it wasn't the BGRABitmap image that needed to be updated, but the form. Swapping out the gImage.draw call for a Repaint call solved the issue.

@Dzandaa:

Thank you for the "minimal project", that's a lot of code to digest.

It was your use of Repaint in your RedrawPicture handler that clued me in to what I was doing wrong. Thanks.