I need help with BeginUpdate and EndUpdate
lazarus / 39-Graphics

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stem · 2020-02-09 14:25

Hi,

I have a procedure which gets a TImage object (myImage) as parameter
and calculates some colors. The colors get stored with

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
myImage.canvas.Pixels[col, row] := myColor;
Everything works fine. To speed up the calculation, I've put
everything in try and finally together with BeginUpdate() and
EndUpdate():

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i try 
myImage.Picture.Bitmap.BeginUpdate();  ... (my code)finally 
myImage.Picture.Bitmap.EndUpdate();end; 
Unfortunately this stops painting the image completely. If I comment
out the two lines with BeginUpdate() and EndUpdate(), everything works
again.

What am I doing wrong?

Thank you.

stem

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circular · 2020-02-09 14:40

myImage.Canvas is the surface of the control, which gets replaced on
repaint.

If you want the pixels to stay in the image you would rather use
myImage.Picture.Bitmap.Canvas.

Note that the Bitmap size must be set up correctly.

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stem · 2020-02-09 15:09

Quote from: circular on February 09, 2020, 03:40:22 pmIf you want the
pixels to stay in the image you would rather use
myImage.Picture.Bitmap.Canvas.
Note that the Bitmap size must be set up correctly.

I replaced my code the way you suggested. The image gets correctly
painted with myImage.Picture.Bitmap.Canvas, but only (again) if I
comment out the two lines with BeginUpdate() and EndUpdate() ...

If the two lines are active, the image is completely black.

stem

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balazsszekely · 2020-02-09 16:41

Set myimage width and height to 500, then:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.Button1Click(Sender: TObject);begin  with
MyImage.Picture.Bitmap do  begin    SetSize(500, 500);   
BeginUpdate(True);    try      Canvas.Pen.Color := clRed;     
Canvas.Line(0, 0, 500, 500);      Canvas.Line(500, 0, 0, 500);   
finally      EndUpdate;    end;  end;end;

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stem · 2020-02-09 21:30

Thank you!