Cursor position in Timage
lazarus / 39-Graphics

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barsoom · 2021-08-16 21:54

I am working with an image, and, for the moment, i need to know the
position (coordinates) of the cursor in the image.

To do that, i have a Timage, and a label.
In the Timage, i added this code to the events 'OnmouseMove' and
'Onmouse leave'
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 to show the (relative) coordinates of the cursor on the
imageprocedure TForm1.Image1MouseMove(Sender: TObject; Shift:
TShiftState; X,  Y: Integer);begin  Label1.Caption := Format('%d,%d',
[X, Y]);  // way 1  //Label1.caption:=
'('+IntToStr(X)+','+IntToStr(Y)+')'; // way 2end;   // Procedure to
clear the label when the mouse leave the imageprocedure
TForm1.Image1MouseLeave(Sender: TObject);begin  Label1.caption :=
'';end; 
As you can see, in 'OnMouseMove' event i tried two different ways to
show the coordinates in the label caption. However, although both ways
'work' somehow, the result is the same in boths, and here is the
problem: The coordinates are only updated once the mouse stop on the
image, but coordinates are not updated meanwhile the cursor is under
movement on the image.

I googled a lot and the procedure seems to be ok, but i do not know
why i have these behaviour.
Any idea about what i am doing wrong? Thanks!

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wp · 2021-08-16 22:10

On which OS/widgetset is this? On Windows, Ubuntu/gtk2 and Ubuntu/qt5
it works correctly.

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barsoom · 2021-08-16 22:34

It is under OS Windows 10 64bits and Lazarus version 2.0.4 FPC 3.0.4
SVN 61665

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wp · 2021-08-16 22:43

My oldest Lazarus of the v2.0.x series is v2.0.8, and it does not show
the issue. And of the 1.x series I have v1.8.4, and it does not show
the issue either.

So, I have no idea what's going on here. Please try to write a little
demo project showing the issue and post it here. Maybe the bug is
somewhere else.

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barsoom · 2021-08-16 23:18

@thanks @wp,
One more time, you are right...

I tried a simple example project, and it worked... then, i added the
image inside a scrollbox, as i have in my project... and it worked...
BUT, when i changed the autoscroll option of the scrollbox to True, it
stop to work correctly. Then, it show the values only when the mouse
stop the movement.

The "funny" issue is that it affect to all the images loaded in the
form!! Take a look to the example project i prepared. I load a image
in two Timage containers. One is directly in the form, and the second
one inside a scrollbox. Play with the checkboxes to chnage some
properties of the scrollbox, and you will see how it affect to the
position information update.

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dsiders · 2021-08-16 23:21

Quote from: barsoom on August 17, 2021, 12:34:03 amIt is under OS
Windows 10 64bits and Lazarus version 2.0.4 FPC 3.0.4 SVN 61665

Does not have any issues on 2.2.0-RC1 or using 2.3.0 from Git. Windows
8.1, 64-bit, FPC 3.2.0 and 3.2.2.

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wp · 2021-08-17 16:58

I can confirm the issue with both Laz 2.3 and Laz 1.8.4. It is
required that the image loaded into the TPicture is quite large (at
first I simply selected the application icon which is too small to see
an effect). There is also some flicker of the scrollbox border when
the mouse is moved. Therefore, I think that the scrollbox enforces a
repaint of the image with every mouse-move. To check this, I added an
OnPaint handler to the image which simply counts up a number with
every repaint requested:
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 var 
Counter: Integer = 0;procedure TForm1.Image2Paint(Sender:
TObject);begin  inc(Counter);  WriteLn(TControl(Sender).Name, ': ',
Counter);end; In fact, the counter increments with every move of the
mouse. When I hook this event handler also to Image1 (the one outside
the scrollbox) I can see that the paint requests always originate from
Image2, even when the mouse is outside Image2 - very strange...

I repeated the test on a VM with Ubuntu and found that there the
repaints do not occur and the cursor display in the test program
updates instantly.

Therefore, I guess that the issue is related to the windows widgetset
only. I think I saw a similar bug report recently, but cannot find it
at the moment.

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barsoom · 2021-08-18 20:37

Thanks @dsiders and @wp!

@wp, you are right, it occurs with relative big picture files.

I also tested other properties of the scrollbox to see how it affect
this issue. If you define the range of each scrollbar, the described
behaviour seems to "dissapear as well.