Can't CopyRect in FPC-program
lazarus / 39-Graphics

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hakelm · 2025-09-04 06:32

Trying to do CopyRect in a simple FPC-program (se below) I get the
following error:

Error Project copyk raised exception class 'External: SIGSEGV'. Infile
lclintF.inc’ at line 182: Result :=
WidgetSet.Rawimage_QueryDescription(AFlags,ADesc);
on the line png0.Canvas.CopyRect(r,png1.Canvas,r);.

The same program run as a procedure in a Lazarus application behaves
as expected.
What have I missed and what can I do?

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 program
copyk; {$mode objfpc}{$H+} uses  {$IFDEF UNIX}  cthreads,  {$ENDIF} 
Classes  ,graphics, GraphType  ; var
png0,png1:TPortableNetworkGraphic; r:trect;begin 
 png0:=TPortableNetworkGraphic.Create;   png0.LoadFromFile('U.png');  
 png1:=TPortableNetworkGraphic.Create;   png1.LoadFromFile('k1.png'); 
 r:=TRect.Create(0, 0, png1.Width, png1.Height);  
 png0.Canvas.CopyRect(r,png1.Canvas,r); 
 png0.SaveToFile('p.png');end. 
I have Lazarus Version: 3.8 Date: 2025-08-13 FPC Version: 3.2.2,
x86_64-linux-gtk2 on Ubuntu 22.4.

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zeljko · 2025-09-04 07:16

Include Interfaces unit

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cdbc · 2025-09-04 07:18

Hi
You are missing one or some of the units, that are present in a GUI
app...
My guess would be:
- to include package 'LCLbase' or 'LCL' in you app, /project
inspector/
- add 'Interfaces' to your uses-clause...
Regards Benny

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Thaddy · 2025-09-04 07:40

Interfaces is enough.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 program copyk; {$mode objfpc}{$H+} uses  {$IFDEF UNIX} 
cthreads,  {$ENDIF}  interfaces,  Classes  ,graphics, GraphType  ; var
png0,png1:TPortableNetworkGraphic; r:trect;begin 
 png0:=TPortableNetworkGraphic.Create;   png0.LoadFromFile('U.png');  
 png1:=TPortableNetworkGraphic.Create;   png1.LoadFromFile('k1.png'); 
 r:=TRect.Create(0, 0, png1.Width, png1.Height);  
 png0.Canvas.CopyRect(r,png1.Canvas,r);   png0.SaveToFile('p.png'); 
 png0.free;   png1.free;end.png's must exist.

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Thausand · 2025-09-04 08:01

Also can have alternative no use LCL but use TFPImage.

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Thaddy · 2025-09-04 09:05

Quote from: Thausand on September 04, 2025, 10:01:51 amAlso can have
alternative no use LCL but use TFPImage.
Would be good, but does it handle png's?

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Thausand · 2025-09-04 09:29

Quote from: Thaddy on September 04, 2025, 11:05:02 amWould be good,
but does it handle png's?
Yes, can have png when clause uses reader/writer for png (or manual
load) https://wiki.freepascal.org/fcl-image#Image_formats

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 program
test; {$mode objfpc}{$h+} uses  {$ifdef linux}cthreads,{$endif}  types
,sysutils,fpimage,fpcanvas,fpimgcanv,fpreadpng,fpwritepng; procedure
copyImgRectToImg(OldFileName,RectFileName,NewFileName:string);var
CompCanvas,RectCanvas:TFPImageCanvas;r:TRect;begin 
CompCanvas:=TFPImageCanvas.Create(TFPMemoryImage.Create(0,0)); 
RectCanvas:=TFPImageCanvas.Create(TFPMemoryImage.Create(0,0));   try 
 CompCanvas.Image.LoadFromFile(OldFileName);   
RectCanvas.Image.LoadFromFile(RectFileName);    
r:=TRect.Create(0,0,RectCanvas.Image.Width,RectCanvas.Image.Height); 
 CompCanvas.CopyRect(0,0,RectCanvas,r);    
CompCanvas.Image.SaveToFile(NewFileName);  finally   
CompCanvas.Free;    RectCanvas.Free;  end;end; // "src.png"  :
https://wiki.freepascal.org/images/5/59/splash_logo.png// "rect.png" :
https://wiki.freepascal.org/images/e/ee/LazarusSource.PNGbegin 
copyImgRectToImg('src.png','rect.png','result.png');end. 
I think that work.

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hakelm · 2025-09-04 17:13

Thanks all.
fpimage did the trick, se below. Interestingly readers and writers
aren't necessary.
But I still can't understand why my original code works in a Lazarus
application but not in a non-gui program.

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 program
copyk2; {$mode objfpc}{$H+} uses  {$IFDEF UNIX}  cthreads,  {$ENDIF} 
Classes  ,fpreadpng,fpimage,FPCanvas, FPImgCanv  ; var r:trect;
 png0,png1:TFPCustomImage; canvas0, canvas1 : TFPCustomCanvas;
//reader:TFPReaderPNG; begin   png0:= TFPMemoryImage.Create(10, 10); 
 //Reader := TFPReaderpng.Create;   //png0.LoadFromFile('U.png',
Reader);   png0.LoadFromFile('U.png');   Canvas0 :=
TFPImageCanvas.Create(png0);    png1:= TFPMemoryImage.Create(10, 10); 
 png1.LoadFromFile('k1.png');   r:=TRect.Create(1, 1, png1.Width-1,
png1.Height-1);   Canvas1 := TFPImageCanvas.Create(png1);  
 canvas0.CopyRect(0,0,canvas1,r);   png0.SaveToFile('p.png');end.

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hakelm · 2025-09-04 17:22

Now I can also confirm that the addition of unit interfaces fixes the
problem.

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Thausand · 2025-09-05 02:21

Quote from: hakelm on September 04, 2025, 07:13:15 pmfpimage did the
trick, se below. Interestingly readers and writers aren't necessary.
You have include reader/writer png else no work png. Clause use
reader/writer is make work so no have make reader/writer manual (but
can make if want or if format not recognize and have explicit
reader/writer).

QuoteBut I still can't understand why my original code works in a
Lazarus application but not in a non-gui program.
Lazarus application have always clause uses interfaces in program
project source-code. This not see default with lazarus ide. Please
have look source lazarus project <name project>.lpr or have use
project/view project source

So when add interfaces for init widget it work because you have now
make same as lazarus app that init widget. If ask why need uses
interfaces then answer is canvas depend LCL (and
TPortableNetworkGraphic depend  graphic, graphic have canvas then all
need LCL). Is how is implement TPortableNetworkGraphic.

This why I have make suggest and have use TFPImage because TFPImage
not depend widget/LCL. I think is more easy and portable when not
display picture and only make manipulate picture. Can have alternative
NOGUI widget but that advanced topic (and have same interfaces and
depend LCL).

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Thaddy · 2025-09-05 05:22

Quote from: hakelm on September 04, 2025, 07:13:15 pmBut I still can't
understand why my original code works in a Lazarus application but not
in a non-gui program.
That is because the GUI code has a widgetset registered and your code
relies on a registered widget set: you could see that while you were
debugging.
Including the interfaces unit registers a widgetset for your platform.
It has only two calls:
in the initialization section it calls CreateWidgetSet() and in the
finalization it calls FreeWidgetSet().
The other option, using fpimage,  does not need a widgetset and I
would prefer that, the example code from Thausand, for smaller console
applications.