App crashes in for-loop
lazarus / 43-Android

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biologic · 2025-03-09 19:22

I have an error in my code, but can not see what's wrong.

If someone can help, many thanks. 


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
TAndroidModule1.ToGrayButtonClick(Sender: TObject);var    bmp:
TBGRABitmap;     p: PBGRAPixel;     memory_stream: TMemoryStream;    
bmp_writer: TFPWriterBMP;     image_width, image_height,   
pixel_number,    number_of_pixels: Integer;     image_byte_array:
array of Byte;     pixel_color_value: Integer = 0;     i : integer;  
pixelcolor : integer;    begin    //ShowMessage('Convert');    
image_width := 512;    image_height := 512;    number_of_pixels :=
image_width * image_height;     SetLength(image_byte_array,
number_of_pixels);     showmessage('after SetLength(array)');    
pixel_color_value := 0;     //ShowMessage('Size in bytes of Integer :
'+inttostr(sizeof(integer)));    // = 4 bytes     // error in for-
loop:     showmessage('number_of_pixels :
'+inttostr(number_of_pixels));     for
pixel_number:=number_of_pixels-1 downto 0 do       <--- error here   
begin      image_byte_array[pixel_number] := pixel_color_value;     
pixel_color_value := pixel_color_value+1;    end;       ----> the
following code is not executed:     ShowMessage('after for-loop');  
 { bmp := TBGRABitmap.Create(image_width, image_height);     try     
 p := bmp.Data;       for pixel_number := bmp.NbPixels-1 downto 0 do 
    begin         if(current_color = 1) then        begin         
p^.red := image_byte_array[pixel_number];          p^.green :=
Byte(0);          p^.blue := Byte(0);        end        else
if(current_color = 2) then        begin          p^.red := Byte(0);  
      p^.green := image_byte_array[pixel_number];          p^.blue :=
Byte(0);        end        else if(current_color = 3) then       
begin          p^.red := Byte(0);          p^.green := Byte(0);      
  p^.blue := image_byte_array[pixel_number];        end;          
inc(p);       end;       bmp.InvalidateBitmap;       bmp_writer :=
TFPWriterBMP.Create;       try         memory_stream :=
TMemoryStream.Create;         try           
 bmp_writer.ImageWrite(memory_stream, bmp);           
 Bitmap1.LoadFromStream(memory_stream);           
 ImageView1.SetImage(Bitmap1.GetImage());         finally         
 memory_stream.Free;         end;       finally       
 bmp_writer.Free;       end;     finally       bmp.Free;     end;    
}       inc(current_color);     if(current_color > 3) then   
 current_color := 1;  end;

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biologic · 2025-03-09 19:42

Solved.

The App crashed when the value of 'pixel_color_value' was greater than
255.

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 for
pixel_number:=number_of_pixels-1 downto 0 do    begin     
image_byte_array[pixel_number] := pixel_color_value;     
pixel_color_value := pixel_color_value+1;      if pixel_color_value >=
255 then         pixel_color_value:=0;    end;

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Joanna · 2025-03-10 01:56

Glad you solved it but why not 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
 pixel_color_value:byte If it should never be greater than 255.

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biologic · 2025-03-10 10:22

Yes, good idea.

Thanks for helping.

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Joanna · 2025-03-10 12:05

You’re welcome