Is it possible to display a png using fpimage and using ptcgraph?
lazarus / 39-Graphics

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TBMan · 2025-09-02 17:27

I found something, but it isn't working. Any help would be
appreciated.

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
bwtest;uses ptcgraph,fpimage,fpreadpng,fpcanvas, fpimgcanv,ptccrt;var 
gm,gd:smallint;  r,c,  x,y:integer;  myImage: TFPMemoryImage;  reader
: TFPCustomImageReader;  canvas : tfpcustomcanvas;   color:word; 
 colors:tfpcolor;     function RGBToInteger(R, G, B: Byte): Integer; 
 begin     Result := (Integer(B) shl 16) or (Integer(G) shl 8) or
Integer(R);   end;   begin   gd := vesa;    Gm := installusermode(800,
600, 256, 2, 10000, 8000);    WindowTitle := 'BW Design';   
initgraph(gd, gm, '');    myImage := TFPMemoryImage.Create(400, 400);
// larger than file dimensions    Reader := TFPReaderPNG.create;   
canvas := tfpimagecanvas.create(myimage);    try     
myImage.LoadFromFile('qc.png',reader);    except      // Handle file
not found or other load errors      WriteLn('Error loading PNG
file');    end;    x := 100; y := 100;  for r := 0 to myImage.Height -
1 do  begin    for c := 0 to myImage.Width - 1 do    begin      color
:= rgbtointeger(canvas.colors[c,r].red,
canvas.colors[c,r].green,canvas.colors[c,r].blue);      PutPixel(x+c,
y+r,color);     end;   end;       repeat until
keypressed;closegraph; end.

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Thausand · 2025-09-03 02:54

Yes, can work display png fpimage use ptcgraph but have caveat.

You example have ptcgraph 256 color. png can have many more color and
not fit (can, if quantize color but then need palette from you) . If
png 256 color then can always make work because png also can have
palette.

If use png fpimage TFpColor then color 64-bit (4 x word, is not usual
because usual is 32-bit) and need scale down. If image have palette
then ptcgraph need use setpalette (https://www.freepascal.org/daily/pa
ckages/graph/ptcgraph/setpalette.html).

Can not make easy example because not know what is colors "qc.png" and
not know how convert color. Maybe can tell or give (example) picture ?

PS: this simple very example 8-bit palette and 64-bit color convert
for ptcgraph.

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} 
sysutils,ptcgraph,ptccrt,  fpimage,fpreadpng; type  TColorType=packed
record    case byte of      0:(r,g,b,a:byte);     
1:(value:longword);  end; function
fpColorToColorType(fpColor:TFPColor):TColorType;begin 
result.value:=0;  result.r:=(fpColor.Red   shr 8) and $00ff; 
result.g:=(fpColor.Green shr 8) and $00ff;  result.b:=(fpColor.Blue
 shr 8) and $00ff;end; procedure start;var  gm,gd:smallint;begin 
gd:=vesa;  gm:=installusermode(800,600,256,2,10000,8000); 
WindowTitle:='BW Design';  initgraph(gd,gm,'');end; procedure
stop;begin  repeat until keypressed;  closegraph;end; procedure
load256ColorPng(Filename:string);var  Image:TFPMemoryImage; 
ColorType:TColorType;  x,y,w,h:integer;  index:integer; 
Color:integer;begin  if FileExists(Filename) then  begin   
Image:=TFPMemoryImage.Create(0,0);    try      // have palette load  
  Image.UsePalette:=true;      Image.LoadFromFile(Filename);       //
make palette color image copy to ptcpas      for index:=0 to
Image.Palette.Count-1 do      begin       
colorType:=fpColorToColorType(Image.Palette[Index]);       
SetRGBPalette(index,ColorType.r,ColorType.g,ColorType.b);      end;  
   // make pixel image copy to ptcpas      x:=100; y:=100;      for
w:=0 to Image.Height-1 do      begin        for h:=0 to Image.Width-1
do        begin          Color:=Image.Pixels[w,h];         
PutPixel(x+w,y+h,Color);        end;      end;    except      //
Handle file not found or other load errors      WriteLn('Error loading
PNG file');    end;  end  else writeln(Filename,' not
exist!');end; begin  start;  // picture: https://bp0.blogger.com/_5Z1N
zpeMhcs/Rut53DRL_DI/AAAAAAAAAdI/XxZbdMkDS1I/s1600-
h/color_palette_256_deluxepaint.png 
load256ColorPng('color_palette_256_deluxepaint.png');  stop;end.

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TBMan · 2025-09-03 13:12

Thanks!

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Thausand · 2025-09-03 21:10

You welcome TBMan 

I tell and sorry, I have make copy-paste you code then adjust and (you
and me) forget to have free Image so have leak memory. Please make add
Image.Free to have fix.

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TBMan · 2025-09-04 01:58

Thanks again, much appreciated!