Draw text in a PNG with text color
lazarus / 39-Graphics

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Prodigy · 2013-02-10 15:04

How to draw a text in a PNG with text color (and text background
transparent)?

This do not work:

Code: [Select]  PNG := TPortableNetworkGraphic.Create;
  PNG.LoadFromFile(...);
  PNG.Canvas.Font.Size:=18;
  PNG.Canvas.Font.Name:='Arial';
  PNG.Canvas.Font.Color :=clRed;
  PNG.Canvas.Brush.Style:=bsClear;
  PNG.Canvas.TextOut(50,50,'A');
  Image1.Picture.Assign(PNG);

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vrull · 2013-03-13 19:54

I think only TBitmap is supported enough to draw on its canvas.  Try
to assign your PNG to a TBitmap object, paint on bitmap canvas, then
assign the result back to PNG.

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Ocye · 2013-03-14 08:49

This works perfect:

Code: [Select]  with TPortableNetworkGraphic.Create do
  try
    Width:=50;
    Height:=50;
    Canvas.TextOut(1,1,'A');
    SaveToFile('test.png');
  finally
    Free;
  end;

Is 50,50 perhaps outside your canvas?

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Prodigy · 2013-03-27 04:24

Quote from: Ocye on March 14, 2013, 09:49:51 amThis works perfect:

Code: [Select]  with TPortableNetworkGraphic.Create do
  try
    Width:=50;
    Height:=50;
    Canvas.TextOut(1,1,'A');
    SaveToFile('test.png');
  finally
    Free;
  end;

Is 50,50 perhaps outside your canvas?

Where is text color?

50,50 is inside my canvas.

Edit:

When the image has transparent color Textout() and TextRect() always
generate white text. Why?

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Prodigy · 2013-03-29 05:02

My code works (help from this post: http://forum.lazarus.freepascal.or
g/index.php/topic,15496.msg83321.html#msg83321):

Code: [Select]var
  LImg, LImgT: TLazIntfImage;
  PNG: TPortableNetworkGraphic;
  PNGText: TPortableNetworkGraphic;
  x, y: Integer;
  TextColor: TColor;
begin
  TextColor := clBlue;
  PNG := TPortableNetworkGraphic.Create;
  PNG.LoadFromFile('...');

  PNGText := TPortableNetworkGraphic.Create;
  PNGText.PixelFormat:=pf32bit;
  PNGText.Canvas.Brush.Color:=clWhite;  //do not change
  PNGText.Canvas.Font.Color:=clBlack; //do not change
  PNGText.SetSize(PNGText.Canvas.TextWidth('X'),PNGText.Canvas.TextHei
ght('X'));//your Text
  PNGText.Canvas.FillRect(Rect(0,0,PNGText.Width,PNGText.Height));
  PNGText.Canvas.TextOut(0,0,'X'); //your Text
  LImgT := PNGText.CreateIntfImage;
  LImg := PNG.CreateIntfImage;
  for x:=0 to LImgT.Width-1 do
    for y:=0 to LImgT.Height-1 do
      if LImgT.Colors[x,y].Red<>High(Word) then
        LImg.Colors[50+x,50+y]:=TColorToFPColor(TextColor);
  PNG.LoadFromIntfImage(LImg);
  LImgT.Free;
  LImg.Free;
  PNG.SaveToFile('test.png');