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Report From: Delphi-BCB/VCL/Graphics [ Add a report in this area ]

Report #: 101632

Status: Open

TPNGImage draws itself slightly incorrectly

Project: Delphi

Build #: XE2

Version: 16.2

Submitted By: Dmitry Kozhinov

Report Type: Minor failure / Design problem

Date Reported: 12/7/2011 10:42:32 AM

Severity: Infrequently encountered problem

Last Updated: 3/20/2012 2:24:39 AM

Platform: All versions

Internal Tracking #: 289092

Resolution: None (Resolution Comments)

Resolved in Build: : None

Duplicate of: None

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Description

For some (not all) indexed PNG images, TPNGImage object draws itself on a form canvas with slightly shifted color values.

This may be important when using TransparentColorValue property of a form - not getting tranparency where expected.

Steps to Reproduce:

1) Use png_indexed2.png file (download from http://www.desktopfay.com/temp/png_indexed2.png). It is filled with RGB(10, 59, 118) color.

2) OnPaint event handler of a form:

var
  aPNGImage : TPNGImage;
begin
  aPNGImage:=TPNGImage.Create;
  aPNGImage.LoadFromFile('C:\temp\png_indexed2.png');
  TransparentColorValue:=RGB(10, 59, 118); {not getting transparent area}
  {TransparentColorValue:=RGB(10, 58, 117); uncomment this to get transparent area}
  Canvas.Draw(0, 0, aPNGImage);
  aPNGImage.Free;
end;

Workarounds

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