From: "Earl F. Glynn"
Subject: Re: Failure with pf1bit but not other PixelFormats?
Date: 13 Oct 1999 00:00:00 GMT
Message-ID: <7u2fgl$89k13@forums.borland.com>
References: <7ttd59$p7u11@forums.borland.com>
Organization: Another Netscape Collabra Server User
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Newsgroups: borland.public.delphi.graphics

Earl F. Glynn wrote in message
news:7ttd59$p7u11@forums.borland.com...

> ... asked why the following code fails when pf1bit PixelFormat is used,
> but not other PixelFormats
>   Grid := TBitmap.Create;
>
>   // With pf1bit the image is all black.  With all other
>   // PixelFormats the desired grid is displayed.
>   Grid.PixelFormat:=pf4bit;
>
>   try
>     Grid.Height:=10;
>     Grid.Width:= Grid.Height;

Based on observations in the Very Large Bitmap experiment,
http://www.efg2.com/Lab/Graphics/VeryLargeBitmap.htm
I defined a bitmap's PixelFormat before its height and width,
since sometimes larger bitmaps could be created this way.
(Before that experiment, I wasn't really consistent in the
order in which I defined a bitmap's properties.)

HOWEVER, this order causes some sort of problem with pf1bit
bitmaps.  If you define
    PixelFormat := pf1bit
before setting the bitmap's height and width, the original
code works fine for pf1bit bitmaps.

   Grid := TBitmap.Create;
   try
     Grid.Height:=10;
     Grid.Width:= Grid.Height;

     // Unclear why this must follow width/height to work correctly.
     // If PixelFormat precedes width/height, bitmap will always be black.
     Grid.PixelFormat:=pf1bit;

So there is a work around for this problem (but I'm not sure why it
works or why the original code failed.)
___
efg

Earl F. Glynn
Overland Park, KS  USA

efg's Computer Lab:  http://www.efg2.com/Lab