Good morning,afternoon,evening, ...

Can anyone explain the way the ScanLine property of a TBitMap is supposed
to work? The example in my Delphi 3 help is _strange_. What I would like to
do,  is set a row of pixels in a BitMap object from an array of TColor read
from
a file more quickly than using the dismally slow

   bitmap.canvas.pixels[i,j]:= ...

Thanks

Mort Canty
Juelich Research Center
Germany

        At last an excuse to figure out how ScanLine works.
The example in the docs seems a little strange because it's
using an indexed (ie palettized) bitmap without specifying
what the palette should be. Here's an example showing how you
can set RGB values:

type
  TRGBTriple = packed record
   R, G, B: byte;
  end;

  PColorArray = ^TColorArray;
  TColorArray = array[0..100000] of TRGBTriple;

procedure TForm1.Button1Click(Sender: TObject);
var BMP: TBitmap;
    j,k: integer;
    P : PColorArray;
    c: byte;
begin
BMP:= TBitmap.Create;
try
 with BMP do
 begin
  PixelFormat:= pf24Bit;
  Width:= 128;
  Height:= 128;
  for j:= 0 to 127 do
  begin
   P:= ScanLine[j];
   for k:= 0 to 127 do
   begin
     c:= j + k;
     with P^[k] do
     begin
       R:= c;
       G:= c;
       B:= c;
     end;
   end;
  end;
 end;
 Canvas.Draw(0,0,BMP);
finally
 BMP.Free;
end;
end;

        This does what I expected it to do. I haven't checked what
happens if I try to assign more than 256 colors altogether on a
256-color system; for that matter I haven't checked what the code
above does on a 256-color system - my guess is you get dismal results,
just as when you try to display a 24-bit bmp file in a TBitmap
on an 8-bit system. I'd guess that on a 256-color system you really
want to use PixelFormat:= pf8Bit, create a palette and assign palette
indices to the pixels, as in the example in the docs.

--
David Ullrich

?his ?s ?avid ?llrich's ?ig ?ile
(Someone undeleted it for me...)