harvey/sys/src/cmd/gs/lib/viewgif.ps

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% 
% This file is part of AFPL Ghostscript.
% 
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% distributor accepts any responsibility for the consequences of using it, or
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% she says so in writing.  Refer to the Aladdin Free Public License (the
% "License") for full details.
% 
% Every copy of AFPL Ghostscript must include a copy of the License, normally
% in a plain ASCII text file named PUBLIC.  The License grants you the right
% to copy, modify and redistribute AFPL Ghostscript, but only under certain
% conditions described in the License.  Among other things, the License
% requires that the copyright notice and this notice be preserved on all
% copies.

% $Id: viewgif.ps,v 1.2 2000/09/19 18:29:11 lpd Exp $
% viewgif.ps
% Display a GIF file.

/read1			% <file> read1 <int>
 { read pop
 } bind def
/read2			% <file> read2 <int>
 { dup read1 exch read1 8 bitshift add
 } bind def

/readGIFheader		% <file> readGIFheader <dict>
 { 20 dict begin
   dup 6 string readstring pop
   dup (GIF87a) eq exch (GIF89a) eq or not
    { (Not a GIF file.\n) print cleartomark stop
    } if
   dup read2 /Width exch def
   dup read2 /Height exch def
   dup read1
   dup 128 ge /GlobalColor exch def
   dup -4 bitshift 7 and 1 add /BitsPerPixel exch def	%***BOGUS?***
   dup 8 and 0 ne /PaletteSorted exch def
   7 and 1 add dup /BitsPerPixel exch def
     1 exch bitshift /PaletteSize exch def
   dup read1 /BackgroundIndex exch def
   dup read1 15 add 64 div /AspectRatio exch def
   GlobalColor
    { PaletteSize 3 mul string readstring pop
      /GlobalPalette exch def
    } if
   currentdict end
 } bind def

/readGIFimageHeader	% <file> readGIFimageHeader <dict>
			% Note: GIF header must be on dict stack
 { 10 dict begin
    { dup read1
      dup (!) 0 get ne { exit } if pop		% extension
      dup read1 pop
       { dup read1 dup 0 eq { pop exit } if { dup read1 pop } repeat
       } loop
    } loop
   (,) 0 get ne
    { (Not a GIF image.\n) print stop
    } if
   dup read2 /Left exch def
   dup read2 /Top exch def
   dup read2 /Width exch def
   dup read2 /Height exch def
   dup read1
   dup 128 ge /LocalColor exch def
   dup 64 and 0 ne /Interlaced exch def
   LocalColor
    { 7 and 1 add /BitsPerPixel exch def
      1 BitsPerPixel bitshift 3 mul string readstring pop
      /Palette exch def
    }
    { pop pop /Palette GlobalPalette def
    }
   ifelse
   currentdict end
 } bind def

/imageGIF		% <imagedict> imageGIF
 { /ImageOut where
    { pop
		% We know BitsPerComponent = 8, Decode = [0 255].
		% and there is only a single data source which is
		% either a filter or a string whose size is exactly
		% the width of the row.
      dup /DataSource get dup type /stringtype eq
       { ImageOut exch writestring
       }
       { pop dup /Width get string
	 1 index /Height get
	  { 1 index /DataSource get 1 index readstring pop
	    ImageOut exch writestring
	  }
	 repeat pop pop
       }
      ifelse 
    }
    { image
    }
   ifelse
 } bind def

/viewGIF		% <file|string> viewGIF -
 { save 20 dict begin
   /saved exch def
   dup type /stringtype eq { (r) file } if
   /F exch def
   /ImageOutFile where { /ImageOut ImageOutFile (w) file def } if
   F readGIFheader /Header exch def
     currentdict Header end begin begin
   DEBUG { Header { exch == == } forall (----------------\n) print flush } if
   F readGIFimageHeader /ImageHeader exch def
     currentdict ImageHeader end begin begin
   DEBUG { ImageHeader { exch == == } forall (----------------\n) print flush } if
   /D F
   <<	/InitialCodeLength F read1
	/FirstBitLowOrder true
	/BlockData true
	/EarlyChange 0
   >> /LZWDecode filter def

   [/Indexed /DeviceRGB 1 BitsPerPixel bitshift 1 sub Palette] setcolorspace
   matrix currentmatrix
   0 1 3 { 2 copy get dup 0 ne { dup abs div } if 3 copy put pop pop } for
   setmatrix
   <<	/ImageType 1
	/ImageMatrix [1 0 0 -1 0 Height]
	/BitsPerComponent 8
	/Decode [0 255]
   Interlaced
    {	/Width Width   /Height 1
	/row Width string def
	/DataSource row
      >> /I exch def
      /inter		% <num> <denom> inter -
       { /denom exch def   /num exch def
         gsave
	 /lines Height denom 1 sub add num sub denom idiv def
	 0 1 lines 1 sub {
	   Height exch denom mul num add sub
	   I /ImageMatrix get 5 3 -1 roll put
	   D row readstring pop pop
	   I imageGIF
	 } for
	 grestore
       }
      bind def
      0 8 inter
      4 8 inter
      2 4 inter
      1 2 inter
    }
    {	/Width Width   /Height Height
	/DataSource D
      >> imageGIF
    }
   ifelse
   saved end end end restore
 } bind def