[Tcl-bugs] [ tktoolkit-Bugs-467524 ] GIF images are not read correctly

[<no...@so...>]

Bugs item #467524, was opened at 2001-10-03 08:47
You can respond by visiting: 
http://sourceforge.net/tracker/?func=detail&atid=112997&aid=467524&group_id=12997

Category: 40. Photo Image|GIF
Group: = 8.3.3
Status: Open
Resolution: None
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
>Assigned to: Jeffrey Hobbs (hobbs)
Summary: GIF images are not read correctly

Initial Comment:

Using "wish", (Tcl/Tk version 8.3.3) reading GIF
formatted images with
the "-from" option to the "image read" command results
in either
a corrupted image or a segmentation fault.

Using a small GIF file (307x187) I tried the following:

% image create photo
image1
% image1 read debris1.gif -from 0 0 100 100
% canvas .c
.c
% pack .c
% .c create image 0 0 -anchor nw -image image1
1

The resulting image that is displayed is corrupt.  In
other instances
using the "-from" option has resulted in a crash of the
"wish"
program due to a segementation fault.

This problem also shows up under Tcl/Tk 8.3.2.  It has
been reproduced
under Solaris 2.6, Solaris 8, Windows NT, and Windows
2000.  I have also noticed that the same code is used
in the Tcl/Tk 8.4 Alpha releases.

The problem seems to be in the the call to
"ReadImage()" in 
"tkImgGIF.c":

1).  The "ReadImage()" function ignores any parameters
that have been
      passed via the "-from" option.

2).  Non-interlaced GIF images will load, but they will
be corrupted.

3).  Interlaced GIF images will typically cause a
segmentation fault
      as they are read, but if not they will still be
corrupted.

I worked on a fix to prevent the problem, but it is not
optimal:

*** /afs/isis.unc.edu/home/m/c/mcknight/tkImgGIF.c     
Wed Oct  3 11:29:46 2001
--- tkImgGIF.c  Wed Oct  3 11:31:34 2001
***************
*** 799,805 ****
      register unsigned char *top;
      int codeSize, clearCode, inCode, endCode,
oldCode, maxCode,
        code, firstCode;
!     
      /*
       *  Initialize the decoder
       */
--- 799,805 ----
      register unsigned char *top;
      int codeSize, clearCode, inCode, endCode,
oldCode, maxCode,
        code, firstCode;
! 
      /*
       *  Initialize the decoder
       */
***************
*** 841,848 ****
      GetCode(chan, 0, 1);
  
      /* Read until we finish the image */
!     for (i = 0, ypos = 0; i < rows; i++) {
!       for (xpos = 0; xpos < len; ) {
  
            if (top == stack) {
                /* Bummer -- our stack is empty.  Now
we have to work! */
--- 841,849 ----
      GetCode(chan, 0, 1);
  
      /* Read until we finish the image */
! 
!     for (i = 0, ypos = 0; i < height; i++) {
!       for (xpos = 0; xpos < width; ) {
  
            if (top == stack) {
                /* Bummer -- our stack is empty.  Now
we have to work! */
***************
*** 947,955 ****
             * there are more in the file and we will
be called to read 
             * one of them later)
             */
!           *pixelPtr++ = cmap[v][CM_RED];
!           *pixelPtr++ = cmap[v][CM_GREEN];
!           *pixelPtr++ = cmap[v][CM_BLUE];
            if (transparent >= 0) {
                *pixelPtr++ = cmap[v][CM_ALPHA];
            }
--- 948,963 ----
             * there are more in the file and we will
be called to read 
             * one of them later)
             */
! 
!             if ( (xpos >= srcX) && (xpos < srcX+len)
&&
!                  (ypos >= srcY) && (ypos <
srcY+rows)) {
! 
!               *pixelPtr++ = cmap[v][CM_RED];
!               *pixelPtr++ = cmap[v][CM_GREEN];
!               *pixelPtr++ = cmap[v][CM_BLUE];
! 
!             }
! 
            if (transparent >= 0) {
                *pixelPtr++ = cmap[v][CM_ALPHA];
            }
***************
*** 970,976 ****
        } else {
            ypos++;
        }
!       pixelPtr = imagePtr + (ypos) * len *
((transparent>=0)?4:3);
      }
      return TCL_OK;
  }
--- 978,989 ----
        } else {
            ypos++;
        }
! 
!         if ( i >= (srcY+rows) ) {
!             break;
!         }
! 
!       pixelPtr = imagePtr + (ypos-srcY) * len *
((transparent>=0)?4:3);
      }
      return TCL_OK;
  }




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