268215 - Incorrect stretch drawing part of 8-bit alpha images

Status: RESOLVED EXPIRED

(Core Graveyard :: GFX: Win32, defect)

Description

[Wang Xianzhu]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.4) Gecko/20030624
Build Identifier: nsImageWin since 3.127 (2004-01-06 08:29) till now (?)

When stretch drawing portion of a 8-bit alpha image, the whole image is drawn
instead of the specified portion.  This will cause problems for rendering XUL
elements with -moz-image-region style.

For example, when a png image of size 300x300 with 8-bit alpha is drawn with the
following call:

nsImageWin::Draw(context, surface, 
  /*aSX*/100, /*aSY*/100, /*aSWitdh*/100, /*aSHeight*/100, 
  /*aDX*/0, /*aDY*/0, /*aDWidth*/200, /*aDHeight*/200);
the whole 300x300 image is drawn, instead of the specified 100x100 subimage.

Problem is in nsImageWin.cpp nsImageWin::DrawComposited:
 680 tor        3.127 
 681                    PRBool scaling = PR_FALSE;
 682                    /* Both scaled and unscaled images come through this code */
 683                    if ((aDWidth != aSWidth) || (aDHeight != aSHeight)) {
 684                      scaling = PR_TRUE;
 685                      aDWidth = aOrigDWidth;
 686                      aDHeight = aOrigDHeight;
 687                      aSWidth = mBHead->biWidth;
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 688                      aSHeight = mBHead->biHeight;
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 689                    }
...............
 738 tor        3.127     RectStretch(aSWidth, aSHeight, aDWidth, aDHeight,
 739                                  0, 0, aDWidth-1, aDHeight-1,

 740 tor        3.126                 mImageBits, mRowBytes, imageRGB,
strideRGB, 24);
                                      ^^^^^^^^^^^
 741 tor        3.127     RectStretch(aSWidth, aSHeight, aDWidth, aDHeight,
 742                                  0, 0, aDWidth-1, aDHeight-1,
 743 tor        3.126                 mAlphaBits, mARowBytes, imageAlpha,
strideAlpha, 8);
                                     ^^^^^^^^^^^^
.........

I think the problem can be resolved by modifying the above code into the following:

  PRBool scaling = PR_FALSE;
  /* Both scaled and unscaled images come through this code */
  if ((aDWidth != aSWidth) || (aDHeight != aSHeight)) {
    scaling = PR_TRUE;
    aDWidth = aOrigDWidth;
    aDHeight = aOrigDHeight;
    //bug aSWidth = mBHead->biWidth;
    //bug aSHeight = mBHead->biHeight;
  }
...............
    RectStretch(aSWidth, aSHeight, aDWidth, aDHeight,
                0, 0, aDWidth-1, aDHeight-1,
                // bug
                mImageBits + aSY * mRowBytes + aSX * 3, 
                mRowBytes, imageRGB, strideRGB, 24);
    RectStretch(aSWidth, aSHeight, aDWidth, aDHeight,
                0, 0, aDWidth-1, aDHeight-1,
                // bug
                mAlphaBits + aSY * mARowBytes + aSX, 
                mARowBytes, imageAlpha, strideAlpha, 8);

Reproducible: Always
Steps to Reproduce:
1.
2.
3.

Comment 1

[Boris Zbarsky [:bzbarsky]]

tor, you checked in the code in question...

Comment 2

[Gervase Markham [:gerv]]

This is an automated message, with ID "auto-resolve01".

This bug has had no comments for a long time. Statistically, we have found that
bug reports that have not been confirmed by a second user after three months are
highly unlikely to be the source of a fix to the code.

While your input is very important to us, our resources are limited and so we
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Comment 3

[Gervase Markham [:gerv]]

This bug has been automatically resolved after a period of inactivity (see above
comment). If anyone thinks this is incorrect, they should feel free to reopen it.