19540 - Background image larger than window - wierd effect during scrolling.

Status: VERIFIED DUPLICATE of bug 1248

(Core :: Layout, defect, P3)

Description

[ivo]

M11, Build ID: 1999111520, Win98 &RH Linux 6.1

When background image is larger than window results to wierd effect during
scrolling. On Linux everything is black but on Win98 screen pixels are taken
from memory so it's very colourful.


Ivo Särak.

Comment 1

[Sean Richardson]

Attachment: Testcases for variety of extreme background sizes/shapes

Comment 2

[Sean Richardson]

* Overview:
The display problem reported here can create a serious usability problem
with a large, slow-loading BODY BACKGROUND image: black text over the
as-yet-unloaded portions of the background cannot be read.

* Steps to Reproduce:
0. This bug is easiest to reproduce with a slow modem link; if the background
   loads too quickly it may be difficult or impossible to reproduce - so use
   a dialup connection if possible, and load it down with a concurrent ftp
   download for maximum effect.
1. Adjust the browser window to 700-750 pixels tall.
2. View the 12/07 testcase above and click on the "Document with 2k by 2k
   background" link.
3. Scroll down to the bottom of the document as soon as possible, and then
   up by one [PgUp].

* Actual Results:
A. Within a second or two after the background begins loading, the entire area
   that it will cover but has not yet covered is changed to black - black text
   on top of that is unreadable. Selecting this text makes it no more readable:
   the black background is inverted too.
B. In step 3, it can be seen that the second tile (vertically) of the
   background loads at the same time as the first tile; the as-yet-unloaded
   part of the first tile will still be black while the first part of the
   second tile is displayed. Where "a" is any natural number from zero up,
   "n" is the height of the background in px, and "x" is the number of rows
   of pixels displayed at a particular time, the text above the regions
   (a)*(n) to (a)*(n)+(x) can be read, and the text above the regions
   (a)*(n)+x+1 to (a+1)*(n)-1 cannot be read, unless it is a colour that
   contrasts sufficiently with black.

* Expected Result:
The background of any area where a background image will be displayed will
remain whatever it was before the background image began to load until the
background image actually appears in that area; no difficulties reading text
while the background image loads.

* Tested with:
1999-12-07-08-M12 nightly binary on Windows NT 4.0sp3
1999-12-05-12-M12 nightly binary on Windows NT 4.0sp3

* Additional Information:
This problem shows to a lesser extent with some of the other extreme
sized background testcases linked from the attachment; some of these
also create performance problems in scrolling.

This may be intentional during development for some good reason;
if that is the case, this bug report should probably get a late
milestone assigned to make sure that the code that turns the
background's area black is turned off or removed prior to shipping.

Changing component to "Layout" as a first try.

Comment 3

[troy]

This looks like a DUP of bug #1248. The bug is that we render parts of an image
that haven't yet loaded and so we display junk there

Pam, when is this bug going to get fixed? It's been around for ever...

*** This bug has been marked as a duplicate of 1248 ***

Comment 4

[pnunn]

Troy:
Its been low on the priority list.
-pn

Comment 5

[leger]

Marking Verified as a dup.