29949 - Crud appears just under the scrollbar thumb (round off error)

Status: VERIFIED FIXED

(Core :: XUL, defect, P5)

Description

[Jesse Ruderman]

Bug: an extra light-gray line appears just under the part of the scrollbar you 
drag (the thumb?).  I have no reliable way to reproduce this bug, so I'll just 
toss out a few methods that all seem to work semi-reliably _on my computer and 
screen size_ :

- load the slashdot front page, or a slashdot article with threshold 3, with 
mozilla maximized. the thumb on the vertical scrollbar should be elongated 
(taller than a square). force the thumb up and down one page at a time: page-
down all the way, then page-up all the way, while watching the bottom of the 
thumb.

- make a long bookmarks list (10 screenfulls long is good) and pgup/pgdn your 
way through that by clicking in the dark part of the scrollbars.

- instead of pguping and pgdning, resize the window one pixel at a time. make 
sure the thumb isn't all the way at the top or bottom of the scrollbar before 
you do this.

In each case, the extra line goes away as soon as you move the thumb again.

Comment 1

[Peter Trudelle]

I can see this sometimes, assigning to evaughan as p5 for m18

Comment 2

[Tom 7]

This happens to me too in M14. This only occurs when I click the down arrow or

click in the darker area under the thumb to jump a page at a time. (Though I can

get it to appear on the right side of my horizontal scrollbar through regular

scrolling (drag the "thumb")). I will attach a screenshot.



My money is on a rounding problem when calculating the scrollbar thumb
height/width.

Comment 3

[Tom 7]

Attachment: Screenshot (GIF)

Comment 4

[Alistair Vining]

Attachment: Yet another image, showing the other issue

Comment 5

[Alistair Vining]

Sometimes the internal image moves without the thumb moving, too.  You can see 
this in the above attachment which shows the results of 4 cursor downs.

I don't see the bug when dragging with the mouse, btw.

Comment 6

[Peter Trudelle]

Mass moving M18 bugs to M19

Comment 7

[Eric Vaughan]

I believe this is a basic round off error when converting from twips to pixels 
in the box code. This really should be fixed for beta2 it happens all over the 
place.

Comment 8

[Eric Vaughan]

*** Bug 31515 has been marked as a duplicate of this bug. ***

Comment 9

[Eric Vaughan]

I have a fix. Currently testing.

Comment 10

[Eric Vaughan]

Fixed

Comment 11

[John Morrison]

verified fixed on mac/linux/win32 builds 20000523 am.

Comment 12

[John Morrison]

Bummer ... this is showing up again on mac/linux/win32 20000602nn verif. builds

Example: load Tinderbox page and hit the down scrollbarbutton. Periodically,
a one-pixel grey line will be drawn about 1px below the scrollbar thumb.
I don't see this problem in horizontal scrollbars, and I don't see it when 
scrolling up the page.

Comment 13

[Gary Frattarola]

I'm taking this one.

Comment 14

[Gary Frattarola]

Fixed in gfx/src/nsTransform2D.cpp
Fixed round off error by making nsTransform2D::TransformCoord(x,y,w,h) round the 
translation values for the scale & translate case in the same way as  
nsTransform2D::TransformCoord(x,y).

Comment 15

[John Morrison]

verified fixed 20000619am win32/linux/mac comm. builds. Thanks.

Comment 16

[Daniel Veditz [:dveditz]]

Adding keyword to bugs which already show a nsbeta2 triage value in the status 
whiteboard so the queries don't get screwed up.