481768 - mouse wheel scrolls too far when viewport is smallish

Status: RESOLVED FIXED

(Core :: DOM: UI Events & Focus Handling, defect)

Description

[Karl Tomlinson (:karlt)]

Attachment: testcase

STR:
mouse over the textarea in the testcase, and move the scroll wheel one
notch down.

Actual results:
hij3 is aligned with the top of the textarea.
(Much of hij2 and hij5 is never visible when scrolling up and down with the
wheel.)

Expected results:
hij2 or at least the bottom part of it to scroll into view.

Although the mouse wheel is set to scroll 3 lines, this should be limited by
the page scroll amount.

Comment 1

[Karl Tomlinson (:karlt)]

Attachment: patch

Comment 2

[Olli Pettay [:smaug][[e-mail]]]

What is the behavior in other browsers? Or elsewhere?
Is this possible something which depends on the OS?

I agree "limited by the page scroll amount" does make sense, but
if that is not what happens elsewhere...

Comment 3

[Olli Pettay [:smaug][[e-mail]]]

Ok, I can't find any consistency in browsers.

Comment 4

[Olli Pettay [:smaug][[e-mail]]]

Attachment: testcase 2, even smaller textarea

Comment 5

[Olli Pettay [:smaug][[e-mail]]]

Attachment: alternative patch

Karl, what do you think about this?
This makes scrolling to work more like what happens when scrollbar's
arrow buttons are pressed, at least with your testcase.

Comment 6

[Karl Tomlinson (:karlt)]

Comment on attachment 365902 [details] [diff] [review]
alternative patch

> Karl, what do you think about this?

Yes, I like that.  (I had wondered whether that behavior might be better.)

>+          nscoord maxLines = (pageScroll / lineHeight);

These parentheses can be removed.

Comment 7

[Olli Pettay [:smaug][[e-mail]]]

http://hg.mozilla.org/mozilla-central/rev/797e33c3e909

(Passed locally mouse scroll related tests.)

Comment 8

[Dão Gottwald [:dao]]

sounds related:

*** 78368 ERROR TEST-UNEXPECTED-FAIL | /tests/toolkit/content/tests/widgets/test_mousescroll.xul | mouse-scroll of 'richlistbox' vertical starting 2 delta 100 eventType DOMMouseScroll hasPixels false - got 4, expected 5

Comment 9

[Olli Pettay [:smaug][[e-mail]]]

Backed out.

Comment 10

[Olli Pettay [:smaug][[e-mail]]]

I guess the testcase needs to be modified a bit.

Comment 11

[Karl Tomlinson (:karlt)]

Attachment: modify testRichListbox in test_mousescroll.xul

This modifies the test to check for scrolling in the correct direction.

Being specific about the item that will be at the top of the richlistbox would involve assumptions about the line-heights of the fonts involved and the height of each richlistitem.  ("mouse-scroll of 'richlistbox' vertical starting 2 delta 100 eventType DOMMouseScroll hasPixels false" gets 3 not 4 on my system.)

Comment 12

[Olli Pettay [:smaug][[e-mail]]]

http://hg.mozilla.org/mozilla-central/rev/da366d419dbc