#2288 SCN_DWELLEND incorrectly called after SCI_CALLTIPSETPOSITION, SCI_CALLTIPSHOW

[Kered13]

I encountered a peculiar bug under a very particular set of circumstances when developing a plugin for Notepad++. After tracking it down, I believe I have identified the problem, confirmed that it is present in the latest version of Scintilla, and I have a potential fix.

Let me start with the reproduction steps:

1. Size the window so there is no horizontal scrollbar.
2. Idle the mouse to trigger an SCN_DWELLSTART notification (leave idle for the rest of the steps).
3. Send SCI_CALLTIPSETPOSITION message.
4. Send SCI_CALLTIPSHOW message.

Expected behavior: No SCN_DWELLEND message.
Actual behavior: An SCN_DWELLEND message is triggered on the next tick.

Detailed explanation that I have found:

The SCI_CALLTIPSETPOSITION message calls InvalidateStyleRedraw. On this next tick this forces a redraw, which eventually invokes ModifyScrollBars. This method attempts to check if the scrollbars need to be updated. For this two values are calculated: horizEndPreferred, which is based on the width of the text; and pageWidth, which is based on the width of the window. If these values differ from nMax and nPage as returned by GetScroll Info, then SetScrollInfo is called using horizEndPreferred is used to set nMax and pageWidth is used to set nPage. However SetScrollInfo clamps nPage to nMax - nMin +1. As a result, when the window is wider than the text the actual new scroll info is not the same as the desired scroll info, and ModifyScrollBars will attempt to set the horizontal scroll info and returns true every time styles are recomputed.

I have attached a patch that I believe should fix this behavior. I have tested it in Notepad++ and found no issues.

[Neil Hodgson]

OK, committed as [6d6294].

Credited to "Derek". If you prefer a different name in the credits please tell me what you would like.

[Kered13]

I am already in the credits ("Derek Brown").

On Mon, Oct 18, 2021, 8:48 AM Neil Hodgson nyamatongwe@users.sourceforge.net wrote:

OK, committed as [6d6294].

Credited to "Derek". If you prefer a different name in the credits please
tell me what you would like.

---

** [bugs:#2288] SCN_DWELLEND incorrectly called after
SCI_CALLTIPSETPOSITION, SCI_CALLTIPSHOW**

Status: open
Group: Bug
Created: Sat Oct 16, 2021 10:40 AM UTC by Kered13
Last Updated: Sat Oct 16, 2021 10:40 AM UTC
Owner: nobody
Attachments:

• 8985.patch (1.6
  kB; application/octet-stream)

I encountered a peculiar bug under a very particular set of circumstances
when developing a plugin for Notepad++. After tracking it down, I believe I
have identified the problem, confirmed that it is present in the latest
version of Scintilla, and I have a potential fix.

Let me start with the reproduction steps:

1. Size the window so there is no horizontal scrollbar.
2. Idle the mouse to trigger an SCN_DWELLSTART notification (leave idle
   for the rest of the steps).
3. Send SCI_CALLTIPSETPOSITION message.
4. Send SCI_CALLTIPSHOW message.

Expected behavior: No SCN_DWELLEND message.
Actual behavior: An SCN_DWELLEND message is triggered on the next tick.

Detailed explanation that I have found:

The SCI_CALLTIPSETPOSITION message calls InvalidateStyleRedraw. On this
next tick this forces a redraw, which eventually invokes ModifyScrollBars.
This method attempts to check if the scrollbars need to be updated. For
this two values are calculated: horizEndPreferred, which is based on the
width of the text; and pageWidth, which is based on the width of the
window. If these values differ from nMax and nPage as returned by GetScroll
Info, then SetScrollInfo
is called using horizEndPreferred is used to set nMax and pageWidth is used
to set nPage. However SetScrollInfo clamps nPage to nMax - nMin +1. As a
result, when the window is wider than the text the actual new scroll info
is not the same as the desired scroll info, and ModifyScrollBars will
attempt to set the horizontal scroll info and returns true every time
styles are recomputed.

I have attached a patch that I believe should fix this behavior. I have
tested it in Notepad++ and found no issues.

---

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[Kered13]

I'm actually already in the credits ("Derek Brown").