(Windows) Cursor hiding takes time related to number of times cursor shape has been changed since it was last hidden #68848

New Issue

Chris Dusto · 2019-08-20T01:42:11+02:00

Chris Dusto commented

2019-08-20 01:42:11 +02:00

System Information
Operating system: Windows 7
Graphics card: AMD Radeon HD 7520G w/ nonstandard drivers

Blender Version
Broken: 2.79b, 2.79c, 2.80

Short description of error
Every time Blender changes the cursor shape under Windows, even if the cursor is already visible, it issues a call to ::ShowCursor(TRUE), which (according to MSDN) always increments an internal counter. To hide the cursor, Blender calls ::ShowCursor(FALSE) in a loop, which ends up taking O(n) time wrt the number of times the cursor's shape has changed since last being hidden. Combined with Windows doing its own stuff during the execution of the API call, this can result in a prolonged lockup. This was extremely noticable in 2.79, but is still an issue in 2.80

Exact steps for others to reproduce the error
scripting.blend This file contains a script that defines an operator, which has the effect of changing the cursor to a random shape every time a mouse move event is received, until the left mouse button is pressed. After running this operator, moving the mouse around a lot, clicking to end the operator, and then doing something that hides the mouse cursor (e.g. in 2.79, clicking within a numeric input field), Blender starts consuming 100% CPU time available to a single thread as in invokes ::ShowCursor(FALSE) in a loop.

Other notes
I had built a 2.79 using the following diff, which resolves the issue:

diff --git a/intern/ghost/intern/GHOST_WindowWin32.cpp b/intern/ghost/intern/GHOST_WindowWin32.cpp
index b3a262537f..1899691116 100644
--- a/intern/ghost/intern/GHOST_WindowWin32.cpp
+++ b/intern/ghost/intern/GHOST_WindowWin32.cpp
@@ -775,11 +775,15 @@ void GHOST_WindowWin32::registerMouseClickEvent(int press)

 void GHOST_WindowWin32::loadCursor(bool visible, GHOST_TStandardCursor cursor) const
 {
-       if (!visible) {
-               while (::ShowCursor(FALSE) >= 0) ;
-       }
-       else {
-               while (::ShowCursor(TRUE) < 0) ;
+       ::CURSORINFO cursorinfo;
+       cursorinfo.cbSize = sizeof(::CURSORINFO);
+       if(!(::GetCursorInfo(&cursorinfo) && (cursorinfo.flags & CURSOR_SHOWING) == (visible ? CURSOR_SHOWING : 0))) {
+               if (!visible) {
+                       while (::ShowCursor(FALSE) >= 0) ;
+               }
+               else {
+                       while (::ShowCursor(TRUE) < 0) ;
+               }
        }

        if (cursor == GHOST_kStandardCursorCustom && m_customCursor) {```
I am currently in the process of compiling a 2.80 with the same patch applied. The additional Windows API function used should be available in all 64-bit versions of Windows (it was introduced in Windows 2000 Professional), and has the effect of completely avoiding modification of the internal counter if the cursor is already in the desired visible/hidden state.

**System Information** Operating system: Windows 7 Graphics card: AMD Radeon HD 7520G w/ nonstandard drivers **Blender Version** Broken: 2.79b, 2.79c, 2.80 **Short description of error** Every time Blender changes the cursor shape under Windows, even if the cursor is already visible, it issues a call to `::ShowCursor(TRUE)`, which (according to MSDN) always increments an internal counter. To hide the cursor, Blender calls `::ShowCursor(FALSE)` in a loop, which ends up taking O(n) time wrt the number of times the cursor's shape has changed since last being hidden. Combined with Windows doing its own stuff during the execution of the API call, this can result in a prolonged lockup. This was _extremely_ noticable in 2.79, but is still an issue in 2.80 **Exact steps for others to reproduce the error** [scripting.blend](https://archive.blender.org/developer/F7673993/scripting.blend) This file contains a script that defines an operator, which has the effect of changing the cursor to a random shape every time a mouse move event is received, until the left mouse button is pressed. After running this operator, moving the mouse around a lot, clicking to end the operator, and then doing something that hides the mouse cursor (e.g. in 2.79, clicking within a numeric input field), Blender starts consuming 100% CPU time available to a single thread as in invokes `::ShowCursor(FALSE)` in a loop. **Other notes** I had built a 2.79 using the following diff, which resolves the issue: ``` diff --git a/intern/ghost/intern/GHOST_WindowWin32.cpp b/intern/ghost/intern/GHOST_WindowWin32.cpp index b3a262537f..1899691116 100644 --- a/intern/ghost/intern/GHOST_WindowWin32.cpp +++ b/intern/ghost/intern/GHOST_WindowWin32.cpp @@ -775,11 +775,15 @@ void GHOST_WindowWin32::registerMouseClickEvent(int press) void GHOST_WindowWin32::loadCursor(bool visible, GHOST_TStandardCursor cursor) const { - if (!visible) { - while (::ShowCursor(FALSE) >= 0) ; - } - else { - while (::ShowCursor(TRUE) < 0) ; + ::CURSORINFO cursorinfo; + cursorinfo.cbSize = sizeof(::CURSORINFO); + if(!(::GetCursorInfo(&cursorinfo) && (cursorinfo.flags & CURSOR_SHOWING) == (visible ? CURSOR_SHOWING : 0))) { + if (!visible) { + while (::ShowCursor(FALSE) >= 0) ; + } + else { + while (::ShowCursor(TRUE) < 0) ; + } } if (cursor == GHOST_kStandardCursorCustom && m_customCursor) {``` I am currently in the process of compiling a 2.80 with the same patch applied. The additional Windows API function used should be available in all 64-bit versions of Windows (it was introduced in Windows 2000 Professional), and has the effect of completely avoiding modification of the internal counter if the cursor is already in the desired visible/hidden state.

Chris Dusto commented

2019-08-20 01:42:11 +02:00

Added subscriber: @TruePikachu

Chris Dusto commented

2019-08-27 16:36:52 +02:00

I can't 100% verify if the patch is stable under 2.80, since I have a now-unsupported-because-of-instability GPU (and I can't manage to track down the issue in the driver far enough to binary patch it), but it is stable for 2.79, and I'd expect it to remain as such for 2.80 since it doesn't touch any of Blender's own data structures.

I can't 100% **verify** if the patch is stable under 2.80, since I have a now-unsupported-because-of-instability GPU (and I can't manage to track down the issue in the driver far enough to binary patch it), but it *is* stable for 2.79, and I'd expect it to remain as such for 2.80 since it doesn't touch any of Blender's own data structures.

Richard Antalik commented

2020-01-08 15:31:50 +01:00

Added subscriber: @iss

Richard Antalik commented

2020-01-08 15:31:50 +01:00

Changed status from 'Needs Triage' to: 'Needs User Info'

Richard Antalik commented

2020-01-08 15:31:50 +01:00

@TruePikachu I tried to reproduce (win10) issue of delay when cursor is hidden. I ran your script, moved mouse for a few minues, clicked to cancel and then clicked on numerical input.
No delay was precieved.

Is this still an issue for you?

@TruePikachu I tried to reproduce (win10) issue of delay when cursor is hidden. I ran your script, moved mouse for a few minues, clicked to cancel and then clicked on numerical input. No delay was precieved. Is this still an issue for you?

Chris Dusto commented

2020-01-08 23:26:50 +01:00

Testing under Windows 7 on unpatched 2.79b, the issue still persists after system updates. I can't test right now on either Windows 10 or any 2.80 version (including dev), but I do have a new system in the mail which I should be able to run measurements on when it arrives.

Testing under Windows 7 on unpatched 2.79b, the issue still persists after system updates. I can't test *right now* on either Windows 10 or any 2.80 version (including dev), but I do have a new system in the mail which I should be able to run measurements on when it arrives.

Richard Antalik commented

2020-01-09 10:49:08 +01:00

We are trying to close as many reports as possible, so if you test this and issue is still there, you can reopen this report if closed. Or respond, that issue is still there.

Richard Antalik commented

2020-01-16 12:06:49 +01:00

Changed status from 'Needs User Info' to: 'Archived'

Richard Antalik closed this issue

2020-01-16 12:06:49 +01:00

Richard Antalik self-assigned this 2020-01-16 12:06:49 +01:00

Richard Antalik commented

2020-01-16 12:06:49 +01:00

Since last asking for information it has been 7 or more days, due to the policy of our bug tracker we will have to close the report.

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(Windows) Cursor hiding takes time related to number of times cursor shape has been changed since it was last hidden #68848