[Spice-devel] [vdagent-win PATCH] handle_mouse_event: fix off-by-one when normalizing mouse coordinates

[Fabiano Fidêncio]

On Mon, Nov 23, 2015 at 9:21 AM, Uri Lublin <uril at redhat.com> wrote:
> On 11/23/2015 01:40 AM, Fabiano Fidêncio wrote:
>>
>> On Sun, Nov 22, 2015 at 4:54 PM, Uri Lublin <uril at redhat.com> wrote:
>>>
>>> Mouse coordinates can be 0..(width-1) and 0..(height-1)
>>>
>>> Normalization of mouse coordinates (for SendInput) was done
>>> against w,h and thus right-most and down-most coordinates
>>> could never be reached.
>>
>>
>> So, you're avoiding a division by zero, right? This is the main point
>> of this patch AFAIU.
>> IMHO, it should be a bit more explicit in the log.
>
>
> Hi Fabiano,
>
> The main point of this patch is to normalize the input value sent
> to Windows with SendInput using w-1 and h-1.
> The normalized right-most point would be 0xFFFF (65536).
> Since the possible values are 0..(w-1) with the new code we
> get 0xFFFF * (w-1)/(w-1)
> instead of what was before 0xFFFF * (w-1)/w .
> For example if w=800, 0xFFFF * (w-1)/w = 65453

I see.

>
>
> I can replace "protection" below with an explicit sentence.

No, you don't have to. It's good as it is.

>
> Thanks,
>     Uri
>
>
>>
>>>
>>> Fix it by normalizing against (w-1) and (h-1).
>>>
>>> Also added protection against a case of 0 or 1 (for any of w,h)
>>> Fixes rhbz#1032037
>>> ---
>>>   vdagent/vdagent.cpp | 10 ++++++----
>>>   1 file changed, 6 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/vdagent/vdagent.cpp b/vdagent/vdagent.cpp
>>> index c976665..595db85 100644
>>> --- a/vdagent/vdagent.cpp
>>> +++ b/vdagent/vdagent.cpp
>>> @@ -567,13 +567,15 @@ bool VDAgent::handle_mouse_event(VDAgentMouseState*
>>> state)
>>>       ZeroMemory(&_input, sizeof(INPUT));
>>>       _input.type = INPUT_MOUSE;
>>>       if (state->x != _mouse_x || state->y != _mouse_y) {
>>> +        DWORD w = _desktop_layout->get_total_width();
>>> +        DWORD h = _desktop_layout->get_total_height();
>>> +        w = (w > 1) ? w-1 : 1; /* coordinates are 0..w-1, protect w==0
>>> */
>>> +        h = (h > 1) ? h-1 : 1; /* coordinates are 0..h-1, protect h==0
>>> */
>>>           _mouse_x = state->x;
>>>           _mouse_y = state->y;
>>>           mouse_move = MOUSEEVENTF_MOVE;
>>> -        _input.mi.dx = (mode->get_pos_x() + _mouse_x) * 0xffff /
>>> -                       _desktop_layout->get_total_width();
>>> -        _input.mi.dy = (mode->get_pos_y() + _mouse_y) * 0xffff /
>>> -                       _desktop_layout->get_total_height();
>>> +        _input.mi.dx = (mode->get_pos_x() + _mouse_x) * 0xffff / w;
>>> +        _input.mi.dy = (mode->get_pos_y() + _mouse_y) * 0xffff / h;
>>>       }
>>>       if (state->buttons != _buttons_state) {
>>>           buttons_change = get_buttons_change(_buttons_state,
>>> state->buttons, VD_AGENT_LBUTTON_MASK,
>>> --
>>> 2.5.0
>>>
>>> _______________________________________________
>>> Spice-devel mailing list
>>> Spice-devel at lists.freedesktop.org
>>> http://lists.freedesktop.org/mailman/listinfo/spice-devel
>>
>>
>> ACK (feel free to ignore my comment if you think the commit message is
>> clear enough).
>>
>



-- 
Fabiano Fidêncio