Scrcpy: In Mac OS, I think the natural scrolling doesn't work

[fsw0422]

Is it just me? I use Mac OS Mojave in 2018 Mac Book Pro 15. Does anybody have the same issue? it seems to be working fine in my Ubuntu though

[rom1v]

What is "natural" scrolling?

[fsw0422]

@rom1v so when you scroll up (two finger swiping "up") it scrolls down and vice versa. there's a option in mouse and touchpad settings in the Mac where you can tick the box

[fsw0422]

Lovely application, but I'm checking if I'm the only one who has the issue. I've installed Scrcpy with brew

[rom1v]

So you are saying that the scroll is reversed in scrcpy?

[fsw0422]

yes so it's acting as if the "natural scroll" has been turned off. do you have a mac? you can probably quickly try it by enabling it in the settings

[rom1v]

do you have a mac?

No, I don't.

If you are comfortable with building it and play with the source code, here is the relevant part:

https://github.com/Genymobile/scrcpy/blob/8bc056b9c68eea7bccfa5d9123a70443fb1d75b2/app/src/input_manager.c#L554-L559

Ref: #49 and f9a63ec272a6051bd2f1a92a580640018124a34c

EDIT: More precisely, do you receive a different direction and y value when you use "natural scroll" compared to when you scroll using a mouse?

[fsw0422]

is this part the server?

[rom1v]

No, it's the client (it's in app/ and is written in C; the server is in server/ and is written in Java).

[fsw0422]

https://wiki.libsdl.org/SDL_MouseWheelEvent seems there is a FLIPPED option on event, but this only has to be activated when the user activates in the settings. Any idea on this?

[rom1v]

SDL_MOUSEWHEEL_FLIPPED is just a possible value of direction (and is already handled in the code):

int mul = from->direction == SDL_MOUSEWHEEL_NORMAL ? 1 : -1; 

[r4dixx]

FYI

Just tested on my machine with LOGD("x=%"PRIu32", y=%"PRIi32" (x%d), direction=%"PRIu32, from->x, from->y, mul, from->direction); right before convert_mouse_wheel's return statement.

Here's what I get:

Natural scroll enabled:

• trackpad: direction=1
• mouse (click): no output
• mouse (wheel): direction=1

Natural scroll disabled:

• trackpad: direction=0
• mouse (click): no output
• mouse (wheel): direction=0

In both cases, when using the trackpad, I get Unknown touch device id -1, cannot reset, so there's that...

Let me know if you need additional testing and/or info!

System info:

Scrcpy built locally from master

• ./run x --version

scrcpy 1.11

dependencies:
 - SDL 2.0.10
 - libavcodec 58.54.100
 - libavformat 58.29.100
 - libavutil 56.31.100

• sw_vers

ProductName:    Mac OS X
ProductVersion: 10.15.1
BuildVersion:   19B88

• uname -a

Darwin parprpmc008675a 19.0.0 Darwin Kernel Version 19.0.0: Thu Oct 17 16:17:15 PDT 2019; root:xnu-6153.41.3~29/RELEASE_X86_64 x86_64

[rom1v]

@r4dixx Thank you for the feedbacks.

Here is a summary of the results (I post them here to keep a trace).

Both with scroll or trackpad, when natural scroll is enabled:

# scroll up
x=0, y=-1 (mul=-1), direction=1

# scroll down
x=0, y=1 (mul=-1), direction=1

When natural scroll is disabled:

# scroll up
x=0, y=1 (mul=1), direction=0

# scroll down
x=0, y=-1 (mul=1), direction=0

So I guess the correct behavior is to just ignore the direction field (which forces the scroll to be "unnatural":

Movements down (scroll backward) generate negative y values and up (scroll forward) generate positive y values.
[…]
If direction is SDL_MOUSEWHEEL_FLIPPED the values in x and y will be opposite. Multiply by -1 to change them back.

https://wiki.libsdl.org/SDL_MouseWheelEvent#Remarks

diff --git a/app/src/input_manager.c b/app/src/input_manager.c
index 7d333c1..49faa11 100644
--- a/app/src/input_manager.c
+++ b/app/src/input_manager.c
@@ -550,13 +550,8 @@ convert_mouse_wheel(const SDL_MouseWheelEvent *from, struct screen *screen,
     to->type = CONTROL_MSG_TYPE_INJECT_SCROLL_EVENT;

     to->inject_scroll_event.position = position;
-
-    int mul = from->direction == SDL_MOUSEWHEEL_NORMAL ? 1 : -1;
-    // SDL behavior seems inconsistent between horizontal and vertical scrolling
-    // so reverse the horizontal
-    // <https://wiki.libsdl.org/SDL_MouseWheelEvent#Remarks>
-    to->inject_scroll_event.hscroll = -mul * from->x;
-    to->inject_scroll_event.vscroll = mul * from->y;
+    to->inject_scroll_event.hscroll = from->x;
+    to->inject_scroll_event.vscroll = from->y;

     return true;
 }

[r4dixx]

Works perfectly. Vertically and horizontally. Thanks a whole bunch!

[rom1v]

Fixed by 3100533e56b2efdfc6f07b96681a7eef25ff63e0.