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subraizada3

Member

Registered: 2013-06-02

Posts: 90

Getting Size/Resolution of Synaptics Touchpad

I set up circular scrolling / chiral scrolling for my synaptics touchpad. However, the activation zones are too large and I have to keep my finger within the middle half of an already small trackpad.
I looked at the values for the edge zones via synclient:

LeftEdge                = 1767
RightEdge               = 5397
TopEdge                 = 1637
BottomEdge              = 4451

These seem like pretty arbitrary numbers to me. Adding the left/right or top/bottom numbers results in another arbitrary number, so either the trackpad has a weird resolution or these zones are not the same size on opposite sides of the trackpad.

xinput --list-props gave

Synaptics Pad Resolution (320):	102, 66

According to some websites I found on the Interwebs, that's the resolution per mm of trackpad, except I don't know the size of the trackpad in millimeters (it might not even be an integer).

Being a perfectionist, I want to keep the edge zones on the trackpad symmetrical while making them smaller, but that's kind of hard to do without knowing the size of the trackpad in this case. Is there any way I can find the size in these units?

Trilby

Inspector Parrot

Registered: 2011-11-29

Posts: 29,615

Website

Re: Getting Size/Resolution of Synaptics Touchpad

... except I don't know the size of the trackpad in millimeters (it might not even be an integer).

I suspect finding a ruler would be the easiest approach.

---

"UNIX is simple and coherent..." - Dennis Ritchie, "GNU's Not UNIX" -  Richard Stallman

subraizada3

Member

Registered: 2013-06-02

Posts: 90

Re: Getting Size/Resolution of Synaptics Touchpad

The problem with that is that the size isn't necessarily a whole number of millimeters - it's kind of hard to measure to a submillimeter precision with a ruler. Also, my trackpad is slightly trapezoidal - the bottom is wider than the top.

I went ahead and measured it anyway. The bottom edge is about 80 mm long, the top is about 72 mm, and it is about 40 mm tall.

The synaptics man page says the Pad Resolution is "vertical, horizontal," so I multiplied it out and the values don't match (that's assuming the default edges are the same on both sides, and both pairs of edge areas (top/bottom and L/R) are measured from the same edge - from my experience with the edge zones, the second should be true as it roughly matches the proportions of the trackpad).

1767 + 5397 = 7164
80 * 66 = 5280
72 * 66 = 4752

1637 + 4451 = 6088
40 * 102 = 4080

Just in case the values were for some reason flipped, I tried the other scenario for the Pad Resolution.
80 * 102 = 8180
72 * 102 = 7344
40 * 66 = 2640

72 mm wide on the top edge with a horizontal resolution of 102 units/mm gets kind of close (7344 / 7164), but then the vertical values don't match.

TL;DR measuring with a ruler doesn't help, or the default edge areas are for some reason not equal on opposite sides of the touchpad.

Last edited by subraizada3 (2014-10-18 03:36:02)