[PATCH libinput 2/2] touchpad: reduce button size, use physical sizes where possible

[Peter Hutterer]

The current 20% is excessive. On the t440s, the button size amounts to ~14mm
from the bottom. On the x220 it amounts to ~9mm, leaving only 31mm as actual
touchpad.

Reduce it to 15% instead, which amounts to 10.5mm on the t440 and 6mm on the
x220. Cap the button height further by making buttons a maximum height of
10mm, anything larger than that is excessive anyway.

Smaller buttons should be acceptable since we can rely on the bottom edge to
be a haptic feedback and thus a good hit-target, somewhat simliar to how
screen edges are good hit-targets.

The top software buttons stay the same size, but prefer a physical size of 6mm
instead (which is 1mm below the button marker line on the T440s). If no y
resolution is available, fall back to the 8% which is 5.6mm on the T440s.

Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
---
10mm height doesn't sound like much at first, but given a normal finger
position that's still quite large and easy to hit. The normal touch point
for a finger is not the top of the finger, but rather a fair bit back, that
X in this incredibly photo-realistic ASCII-art:
	       _____
  |           //   \\               |
  |           \\_X__\\              |
  |            \      \             |
  +-------------\      \-----------+


 src/evdev-mt-touchpad-buttons.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/evdev-mt-touchpad-buttons.c b/src/evdev-mt-touchpad-buttons.c
index 68b25dc..0957d03 100644
--- a/src/evdev-mt-touchpad-buttons.c
+++ b/src/evdev-mt-touchpad-buttons.c
@@ -564,11 +564,28 @@ tp_init_buttons(struct tp_dispatch *tp,
 	if (tp->buttons.is_clickpad && !tp->buttons.use_clickfinger) {
 		int xoffset = absinfo_x->minimum,
 		    yoffset = absinfo_y->minimum;
-		tp->buttons.bottom_area.top_edge = height * .8 + yoffset;
+		int yres = absinfo_y->resolution;
+
+		/* button height: 10mm or 15% of the touchpad height,
+		   whichever is smaller */
+		if (yres > 1 && (height * 0.15/yres) > 10) {
+			tp->buttons.bottom_area.top_edge =
+				absinfo_y->maximum - 10 * yres;
+		} else {
+			tp->buttons.bottom_area.top_edge = height * .85 + yoffset;
+		}
+
 		tp->buttons.bottom_area.rightbutton_left_edge = width/2 + xoffset;
 
 		if (tp->buttons.has_topbuttons) {
-			tp->buttons.top_area.bottom_edge = height * .08 + yoffset;
+			/* T440s has the top button line 5mm from the top,
+			   make the buttons 6mm high */
+			if (yres > 1) {
+				tp->buttons.top_area.bottom_edge =
+					yoffset + 6 * yres;
+			} else {
+				tp->buttons.top_area.bottom_edge = height * .08 + yoffset;
+			}
 			tp->buttons.top_area.rightbutton_left_edge = width * .58 + xoffset;
 			tp->buttons.top_area.leftbutton_right_edge = width * .42 + xoffset;
 		} else {
-- 
1.9.3