commit a59ff74c9091568698564ac2d4013e4a4df09d7f
author Andrew de los Reyes <adlr@chromium.org> Wed Sep 10 17:11:49 2014
committer chrome-internal-fetch <chrome-internal-fetch@google.com> Wed Sep 17 01:24:37 2014
tree 4f7c9ac423bc79f0c3130feb2465d033b97b1b40
parent b86f7aebe6ce13a2d38d77f56b4b20175b1d3ae3

ScalingFilterInterpreter: Special-case small mice moves

When using mice, it's frustrating when moving one device pixel moves
the cursor > 1 pixels on the screen. This CL avoids this problem by
looking for the special case of exactly 1 device pixel move, then
reducing the motion to just 1 pixel of motion.

We actually go a little under 1 pixel because it will be increased on
external displays later in the stack.

BUG=chromium:412864
TEST=logitech-t620/low_dpi_move regression test
Change-Id: I822237cb4acec30dd7e1e78d6e15e5cc9b8e2543
Reviewed-on: https://chromium-review.googlesource.com/217496
Reviewed-by: Charles Mooney <charliemooney@chromium.org>
Tested-by: Andrew de los Reyes <adlr@chromium.org>
Commit-Queue: Andrew de los Reyes <adlr@chromium.org>

src/scaling_filter_interpreter.cc

diff --git a/src/scaling_filter_interpreter.cc b/src/scaling_filter_interpreter.cc
index e5ace57..e24cdfb 100755
--- a/src/scaling_filter_interpreter.cc
+++ b/src/scaling_filter_interpreter.cc
@@ -201,12 +201,38 @@
 void ScalingFilterInterpreter::ConsumeGesture(const Gesture& gs) {
   Gesture copy = gs;
   switch (copy.type) {
-    case kGestureTypeMove:
+    case kGestureTypeMove: {
+      int original_rel_x =
+          copy.details.move.ordinal_dx * mouse_cpi_.val_ / 25.4;
+      int original_rel_y =
+          copy.details.move.ordinal_dy * mouse_cpi_.val_ / 25.4;
       copy.details.move.dx *= screen_x_scale_;
       copy.details.move.dy *= screen_y_scale_;
       copy.details.move.ordinal_dx *= screen_x_scale_;
       copy.details.move.ordinal_dy *= screen_y_scale_;
+      // Special case of motion: if a mouse move of 1 device unit
+      // (rel_[xy] == 1) would move the cursor on the screen > 1
+      // pixel, force it to just one pixel. This prevents low-DPI mice
+      // from jumping 2 pixels at a time when doing slow moves.
+      // Note, we use 1 / 1.2 = 0.8333 instead of 1 for the number of
+      // screen pixels, as external monitors get a 20% distance boost.
+      // Mice are most commonly used w/ external displays.
+      if (device_mouse_.val_ &&
+          ((original_rel_x == 0) != (original_rel_y == 0))) {
+        const double kMinPixels = 1.0 / 1.2;
+        if (fabs(copy.details.move.dx) > kMinPixels &&
+            abs(original_rel_x) == 1) {
+          copy.details.move.dx = copy.details.move.ordinal_dx =
+              copy.details.move.dx > 0.0 ? kMinPixels : -kMinPixels;
+        }
+        if (fabs(copy.details.move.dy) > kMinPixels &&
+            abs(original_rel_y) == 1) {
+          copy.details.move.dy = copy.details.move.ordinal_dy =
+              copy.details.move.dy > 0.0 ? kMinPixels : -kMinPixels;
+        }
+      }
       break;
+    }
     case kGestureTypeScroll:
       if (devclass_ != GESTURES_DEVCLASS_MOUSE) {
         copy.details.scroll.dx *= screen_x_scale_;