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Diffstat (limited to 'en/devices/input/key-layout-files.html')
| -rw-r--r-- | en/devices/input/key-layout-files.html | 31 |
1 files changed, 22 insertions, 9 deletions
diff --git a/en/devices/input/key-layout-files.html b/en/devices/input/key-layout-files.html index 22faf84e..486b4fcb 100644 --- a/en/devices/input/key-layout-files.html +++ b/en/devices/input/key-layout-files.html @@ -133,19 +133,32 @@ axis 0x05 invert BRAKE <p>In the above example, if the value of <code>ABS_RZ</code> is <code>2</code> then <code>AXIS_BRAKE</code> is set to <code>-2</code>.</p> -<h4 id="center-flat-position-option">Center Flat Position Option</h4> -<p>The center flat position is the neutral position of the axis, such as when -a directional pad is in the very middle of its range and the user is not -touching it.</p> +<h4 id="center-flat-option">Center Flat Option</h4> +<p> A joystick device may report input events even when the joystick is not being used, due to noise. +This noise typically comes from the left and/or right sticks, and causes the driver to report + a position value near 0. +The "center flat" value specifies the amount of noise to expect from the controller at rest.</p> <p>The Linux input protocol provides a way for input device drivers to specify -the center flat position of joystick axes but not all of them do and some of -them provide incorrect values. To resolve this issue, an axis declaration may be -followed by a <code>flat</code> option that specifies the value of the center -flat position for the axis.</p> +the center flat value of joystick axes, but not all drivers report it and some of them provide +incorrect values. To resolve this issue, an axis declaration may be followed by a +<code>flat</code> option that specifies the width of the region around the center +position of the axis that should be considered as centered.</p> +<p> For example, if a device driver reports values for <code>AXIS_X</code> between 0 and 100, +then 0 will be mapped to -1 and 100 will be mapped to 1 by the Android input system. +The center of the range will be 50 in the unscaled coordinates and 0 in the scaled coordinates. +If a flat value is equal to 10, +then the developers should assume that any <code>AXIS_X</code> value reported between +-0.1 and 0.1 (between 40 and 60 in unscaled coordinates) is noise, and treat those values coming +from the joystick as zero.</p> +<p class="note"><strong>Note</strong>: While the key layout file specifies the value + for the driver coordinate space, +the value reported by android.view.InputDevice.MotionRange#getFlat() is in the Android +coordinate space.</p> + <pre class="devsite-click-to-copy"> axis 0x03 Z flat 4096 </pre> -<p>In the above example, the center flat position is set to <code>4096</code>. +<p>In the above example, the center flat value is set to <code>4096</code>. </p> <h3 id="comments">Comments</h3> |