__set_bit(INPUT_PROP_DIRECT, input_dev->propbit);
INPUT_PROP_DIRECT特性表明设备的坐标直接和屏幕坐标向对应（无需琐碎的转换操作，像缩放，反转，旋转等）。非直接输入设备则需要一些必要的变换，比如触摸板上绝对到相对的变换。典型的直接输入设备有：触摸屏，手写板；非直接输入设备有：触摸板，鼠标。
frameworks/native/services/inputflinger/InputReader.cpp
if (getEventHub()->hasInputProperty(getDeviceId(), INPUT_PROP_DIRECT)) {
// The device is a touch screen.
mParameters.deviceType = Parameters::DEVICE_TYPE_TOUCH_SCREEN;
} else if (getEventHub()->hasInputProperty(getDeviceId(), INPUT_PROP_POINTER)) {
// The device is a pointing device like a track pad.
mParameters.deviceType = Parameters::DEVICE_TYPE_POINTER;
} else if (getEventHub()->hasRelativeAxis(getDeviceId(), REL_X)
|| getEventHub()->hasRelativeAxis(getDeviceId(), REL_Y)) {
// The device is a cursor device with a touch pad attached.
// By default don‘t use the touch pad to move the pointer.
mParameters.deviceType = Parameters::DEVICE_TYPE_TOUCH_PAD;
} else {
// The device is a touch pad of unknown purpose.
mParameters.deviceType = Parameters::DEVICE_TYPE_POINTER;
}