1:orphan: 2 3.. _touchpads: 4 5============================================================================== 6Touchpads 7============================================================================== 8 9This page provides an outline of touchpad devices. Touchpads aren't simply 10categorised into a single type, instead they have a set of properties, a 11combination of number of physical buttons, multitouch support abilities and 12other properties. 13 14.. _touchpads_buttons: 15 16------------------------------------------------------------------------------ 17Number of buttons 18------------------------------------------------------------------------------ 19 20.. _touchapds_buttons_phys: 21 22.............................................................................. 23Physically separate buttons 24.............................................................................. 25 26Touchpads with physical buttons usually provide two buttons, left and right. 27A few touchpads with three buttons exist, and Apple used to have touchpads 28with a single physical buttons until ca 2008. Touchpads with only two 29buttons require the software stack to emulate a middle button. libinput does 30this when both buttons are pressed simultaneously. 31 32Note that many Lenovo laptops provide a pointing stick above the touchpad. 33This pointing stick has a set of physical buttons just above the touchpad. 34While many users use those as substitute touchpad buttons, they logically 35belong to the pointing stick. The \*40 and \*50 series are an exception here, 36the former had no physical buttons on the touchpad and required the top 37section of the pad to emulate pointing stick buttons, the \*50 series has 38physical buttons but they are wired to the touchpads. The kernel re-routes 39those buttons through the trackstick device. See :ref:`t440_support` for more 40information. 41 42.. _touchpads_buttons_clickpads: 43 44.............................................................................. 45Clickpads 46.............................................................................. 47 48Clickpads are the most common type of touchpads these days. A Clickpad has 49no separate physical buttons, instead the touchpad itself is clickable as a 50whole, i.e. a user presses down on the touch area and triggers a physical 51click. Clickpads thus only provide a single button, everything else needs to 52be software-emulated. See :ref:`clickpad_softbuttons` for more information. 53 54Clickpads are labelled by the kernel with the **INPUT_PROP_BUTTONPAD** input 55property. 56 57.. _touchpads_buttons_forcepads: 58 59.............................................................................. 60Forcepads 61.............................................................................. 62 63Forcepads are Clickpads without a physical button underneath the hardware. 64They provide pressure and may have a vibration element that is 65software-controlled. This element can simulate the feel of a physical 66click or be co-opted for other tasks. 67 68 69.. _touchpads_touch: 70 71------------------------------------------------------------------------------ 72Touch capabilities 73------------------------------------------------------------------------------ 74 75Virtually all touchpads available now can **detect** multiple fingers on 76the touchpad, i.e. provide information on how many fingers are on the 77touchpad. The touch capabilities described here specify how many fingers a 78device can **track**, i.e. provide reliable positional information for. 79In the kernel each finger is tracked in a so-called "slot", the number of 80slots thus equals the number of simultaneous touches a device can track. 81 82.. _touchapds_touch_st: 83 84.............................................................................. 85Single-touch touchpads 86.............................................................................. 87 88Single-finger touchpads can track a single touchpoint. Most single-touch 89touchpads can also detect three fingers on the touchpad, but no positional 90information is provided for those. In libinput, these touches are termed 91"fake touches". The kernel sends **BTN_TOOL_DOUBLETAP**, 92**BTN_TOOL_TRIPLETAP**, **BTN_TOOL_QUADTAP** and **BTN_TOOL_QUINTTAP** 93events when multiple fingers are detected. 94 95.. _touchpads_touch_mt: 96 97.............................................................................. 98Pure multi-touch touchpads 99.............................................................................. 100 101Pure multi-touch touchpads are those that can track, i.e. identify the 102location of all fingers on the touchpad. Apple's touchpads support 16 103touches, others support 5 touches like the Synaptics touchpads when using 104SMBus. 105 106These touchpads usually also provide extra information. Apple touchpads 107provide an ellipse and the orientation of the ellipse for each touch point. 108Other touchpads provide a pressure value for each touch point (see 109:ref:`touchpads_pressure_handling`). 110 111Note that the kernel sends **BTN_TOOL_DOUBLETAP**, 112**BTN_TOOL_TRIPLETAP**, **BTN_TOOL_QUADTAP** and **BTN_TOOL_QUINTTAP** 113events for all touches for backwards compatibility. libinput ignores these 114events if the touchpad can track touches correctly. 115 116.. _touchpads_touch_partial_mt: 117 118.............................................................................. 119Partial multi-touch touchpads 120.............................................................................. 121 122The vast majority of touchpads fall into this category, the half-way 123point between single-touch and pure multi-touch. These devices can track N 124fingers, but detect more than N. For example, when using the serial 125protocol, Synaptics touchpads can track two fingers but may detect up to 126five. 127 128The number of slots may limit which features are available in libinput. 129Any device with two slots can support two-finger scrolling, but 130:ref:`thumb-detection` or :ref:`palm_detection` may be limited if only two 131slots are available. 132 133.. _touchpads_touch_semi_mt: 134 135.............................................................................. 136Semi-mt touchpads 137.............................................................................. 138 139A sub-class of partial multi-touch touchpads. These touchpads can 140technically detect two fingers but the location of both is limited to the 141bounding box, i.e. the first touch is always the top-left one and the second 142touch is the bottom-right one. Coordinates jump around as fingers move past 143each other. 144 145Many semi-mt touchpads also have a lower resolution for the second touch, or 146both touches. This may limit some features such as :ref:`gestures` or 147:ref:`scrolling`. 148 149Semi-mt are labelled by the kernel with the **INPUT_PROP_SEMI_MT** input 150property. 151 152.. _touchpads_mis: 153 154------------------------------------------------------------------------------ 155Other touchpad properties 156------------------------------------------------------------------------------ 157 158.. _touchpads_external: 159 160.............................................................................. 161External touchpads 162.............................................................................. 163 164External touchpads are USB or Bluetooth touchpads not in a laptop chassis, 165e.g. Apple Magic Trackpad or the Logitech T650. These are usually 166:ref:`touchpads_buttons_clickpads` the biggest difference is that they can be 167removed or added at runtime. 168 169One interaction method that is only possible on external touchpads is a 170thumb resting on the very edge/immediately next to the touchpad. On the far 171edge, touchpads don't always detect the finger location so clicking with a 172thumb barely touching the edge makes it hard or impossible to figure out 173which software button area the finger is on. 174 175These touchpads also don't need :ref:`palm_detection` - since they're not 176located underneath the keyboard, accidental palm touches are a non-issue. 177 178.. _touchpads_pressure_handling: 179 180.............................................................................. 181Touchpads pressure handling 182.............................................................................. 183 184Pressure is usually directly related to contact area. Human fingers flatten 185out as the pressure on the pad increases, resulting in a bigger contact area 186and the firmware then calculates that back into a pressure reading. 187 188libinput uses pressure to detect accidental palm contact and thumbs, though 189pressure data is often device-specific and unreliable. 190 191.. _touchpads_circular: 192 193.............................................................................. 194Circular touchpads 195.............................................................................. 196 197Only listed for completeness, circular touchpads have not been used in 198laptops for a number of years. These touchpad shaped in an ellipse or 199straight. 200 201.. _touchpads_tablets: 202 203.............................................................................. 204Graphics tablets 205.............................................................................. 206 207Touch-capable graphics tablets are effectively external touchpads, with two 208differentiators: they are larger than normal touchpads and they have no 209regular touchpad buttons. They either work like a 210:ref:`touchpads_buttons_forcepads` Forcepad, or rely on interaction methods that 211don't require buttons (like :ref:`tapping`). Since the physical device is 212shared with the pen input, some touch arbitration is required to avoid touch 213input interfering when the pen is in use. 214 215.. _touchpads_edge_zone: 216 217.............................................................................. 218Dedicated edge scroll area 219.............................................................................. 220 221Before :ref:`twofinger_scrolling` became the default scroll method, some 222touchpads provided a marking on the touch area that designates the 223edge to be used for scrolling. A finger movement in that edge zone should 224trigger vertical motions. Some touchpads had markers for a horizontal 225scroll area too at the bottom of the touchpad. 226