Touchscreen Input and Virtual Keyboards

Emacs was first written assuming that its users were to use it from a desktop computer or computer terminal, equipped with a keyboard and perhaps a suitable pointing device such as a mouse (Mouse Input). Emacs is also capable of receiving input from alternative sources of input, enabling users to interact with it even if it is installed on a computer that substitutes such input sources for the customary combination of keyboard and mouse.

Using Emacs on Touchscreens

Touchscreen input is the manipulation of a frame's contents by the placement and motion of tools (instanced by fingers and such pointing devices as styluses) on a monitor or computer terminal where it is displayed. Two factors, the order and position on which such tools are placed, are compared against predefined patterns dubbed gestures, after which any gesture those factors align with designates a series of actions to be taken on the text beneath the tools; the gestures presently recognized are:

Tapping, briefly placing and lifting a tool from the display, will select the window that was tapped, and execute any command bound to mouse-1 at that location in the window. If a link (Mouse References) exists there, then Emacs will follow that link instead (insofar as such action differs from that taken upon the simulation of a mouse-1 event).
Scrolling, which is continuous vertical or horizontal motion on the screen, will scroll the contents of the window beneath the tool's initial location in the direction of movement. The user option touch-screen-enable-hscroll governs whether horizontal scrolling (Horizontal Scrolling) is performed in reaction to this gesture.
Dragging, which is performing a long-press by placing a tool on the display and leaving it there awhile before moving it to another position, will move point to the tool's initial position, and commence selecting text under the tool as it continues its motion, as if mouse-1 were to be held down and a mouse moved analogously. Mouse Commands. To the detriment of text selection, it can prove challenging to position a tool accurately on a touch screen display. The user option touch-screen-word-select, which when enabled, prompts dragging to select the complete word under the tool. (Normally, the selection is only extended to encompass the character beneath the tool.) In the same vein, it may be difficult to select all of the text intended within a single gesture. If the user option touch-screen-extend-selection is enabled, taps on the locations of the point or the mark within a window will begin a new "drag" gesture, where the region will be extended in the direction of any subsequent movement. Difficulties in making accurate adjustments to the region from the cursor being physically obscured by the tool can be mitigated by indicating the position of the point within the echo area. If touch-screen-preview-select is non-nil, the line surrounding point is displayed in the echo area (Echo Area) during the motion of the tool, below which is another line indicating the position of point relative to the first.
Pinching, the placement of two tools apart on the screen followed by adjustments to their position such as to increase or decrease the distance between them will modify the text scale (Text Scale) in proportion to the change in that distance.

Emacs registers a long-press after the time a tool has been placed upon the screen exceeds 0.7 seconds. This delay can be adjusted through customizing the variable touch-screen-delay.

Using Emacs with Virtual Keyboards

When there is no physical keyboard attached to a system, its windowing system might provide an on-screen keyboard, widely known as a "virtual keyboard", containing rows of clickable buttons that send keyboard input to the application, much as a real keyboard would. This virtual keyboard is hidden when the focused program is not requesting text input as it occupies scarce space on display, and programs are therefore enjoined to display it once they are ready to accept keyboard input. Systems running X detect when the presence of the virtual keyboard is warranted, but on others such as Android Emacs is responsible for displaying it when need be, generally in reaction to a touch screen "tap" gesture (Touchscreens) or the minibuffer being brought into use (Minibuffer). When a "tap" gesture results in a command being executed, Emacs checks whether the command is meant to set the point by searching for it in the list touch-screen-set-point-commands. If it is, and the text beneath the new point is not read-only, the virtual keyboard is activated, in anticipation of the user input there. The default value of touch-screen-set-point-commands holds only the command mouse-set-point (Mouse Commands), which is the default binding of mouse-1, and therefore of touchscreen tap gestures as well. The user option touch-screen-display-keyboard compels Emacs to display the virtual keyboard on all tap gestures even if the text is read only; it may also be set buffer locally, in which case Emacs will always display the keyboard in response to a tap on a window displaying the buffer it is set in. There are moreover several functions that display or hide the on-screen keyboard. For more details, On-Screen Keyboards. Since it may not be possible for Emacs to display the virtual keyboard while it is executing a command, Emacs implements a feature on window systems frequently equipped with no physical keyboard, by which two rapid clicks of a hardware button that is always present on the device induces a quit. Quitting. No such button is enabled on X, but one can be configured through the variable x-quit-keysym, whereas the default key is the volume down button on Android, which is also configurable through a variable, android-quit-keycode. Most input methods designed to work with virtual keyboards edit text differently from desktop input methods. On a conventional desktop windowing system, an input method will simply display the contents of any ongoing character composition on screen, and send key events reflecting its contents to Emacs after it is confirmed by the user. By contrast, virtual keyboard input methods directly perform edits to the selected window of each frame; this is known as "text conversion", or "string conversion" under the X Window System. Emacs enables these input methods whenever the buffer local value of text-conversion-style is non-nil, that is to say, generally inside derivatives of text-mode and prog-mode. Text conversion is performed asynchronously whenever Emacs receives a request to perform the conversion from the input method, and Emacs is not currently reading a key sequence for which one prefix key has already been read (Keys). After the conversion completes, a text-conversion event is sent. Misc Events. If the input method needs to work on a region of the buffer, then the region is designated the "composing region" (or "preconversion region"). The variable text-conversion-face controls whether to display the composing region in a distinctive face, and if so, which face to employ.