Check-in [6e28dd017c]

{"tip": {
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</tr></thead><tbody>

<tr class='state-draft type-project version-87'>
<td valign='top'><a href='./tip/570.md'>570</a></td>
<td valign='top'>Project</td>
<td valign='top'>8.7</td>
<td valign='top'>Draft</td>
<td valign='top' ><a href='./tip/570.md'>Gesture Support for Finger Scrolling and &quot;Pinch to Zoom&quot;</a></td>
<td></td>
</tr>
<tr class='state-final type-project version-87'>
<td valign='top'><a href='./tip/569.md'>569</a></td>
<td valign='top'>Project</td>
<td valign='top'>8.7</td>
<td valign='top'>Final</td>

# TIP 570: Gesture Support for Finger Scrolling and "Pinch to Zoom"
	Author:         Harald Oehlmann <[email protected]>
	State:          Draft
	Type:           Project
	Vote:           Done
	Created:        18-Mar-2020
	Post-History:
	Keywords:       Tk, bindings
	Tcl-Version:    8.7
-----

# Abstract

Support for the gestures "finger scroll" and "pinch to zoom" are proposed in a
platform neutral way.

**NB:** This tip is not ready specified yet.
Anybody is invited to contribute.

# Specification

## Overview

Many systems (e.g. Windows, Linux Window Manager, Mac-OS, Android) nowdays
support gestures in a generic manner.  The gestures may be different and the
input media may be different.  Possible input media are a touch-screen or a
touchpad.

The aim of this TIP is to make gestures provided by the system available within Tk.

The targeted gestures are:

   *   scrolling, for example by pointing two fingers on the touch-screen and
       moving it. This is often identical to the pan gesture.
   *   zooming, for example by pinching two fingers on a touch-screen.

There is a direct relation to the displayed image if a touch-screen is used.
The scroll gesture gives a source and target point on the screen.

## Platforms

The following discussion is about possible implementations on different platforms

### Windows

Peter Spjuth has authored a Windows implementation in tk.branch
[pspjuth-touch](https://core.tcl-lang.org/tk/timeline?r=pspjuth-touch)

The two gestures are implemented by the following virtual bind tags:

  * Zoom: `<<PinchToZoom>>` with substitutions `%W %d %x %y %X %Y`
      * `%W`: Window (below the fingers)
	  * `%d`: descriptive dict (**gesture**=**zoom**, **distance**=finger
        distance)
      * `%x,%y`: position.
  * Scroll: `<<Gesture>>` with substitutions `%W %d %x %y %X %Y`
      * `%W`: Window (below the fingers)
	  * `%d`: descriptive dict (**gesture**=**pan**, **distance**=finger
        distance > 0 for two fingers)
      * `%x,%y`: position

### AndroWish

Christian Werner has defined the following virtual binding tags.  This
information is copied and adapted from [the Androwish
documentation](http://www.androwish.org/home/wiki?name=sdltk+command).

  * Zoom: `<<PinchToZoom>>` with substitutions `%X %Y %x %y %s`
      * `%X` and `%Y` are substituted with the root window coordinate of the
        center of the two fingers
      * `%x` with the distance between the two fingers
      * `%y` with the angle measured in 64 times degrees CCW starting at 3 o'clock.
      * `%s` is the finger state: `0` (zoom motion), `1` (zoom start, i.e. 2nd
        finger down event), `2` (zoom end by 1st finger up event), `3` (zoom
        end by 2nd finger up event)
   *   Scroll: `<<FingerDown>>`, `<<FingerUp>>`, `<<FingerMotion>>`

    Scrolling by two fingers may be implemented by observing those events. The
    following substitutions are supported for all these three finger-related
    events:

      * `%x` and `%y` are the finger position scaled to {0...9999} of the
        device screen or viewport
      * `%X` and `%Y` are the motion difference scaled to {-9999...+9999}
      * `%t` is the pressure scaled to {0...9999}, and
	  * `%s` is the finger identifier {1...10}

### Linux

### Mac-OS

# Rationale


# Implementation

The following fragments are known:

   *   tk.branch [pspjuth-touch](https://core.tcl-lang.org/tk/timeline?r=pspjuth-touch)
   *   AndroWish

# Discussion


# Copyright

This document has been placed in the public domain.