Check-in [46186ab755]

{"tip": {
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<th>Type</th>
<th>Tcl Version</th>
<th>Status</th>
<th>Title</th>
<th>Impl.</th>
</tr></thead><tbody>

<tr class='state-draft type-project'>
<td valign='top'><a href='./tip/570.md'>570</a></td>
<td valign='top' colspan=2>Project</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>
<td valign='top' ><a href='./tip/569.md'>Eliminate Comments That Serve Lint</a></td>
<td></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
	Tk-Version:    8.7
-----

# Abstract

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

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>> %W %d %x %y %X %Y" : W: Window(below the fingers), d: descriptive dict (gesture =zoom, distance=finger distance), x,y: position.
   *   Scroll: "<<Gesture>> %W %d %x %y %X %Y": 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 from [http://www.androwish.org/home/wiki?name=sdltk+command].

   *   Zoom: "<<PinchToZoom>> %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, and %y with the angle measured in 64 times degrees CCW starting at 3 o'clock. The finger state is reported in the %s substitution as 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. Documentation: A touch movement (sliding) event. The fields %x and %y are substituted with the finger position scaled to {0...9999} of the device screen or viewport, %X and %Y with the motion difference scaled to {-9999...+9999}, %t with the pressure scaled to {0...9999}, and %s with the finger identifier {1...10}. These substitutions are performed for all finger related touch events. 

### 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.