Category: apps

Flexiblere Online-Meetings mit “Gather”

Wenn sich 10 Personen in der Realität treffen, sitzen nicht immer alle an einem Tisch und reden miteinander. Es gibt immer auch Kleingruppen, die sich spontan entwickeln und wieder trennen und wieder neu fügen.

Klassische Video-Konferenzdienste wie Google Meet, Zoom, Whereby, Webex, Microsoft Teams, Facetime, etc sind spezialisiert auf einen gemeinsamen “Meetingraum”, meist mit einer Galerie von Leuten in Rechtecken, oder einem “zeige nur die Person, die gerade spricht”-Interface auf kleineren Geräten (smartphones).

Es gibt aber auch flexiblere Video-Meeting Dienste, wo man Teilgruppen bilden kann und sich in solchen ein und ausklinken kann, ohne den Dienst zu “verlassen”.

Der scheinbar populärste solcher Dienste heißt “Gather“. Er kombiniert ein retro 2D Videospiel “look & feel” mit eingebetteten Mini-Spielen und klassischen Video-Konferenz Funktionen.

Nach kurzem googeln fand ich einen englischen Artikel und einen deutschen Artikel, in denen der Dienst mehr oder weniger kritisch beleuchtet wird.

Gather bietet eine kostenlose Variante (bis zu 25 Teilnehmer).

Alternative ähnliche Dienste listet dieser Artikel (englisch):

Undo/Redo in Java using Protostuff serialization and binary diffs

Many applications need Undo/Redo functionality. Commonly used implementation patterns are:

  • Command Pattern
  • Memento Pattern (state snapshots)
  • State diffs

When using the Command Pattern one would encapsulate both the change logic and its reversal in command objects. Undo/Redo is implemented by managing stacks of those objects. This approach has its limitations, for example for changes that are unidirectional in nature, like anything involving randomness, encryption, etc.

State snapshots save the full state of the edited data as object graphs or some representation thereof. This is also called the Memento Pattern. It often uses serialization and typically compression of the object graph to reduce memory use and ensure immutable snapshots that can also be stored out-of-process, if desired.

State diffs are based on the idea of State snapshots, but only store the difference between states. This can vastly reduce memory consumption of your Undo/Redo history. It is based on diffing algorithms that compute the delta between two states (or their memento) and allow Undo/Redo by applying the deltas as patches against a given state. A disadvantage is that jumping to a state involves a whole chain of patch applications. But it is a good approach when the user mainly navigates the Undo/Redo history sequentially.

A highly reusable implementation of Undo/Redo using State Diffs is available at my github account: https://github.com/odoepner/diffing-history

It uses the following Open Source libraries:

  • Protostuff for object graph serialization using runtime schema
  • JavaxDelta for binary diffing and patching

It provides the following features:

  • Unlimited Undo and Redo
  • Can handle any type of Java objects
  • Low memory footprint
  • Straightforward type-safe API
  • Supports stack size listeners
  • Gzip compression for the serialized current state

It is Open Source under the Unlicense.

Usage

The main API is the History interface.
Create an instance of DiffingHistory to get started.
The DiffingHistoryTest calls all History methods and illustrates the API.

Testing HTML5 / CSS3 editor BlueGriffon

I used to use the now-outdated Mozilla based editor Kompozer, which was a bug-fix fork of Nvu.

Today I realized that in the meantime (since 2015) the Nvu author Daniel Glazman has developed BlueGriffon, an Open Source next-generation Web Editor based on the current rendering engine of Firefox.

I just installed it on Windows at work and my Debian laptop at home and plan to give it a try.

If it is easy to use and generates clean standards-compliant code, I might use it for Web UI mock-ups and other prototyping. :)

Using libgdx for cross-platform app development

I am looking for a framework that allows me to develop modern apps (mobile, web, desktop) all from one Java codebase. I prefer Java because I know it very well, it is already cross-platform and a statically typed language that allows IntelliJ, Eclipse and Netbeans to be better than any dynamically typed scripting language editor could ever be.

Currently my favorite is libgdx. I am planning to use it with IntelliJ Community Edition and with Maven.

By using RoboVM, libgdx even supports iOS.

For user input (forms) libgdx provides the scene2d.ui widgets. I hope that will be sufficient for most of my UIs. Now I just have to get OpenGL to work on my Linux box …

Make apps4halifax – Intro

Halifax Regional Municipality is introducing ‘apps4halifax‘, its first-ever Open Data App Contest. Similar initiatives have been successful in Ottawa, Edmonton and many other cities worldwide.

Residents can submit ideas or code apps using the HRM Open Data catalog. The best submissions may win cash prizes and awards.

The Open Data catalog is implemented using the Socrata Open Data Portal. The SODA 2.0 restful web service API allows developers to query and consume live data from the public data-sets.

The Socrata developer documentation explains how to use queries to endpoints, supported datatypes and response formats.

The currently available data-sets include Crime occurrences, Building types, Buildings, Bus Routes, Bus Stops, Bylaw Areas, Civic Addresses, Community Boundaries, Park Recreation Features, Parks, Polling Districts, Streets, Trails, Transit Times, Waste collections and Zoning Boundaries.

You can construct web service query URLs like this:

You can determine the RESOURCE-ID for a dataset like this:

  1. Go to https://www.halifaxopendata.ca/
  2. Click on a dataset name
  3. Click the “Export” button
  4. Under “Download As”, copy one of the links, e.g. JSON
  5. The resource id is the part of the URL between “views/” and “/rows.json”

As an extremely useful example, you could query fun things like all HRM garbage collections occurring on Wednesdays:

http://www.halifaxopendata.ca/resource/ga7p-4mik.json?collect=’WEDNESDAY’

As a simple and quick way to create web pages that interact with these web services you could use JQuery and its getJSON() function.

I will probably follow up with more posts on this topic soon.