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© 2021, V10.4

The art of presentation
Until the middle of the last century, speakers of a lecture or other presentation had no other visual aid than facial expressions and gestures, and, mainly for scientific lectures, chalk and blackboard. It is a fact that for most listeners the visual impact is important for better understanding and long-term memorization. The presentation technique evolved and slide projectors were installed in almost every conference room. But the production of slides were expensive in time and money and slides had one major disadvantage: often too much information were displayed at the time a slide was shown. To obtain a synchronization between spoken word and displayed picture, a slide should contain only few items. The balance between spare information and pretty layout was difficult to obtain.

With the widespread of overhead projectors in the sixties and seventieth the main problem of slide-based presentations was circumvented: The production of the transparencies was quite simple (in the beginning most of them were hand-written), and to obtain the synchronization a simple trick was used: An opaque sheet layed on the transparency hides the bottom part and the speaker can pull it down step-by-step as the presentation goes on. This was a very efficient and simple kind of animation.

When personal computers became available in the eighties, they could be used to replace the hand-written transparencies with pretty computer-generated graphics printed on a transparency. The presentation trick remained the same. Only when video beamers became affordable in the ninetieth, the overhead projector became obsolete and the computer screen containing the visual information is displayed in real-time to the audience.

To simplify the creation of computer based screen-slides, an application software is appropriate. Microsoft's Powerpoint became a quasi-standard, but other products are also available (like OpenOffice Impress). In order to visualize the slide step-by-step an animation tool is used. This has a major drawback: while preparing your presentation, you have to schedule with great care the appearance of all animated items. And, when giving your lecture, you have to remember this scenario even if your preparation has be done weeks ago.

Lazy of animation tools
It is not only nostalgia to reinvent the hiding sheet from the overhead projector era. It has the distinct advantage to let you hide and show items interactively at the time of presentation. But instead of a real sheet moved by hand, you move a colored, opaque or semi-transparent borderless window by dragging it with the mouse. This small, but useful presentation utility is called CoverSheet. Just have a look at the following demonstration:



How CoverSheet works:
When CoverSheet starts, a opaque or semi-transparent window (with no border nor title bar) is shown which covers most of the screen. You move it by dragging it with the mouse to any other position. Alternatively you can use the cursor keys to move it, whenever the mouse cursor is inside the window (no activation click is necessary to gain the keyboard focus). Of course, the above demonstration can easily be done by using the animation facility of the presentation tool. But CoverSheet can be very useful, when animation is not easily available, like covering a part of a picture or graphics to direct attention to what is already visible. And the partial transparency let you better anticipate what is coming next. See the following demonstration:




CoverSheet   for programming courses:
I like to use CoverSheet for programming courses. The students should keep track of the program line-per-line. For making a life demonstration I tried to write the code down in real-time, but I am not as good as a typewriter. With CoverSheet, I am in my favorite IDE editor using a big font and uncover the program line-per-line, while explaining the code. No need to use my old bamboo pole anymore to point to the code at the beamer screen.






CoverSheet's options:
Some options of CoverSheet may be adapted to your personal penchant, such as the color and opacity of the sheet. At startup these parameters are read from a easily editable xml-file.



CoverSheet's internals:
CoverSheet is written in Java, but uses a native transparent window (not available in Java). The Java Native Interface (JNI) together with JAW (Java API Wrapper) and JawGadet establish the link between Java and the Windows OS. Therefore CoverSheet only runs under Windows (Windows 2000, XP, Vista). The Java Runtime Environment (JRE) must be installed.

This implementation is not as efficient as using native code exclusively, but has the advantage that the source code written in Java is easily modified and recompiled (source code included in distribution).