Delphi Programming Guide
Delphi Programmer 

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Part I - Foundations
  Chapter 1 – Delphi 7 and Its IDE
  Chapter 2 – The Delphi Programming Language
  Chapter 3 – The Run-Time Library
  Chapter 4 – Core Library classes
  Chapter 5 – Visual Controls
  Chapter 6 – Building the User Interface
  Chapter 7 – Working with Forms
Part II - Delphi Object-Oriented Architectures
  Chapter 8 – The Architecture of Delphi Applications
  Chapter 9 – Writing Delphi Components
  Chapter 10 – Libraries and Packages
  Chapter 11 – Modeling and OOP Programming (with ModelMaker)
  Chapter 12 – From COM to COM+
Part III - Delphi Database-Oriented Architectures
  Chapter 13 – Delphi's Database Architecture
  Chapter 14 – Client/Server with dbExpress
  Chapter 15 – Working with ADO
  Chapter 16 – Multitier DataSnap Applications
  Chapter 17 – Writing Database Components
  Chapter 18 – Reporting with Rave
Part IV - Delphi, the Internet, and a .NET Preview
  Chapter 19 – Internet Programming: Sockets and Indy
  Chapter 20 – Web Programming with WebBroker and WebSnap
  Chapter 21 – Web Programming with IntraWeb
  Chapter 22 – Using XML Technologies
  Chapter 23 – Web Services and SOAP
  Chapter 24 – The Microsoft .NET Architecture from the Delphi Perspective
  Chapter 25 – Delphi for .NET Preview: The Language and the RTL
  Appendix A – Extra Delphi Tools by the Author
  Appendix B – Extra Delphi Tools from Other Sources
  Appendix C – Free Companion Books on Delphi
  List of Figures    
  List of tables    
  List of Listings    
  List of Sidebars  

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Unusual Techniques: Alpha Blending, Color Key,
and the Animate API

One of the recent Delphi features related to forms is support for new Windows APIs that affect the way forms are displayed (in Windows 2000/XP, but not available under Qt/CLX). Alpha blending allows you to merge the content of a form with what's behind it on the screen—functionality you'll rarely need, at least in a business application. The technique is more interesting when applied to bitmap (with the new AlphaBlend and AlphaDIBBlend API functions) than to a form. In any case, by setting the AlphaBlend property of a form to True and giving to the AlphaBlendValue property a value lower than 255, you'll be able to see in transparency what's behind the form. The lower the AlphaBlendValue, the more the form will fade. You can see an example of alpha blending in Figure 7.7, taken from the ColorKeyHole example.

Click To expand
Figure 7.7: The output of the ColorKeyHole, showing the effect of the new TransparentColor and AlphaBlend properties and the Animate-Window API

Another unusual Delphi feature is the TransparentColor boolean property, which allows you to indicate a transparent color that will be replaced by the background, creating a sort of hole in a form. The actual transparent color is indicated by the TransparentColorValue property. Again, you can see an example of this effect in Figure 7.7.

Finally, you can use a native Windows technique, animated display, which is not directly supported by Delphi (beyond the display of hints). For example, instead of calling the Show method of a form, you can write

AnimateWindow (Form3.Handle, 2000, AW_BLEND);

Notice you have to call the Show method at the end for the form to behave properly. You can also obtain a similar animation effect by changing the AlphaBlendValue property in a loop. The AnimateWindow API can also be used to control how the form is brought into view, starting from the center (with the AW_CENTER flag) or from one of its sides (AW_HOR_POSITIVE, AW_HOR_NEGATIVE, AW_VER_POSITIVE, or AW_VER_NEGATIVE), as is common for slide shows.

You can apply this same function to windowed controls, obtaining a fade-in effect instead of the usual direct appearance. I have serious doubts about the waste of CPU cycles these animations cause, but I must say that if they are applied properly and in the right program, they can improve the user interface.

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