Portal:HowTo Demos

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Revision as of 21:56, 7 January 2021 by Trev (talk | contribs) (Networking: Add entry "resuming a file download")

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Portal:HowTo Demos

This portal collects together in one place a significant number of short demonstration programs that have been posted on the Free Pascal and Lazarus Forums. Each of the demonstration programs generally provides a simple example of one particular development technique.

The Portal was the brainchild of Handoko who also provided the initial list of demonstration programs from the Forums.


  • OpenGL ES2 Circle. Requirement: LAMW. Drawing a circle using jCanvasES2.DrawLine instead of DrawCircle.
  • OpenGL ES2 Rectangle. Requirement: LAMW. Drawing a rectangle using jCanvasES2.DrawPolyFill instead of DrawRect.

File handling


  • Generating a huge text file. Demonstrates a technique for reducing program responsiveness to improve performance.
  • Retrieve https web page. Cross-platform. No openssl DLLs/libraries need to be deployed. No third party components required.


  • Get pixel color of an image. It may sound easy but actually it is not so easy.
  • Fading images using BGRABitmap. Requirement: BGRABitmap. Build your own slideshow and learn doing proportional scaling using aspect ratio of the picture.
  • TCanvas Text. How to draw superscript and subscript text using TCanvas.
  • Rock, Paper, Scissors. A simple game. Note for Unix/like operating systems: change the path delimiter to make the code work.


  • FTP Connect. Requirement: Synapse (can be installed using OPM). How to connect to a FTP server.
  • HTML to Text. Requirement: fasthtmlparser. Extract data from a web page.
  • Retrieve https web page. Cross-platform. No openssl DLLs/libraries need to be deployed. No third party components required.
  • Simple webserver. Multi-threaded, cross-platform. No third party components required.

User Interface

  • Searchable StringGrid. Requirement: DBFLaz. Load data from a dbf, show it on a TStringGrid, search and highlight the cells. See here and here.
  • Darkening a Form. Requirement: BGRAControls. How to darken the Main Form when a modal window is shown.
  • Scaling a Form. How to scale a form by using TForm.ScaleBy. Unfortunately it does not work correctly on Linux.
  • Vertical Menu. How to make a vertical menu using TPanel and TScrollBox.
  • ShowMessage in Console Mode. Requirement: LCL needed to be in the project’s required packages. How to use ShowMessage in a console mode program.
  • Adding CHM Help. A demo project to call a CHM help file from three buttons as context-sensitive help (press F1), or from a help menu.
  • Speedbutton demonstration of using four arrow speedbuttons for moving an object. Shows how to handle speedbutton glyph states.