Drawing Spirals by Erick Tejkowsi 02-21-02 Printer Version

Today we'll look at how to draw a spiral with REALbasic. In the process, we will also learn an important secret of top programmers: let someone else do the work!

Intro

A friend once told me that the best programmers are lazy ones. His point wasn't that lazy employees were better than hard workers. Rather, "lazy" coders are often better, because they know how to work smarter not harder.

This week we'll look at how to draw a spiral. Rather than calculate the formula to do this task, we will adapt a Visual Basic spiral example. Because of its close similarity to REALbasic, Visual Basic code is often a great source for programming ideas. The web is littered with thousands of Visual Basic code examples that are ripe for the taking.

For the first step in this week's tutorial, look at a Visual Basic spiral code example. Try to read through the code and see if you can guess how it might translate to REALbasic. Some hints might help you decipher this example:

• Focus your attention on the Form_Paint subroutine. It is equivalent to the Paint event of REALbasic's Canvas control.
• The coordinate system for drawing Visual Basic graphics works like REALbasic, with the origin in the top left corner of the Canvas.
• Ditch the Declare statements. We don't need them.

Build the Interface and Add the Code

This week's example is simple to create. Launch REALbasic, open Window1 and add a Canvas and a Slider control to it. Double click the Canvas to open the Code Editor and place the following code in its Paint event:

  
  dim x,y,n,xmid,ymid as integer
  dim angle, radius as double
  dim lastx,lasty as integer
  
  
  XMid = Me.Width / 2
  YMid = Me.Height / 2
  lastx=XMid
  lasty=YMid
  g.foreColor = rgb(255,255,255)
  g.fillrect 0,0,me.width,me.height
  g.foreColor = rgb(0,100,0)
  g.penwidth = slider1.value
  g.penheight = slider1.value
  
  For n = 1 To 1000
    Angle = n * 0.1
    Radius = Radius + Angle * 0.01
    x = XMid + Cos(Angle) * Radius
    y = YMid - Sin(Angle) * Radius
    g.drawline x,y,lastx,lasty
    
    lastx = x
    lasty = y
  next
 

Finally, add the following line of code to the ValueChanged event of Slider1.

Canvas1.refresh 

That's it! Select Debug-Run to test your work. Then, go back and compare your code with the Visual Basic version. Can you figure out how we replaced the drawing commands from Visual Basic with the drawing commands of REALbasic? We also added a little fanciness to the project to make it a tad more interactive. The slider control changes the width of our pen which draws with a green color.

Your final result should look something like this:

Conclusion

As you can see, borrowing code has its benefits. This example was easy, but calculating a formula for drawing sprials is not something that immediately comes to mind for most people. With a little mental work, you can adapt existing code examples to suit your needs. And, never forget the programmer's motto : "REUSE CODE!". If you don't believe me on this one, take a look at the DLL folder in Windows some time. Download the finished product here and see you next week!