Rendering Ellipses with Recursion

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Key Constructs

Generating 'midpoint' nested objects that are in the polygon 'family' (in a manner of speaking) rely on the following type of code fragment:

   // arrays for inner polygon... newXPts = Array(vertexCount); newYPts = Array(vertexCount); for(var v=0; v<vertexCount; v++) {    // clockwise from upper-left vertex...    newXPts[v] = (oldXPts[v]+                   oldXPts[(v+1)%vertexCount])/2;    newYPts[v] = (oldYPts[v]+                   oldYPts[(v+1)%vertexCount])/2; }

Recursion is a very useful technique for rendering visually rich and complex patterns that are based on simple geometric objects such as triangles and ellipses.

Performance is always a key factor when you write recursively invoked ECMAScript functions, and in some cases you might need to find an iteration-based equivalent algorithm that produces the desired results.

CD-ROM Library

The folder for this chapter on the book's companion CD-ROM contains the SVG documents that are required for viewing the following graphics images:

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