Plotting Fractals in WebAssembly

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4: Optimised WAT Implementation 5: Plotting a Julia Set 6: Zooming In
    5.1: Web Page Changes

5: Plotting a Julia Set

Now that we have an efficient means of plotting the Mandelbrot Set, we can add a second HTML canvas element to display the Julia Set.

For every point on the Mandelbrot Set, there is a corresponding Julia Set. So as the mouse pointer moves over the Mandelbrot Set, a completely new Julia Set needs to be rendered. Consequently, every time a mousemove event goes off over the Mandelbrot canvas, our now dual-purpose plot function needs to be called.

This is where we start to see the benefits of writing in WebAssembly Text. Since we can focus on low-level efficiency, we can produce a very small, very fast program.

To plot the additional Julia Sets, we need to make two sets of changes:

  1. Web Page Changes
  2. WebAssembly Changes

Here’s a working version of the Mandelbrot Set with Dynamic Julia Sets

How Big is the WASM Module Now?

Good question, glad you asked… 😃

Now that we have a single WebAssembly module that can plot both the Mandelbrot and Julia Sets, it is worth looking at the size of the compiled module:

$ ll
total 56
drwxr-xr-x   8 chris  staff    256  9 Dec 19:04 .
drwxr-xr-x  10 chris  staff    320  9 Dec 18:41 ..
drwxr-xr-x   3 chris  staff     96  9 Dec 14:42 01
drwxr-xr-x   3 chris  staff     96  9 Dec 14:42 02
-rw-r--r--   1 chris  staff    894  9 Dec 16:26
-rw-r--r--   1 chris  staff   6812  9 Dec 18:25 mb-julia-set.html
-rw-r--r--   1 chris  staff    712  9 Dec 19:04 mj_plot.wasm
-rw-r--r--   1 chris  staff  11936  9 Dec 14:08 mj_plot.wat

Wow! Only 712 bytes!

This is not as small as the program could be, but its a big step forwards (downwards?) compared to the 74Kb module mentioned in the introduction.