Last time, we explored a way to improve SqueakJS UI responsiveness by replacing Squeak Morphic entirely, with morphic.js. Now let’s look at a technique that reuses all the Squeak Morphic code we already have.
many worlds, many canvases
Traditionally, Squeak Morphic has a single “world” where morphs draw themselves. To be a coherent GUI, Morphic must provide all the top-level effects we’ve come to expect, like dragging windows and redrawing them in their new positions, and redrawing occluded windows when they are brought to the top. Today, this comes at an acceptable but noticeable cost. Until WebAssembly changes the equation again, we want to do all we can to shift UI work from Squeak Morphic to the HTML5 environment hosting it. This will also make the experience of using SqueakJS components more consistent with that of the other elements on the page.
Just as we created an HTML5 canvas for morphic.js to use in the last post, we can do so for individual morphs. This means we’ll need a new Canvas subclass, called HTML5FormCanvas:
Object
...
Canvas
FormCanvas
HTML5FormCanvas
An HTML5FormCanvas draws onto a Form, as instances of its parent class do, but instead of flushing damage rectangle from the Form onto the Display, it flushes them to an HTML5 canvas. This is enabled by a primitive I added to the SqueakJS virtual machine, which reuses the normal canvas drawing code path.
Accompanying HTML5FormCanvas are new subclasses of PasteUpMorph and WorldState:
Object
Morph
...
PasteUpMorph
HTML5PasteUpMorph
Object
WorldState
HTML5WorldState
HTML5PasteUpMorph provides a message interface for other Smalltalk objects to create HTML5 worlds, and access the HMTL5FormCanvas of each world and the underlying HTML5 canvas DOM element. An HTML5WorldState works on behalf of an HTML5PasteUpMorph, to establish event handlers for the HTML5 canvas (such as for keyboard and mouse events).
HTML5 Morphic in action
You don’t need to know all of that just to create an HTML5 Morphic world. You only need to know about HTML5PasteUpMorph. In particular, (HTML5PasteUpMorph class)>>newWorld. All of the traditional Squeak Morphic tools can use HTML5PasteUpMorph as a drop-in replacement for the usual PasteUpMorph class.
There are two examples of single-window Morphic worlds in the current Caffeine release, for a workspace and classes browser. I consider these two tools to be the “hello world” exercise for UI framework experimentation, since you can use them to implement all the other tools.
We get an immediate benefit from the web browser handling window movement and clipping for us, with opaque window moves rendering at 60+ frames per second. We can also interleave Squeak Morphic windows with other DOM elements on the page, which enables a more natural workflow when creating hybrid webpages. We can also style our Squeak Morphic windows with CSS, as we would any other DOM element, since as far as the web browser is concerned they are just HTML5 canvases. This makes effects like the rounded corners and window buttons trays that Caffeine uses very easy.
Now, we have flexible access to the traditional Morphic tools while we progress with adapting them to new worlds like morphic.js. What shall we build next?
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