Not able to retrieve a function layer by name using v5.4 about jcanvas HOT 3 CLOSED

I recently changed the v5.4b code to fix a bug. To ensure layers can be
drawn across multiple canvases, I have to clone the layer first. I used to
do this using the Function constructor, but that destroyed the function's
access to closure variables. Therefore, I wrapped the function in a closure
to fix this.

Frankly, I don't see any real need to override the context. At this point,
I'm more interested in trying to fix what you've just described.

-Caleb

On Sat, Jun 9, 2012 at 7:50 AM, BillyRayPreachersSon <
[email protected]

wrote:

Hi,

I've just tested some of my code against v5.4, and found that it's no
longer possible to retrieve a function layer by its name as you can with
non-function layers. This is possible with v5.3.1.

Take the following scenario:

var MyObj = {
       canvas: $('<canvas />'),

       addLayer: function() {
               this.canvas.addLayer(this.drawLines);
       },

       drawLines: function lines(ctx) {
               console.log('MyObj.drawLines is being called');
               console.log('"this" context = ', this);
       }
}

Under v5.3.1, here's what I got:

MyObj.addLayer()
       'MyObj.drawLines is being called'
       "this" context = <canvas>

MyObj.canvas.getLayer('lines')
       function lines(ctx) { console.log(...) }

MyObj.canvas.getLayers()
       [function lines(ctx) { console.log(...) }]

Under v5.4, here's what I get:

MyObj.addLayer()

MyObj.canvas.drawLayers()                               // this is no
longer automatic, but I've included it to give a fair comparison
       'MyObj.drawLines is being called'
       "this" context = <canvas>
       [<canvas>​]

MyObj.canvas.getLayer('lines')
       undefined

MyObj.canvas.getLayers()
       [function (Y){return W.call(this,Y)}]

While on the subject of function layers, would it be possible to add a
facility to provide a context for "this" when adding the layer? At present,
"this" refers to the canvas - which is fine in some cases. However, it
would be nice to be able to override this without having to restort to code
like this:

var MyObj2 = {
       canvas: $('<canvas />'),

       addLayer: function() {
               var boundLinesFunc = $.proxy(this.drawLines, this);
               this.canvas.addLayer(function lines(ctx) {
boundLinesFunc(ctx) });
       },

       drawLines: function lines(ctx) {
               console.log('MyObj2.drawLines is being called');
               console.log('"this" context = ', this);
       }
}

The reason for the named local function in the call to
this.canvas.addLayer() is because $.proxy doesn't keep the function name. I
could probably use .call() or .apply() here, but I think it would make code
flow much easier if the context could be set when the layer was added.

Thanks!

Dan

---

Reply to this email directly or view it on GitHub:
#18

from jcanvas.

Just wanted to let you know:

I added the ability to name function layers in v5.4. You can do so simply by naming the function expression you pass to it. For example,

$("canvas").addLayer(function myLayerName() {
// Do something here
});

For more flexibility, you can also pass an object instead, with the function as the object's 'fn' property:

$("canvas").addLayer({
name: "myLayerName",
fn: function() {
// Do something here
}
});

I hope that helps.
-Caleb

from jcanvas.

Great - thanks :-)

from jcanvas.