The onLoad method is called at the same time (in terms of lifecycle) as the
AttachEvent - consider something like
canvas.addAttachHandler(e -> {
// collect info here
});
It looks like you already implement that event handler interface,
AttachEvent.Handler, so you're already being notified via the call to
onAttachOrDetach.
The code you have already ostensibly to measure the size of the canvas
isn't doing what you think it should be doing - the method call is
getCoordinateSpaceWidth/getCoordinateSpaceHeight. This doesn't ask "how big
is the canvas in pixels on my screen" but instead "how many pixels are in
the canvas I've created. Try resizing the window - your "20x20" rectangle
at position "10x10" is likely substantially larger than you would expect,
because it lives within that coordinate space. You probably also notice
that its borders are quite fuzzy too...
This is a common point of confusion when getting started with <canvas>,
especially with high-density displays, where you would desire a bigger
coordinate space than the "actual pixels" that the canvas occupies. This
makes sure you are able to draw in the "sub pixels" that the screen uses to
represent content.
To get the "real" size, use getOffsetWidth() and getOffsetHeight(). With
those values, *tell* the canvas how big you want it to be (via
setCoordinateSpaceHeight/setCoordinateSpaceWidth), but you may want to
check if there are subpixels to worry about, and multiple accordingly.
GWT's Canvas is a fairly thin wrapper over the DOM's own canvas element. If
you're just getting started with this, consider using elemental2's Canvas
(in com.google.elemental2:elemental2-dom), and doing some reading on the
browser feature itself, such as at
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/canvas.
On Thursday, December 12, 2024 at 11:07:53 AM UTC-6 [email protected]
wrote:
> Hello everyone:
>
> I am not sure how to get the correct size of a Canvas.
>
> When I create the Canvas, it keeps telling me it is 300 x 150.
> I get that size if I try to grab it in the onModuleLoad method
> or from an attach event. They both keep telling me the Canvas
> is 300 x 150.
>
> But when I use a ClickEvent handler, the clicks are for an element
> which is 900 x 450.
>
> I tried extending the Canvas into a MyCanvas so I could add code
> to the onload method, but its constructor is private so I can't override
> it.
>
> I am attaching my sample code.
>
> You can see it running here:
> https://dev.3dmathpuzzles.com/3dmp/play.html
>
> Any guidance on this?
>
> Thank you,
> Neil
>
> --
> Neil Aggarwal, (972) 834-1565, http://www.propfinancing.com
> We offer 30 year loans on single family houses!
>
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