[Newbies] Fading a PNG

[Steven Greenberg]

Following Bert's advice, I see that HaloMorph overrides #drawSubmorphsOn:
and calls its Canvas using asAlphaBlendingCanvas.  That seems like a good
place to start.

I tried subclassing ImageMorph and adding this method:

    drawOn: aCanvas
        ^ super drawOn: (aCanvas asAlphaBlendingCanvas: alphaValue).

Unfortunately, it didn't display anything at all.  I tried alpha values of
0.5 and 1.0.  If I remove the alpha blending stuff, and simply call:

    ^ super drawOn: aCanvas.

it works like a normal ImageMorph, so at least I know it isn't broken
someplace else.

Any suggestions on how to get asAlphaBlendingCanvas to blend some alphas?




On 4/23/07, Steven Greenberg <greenbes at puzzlingevidence.net> wrote:
>
> Thanks for the pointer!  I didn't try that code in the workspace, but if
> you enable "haloTransitions" using the Preferences browser then the halos
> fade in and out.
>
>     Thanks,
>     Steve
>
>
>
> On 4/22/07, Bert Freudenberg <bert at freudenbergs.de> wrote:
> >
> >
> > On Apr 23, 2007, at 0:44 , Steven Greenberg wrote:
> >
> > > I have a PNG image that I'd like to display fading out.  I tried
> > > the BitBlt method suggested by "Team RAR" to fade the image, but I
> > > can't make it work.
> > >
> > > The image loads properly from a file and displays fine as an
> > > ImageMorph.  I have been able to use a TransformationMorph to
> > > rotate and scale it, and PNG transparency is working properly.
> > >
> > > Is the "Team RAR" BitBlt method the only way, or are there
> > > alternatives?
> > >
> > > I'm running a 3.9 image, and my display depth is set to 32 bits.
> > >
> >
> > Normally you would just use an alpha-blending canvas. See HaloMorph
> > fadeIn/fadeOut and draw methods. To try those halos, enable this:
> >
> >         Preferences enable: #haloTransitions
> >
> > Now when I tried then the halo icons do not actually show until alpha
> > is one. No idea why that is.
> >
> > - Bert -
> >
> >
> > _______________________________________________
> > Beginners mailing list
> > Beginners at lists.squeakfoundation.org
> > http://lists.squeakfoundation.org/mailman/listinfo/beginners
> >
>
>
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