[Newbies] Fading a PNG

Steven Greenberg greenbes at puzzlingevidence.net
Mon Apr 23 12:38:00 UTC 2007


I am able to draw morphic primitives with the alpha channel working properly
by overriding #drawOn: in my subclass.  I am not able to make it work for an
ImageMorph.

I'm running squeak 3.9-7067 on XP.

    Thanks again,
    Steve



On 4/23/07, Bert Freudenberg <bert at freudenbergs.de> wrote:
>
> Try drawing something other than an image. I have a hunch the alpha-
> bitblt is wrong ...
>
> Btw, which platform are you on? Which VM?
>
> - Bert -
>
> On Apr 23, 2007, at 9:32 , Steven Greenberg wrote:
>
> > 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 -
>
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