Re: Fading a PNG

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@xxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx > 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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