It is this code that apply the blendAlphaScaled.

BalloonEngine>>bitBlt: aBitBlt
| destWidth |
bitBlt := aBitBlt.
bitBlt isNil ifTrue:[^self].
destWidth := bitBlt destForm width.
destWidth > span size ifTrue:[span := Bitmap new: destWidth].
self class primitiveSetBitBltPlugin: bitBlt getPluginName.
self clipRect: bitBlt clipRect.
bitBlt
sourceForm: (Form extent: span size @ 1 depth: 32 bits: span);
sourceRect: (0 at 0 extent: 1 at span size);
colorMap: (Color colorMapIfNeededFrom: 32 to: bitBlt destForm depth);
combinationRule: (bitBlt destForm depth >= 8 ifTrue:[34" blendAlphaScaled
"] ifFalse:[Form paint]).

Best,
Karl

On Mon, Sep 21, 2020 at 9:31 PM Thiede, Christoph <
Christoph.Thiede at student.hpi.uni-potsdam.de> wrote:

> Thanks for the pointer, Stef. I think we really need some kind of
> documentation of the form rules to decide whether we can apply Marcel's
> solution. Did anyone ever read something about it?
>
>
> Best,
>
> Christoph
> <http://www.hpi.de/>
> ------------------------------
> *Von:* Squeak-dev <squeak-dev-bounces at lists.squeakfoundation.org> im
> Auftrag von Stéphane Rollandin <lecteur at zogotounga.net>
> *Gesendet:* Samstag, 19. September 2020 22:34:21
> *An:* squeak-dev at lists.squeakfoundation.org
> *Betreff:* Re: [squeak-dev] ColorForm with transparency not working
> properly
>
> > But unfortunately, I could not find any documentation about the
> > different Form rules such as #blend, #over, #paint etc. Can you give me
> > some pointers?
> Related thread:
> http://forum.world.st/ImageForm-color-with-alpha-td5090574.html
>
> Stef
>
>
>
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