Hi Tim,

Yes. In Squeak there is a bug in #asFormOfDepth: . The last lines are:

	"Special case: For a 16 -> 32 bit conversion fill the alpha channel  
because it gets lost in translation."
	(self depth = 16 and:[d= 32]) ifTrue:[newForm fillAlpha: 255].

But they should be as in Cuis:

	"If we build a 32bpp from one of smaller depth,
	it will have zero in the alpha channel (until BitBlt is fixed!)"
	d = 32 ifTrue: [
		newForm fixAlpha ].

I think this should fix your problem.

Besides, the sample code I sent gets transparent, although the stuff  
in the Form, 16rFF000000, is opaque black. This is because of another  
bug, this one at #colorFromPixelValue:depth: . I suggest taking the  
code verbatim from Cuis.

Cheers,
Juan Vuletich

Quoting tim Rowledge <tim at rowledge.org>:

> On 11-10-2014, at 5:00 AM, J. Vuletich (mail lists)  
> <juanlists at jvuletich.org> wrote:
>>
>> What do you get if you evaluate:
>>
>> f _ Form extent: 8 at 8 depth: 16.
>> f32 _ f asFormOfDepth: 32.
>> {f colorAt: 1 at 1. f32 colorAt: 1 at 1 }
>>
>> If you get transparent twice, then the problem is not in  
>> #formOfDepth:, but in your Scratch filters... If that is the case,  
>> an alternative to fixing them to support 16bpp would be to do all  
>> the stuff in 32bpp.
>
> I get transparent in both cases, but
> a) this is done *before* the scratch filtering in order to make  
> 32bpp forms because the plugin code to do swirlies etc only handles  
> 32bpp. (I’d love to alter this; a move to using 16bpp everywhere in  
> Scratch would benefit the Pi greatly since it is frequently memory  
> bus bound)
> b) inspect the two bitmaps; you’ll see that the 8bpp one has 0s but  
> the 32bpp has 16rFF000000s.
> c) display each of them with ‘paint’ and you’ll notice that the  
> 32bpp one is black and the 8bpp one is invisible
>
> |f f32|
> f := Form extent: 8 at 8 depth: 16.
> f32 := f asFormOfDepth: 32.
> f displayOn: Display at: 500 at 10 rule: Form paint.
> f32 displayOn: Display at: 510 at 10 rule: Form paint.
> {f . f32 }
>
> Inspect that to see what I mean.
>
> If I use a hacked asFormOfDepth: that does not do the alpha channel  
> ‘fixing’ then both Forms are transparent. This doesn’t surprise me  
> much since that is what asFormOfDepth: did in Squeak in the ancient  
> days when Scratch was first written by scraping tiny symbols on  
> polished stone slabs.
>
>>
>> Can you prepare an image for us to try? It would help us give  
>> better answers.
>
> No need, since this is not stuff I’ve changed (At least.. not  
> knowingly. Always a chance I’ve screwed something up somewhere, of  
> course)
> However, the image is available from  
> https://github.com/raspberrypi/scratch/blob/master/NuScratchBeta10.tgz in a  
> package which includes the Pi vm etc. Just shift-click on the top  
> half of the ‘R’ in the Scratch logo and ‘turn fill screen off’ to  
> get to the desktop.
>
>
> tim
> --
> tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
> Useful Latin Phrases:- Romani quidem artem amatoriam invenerunt. =  
> You know, the Romans invented the art of love.