Any chance to fix this bug for 5.3?

The following would still be a functional workaround:
[cid:fd67b6ba-ce69-44a3-94d8-362b808bcc7e]

(
Reminder: The bug can be reproduced using
"Example 3"
f := Form extent: 1 asPoint depth: 16.
f colorAt: 0 @ 0 put: Color red.
g := f asFormOfDepth: 32.
g colorAt: 0 @ 0
Expected: Color red
Actual: (Color r: 0.973 g: 0.0 b: 0.0)
)

Best,
Christoph
________________________________
Von: Squeak-dev <squeak-dev-bounces at lists.squeakfoundation.org> im Auftrag von Tobias Pape <Das.Linux at gmx.de>
Gesendet: Montag, 9. September 2019 16:56:03
An: The general-purpose Squeak developers list
Betreff: Re: [squeak-dev] Bug in Form>>#asFormOfDepth:?


> On 09.09.2019, at 15:53, Thiede, Christoph <Christoph.Thiede at student.hpi.uni-potsdam.de> wrote:
>
> Hi Tobias,
>
> oops, I mistook the depth with the number of bits per channel. Sorry and many thanks for your explanations!
>
> How would one fix the upscaling issue? Form>>#colormapIfNeededFor: returns nil in example 3, the comment in Color>>#colorMapIfNeededFrom:to: states this task is delegated to BitBlt. Is this comment wrong or is the defect in the primitive called that is in BitBlt>>#copyBits?
>
No, that part is only for cross-conversion of Forms and ColorForms
-t

> Best,
> Christoph
>
> Von: Squeak-dev <squeak-dev-bounces at lists.squeakfoundation.org> im Auftrag von Tobias Pape <Das.Linux at gmx.de>
> Gesendet: Montag, 9. September 2019 14:56 Uhr
> An: The general-purpose Squeak developers list
> Betreff: Re: [squeak-dev] Bug in Form>>#asFormOfDepth:?
>
> Hi Christoph,
>
> > On 09.09.2019, at 13:25, Thiede, Christoph <Christoph.Thiede at student.hpi.uni-potsdam.de> wrote:
> >
> > Hi all,
> >
> > consider the following example (print it):
> >
> > "Example 1"
> > f := Form extent: 1 asPoint depth: 1.
> > f colorAt: 0 @ 0 put: Color red.
> > g := f asFormOfDepth: 2.
> > g colorAt: 0 @ 0
> >
> > Expected output: Color red.
> > Actual output: Color black!
>
> No, Forms of depth 1 are black and white, and of depth2 are gray.
>
> >
> > Other examples:
> >
> > "Example 2"
> > f := Form extent: 1 asPoint depth: 1.
> > f colorAt: 0 @ 0 put: Color red.
> > g := f asFormOfDepth: 32.
> > g colorAt: 0 @ 0 "--> (Color r: 0.0 g: 0.0 b: 0.004)"
>
> yes, because you go from black/white to 32bit. I would have expected r0g0b0, but there might some rounding go on.
>
> >
> > "Example 3"
> > f := Form extent: 1 asPoint depth: 16.
> > f colorAt: 0 @ 0 put: Color red.
> > g := f asFormOfDepth: 32.
> > g colorAt: 0 @ 0 "--> (Color r: 0.973 g: 0.0 b: 0.0)"
>
>
>
> Something's wonky here!
> If we do
>
>         (((Form extent: 1 asPoint depth: 16)
>                 colorAt: 0 @ 0 put: Color red)
>                 asFormOfDepth: 32)
>         pixelValueAt: 0 at 0
>
> we get
>         4294443008 (aka 0xFFF80000)  which is a 32bit value.
> But the meaning is
>
>         11111111 11111000 00000000 00000000
>         ^ alpha  ^ r      ^ g      ^ b
>
> which means that the r component is not  "upscaled" during the #asFormOfDepth: process o.O (see PS)
>
>
>
>
> >
> > I am not familiar with color depths, but afaik Color red could be stored exactly using only 1 bit? Do I misunderstand the concept or is this really a bad output?
>
> No, the first bit depth to support red is 4 bit.
>
> Have a look at Color class>>colorFromPixelValue: p depth: d
>
> BTW: You can use a ColorForm to work with your own palette, so that you can have for example a 1-bit form with 1=yellow & 0=red…
>
>
> Best regards
>         -Tobias
>
> >
> > (I came across to this when performing #collectColors: on an 8 bit ColorForm loaded from disk, which did not work as expected.)
> >
> > Best,
> > Christoph
>
> PS: PS:
> Color red is r:1.0 g:0.0 b:0.0 but stored in a different fashion:
>
> Color comment:
> "
> Think of Color's instance variables as:
>         r       amount of red, a Float between 0.0 and 1.0.
>         g       amount of green, a Float between 0.0 and 1.0.
>         b       amount of blue, a Float between 0.0 and 1.0.
> (But, in fact, the three are encoded as values from 0 to 1023 and combined in a single integer, rgb.  The user does not need to know this.)
> "
> that means "Color red" is stored as 0x3FF00000 or,
>
> 1111111111 0000000000 0000000000
> ^ red      ^ green    ^ blue
>
> that makes 10 bit per component.
>
> However, in the 16 bit form we have only 5 bit per component, so,
>
>         f := Form extent: 1 asPoint depth: 16.
>         f colorAt: 0 @ 0 put: Color red.
>         f pixelValueAt: 0 at 0.
>
> yields 0x7C00 aka
>
> 11111 00000 00000
> ^ r   ^ g   ^ b



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