For the question
   "Do we really want to do that, have a stream of Morphs (or other
graphical objects)?"
I think an interesting article to read is
https://smalltalkrenaissance.wordpress.com/2015/06/29/silk-is-just-too-flexible/

A hierarchy of morphs (elements) may be regarded as well as a stream.


Canvas has a useful class comment [3]

It could be that
    NullEncoder
        FlattenEncoder
are just helper classes to structure the code.



FlattenEncoder has the comment

    "The simplest possible encoding:  leave the objects as is."


Maybe the simplest thing for the class comment of NullEncoder is just
to refer to the class comment of FlattenEncoder and Canvas.

[3] Class comment of 'Canvas'
A canvas is a two-dimensional medium on which morphs are drawn in a
device-independent manner. Canvases keep track of the origin and
clipping rectangle, as well as the underlying drawing medium (such as
a window, pixmap, or postscript script).

Subclasses must implement (at least) the following methods:
	* Drawing:
		#fillOval:color:borderWidth:borderColor:
		#frameAndFillRectangle:fillColor:borderWidth:borderColor:
		#drawPolygon:color:borderWidth:borderColor:
		#image:at:sourceRect:rule:
		#stencil:at:sourceRect:rule:
		#line:to:width:color:
		#paragraph:bounds:color:
		#text:bounds:font:color:
	* Support
		#clipBy:during:
		#translateBy:during:
		#translateBy:clippingTo:during:
		#transformBy:clippingTo:during:

On 9/29/17, Nicolas Cellier <nicolas.cellier.aka.nice at gmail.com> wrote:
> The target inst. var. is used exclusively by the PostscriptCanvas.
> And IMO it is a classical mistake of inheritance versus composition.
>
> A PostScript canvas will have to encode the sequence of graphics
> instruction into a stream of PostScript instructions written into a
> PostScript file.
> For this purpose, it has a target PostscriptEncoder, which is itself an
> encoder already.
>
> An Encoder implements a processing unit that transform a stream by using a
> kind of generic double dispatching.
>
> Why the PostscriptCanvas has to be considered as an Encoder itself is very
> suspect, unless we ask
>
>     canvas write: aMorph.
>
> Do we really want to do that, have a stream of Morphs (or other graphical
> objects)?
>
> 2017-09-29 17:33 GMT+02:00 H. Hirzel <hannes.hirzel at gmail.com>:
>
>> Tobias
>>
>> You write that NullEncoder and subclasses could be summarized as
>>
>>     "Put objects onto another thing with encoding inbetween".
>>
>> which I think is helpful for understanding.
>>
>> Maybe we consider for the class comment of NullEncoder
>>
>>     "Put objects onto another thing with encoding/transformation
>> inbetween".
>>
>>
>> But also note that this is not only related to PostscriptCanvas as we
>> have
>>
>>
>> NullEncoder
>>     FlattenEncoder
>>          Canvas
>>              FormCanvas
>>
>> FormCanvas has some nice usage examples.
>>
>> #test1 is
>>
>> test1
>>         "FormCanvas test1"
>>
>>         | canvas |
>>         canvas := FormCanvas extent: 200 at 200.
>>         canvas fillColor: (Color black).
>>         canvas line: 10 at 10 to: 50 at 30 width: 1 color: (Color red).
>>         canvas frameRectangle: ((20 at 20) corner: (120 at 120)) width: 4
>> color:
>> (Color green).
>>         canvas point: 100 at 100 color: (Color black).
>>         canvas drawString: 'Hello, World!' at: 40 at 40 font: nil color:
>> (Color cyan).
>>         canvas fillRectangle: ((10 at 80) corner: (31 at 121)) color: (Color
>> magenta).
>>         canvas fillOval: ((10 at 80) corner: (31 at 121)) color: (Color cyan).
>>         canvas frameOval: ((40 at 80) corner: (61 at 121)) color: (Color blue).
>>         canvas frameOval: ((70 at 80) corner: (91 at 121)) width: 3 color:
>> (Color
>> red alpha: 0.2).
>>         canvas fillRectangle: ((130 at 30) corner: (170 at 80)) color: (Color
>> lightYellow).
>>         canvas showAt: 0 at 0.
>>
>>
>> This works fine in an MVC project
>>
>> --Hannes
>>
>> On 9/29/17, Tobias Pape <Das.Linux at gmx.de> wrote:
>> > Hi Hannes
>> >
>> >> On 29.09.2017, at 15:21, H. Hirzel <hannes.hirzel at gmail.com> wrote:
>> >>
>> >> And there is no 'FlattenEncoder' in Pharo 6
>> >
>> >>
>> >>
>> >> On 9/29/17, H. Hirzel <hannes.hirzel at gmail.com> wrote:
>> >>> We have
>> >>>
>> >>> NullEncoder
>> >>>    FlattenEncoder
>> >>>        Canvas
>> >
>> > So here's the Thing: I looked in 3.8, and there's:
>> >
>> > Object
>> >  NullEncoder          - Morphic-Postscript Filters
>> >   FlattenEncoder      - Morphic-Postscript Filters
>> >    Canvas             - Morphic-Support
>> >     PostscriptCanvas  - Morphic-Postscript Canvases
>> >
>> > But also note that they all have a callback via class>>filterSelector:
>> >
>> > NullEncoder>>filterSelector           ^ #writeOnFilterStream:
>> > FlattenEncoder>>filterSelector                ^ #flattenOnStream:
>> > Canvas>>filterSelector                        ^ #drawOnCanvas:
>> > PostscriptCanvas>>filterSelector      ^ #fullDrawPostscriptOn:
>> >
>> > I think part of that happened because this all shared common
>> functionallity,
>> > In the sense that all those things "Put objects onto another thing with
>> > encoding inbetween".
>> > Thinking of things like a n-dimensonal stream or so…
>> >
>> > I checked and It is like that even in Squeak 3.6, 3.0, 2.8.
>> > Squeak 1.13 does not have any of those, and it has no Morphic.
>> >
>> > Self Morphic does not have such Encoders, tho.
>> >
>> > In the end it all seems to be related to the PostScript Canvas, which,
>> > understandably, has to have access to certain objects and actually has
>> > to
>> > "encode" them into a file.
>> >
>> > Best regards
>> >       -Tobias
>> >
>> >
>> >
>> >>>
>> >>> there are no direct users of NullEncoder and FlattenEncoder.
>> >>>
>> >>> FlattenEncoder class comment is just
>> >>>
>> >>>    'The simplest possible encoding:  leave the objects as is.'
>> >>>
>> >>> a bit terse. Does not really say what the issue is about.
>> >>>
>> >>>
>> >>>
>> >>> On 9/29/17, H. Hirzel <hannes.hirzel at gmail.com> wrote:
>> >>>> P.S.
>> >>>>
>> >>>> There is no NullEncoder in Pharo.
>> >>>>
>> >>>> The class Canvas is not in a package 'Morphic-Support' but in a
>> >>>> package 'Graphics-Canvas'.
>> >>>>
>> >>>> There is no 'Graphics-Canvas' package in Squeak. [2]
>> >>>>
>> >>>> Seems like a good idea to move Canvas and subclasses to a package
>> >>>> 'Graphics-Canvas' as well.
>> >>>>
>> >>>>
>> >>>> [2] Graphics package in Squeak 6.0a-17405
>> >>>>
>> >>>> Graphics-Display Objects
>> >>>> Graphics-External-Ffenestri
>> >>>> Graphics-Files
>> >>>> Graphics-Fonts
>> >>>> Graphics-Primitives
>> >>>> Graphics-Text
>> >>>> Graphics-Transformations
>> >>>> GraphicsTests-Files
>> >>>> GraphicsTests-Primitives
>> >>>> GraphicsTests-Text
>> >>>>
>> >>>> On 9/29/17, H. Hirzel <hannes.hirzel at gmail.com> wrote:
>> >>>>> Hello
>> >>>>>
>> >>>>> NullEncoder is subclass of object ([1] for full hierachy). It is a
>> >>>>> superclass of Canvas.
>> >>>>>
>> >>>>> What is the function of NullEncoder. No class comment so far?
>> >>>>>
>> >>>>> Regards
>> >>>>> Hannes
>> >>>>>
>> >>>>>
>> >>>>> ------------------------------------------------------------
>> -------------------------------------------------------------------
>> >>>>>
>> >>>>> [1] NullEncoder printHierarchy '
>> >>>>> ProtoObject #()
>> >>>>>   Object #()
>> >>>>>           NullEncoder #(''target'' ''filterSelector'')
>> >>>>>                   FlattenEncoder #()
>> >>>>>                           ByteEncoder #()
>> >>>>>                                   PrintableEncoder #()
>> >>>>>                                           PostscriptEncoder #()
>> >>>>>
>>  PostscriptEncoderToDisk #()
>> >>>>>                                           PropertyListEncoder #()
>> >>>>>                           Canvas #()
>> >>>>>                                   ColorMappingCanvas
>> >>>>> #(''myCanvas'')
>> >>>>>                                           AlphaBlendingCanvas
>> #(''alpha'')
>> >>>>>                                           ShadowDrawingCanvas
>> #(''shadowColor'')
>> >>>>>                                   FormCanvas #(''origin''
>> ''clipRect'' ''form'' ''port''
>> >>>>> ''shadowColor'')
>> >>>>>                                           BalloonCanvas
>> #(''transform'' ''colorTransform'' ''engine''
>> >>>>> ''aaLevel'' ''deferred'')
>> >>>>>                                           BlueFormCanvas #()
>> >>>>>                                           ColorPatchCanvas
>> #(''stopMorph'' ''foundMorph'' ''doStop'')
>> >>>>>                                           MultiResolutionCanvas
>> #(''deferredMorphs'')
>> >>>>>                                   PluggableCanvas #()
>> >>>>>                                           BufferedCanvas
>> #(''remote'' ''previousVersion'' ''lastTick''
>> >>>>> ''dirtyRect'' ''mirrorOfScreen'')
>> >>>>>                                           CachingCanvas
>> #(''cacheCanvas'' ''mainCanvas'')
>> >>>>>                                           ClippingCanvas
>> #(''canvas'' ''clipRect'')
>> >>>>>                                           MultiCanvas
>> >>>>> #(''canvases''
>> ''extent'' ''depth'')
>> >>>>>                                           NullCanvas #()
>> >>>>>                                   PostscriptCanvas #(''origin''
>> ''clipRect'' ''currentColor''
>> >>>>> ''shadowColor'' ''currentFont'' ''morphLevel'' ''gstateStack''
>> >>>>> ''fontMap'' ''usedFonts'' ''psBounds'' ''topLevelMorph''
>> >>>>> ''initialScale'' ''savedMorphExtent'' ''currentTransformation''
>> >>>>> ''printSpecs'' ''pages'')
>> >>>>>                                           DSCPostscriptCanvas #()
>> >>>>>
>>  DSCPostscriptCanvasToDisk #()
>> >>>>>                                           EPSCanvas #()
>> >>>>>                                   RemoteCanvas #(''innerClipRect''
>> ''outerClipRect'' ''transform''
>> >>>>> ''connection'' ''shadowColor'')'
>> >>>>>
>> >>>>
>> >>>
>> >>
>> >
>> >
>> >
>>
>>
>