[squeak-dev] What is the task of NullEncoder?H. Hirzel hannes.hirzel at gmail.comThu Oct 5 00:32:52 UTC 2017
Attached is an updated of the previous demo of a HTML export for Morphs.
2 classes - with a dozen of methods in total provides basic Morphic
export by using the NullEncoder/Canvas hierarchy.
So far it shows a subclass of Canvas which makes use of the 'target'
instance variable and where the combination of graphics command and
write commands in this pipe and filter architecture is useful.
I implement
fullDrawHTMLOn:
in the Morph hierarchy following the
fullDrawPostscriptOn:aCanvas
example.
No support of borders and rounded corners yet. By making use
of/overriding the existing drawOn: methods this should be possible.
HTML and CSS are not yet separated.
In fact two encoders might be needed
1. HTMLEncoder
2. CSSEncoder
which should work together. I am not sure yet how to handle this.
--Hannes
Note: Another example would be to have a "JSONCanvas" which generates
morph descriptions in JSON.
On 10/2/17, H. Hirzel <hannes.hirzel at gmail.com> wrote:
> Hello Marcel, Nicolas, Tobias and Dave
>
> Thank you Marcel W. for the illustrations and pointing out that the
> NullEncoder (figures now included [5]) implements a pipe/and filter
> hierarchy.
>
> The video about app architectures [6] in which you describe different
> architecture styles is helpful. In particular you point out that the
> choice of a pipe/filter architecture has advantages in terms of memory
> consumption.
>
> Tobias, you ask
> [the fact that some canvas subclasses do not use the 'target' object]
> <citation>
>> That’s only technically true, and really an oversight. All canvases
>> write their output somewhere, be it a bitmap, native display surface or
>> other ‘DisplayMedium'. A canvas is a filter for converting morphs to this
>> target ‘DisplayMedium’.
>>
>> And having filter-canvases would be really cool :-)
>
> You mean like ColorMappingCanvas, AlphaBlendingCanvas, and
> ShadowDrawingCanvas?
> (Which, by your account, should not have an own myCanvas but rather
> reuse target…)?
> </citation>
>
> My answer is that I do not see any benefit of using 'target' in these
> classes.
>
> But Marcel Weiher gave as well an example of a more elaborate
> NullEncoder/FlattenEncoder/Canvas hierarchy to be used in a
> pipe/filter architecture style. [7]
>
> So let's try to add more output classes to see how we can benefit from
> this architecture style.
>
> Marcel Weiher noted in 1999 [8]
> <citation>
> [10 Sept 1999,MPW]
> The current MorphicPostscript support includes both EPS and multi-page
> Postscript generation.
>
> BookMorphs generate multi-page files, all other Morphs generate an EPS
> ready for inclusion, though currently without a bitmap preview.
>
> Postscript generation is split between a high-level class that maps
> Morphic drawing commands to Postscript imaging model commands and a
> low level class for generating actual Postscript code for the
> commands, in order to facilitate drop-in replacements for SPDF, SVG or
> comparable formats.
>
> I also think this is a good base for supporting other device
> independent graphic models and even direct device independent drawing.
> </citation>
>
> So the best thing to see how the mechanism / architecture works is
> actually to try out to add a few more "output encoders"
>
> For example to render
> 1. a bookmorph (or just a series of morphs serving as 'slides') as a
> sequence
> of web pages or a series of slides in a presentation program,
> 2. a morph a SVG code
> 3. morphs as JSON descriptions to be used by a web services.
> 4. a sequence of morphs as a presentation for LibreOffice Impress export
> (LO Impress offers a 'flat XML format')
> 5. Powerpoint slides (zip archive generation needed)
>
>
> I attach a demo / start of a MorphicHTMLCanvas implementation
> (Monticello mcz file).
> The description of the implementation steps are under [9].
>
> The demo does not actually run but brings up the context where it
> shows that it is useful to have access to a 'target' object -- a
> HTML/CSS encoder - from within the morph hierarchy.
>
> Run
> MorphicHTMLCanvas0Test new test01
>
> The screen shot shows the method call hierarchy.
>
> The demo does not show yet at which abstraction level in terms of
> "drawing commands"
>
> aMorph fullDrawHTMLOn: self.
>
> should operate. A more elaborate version of MorphicHTMLCanvas and a
> JSON example added will follow.
>
> Kind regards
> Hannes
>
>
>
> [5] NullEncoder http://wiki.squeak.org/squeak/5052
>
> NullEncoder implements a filter
>
> Object subclass: #NullEncoder
> instanceVariableNames: 'target filterSelector'
> classVariableNames: ''
> poolDictionaries: ''
> category: 'Morphic-Support'
>
>
>
> [6] UIKonf 2017 – Day 1 – Marcel Weiher – High Performance App Architecture
> https://www.youtube.com/watch?v=kHG_zw75SjE
>
> pipe/filter architecture at
>
> minute 12:00, but 0:00..12:00 is useful to get the context
> - traditional call/return 'architecture' style
>
>
> [7] Marcel Weiher --
> http://forum.world.st/attachment/4974704/1/filterstream-hierarchy.pdf
>
> [8] Squeak Postscript support http://wiki.squeak.org/squeak/753
>
>
> --------------------------------------------------
> [9] Implementation steps to create a HTML/CSS canvas for rendering
> morphs as a web code.
>
>
> "1. create a canvas for rendering Morphs as HTML"
>
> Canvas subclass: #MorphicHTMLCanvas0
> instanceVariableNames: 'morphLevel'
> classVariableNames: ''
> poolDictionaries: ''
> category: 'Add-Ons-HTML0'
>
>
> "2. create a test class for it"
>
> TestCase subclass: #MorphicHTMLCanvas0Test
> instanceVariableNames: ''
> classVariableNames: ''
> poolDictionaries: ''
> category: 'Add-Ons-HTML0'
>
>
> "3. Add an encoder to be used by MorphicHTMLCanvas0 for generating
> HTML/CSS"
>
> PrintableEncoder subclass: #HTMLCSSEncoder0
> instanceVariableNames: ''
> classVariableNames: ''
> poolDictionaries: ''
> category: 'Add-Ons-HTML0'
>
>
> "4a. Attach the HTMLCSSEncoder0 to the MorphicHTMLCanvas0"
> MorphicHTMLCanvas0 class
>
> defaultTarget
> ^HTMLCSSEncoder0 stream
>
>
> "4b. Add creation method"
> MorphicHTMLCanvas0 class
>
> morphAsHTML: aMorph
> | htmlCanvas |
> htmlCanvas := self new.
> htmlCanvas reset.
> htmlCanvas fullDrawMorph: aMorph .
> ^htmlCanvas contents.
>
>
> "4c. Add main method for rendering morphs as HTML"
>
> MorphicHTMLCanvas0
>
> fullDraw: aMorph
> aMorph fullDrawHTMLOn: self.
>
>
> "5. within the Morph hierarchy implement messages to 'draw' morphs as HTML"
> Object
> fullDrawHTMLOn: aStream
> "do not do anything yet"
>
>
> "6. Morph"
>
> fullDrawHTMLOn: aCanvas
>
> self halt.
>
> "Here I can access
>
> aCanvas target
>
> and directly generate HTML and CSS code"
>
>
> "7a. set up test environment "
> MorphicHTMLCanvas0Test
> test01
>
> self assert: (MorphicHTMLCanvas0 morphAsHTML: self createTestMorph)
> notNil
>
> "7b. an example morph for testing"
> MorphicHTMLCanvas0Test
>
> createTestMorph
> "MorphicHTMLCanvas0Test new createTestMorph openInWorld"
> | slide |
> slide := RectangleMorph new extent: 800 @ 600;
> position: 10 @ 50;
> color: Color blue.
> slide addMorph: (RectangleMorph new extent: 100 @ 100;
> position: 20 @ 60;
> color: Color yellow).
> ^ slide
>
>
>
>
>
>
> On 10/2/17, Marcel Weiher <marcel.weiher at gmail.com> wrote:
>>> On Sep 30, 2017, at 7:34 , Tobias Pape <Das.Linux at gmx.de
>>> <mailto:Das.Linux at gmx.de>> wrote:
>>>
>>>
>>> No, thats Marcel Weiher. He did a quite a lot Squeak/Postscript Stuff.
>>> I CC'ed him.
>>>
>>> Marcel, can you comment on the Encoder Hierarchie?
>>> (Full thread here)
>>
>> Hi Tobias et al,
>>
>> thanks for tagging me. :-)
>>
>> The “Encoder” classes are a Squeak version of an “object oriented pipes
>> and
>> filters” system I implemented in Objective-C in the late 90s:
>> https://github.com/mpw/MPWFoundation/tree/master/Streams.subproj
>> <https://github.com/mpw/MPWFoundation/tree/master/Streams.subproj>
>>
>> Why? Well, because the Postscript generation code was based on my
>> Objective-C Postscript processing code
>> (http://www.metaobject.com/Technology/#EGOS
>> <http://www.metaobject.com/Technology/#EGOS>), which is heavily based on
>> these filters.
>>
>> I have found the filters to be incredibly useful over the last 20 years,
>> partly because they compose so well: just like Unix pipes and filters,
>> they
>> are symmetric so that their input protocol ( #writeObject: ) is the same
>> as
>> their output protocol ( #writeObject:). The filterSelector is there to
>> allow filter-specific processing using double dispatch, but once the
>> processing is done the result is once again normalized to a #writeObject:
>> You can therefore combine these filters any way you want.
>>
>>
>>
>>
>> Another feature is that they are, like Unix filters, fundamentally
>> incremental, so multiple processing steps are interleaved and both input
>> and
>> output can stream directly to/from disk/network. When doing pre-press in
>> the early 90ies (file sizes >> memory sizes) this was a useful feature,
>> and
>> it is still helpful today, see for example the first part of my UIKonf
>> talk:
>>
>> https://www.youtube.com/watch?v=kHG_zw75SjE
>> <https://www.youtube.com/watch?v=kHG_zw75SjE>
>>
>> More recently, the fact that filters are dataflow-oriented and therefore
>> don’t care much about the control flow has made them useful in
>> implementing
>> asynchronous processing pipelines Think “FRP” just simpler, more
>> readable
>> and faster. The Microsoft To-Do network stack is implemented using this.
>>
>> With all the references to Unix P/F, it is probably no surprise that this
>> also subsumes Unix I/O, just with the advantage of an OO hierarchy of
>> shareable behavior. Oh, and also the interesting feature of subsuming
>> both
>> filters and (output) streams, so ‘stdout’ in Objective-Smalltalk is one
>> of
>> these, a ByteStream that knows how to serialize objects and output them
>> to
>> some target that expects bytes. And in ‘stsh’ it’s a slight variant of
>> MPWByteStream that is more helpful to a human interacting.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>
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