[Chart] Fwd: [diagrams] Re: [GSoC 2013] Progress - Porting Charts to Diagrams
Tim Docker
tim at dockerz.net
Wed Jun 12 22:54:42 BST 2013
Hi,
I think your analysis is good. In the context of the backend, it makes
sense to separate out the color from the various styles.
On the other hand, in the context of the chart use API, it makes sense
to have all of the properties of a line in a single data type - it's
simpler for the caller to say style this plot line using properties as
per this value.
Possible solutions are:
1) Leave it and put up with the inconsistency...
2) Have separate types in the backend API / user API for LineStyle,
FillStyle and FontStyle
3) Remove withSourceColor from the backend API, and require
backends to give the logical behaviour (ie setting the FillStyle doesn't
affect the color of lines). This would mean the cairo backend would have
to do a bit more work to be correct.
Either 2 or 3 is ok with me.
Tim
On 13/06/13 00:45, Jan Bracker wrote:
> Hi everybody,
>
> a small follow up: While thinking about and implementing the smaller
> API I noticed that due to the internals of Cairo the source color is
> used to render everything. When setting a style (font, fill, line) the
> source color is changed according to that style. This means each of
> the "with...Style" or "withSourceColor" functions constantly overrides
> the source color. Is this really desired behaviour? Shouldn't the fill
> color apply to fills, the line color to strokes and the font color to
> text rendering? If so the source color ("withSourceColor") is a
> useless concept. Of course keeping these color seperate will expand
> the cairo rendering backend, but I think it is useful to avoid
> confusion to which color is used where.
>
> Example:
>
> 1: withLineStyle ls $ withFillStyle fs $ fillPath p >> strokePath p
>
> should be the same as (according to my thoughts):
>
> 2: withFillStyle fs $ withLineStyle ls $ fillPath p >> strokePath p
>
> but with the current implementation 1 would render both with the fill
> color and 2 would render them with the line color.
>
> Jan
>
>
>
> 2013/6/12 Jan Bracker <jan.bracker at googlemail.com
> <mailto:jan.bracker at googlemail.com>>
>
> Hi everybody,
>
> Brent: Thanks you for the offer and thanks for your great help on
> those nasty type errors yesterday.
>
> On IO in Diagrams: We looked into the SVGFont rendering stuff and
> noticed that it has a call to unsafePerformIO (which let us scream
> in pain and agony :-P ). We though it would be nice to remove this
> hidden call and actually offer a function that makes it explicit.
> I am not sure why it is there and assume its purpose is to keep
> everything pure. Your suggestion to produce a IO Diagram is what
> we thought of too. We are not sure which changes would be required
> up to now, but we will come back to you when we do know.
>
> On general note: I have worked on abstracting the backend the last
> two days. Here what I accomplished by now:
>
> - I have fully converted my branch to use the abstract rendering
> backend ChartBackend [0] instead of the CRender monad directly.
>
> - There is a implementation of the backend with Cairo in the
> Backend.Cairo module [1].
>
> - The current HEAD of the backend-experiment branch [2] is stable
> (commit ad715c4d216e8fcb494f9919d4fb5459ce7d85c2).
>
> - I added reference images [3] of all tests to compare with the
> results that the original code delivered.
>
> - All tests are running using the new backend code and pixel-diffs
> [4] of the produced PNGs show that they render exactly the same.
>
> - I ran into the issue that the ToRenderable class was complicated
> to abstract. My abstraction involved a associated type with two
> parameters that are in relation to each other [5,6]. After talking
> with Tim I removed the ToRenderable code completely and instead
> just exported specific functions for all types directly. This also
> made the examples easier to adjust, since the new ToRenderable
> class made type annotations necessary everywhere, which, in my
> point of view, defeats the purpose of the toRenderable function.
> It was easier just calling the specific function directly. I think
> the change of API is acceptable, since the generalised backend
> lets type parameters popup everywhere anyway.
>
> The next steps:
>
> - Tim suggested this simplified API instead of the rather
> extensive [0] version used right now: http://hpaste.org/89758 . I
> will work on trimming down the current API and providing all
> complex functions in terms of the new API.
> - The only downside I see is the Matrix type which (I assume)
> comes from Cairo.Matrix [7]. I would just give a naive
> implementation that contains 6 double values for the affine
> transformations and provide a similar custom API.
> - I will also try to provide a small EDSL for writing paths to
> make that easier (I guess some short combinators and a monoid
> instance will do fine).
>
> Jan
>
> [0]:
> https://github.com/jbracker/haskell-chart/blob/backend-experiment/chart/Graphics/Rendering/Chart/Types.hs#L85
> [1]:
> https://github.com/jbracker/haskell-chart/blob/backend-experiment/chart/Graphics/Rendering/Chart/Backend/Cairo.hs#L80
> [2]:
> https://github.com/jbracker/haskell-chart/tree/ad715c4d216e8fcb494f9919d4fb5459ce7d85c2
> [3]:
> https://github.com/jbracker/haskell-chart/tree/backend-experiment/chart/tests-reference
> [4]:
> https://github.com/jbracker/haskell-chart/blob/backend-experiment/chart/gen-diffs-png.sh
> [5]:
> https://github.com/jbracker/haskell-chart/blob/backend-experiment/chart/Graphics/Rendering/Chart/Renderable.hs#L77
> [6]:
> https://github.com/jbracker/haskell-chart/blob/backend-experiment/chart/Graphics/Rendering/Chart/Layout.hs#L163
> [7]:
> http://hackage.haskell.org/packages/archive/cairo/0.12.4/doc/html/Graphics-Rendering-Cairo-Matrix.html
>
>
> 2013/6/11 Brent Yorgey <byorgey at seas.upenn.edu
> <mailto:byorgey at seas.upenn.edu>>
>
> Hi Jan and all,
>
> Looks like some great progress! I'm excited. =) Just a couple
> thoughts: one, let me know if you want help staring at the
> funny type
> errors with Legend and whatnot. I'm not familiar with the
> Chart code
> but perhaps I can help figure out a good solution for the
> abstraction.
>
> My other general comment is that I know you and Tim have
> talked a bit
> about the problems with having font stuff in IO whereas
> diagrams is
> pure. However, from my point of view it wouldn't be that big of a
> deal if Chart produced an IO Diagram rather than just a Diagram.
> Maybe I haven't thought about it sufficiently but it seems
> like this
> would be an easy solution to the problem of needing IO. I'm
> happy to
> talk about it in more detail if you want, and if there are
> ways that
> the diagrams API could change to make any of this easier I'm
> happy to
> discuss that as well. I'm in the middle of some big
> refactoring anyway
> (though don't worry, I don't think it will affect your work on
> porting
> Chart very much).
>
> -Brent
>
> On Mon, Jun 10, 2013 at 05:24:34PM +0200, Jan Bracker wrote:
> > Hi,
> >
> > Andy: The goal is to abstract Charts from Cairo so we can
> plug in another
> > backend (target is Diagrams). And by that we would also be
> able to use
> > Sunroof through diagrams. Of course in the end it should
> also be possible
> > to implement a Sunroof backend on its own.
> >
> > Tim:
> >
> > > Rather than have the CRender monad take an extra
> parameter, I guess one
> > > could just have a separate data type for each backend (ie
> CRenderCairo and
> > > CRenderDiagrams) and have the drawing code abstracted over
> a typeclass
> > > implemented by both. Not sure if this would be better...
> > >
> >
> > I tried your approach in a new branch:
> >
> https://github.com/jbracker/haskell-chart/tree/backend-experiment
> >
> > It seems to be working quite well. So I started generalizing
> everything
> > outside of the cairo module to use a general ChartBackend m
> instead of a
> > CRender to draw everything. There are a few spots that are
> giving me a hard
> > time:
> >
> > Renderable was implemented in terms of CRender. So I added
> another type
> > parameter and that worked fine until I hit Legend. There I
> also added a
> > type parameter. But that blew up the ToRenderable instance.
> So I had to
> > insert a associated type to relate types to each other.
> After doing so I
> > was not able to fix whatever went wrong in Plot.Pie. The
> 'ToRenderable
> > PieLayout' instance gives me this error:
> >
> > Graphics/Rendering/Chart/Plot/Pie.hs:121:62:
> > Could not deduce (RenderableT m a0 ~ PieChart)
> > from the context (ChartBackend m)
> > bound by the type signature for
> > toRenderable :: ChartBackend m =>
> > RenderableT m PieLayout -> Renderable m ()
> > at Graphics/Rendering/Chart/Plot/Pie.hs:(117,5)-(125,29)
> > The type variable `a0' is ambiguous
> > Possible fix: add a type signature that fixes these type
> variable(s)
> > In the return type of a call of `pie_plot_'
> > In the second argument of `($)', namely `pie_plot_ p'
> > In the second argument of `addMargins', namely
> > `(toRenderable $ pie_plot_ p)'
> >
> > I think I know what is going wrong, but I have no idea how
> to specify the
> > instance it should use there. Maybe I am just to tired to
> see the solution.
> >
> > Right now I am trying to make things work without extra type
> parameters,
> > though the definitions that are based on CRender are giving
> me a hard time,
> > because then I end up with rank N types.
> >
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>
>
>
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