Adding some primitive to the Canvas

[mathk]

Here are some primitive for drawing on a canvas.

[HeinrichApfelmus]

Looks good. However, note that the Canvas API has already seen some extension in the develop branch.

Sorry for not having merged these older changes into the master branch yet, I will have to do some branch maintenance on my local repo.

[mathk]

Ok.

It seems that it is all in the develop branch. I would like to had the State monad for avoiding passing Canvas all over the place. A also I would like to had an other monad to combine the different method for drawing line on canvas. Avoiding the need to manually call beginPath and stroke.

What do you think?

[mathk]

I have merge the develop work on canvas and added a couple of other function. You can fine a new design for drawing on a canvas.

I have add 2 new datatype Drawing and DrawingPath. Both can be combine to shape more complex drawing.

For example here is the intended way to draw on a canvas:

    testCanvas = do
        canvas <- UI.canvas #
                    set UI.height 150 # 
                    set UI.width 300 # 
                    set style [("border", "solid black 1px")] #
        UI.renderDrawing canvas 
            ((UI.openedPath red 4.0 
                (UI.line (10.0,10.0) (100.0,100.0) <>
                (UI.move (150.0,100.0)) <>
                (UI.bezierCurve [(180.0,30.0), (250.0,180.0), (300.0,100.0)]))) <>
            (UI.openedPath red 4.0 (UI.arc (125.0, 115.0) 30.0 0.0 360.0)))
            element canvas
              where red = UI.solidColor (UI.RGB 0xFF 0 0) 

For the time being there is more a work in progress than a final design. Let me know if all is ok.

[mathk]

I am reopening this pull request. Let me know if the code looks ok for you. Thanks

[HeinrichApfelmus]

I'll have a look, but I'm currently short on time, so this may take a while. Sorry about that.

[HeinrichApfelmus]

Sorry about the rather long delay, I finally managed to take a look at your code.

The DrawingPath and Drawing monoids are good ideas, they are the first steps towards a more declarative drawing API. However, for Threepenny-GUI, I do not wish to implement a more declarative API. That may sound surprising, but the reason is simple: the diagrams package already does a thorough job at this! I think that the way to go is to make a Canvas backend for the diagrams package.

(That said, for the moment (October 2014), I temporarily advise against trying to implement a Canvas backend for Diagrams. I first want to improve the JavaScript FFI used by Threepenny.)