From: Michael Neumann <mneumann@...>
Date: 2004-10-22T18:13:24+09:00
Subject: Re: CamelCase issues

On Fri, Oct 22, 2004 at 04:49:18PM +0900, Stefan Schmiedl wrote:
> On Fri, 22 Oct 2004 07:36:12 +0900,
> Michael Neumann <mneumann@ntecs.de> wrote:
> [...]
> > It's similar as in the following example (where render_table_header_on =~ draw_line_on):
> >
> >   def draw_line_on(canvas, x, y, w, h)
> >     ...
> >   end
> >
> >   def draw_box_on(canvas, x, y, w, h)
> >     ...
> >   end
> >
> >   def draw_on(canvas)
> >     draw_line_on(canvas, ....)
> >     draw_box_on(canvas, ...)
> >   end
> 
> Who does all of this drawing? It looks like some unknown power is doing
> (and knowing) way too much.

The component! For example the button component has to draw itself onto
the screen, for which it needs a canvas. 

Well, my example above was not good choosen. Better would have been:

  class Button < Component
    # this one is called from 'outside'  
    def draw_on(canvas)
      draw_frame(canvas)
      draw_inner(canvas)
    end

    private

    # helper method
    def draw_frame(canvas)
      if @pressed
        canvas.color = :lightgray
        canvas.line(x, y, x+w, y)
        canvas.line(x+w, y, x+w, y+h)
        ...
      else
        ...
      end
    end

    # helper method
    def draw_inner(canvas)
      canvas.text(@caption)
    end
  end

Of course the canvas implements the drawing primitives.
Now think the same for the Web and Html generation.

> > Of course I'd removed the "_on" in the GUI case. 
> > The actual "drawing" is done this way (inside render_xxxx_on):
> >
> >   renderer.table {
> >     renderer.row {
> >       ...
> 
> If I were the renderer, I'd have a headache from all the knowledge that
> you must have stuffed into my poor brain :-) There must be a better way
> to do this.

Hm, but somewhere you have to implement how the component looks like, no?
The above is equivalent to:

  cgi.table {
    cgi.tr {
      cgi.td { ... } +
      cgi.td { ... }
    }
  }

But in a more imperatively fashion, similar as for drawing a GUI on the
canvas, where you don't do this ('+'):

  canvas.box(...) {
    canvas.line(1, 1, 10, 10) +
    canvas.line(...) +
    ...
  }

Regards,

  Michael