Re: [PyX-user] Ordering of bitmap vs. lines

[Arnd B. <arn...@we...>]

Hi Joerg,

On Mon, 10 Dec 2012, Joerg Lehmann wrote:

> Hi Arnd,
>
> Indeed in PyX 0.12.1, the graph code uses the newly introduced canvas
> layer system to specify the drawing order of various parts of the graph.
> This fixes an old bug (graph grids had been drawn above the axis ticks).
> Unfortunately, this also breaks old scripts - that's why PyX is still,
> even after so many years, in an alpha state - and documentation is still
> lacking a bit...

Well, as it works so nicely for so many bachelor/diploma/PhD theses
and papers, one tends to forget this ... ;-).

> In any case, in order to draw the bitmap below lines and/or symbols of,
> e.g., a function plot use:
>
>   g.layer("filldata").insert(...)

I tried to understand the new layers a bit and got to the following point:

# <--- snip here
from pyx import *

c = canvas.canvas()
layer1 = c.layer("level1")
layer1.text(0, 0, "Hello, layer1")
layer2 = c.layer("level2", below="level1")
#layer2 = c.layer("level2", below=layer1)          # <--- this works
layer2.stroke(path.line(0, 0, 2, 0.5), [style.linewidth.THICK,
color.rgb.red])
c.writeEPSfile()
# <--- and here


Gives:
Traceback (most recent call last):
   File "hello_layer1.py", line 6, in <module>
     layer2 = c.layer("level2", below="level1")
   File ".../pyx/canvas.py", line 230, in layer
     self.layers[name] = self.insert(canvas(texrunner=self.texrunner),
                       after=above, before=below)
   File ".../pyx/canvas.py", line 259, in insert
     self.items.insert(self.items.index(before), item)
ValueError: 'level1' is not in list

So it seems that a string is not the right way of specifying a layer:

Looking at the code, it cannot work this way, as the `below`
string given to `canvas.layer(...)` is passed as `before`
argument to `canvas.insert(...)` which is then
used to via `self.items.index(before)` to obtain
the right index in the list `self.items` containing the
different canvas(=layer) instances.

So the solution is to provide the layer instance as argument
to `below`. Is this the intended way?
If yes, I am not sure, whether I read the doc-string to `canvas.layer`
correctly, as I interpreted it such that strings would
also be correct for `above` and `below` and not just the `name`.

Best, Arnd