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An independent implementation of the CSS layout algorithm.

Project Description

Colosseum

An independent implementation of the CSS layout algorithm. This implementation is completely standalone - it isn’t dependent on a browser, and can be run over any box-like set of objects that need to be laid out on a page (either physical or virtual)

At present, the implementation is partial; only portions of the box and flexbox section of the specification are defined:

Name Value
width, height positive number
min_width, min_height positive number
max_width, max_height positive number
left, right, top, bottom number
margin, margin_left, margin_right, margin_top, margin_bottom number
padding, padding_left, padding_right, padding_top, padding_bottom positive number
border_width, border_left_width, border_right_width, border_top_width, border_bottom_width positive number
flex_direction "column", "row"
justify_content "flex-start", "center", "flex-end", "space-between", "space-around"
align_items, align_self "flex-start", "center", "flex-end", "stretch"
flex positive number
flex_wrap "wrap", "nowrap"
position "relative", "absolute"

Quickstart

In your virtualenv, install Colosseum:

$ pip install colosseum

Colosseum provides a CSS class that allows you to define CSS properties, and apply them can be applied to any DOM-like tree of objects. There is no required base class; Colosseum will duck-type any object providing the required API. The simplest possible DOM node is the following:

from colosseum import Layout

class MyDOMNode:
    def __init__(self, style):
        self.parent = None
        self.children = []
        self.layout = Layout(self)
        self.style = style.bind(self)

    def add(self, child):
        self.children.append(child)
        child.parent = self

That is, a node must provide:

  • a parent attribute, declaring the parent in the DOM tree; the root of the DOM tree has a parent of None.
  • a children attribute, containing the list of DOM child nodes.
  • a layout attribute, for storing the final position of the node.
  • a style attribute - generally a CSS declaration, bound to the node.

With that a compliant DOM node definition, you can then and query the layout that results:

>>> from colosseum import CSS, ROW, COLUMN
>>> node = MyDOMNode(style=CSS(width=1000, height=1000, flex_direction=ROW))
>>> node.add(MyDOMNode(style=CSS(width=100, height=200)))
>>> node.add(MyDOMNode(style=CSS(width=300, height=150)))
>>> node.style.apply()
>>> layout = node.layout
>>> print(node.layout)
<Layout (1000x1000 @ 0,0)>
>>> layout.width
1000
>>> layout.height
1000
>>> layout.top
0
>>> layout.left
0
>>> for child in node.children:
...     print(child.layout)
<Layout (100x200 @ 0,0)>
<Layout (300x150 @ 100,0)>

Calling node.style.apply() forces the box model to be evaluated. Once evaluated, the layout will be cached. Modifying any CSS property on a node will mark the layout as dirty, and calling apply() again will cause the layout to be re-evaluated. For example, if we switch the outer node to be a “column” flex box, rather than a “row” flex box, you’ll see the coordinates of the child boxes update to reflect a vertical, rather than horizontal layout:

>>> node.style.flex_direction = COLUMN
>>> node.style.apply()
>>> print(node.layout)
<Layout (1000x1000 @ 0,0)>
>>> for child in node.children:
...     print(child.layout)
<Layout (100x200 @ 0,0)>
<Layout (300x150 @ 0,200)>

If the layout is not dirty, the layout will not be recomputed.

Style attributes can also be set in bulk, using the set() method on the style attribute:

>>> node.style.set(width=1500, height=800)
>>> node.style.apply()
>>> print(node.layout)
<Layout (1500x800 @ 0,0)>

Style attributes can also be removed by deleting the attribute on the style attribute. The value of the property will revert to the default:

>>> node.style.set(margin_top=10, margin_left=20)
>>> node.style.apply()
>>> print(node.layout)
<Layout (1500x800 @ 20,10)>
>>> del(node.style.margin_left)
>>> print(node.style.margin_left)
0
>>> print(node.layout)
<Layout (1500x800 @ 0,10)>

Layout values are given relative to their parent node. If you want to know the absolute position of a node on the display canvas, you can request the origin attribute of the layout. This will give you the point on the canvas from which all the node’s attributes are measured. You can also request the absolute attribute of the layout, which will give you the position of the element on the entire canvas:

>>> node.style.set(margin_top=10, margin_left=20)
>>> node.style.apply()
>>> print(node.layout)
<Layout (1500x800 @ 20,10)>
>>> for child in node.children:
...     print(child.layout)
<Layout (100x200 @ 0,0)>
<Layout (300x150 @ 0,200)>
>>> print(node.style.layout.origin)
<Point (0,0)>
>>> for child in node.children:
...     print(child.style.layout.origin)
<Point (20,10)>
<Point (20,10)>
>>> print(node.style.layout.absolute)
<Point (20,10)>
>>> for child in node.children:
...     print(child.style.layout.absolute)
<Point (20,10)>
<Point (20,210)>

Community

Colosseum is part of the BeeWare suite. You can talk to the community through:

We foster a welcoming and respectful community as described in our BeeWare Community Code of Conduct.

Contributing

If you experience problems with Colosseum, log them on GitHub. If you want to contribute code, please fork the code and submit a pull request.

Acknowledgements

The algorithm and test suite for this library is a language port of CSS-layout project, open-sourced by Facebook.

Release History

Release History

History Node

0.1.6

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0.1.5

This version
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0.1.4

History Node

0.1.3

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0.1.2

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0.1.1

History Node

0.1.0

History Node

0.0.1

Download Files

Download Files

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File Name & Checksum SHA256 Checksum Help Version File Type Upload Date
colosseum-0.1.4-py3-none-any.whl (24.2 kB) Copy SHA256 Checksum SHA256 py3 Wheel Apr 1, 2017
colosseum-0.1.4.tar.gz (36.4 kB) Copy SHA256 Checksum SHA256 Source Apr 1, 2017

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