Move projections into their own module
This commit is contained in:
Arjan Molenaar
parent
77301b1ee1
commit
a983259636
@ -27,7 +27,7 @@ Projections
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There's one special thing about Variables: since each item has it's own coordinate system ((0, 0) point, handy when the item is rendered), it's pretty hard to make sure (for example) a line can connect to a box and ''stays'' connected, even when the box is dragged around. How can such a constraint be maintained? This is where Projections come into play. A Projection can be used to project a variable on another space (read: coordinate system).
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The default projection (to canvas coordinates) is located in `gaphas.canvas` and is known as `CanvasProjection`.
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The default projection (to canvas coordinates) is located in `gaphas.projections` and is known as `CanvasProjection`.
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When a constraint contains projections, it is most likely that this constraint connects two items together. At least the constraint is not entirely bound to the item's coordinate space. This knowledge is used when an item is moved. A move operation typically only requires a change in coordinates, relative to the item's parent item (this is why having a (0,0) point per item is so handy). This means that constraints local to the item not not need to be resolved. Constraints with links outside the item's space should be solved though. Projections play an important role in determining which constraints should be resolved.
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113
gaphas/canvas.py
113
gaphas/canvas.py
@ -35,6 +35,7 @@ import cairo
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from gaphas import solver, table, tree
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from gaphas.decorators import AsyncIO, nonrecursive
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from gaphas.state import observed, reversible_method, reversible_pair
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from gaphas.projections import CanvasProjection
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#
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# Information about two connected items
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@ -896,118 +897,6 @@ class Canvas:
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raise AttributeError("There should be at least one point specified")
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class VariableProjection(solver.Projection):
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"""
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Project a single `solver.Variable` to another space/coordinate system.
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The value has been set in the "other" coordinate system. A
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callback is executed when the value changes.
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It's a simple Variable-like class, following the Projection protocol:
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>>> def notify_me(val):
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... print('new value', val)
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>>> p = VariableProjection('var placeholder', 3.0, callback=notify_me)
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>>> p.value
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3.0
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>>> p.value = 6.5
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new value 6.5
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"""
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def __init__(self, var, value, callback):
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self._var = var
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self._value = value
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self._callback = callback
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def _set_value(self, value):
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self._value = value
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self._callback(value)
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value = property(lambda s: s._value, _set_value)
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def variable(self):
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return self._var
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class CanvasProjection:
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"""
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Project a point as Canvas coordinates. Although this is a
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projection, it behaves like a tuple with two Variables
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(Projections).
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>>> canvas = Canvas()
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>>> from gaphas.item import Element
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>>> a = Element()
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>>> canvas.add(a)
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>>> a.matrix.translate(30, 2)
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>>> canvas.request_matrix_update(a)
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>>> canvas.update_now()
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>>> canvas.get_matrix_i2c(a)
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cairo.Matrix(1, 0, 0, 1, 30, 2)
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>>> p = CanvasProjection(a.handles()[2].pos, a)
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>>> a.handles()[2].pos
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<Position object on (10, 10)>
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>>> p[0].value
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40.0
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>>> p[1].value
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12.0
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>>> p[0].value = 63
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>>> p._point
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<Position object on (33, 10)>
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When the variables are retrieved, new values are calculated.
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"""
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def __init__(self, point, item):
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self._point = point
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self._item = item
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def _on_change_x(self, value):
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item = self._item
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self._px = value
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self._point.x.value, self._point.y.value = item.canvas.get_matrix_c2i(
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item
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).transform_point(value, self._py)
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item.canvas.request_update(item, matrix=False)
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def _on_change_y(self, value):
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item = self._item
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self._py = value
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self._point.x.value, self._point.y.value = item.canvas.get_matrix_c2i(
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item
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).transform_point(self._px, value)
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item.canvas.request_update(item, matrix=False)
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def _get_value(self):
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"""
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Return two delegating variables. Each variable should contain
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a value attribute with the real value.
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"""
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item = self._item
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x, y = self._point.x, self._point.y
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self._px, self._py = item.canvas.get_matrix_i2c(item).transform_point(x, y)
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return self._px, self._py
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pos = property(
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lambda self: list(
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map(
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VariableProjection,
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self._point,
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self._get_value(),
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(self._on_change_x, self._on_change_y),
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)
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)
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)
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def __getitem__(self, key):
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# Note: we can not use bound methods as callbacks, since that will
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# cause pickle to fail.
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return self.pos[key]
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def __iter__(self):
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return iter(self.pos)
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# Additional tests in @observed methods
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__test__ = {
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"Canvas.add": Canvas.add,
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167
gaphas/projections.py
Normal file
167
gaphas/projections.py
Normal file
@ -0,0 +1,167 @@
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class Projection:
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"""
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Projections are used to convert values from one space to another,
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e.g. from Canvas to Item space or visa versa.
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In order to be a Projection the ``value`` and ``strength``
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properties should be implemented and a method named ``variable()``
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should be present.
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Projections should inherit from this class.
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Projections may be nested.
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This default implementation projects a variable to it's own:
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>>> v = Variable(4.0)
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>>> v
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Variable(4, 20)
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>>> p = Projection(v)
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>>> p.value
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4.0
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>>> p.value = -1
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>>> p.value
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-1.0
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>>> v.value
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-1.0
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>>> p.strength
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20
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>>> p.variable()
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Variable(-1, 20)
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"""
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def __init__(self, var):
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self._var = var
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def _set_value(self, value):
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self._var.value = value
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value = property(lambda s: s._var.value, _set_value)
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strength = property(lambda s: s._var.strength)
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def variable(self):
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"""
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Return the variable owned by the projection.
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"""
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return self._var
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def __float__(self):
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return float(self.variable()._value)
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def __str__(self):
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return f"{self.__class__.__name__}({self.variable()})"
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__repr__ = __str__
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class VariableProjection(Projection):
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"""
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Project a single `solver.Variable` to another space/coordinate system.
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The value has been set in the "other" coordinate system. A
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callback is executed when the value changes.
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It's a simple Variable-like class, following the Projection protocol:
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>>> def notify_me(val):
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... print('new value', val)
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>>> p = VariableProjection('var placeholder', 3.0, callback=notify_me)
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>>> p.value
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3.0
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>>> p.value = 6.5
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new value 6.5
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"""
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def __init__(self, var, value, callback):
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self._var = var
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self._value = value
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self._callback = callback
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def _set_value(self, value):
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self._value = value
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self._callback(value)
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value = property(lambda s: s._value, _set_value)
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def variable(self):
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return self._var
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class CanvasProjection:
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"""
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Project a point as Canvas coordinates. Although this is a
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projection, it behaves like a tuple with two Variables
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(Projections).
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>>> canvas = Canvas()
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>>> from gaphas.item import Element
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>>> a = Element()
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>>> canvas.add(a)
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>>> a.matrix.translate(30, 2)
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>>> canvas.request_matrix_update(a)
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>>> canvas.update_now()
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>>> canvas.get_matrix_i2c(a)
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cairo.Matrix(1, 0, 0, 1, 30, 2)
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>>> p = CanvasProjection(a.handles()[2].pos, a)
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>>> a.handles()[2].pos
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<Position object on (10, 10)>
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>>> p[0].value
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40.0
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>>> p[1].value
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12.0
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>>> p[0].value = 63
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>>> p._point
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<Position object on (33, 10)>
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When the variables are retrieved, new values are calculated.
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"""
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def __init__(self, point, item):
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self._point = point
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self._item = item
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def _on_change_x(self, value):
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item = self._item
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self._px = value
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self._point.x.value, self._point.y.value = item.canvas.get_matrix_c2i(
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item
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).transform_point(value, self._py)
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item.canvas.request_update(item, matrix=False)
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def _on_change_y(self, value):
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item = self._item
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self._py = value
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self._point.x.value, self._point.y.value = item.canvas.get_matrix_c2i(
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item
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).transform_point(self._px, value)
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item.canvas.request_update(item, matrix=False)
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def _get_value(self):
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"""
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Return two delegating variables. Each variable should contain
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a value attribute with the real value.
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"""
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item = self._item
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x, y = self._point.x, self._point.y
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self._px, self._py = item.canvas.get_matrix_i2c(item).transform_point(x, y)
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return self._px, self._py
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pos = property(
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lambda self: list(
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map(
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VariableProjection,
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self._point,
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self._get_value(),
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(self._on_change_x, self._on_change_y),
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)
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)
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)
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def __getitem__(self, key):
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# Note: we can not use bound methods as callbacks, since that will
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# cause pickle to fail.
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return self.pos[key]
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def __iter__(self):
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return iter(self.pos)
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@ -34,6 +34,8 @@ every constraint is being asked to solve itself
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variables to make the constraint valid again.
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"""
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from gaphas.state import observed, reversible_pair, reversible_property
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from gaphas.projections import Projection
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# epsilon for float comparison
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# is simple abs(x - y) > EPSILON enough for canvas needs?
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@ -309,63 +311,6 @@ class Variable:
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return self._value.__rtruediv__(other)
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class Projection:
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"""
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Projections are used to convert values from one space to another,
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e.g. from Canvas to Item space or visa versa.
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In order to be a Projection the ``value`` and ``strength``
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properties should be implemented and a method named ``variable()``
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should be present.
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Projections should inherit from this class.
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Projections may be nested.
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This default implementation projects a variable to it's own:
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>>> v = Variable(4.0)
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>>> v
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Variable(4, 20)
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>>> p = Projection(v)
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>>> p.value
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4.0
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>>> p.value = -1
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>>> p.value
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-1.0
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>>> v.value
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-1.0
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>>> p.strength
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20
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>>> p.variable()
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Variable(-1, 20)
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"""
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def __init__(self, var):
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self._var = var
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def _set_value(self, value):
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self._var.value = value
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value = property(lambda s: s._var.value, _set_value)
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strength = property(lambda s: s._var.strength)
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def variable(self):
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"""
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Return the variable owned by the projection.
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"""
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return self._var
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def __float__(self):
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return float(self.variable()._value)
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def __str__(self):
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return f"{self.__class__.__name__}({self.variable()})"
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__repr__ = __str__
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class Solver:
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"""
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Solve constraints. A constraint should have accompanying
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