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"""Storage of per-context values of various types
Because OpenGL needs persistent references to the
objects we're constructing to shadow Python objects,
we have to store references to the objects somewhere
For any given Python GUI library, we can use a weakref
to the library's representation of the GL context to
call the cleanup function. That means some per-GUI
library code in OpenGL (or the library), but it gives
us very natural operations within OpenGL.
"""
from OpenGL import platform
storedPointers = {
# map from contextID: { constant: value }
}
storedWeakPointers = {
# map from contextID: WeakValueDictionary({ constant: value })
}
STORAGES = [ storedPointers, storedWeakPointers ]
def getContext( context = None ):
"""Get the context (if passed, just return)
context -- the context ID, if None, the current context
"""
if context is None:
context = platform.GetCurrentContext()
if context == 0:
from OpenGL import error
raise error.Error(
"""Attempt to retrieve context when no valid context"""
)
return context
def setValue( constant, value, context=None, weak=False ):
"""Set a stored value for the given context
constant -- Normally a GL constant value, but can be any hashable value
value -- the value to be stored. If weak is true must be
weak-reference-able. If None, then the value will be deleted from
the storage
context -- the context identifier for which we're storing the value
weak -- if true, value will be stored with a weakref
Note: you should always pass the same value for "weak" for a given
constant, otherwise you will create two storages for the constant.
"""
if getattr( value, '_no_cache_', False ):
return
context = getContext( context )
if weak:
storage = storedWeakPointers
cls = weakref.WeakValueDictionary
else:
storage = storedPointers
cls = dict
current = storage.get( context )
if current is None:
storage[context] = current = cls()
previous = current.get( constant )
if value is None:
try:
del current[ constant ]
except (KeyError,TypeError,ValueError), err:
pass
else:
# XXX potential for failure here if a non-weakref-able objects
# is being stored with weak == True
current[ constant ] = value
## print 'previous', previous, value, constant
return previous
def delValue( constant, context=None ):
"""Delete the specified value for the given context
constant -- Normally a GL constant value, but can be any hashable value
context -- the context identifier for which we're storing the value
"""
context = getContext( context )
found = False
for storage in STORAGES:
contextStorage = storage.get( context )
if contextStorage:
try:
del contextStorage[ constant ]
found = True
except KeyError, err:
pass
return found
def getValue( constant, context = None ):
"""Get a stored value for the given constant
constant -- unique ID for the type of data being retrieved
context -- the context ID, if None, the current context
"""
context = getContext( context )
for storage in STORAGES:
contextStorage = storage.get( context )
if contextStorage:
value = contextStorage.get( constant )
if value is not None:
return value
return None
def cleanupContext( context=None ):
"""Cleanup all held pointer objects for the given context
Warning: this is dangerous, as if you call it before a context
is destroyed you may release memory held by the context and cause
a protection fault when the GL goes to render the scene!
Normally you will want to get the context ID explicitly and then
register cleanupContext as a weakref callback to your GUI library
Context object with the (now invalid) context ID as parameter.
"""
if context is None:
context = platform.GetCurrentContext()
for storage in STORAGES:
try:
del storedPointers[ context ]
except KeyError, err:
return False
else:
return True
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