I think this feature was originally intended to work (since TransformedPath exists) but it wasn't working [in the way that I was expecting it to]. I made a change which now only invalidates non-affine transformations if it is really necessary. This change required a modification to the way invalidation was passed through the transform stack, since certain transform subclasses need to override the mechanism. I will try to explain the reason why this is the case:
Suppose a TransformNode is told that it can no longer store the affine transformed path by its child node, then it must pass this message up to its parent nodes, until eventually a TransformedPath instance is invalidated (triggering a re-computation). With Transforms this recursion can simply pass the same invalidation message up, but for the more complex case of a CompositeTransform, which represents the combination of two Transforms, things get harder. I will devise a notation to help me explain: Let a composite transform, A, represent an affine transformation (a1) followed by a non affine transformation (vc2) [vc stands for very complicated] we can write this in the form (a1, vc2). Since non-affine Transform instances are composed of a non-affine transformation followed by an affine one, we can write (vc2) as (c2, a2) and the composite can now be written as (a1, c2, a2). As a bit of background knowledge, computing the non-affine transformation of A involves computing (a1, c2) and leaves the term (a2) as the affine component. Additionally, a CompositeTransform which looks like (c1, a1, a2) can be optimised such that its affine part is (a1, a2). There are four permutations of CompositeTransforms: A = (a1, c2, a2) B = (c1, a1, a2) C = (c1, a1, c2, a2) D = (a1, a2) When a child of a CompositeTransform tells us that its affine part is invalid, we need to know which child it is that has told us. This statement is best demonstrated in transform A: If the invalid part is a1 then it follows that the non-affine part (a1, c2) is also invalid, hence A must inform its parent that its entire transform is invalid. Conversely, if the invalid part is a2 then the non-affine part (a1, c2) is unchanged and therefore can pass on the message that only its affine part is invalid. The changes can be found in https://github.com/PhilipElson/matplotlib/compare/path_transform_cache and I would really appreciate your feedback. I can make a pull request of this if that makes in-line discussion easier. Many Thanks, ------------------------------------------------------------------------------ Virtualization & Cloud Management Using Capacity Planning Cloud computing makes use of virtualization - but cloud computing also focuses on allowing computing to be delivered as a service. http://www.accelacomm.com/jaw/sfnl/114/51521223/ _______________________________________________ Matplotlib-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/matplotlib-devel
