[cairo] API Shakeup: cairo_current_matrix

[Robert O'Callahan]

On Thu, 2005-06-16 at 12:48 -0700, Carl Worth wrote:
> We've already got all the const-correctness we need in the API to be
> able to return a "const cairo_matrix_t *" from the two get_matrix
> functions, (cairo_get_matrix and cairo_pattern_get_matrix).
> 
> Here's a patch that implements this.

I thought we discussed this before and you had decided not to do it. The
problem with this API is that although the matrix is "const" to the
user, it can still be changed by cairo and those changes will be visible
to the user. Therefore specifying what exactly that matrix will be at
any given time, either formally or informally, is quite hard. At a
minimum you need to document which cairo API calls will change the
matrix and guarantee that all others do not. (Although it will still be
error-prone when users accidentally reuse a stale CTM pointer.)

Rob