[cairo] [PATCH] Improve handling of degenerate font matrices

[Andrea Canciani]

On Sun, Feb 6, 2011 at 12:26 AM, Behdad Esfahbod <behdad at behdad.org> wrote:
> On 02/05/11 05:20, Andrea Canciani wrote:
>> A first step towards the handling of degenerate matrices can be the handling of
>> degenerate font scale matrices.
>>
>> This should be relatively easy, because cairo already supports 0-size fonts and
>> because this drawing operation always degenerates in either a noop or a clear
>> operation (depending on the mask-boundedness of the operator).
>>
>> The two 0001 attachments conflict (intentionally). Both change set_font_size
>> to reuse the code from set_font_matrix, but one in cairo-gstate.c, the other
>> one in cairo.c. I like the change in cairo.c better, because it
>> effectively makes
>> set_font_size an utility function wrapping set_font_matrix and avoids any
>> special-case for it in the "real code" (it just provides the utility
>> function in the
>> public API).
>
> Completely agree.
>
>
> Can you post a branch?

The proposed changes (with the preferred 0001) are in:

http://cgit.freedesktop.org/~ranma42/cairo/log/?h=wip/0matrix

Andrea

>
> behdad
>
>> 0002 makes it possible to create scaled fonts with 1 rank matrices. This
>> needs to be tested (as in "tests for it should be added"). It currently adds
>> a failure in invalid-matrix, but this is expected, because the "invalid" matrix
>> is now considered ok.
>>
>> 0003 is the "real" thing.
>>
>> 0004 is just a cleanup patch.
>>
>> I don't completely understand what
>> _cairo_matrix_compute_basis_scale_factors is supposed to do.
>> It is only used in font code and its documentation seems to be font-oriented
>> and incorrect. Was it supposed to be an SVD?
>>
>> Degenerate matrices should be mostly ok for paint, mask and fill if we
>> extend pattern_is_solid_color to also handle them (ok, I'm cheating,
>> we need a new "simplify_pattern" function, because degenerate matrices
>> could produce non-solid gradients).
>>
>> Stroking will be harder, because we will need to make sure that degenerate
>> pens work correctly. On the lucky side, degenerate pens are actually easier
>> to stroke with than generic pens.
>>
>> Andrea
>>
>>
>>
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>