diff options
author | Edward Welbourne <edward.welbourne@qt.io> | 2020-09-09 14:59:32 +0200 |
---|---|---|
committer | Edward Welbourne <edward.welbourne@qt.io> | 2020-09-30 16:26:49 +0200 |
commit | 1c591fd9246ca776304a3c370dd2578bd886feac (patch) | |
tree | 02a46d7f631832955487de2fd5c5b5856dfbcfad /src/plugins | |
parent | c25687fa0b6e4be043e1f8c92c093d8b06ca06c4 (diff) |
Deal with {und,ov}erflow issues in QLine's length handling
Use std::hypot() instead of sqrt() of a sum of squares.
This ensures length() can't be zero when isNull() is false.
Use length() in QLine::setLength() rather than duplicating that.
Clarify and expand some documentation; isNull() never said what
constituted validity, nor did unitVector() mention that is should not
be used on a line for which isNull() is true. Make clear that lines of
denormal length cannot be rescaled accurately.
Given that we use fuzzy comparison to determine equality of
end-points, isNull() can be false for a line with displacements less
than sqrt(numeric_limits<qreal>::denorm_min()) between the coordinates
of its end-points (as long as these are not much bigger); squaring
these would give zero, hence a zero length, where using hypot() avoids
the underflow and gives a non-zero length. Having a zero length for a
line with isNull() false would lead to problems in setLength(), which
uses an isNull() pre-test, protecting a call to unitVector().
(It was already possible for a null line to have non-zero length; this
now arises in more cases.)
Restored QLine::setLength() to the form it had before a recent change
to avoid division by zero (which resulted from underflow in computing
the length of a non-null line) but allow for the possibility that the
unit vector it computes as transient may not have length exactly one.
Add tests against {ov,und}erflow problems in QLine. Reworked the test
added during the divide-by-zero fix to make it part of the existing
test.
Pick-to: 5.15 5.12
Change-Id: I7b71d66b872ccc08a64e941acd36b45b0ea15fab
Reviewed-by: Sze Howe Koh <szehowe.koh@gmail.com>
Diffstat (limited to 'src/plugins')
0 files changed, 0 insertions, 0 deletions