On 5/27/20 3:58 PM, Matthew Woehlke wrote:
*Nothing* there clearly states, at least to my reading, whether the "new" transform happens*before* or*after* any existing transforms that the QTransform is already doing. IMO, changing this to clarify that would help significantly.
Sure, augmenting the docs would help. But <devil's advocate> the whole point of the API is for its usage to be straightforward. If you do
QTransform t; t.translate(); t.rotate(); t.scale(); auto result = t.map(foo);
the "obvious" meaning should be that foo is getting first translated, then rotated, then scaled; not the other way around.
If this is achieved by pre or postmultiplication of (transposed) matrices matters only if you're into Algebra&Geometry™ -- i.e. poking into the actual matrix, or if you're combining two transforms by means of operator*. Otherwise, it is not interesting at all in 99% of the cases, where you'd just set the transform on a painter or an item similar.
If you really want to use the "low levels", please also note that operator* is helping you:
QTransform t1, t2;
QTransform t = t1 * t2; // ok...
auto result = foo * t; // can only premultiply!
// operator*(t, foo) does not exist
So you've built foo * t1 * t2, with t1 applied first. (This in turn should reveal how QTransform works internally.)
</devil's advocate> My 2 c, -- Giuseppe D'Angelo | giuseppe.dang...@kdab.com | Senior Software Engineer KDAB (France) S.A.S., a KDAB Group company Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com KDAB - The Qt, C++ and OpenGL Experts
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