Hi Tomi,
On 19 Apr 2022, at 21:49, Tomi Pannila <tpann...@gmail.com> wrote:
Hi Qt developers,
could you please explain how your method "QRect::contains(const QRect &r, bool
proper)" at
https://code.qt.io/cgit/qt/qtbase.git/tree/src/corelib/tools/qrect.cpp?h=dev
satisfies your API design principles
1. Have clear and simple semantics
2. Be intuitive
3. Be easy to memorize
4. Lead to readable code
from https://wiki.qt.io/API_Design_Principles ?
Short answer: It doesn’t. It’s a very old API from the early days of Qt, and
wouldn’t be done this way today anymore. At the very least, the boolean
argument should be replaced by an enum indicating what the mode does.
rect.contains(otherRect, true) is not understandable without reading
documentation. rect.contains(otherRect, QRect::IncludeEdges) would be already
much better.
More precisely, I'm talking about the edge related stuff, which is not
documented properly in Qt documentation. The meaning of an edge is not
defined(?).
As we’re dealing with integers, it’s the difference between less and
less-equal, but I agree it’s not documented all to well.
What files make use of the edge property?
Wouldn't it be better to create a separate class for edged rectangles, if
rectangles with edges are needed?
No. You don’t want to add a complete new class for one test functions like
contains(). QRect is being passed into and returned from quite a lot of methods
in Qt, and you wouldn’t want to have to overload all of those with both a QRect
and a QInclusiveRect. In addition, you’d duplicate lots of APIs and both
classes would behave the same for most methods.
With separate class one could have custom edge sizes as a bonus.
That would be a rect with a border. But where do you stop then? One border
width for all sizes of configurable for each side independently? In addition,
you’d need more data to store that information making the class bigger.
So far there hasn’t been a need to have this as a general purpose class in Qt.
It would also be good if in your documentation you would define mathematically
what is meant by a rectangle.
Something like
"
For $x1 < 2$ and $y1 < y2$,
$$QRect(x1, x2, y1, y2) := \set{ (x, y) \in int^2 \quad | \quad x1 \le x \le
x2 \quad \text{and} \quad y1 \le y \le y2 }$$
"
could work together with mathjax, https://www.mathjax.org/ .
I can guess that x1 x2, with x2 < x1, is "allowed" in QRect due to easier
manipulation of QRects in some cases (all ints) (references to such cases?),
but it flips the left accessor to actually right(?), hence making it illogical.
Similarly for y1 and y2. I see the isValid method.
I mean, one could have "int left, top;" and "unsigned int width, height;" instead of
"int x1, x2, y1, y2" to describe QRect.
Earlier I was browsing qcosmeticstroke.cpp where clip check with a point is
multiple times checked(?) with
"
const QRect &cl = stroker->clip;
if (x < cl.x() || x > cl.right() || y < cl.y() || y > cl.bottom())
return;
"
https://code.qt.io/cgit/qt/qtbase.git/tree/src/gui/painting/qcosmeticstroker.cpp
Yeah, that could probably use rect.contains(point).
I was expecting to see this kind of implementation, with negation, in
QRect::contains. I was also thinking if performance in rendering
is so important that a call to QRect::contains cannot be made, and that for
some reason QRect::contains cannot be made inline.
Perhaps there is a way to include an inline implementation of QRect::contains
to QRect.h which could be used here?
I doubt that some contains() calls would be preformance critical in that code
path.
At
https://doc-snapshots.qt.io/qt6-dev/qrect.html
something is mentioned about "historical reasons". No further arguments or
links given. Perhaps this is the source of the confusion I have?
Are these historical reasons permanent or do you plan to move away from these
historical reasons? What would go wrong if you abandon the historical reasons?
Historical reasons means this has been the behaviour for the last 25 years, and
a huge amount of code relies on this behaviour. Changing it would lead to
subtle breaks in lots of places for our users, breakage that is not easily
found at compile time. So we don’t want to change it to not break lots of user
code out there relying on it.
I'm aware that QRect has been illogical for a long time
https://www.qtcentre.org/threads/6561-what-are-the-historical-reasons-mentioned-in-the-QRect-class-reference
I have no commits in Qt. This is my first post to development mailing list.
Welcome then! :)
Cheers,
Lars
Best Regards,
Tomi Pannila
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