[kig] [Bug 359805] strange loss of drawing precision when drawing circles

[Maurizio Paolini via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=359805

--- Comment #15 from Maurizio Paolini  ---
Opened a qt bug report:
https://bugreports.qt.io/browse/QTBUG-52312

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[kig] [Bug 359805] strange loss of drawing precision when drawing circles

[Maurizio Paolini via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=359805

--- Comment #14 from Maurizio Paolini  ---
A standalone minimal C++ program using Qt5 and drawEllipse shows that the
precision
loss with circles having large radius is actually a Qt problem!
I will try to file a qt bug report about this problem.

However I suspect that using drawEllipse in this situation is not the right way
to go...
indeed this will cause the creation of a very large Rect and QRectF that will
intersect
the visible part in a tiny region.  This *might* entail a big performance loss.

Using drawCurve could be an option (only for circles with big radius), however
some adaptation
is required.

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[kig] [Bug 359805] strange loss of drawing precision when drawing circles

[Maurizio Paolini via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=359805

--- Comment #13 from Maurizio Paolini  ---
Created attachment 98047
  --> https://bugs.kde.org/attachment.cgi?id=98047=edit
same as previous, but with unmodified kig

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[kig] [Bug 359805] strange loss of drawing precision when drawing circles

[Maurizio Paolini via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=359805

--- Comment #12 from Maurizio Paolini  ---
Created attachment 98046
  --> https://bugs.kde.org/attachment.cgi?id=98046=edit
png showing a (different) problem when drawing circles/arcs

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[kig] [Bug 359805] strange loss of drawing precision when drawing circles

[Maurizio Paolini via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=359805

--- Comment #11 from Maurizio Paolini  ---
Anyway, there are still problems when drawing arcs and circles; apparently of a
different
nature: it becomes apparent when the radius of circle/arc is much larger then
the size
for the displayed canvas.  I will attach an image that shows the problem.
It shows a zoom (window from (1.8;1.8) to (2.2;2.2) ) of a construction of an
arc by three
points (one endpoint is inside the window) and the circle that supports that
arc: it should
be perfectly superposed.  However the figure was obtained by forcing kig to
draw the arc
using the generic method for curves.
As can be seen, the generic method for curves works far better then with the
direct use of
Qt primitives.  kig with its standard drawArc would produce a drawing more or
less superposed
with the circle.  At the moment I don't know if this is a Qt problem or a kig
problem

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[kig] [Bug 359805] strange loss of drawing precision when drawing circles

[Maurizio Paolini via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=359805

--- Comment #10 from Maurizio Paolini  ---
An identical problem is present when drawing circular arcs!  Since the
correction is minimal and perfectly similar to what was done for circular arcs
I took the liberty of pushing it into
origin/master.
The commit is visible as:
http://commits.kde.org/kig/2f22efe4cb70960cf2362680783477ed44b2492e

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[kig] [Bug 359805] strange loss of drawing precision when drawing circles

[Maurizio Paolini via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=359805

--- Comment #9 from Maurizio Paolini  ---
solved via reviewboard:
https://git.reviewboard.kde.org/r/127354/

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[kig] [Bug 359805] strange loss of drawing precision when drawing circles

[Maurizio Paolini via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=359805

--- Comment #8 from Maurizio Paolini  ---
(In reply to Rex Dieter from comment #7)
> I'd recommend submitting your patch to reviewboard.kde.org, that's the ideal
> way.

Done... but no comments so far.  Now I am not sure what to do.  Should I push
my commit?
Should I wait some more (how long)?

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[kig] [Bug 359805] strange loss of drawing precision when drawing circles

[Rex Dieter via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=359805

Rex Dieter  changed:

   What|Removed |Added

 Ever confirmed|0   |1
 Status|UNCONFIRMED |CONFIRMED

--- Comment #7 from Rex Dieter  ---
I'd recommend submitting your patch to reviewboard.kde.org, that's the ideal
way.

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[kig] [Bug 359805] strange loss of drawing precision when drawing circles

[Maurizio Paolini via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=359805

Maurizio Paolini  changed:

   What|Removed |Added

  Attachment #97700|0   |1
is obsolete||

--- Comment #6 from Maurizio Paolini  ---
Created attachment 97715
  --> https://bugs.kde.org/attachment.cgi?id=97715=edit
patch file (clean version)

the previous patch file contained unrelated differences

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[kig] [Bug 359805] strange loss of drawing precision when drawing circles

[Maurizio Paolini via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=359805

--- Comment #5 from Maurizio Paolini  ---
Created attachment 97700
  --> https://bugs.kde.org/attachment.cgi?id=97700=edit
patch proposal

This patch adds toScreenF methods alongside toScreen and uses it to create a
QRectF instead of a QRect in CircleImp::draw

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[kig] [Bug 359805] strange loss of drawing precision when drawing circles

[Rex Dieter via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=359805

Rex Dieter  changed:

   What|Removed |Added

 CC||rdie...@math.unl.edu

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[kig] [Bug 359805] strange loss of drawing precision when drawing circles

[Maurizio Paolini via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=359805

--- Comment #4 from Maurizio Paolini  ---
A simple workaround to the problem consists in commenting the
method "CircleImp::draw" in both objects/circle_imp.cc and
objects/circle_imp.h.

In this way kig falls back to the generic method for drawing conics, which
works fine
for circles.  With this workaround the last attachments with two tangent
circles gives
the expected behaviour

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