Generalize Text::angle() logic

May fix #765

qucs/element.cpp

@@ -70,28 +70,37 @@ void Text::draw(QPainter *painter, QRectF* br) const {
 }
 
 double Text::angle() const {
- // Historically Text uses mSin and mCos values to store
- // its rotation factor.
+ // Historically Text uses mSin and mCos values to describe
+ // at what angle the text is rotated.
  //
- // The actual rotation was implemented as a clever
- // tranformation for a painter, like:
- // QTransform(mCos, -mSin, mSin, mCos, …
+ // It employed some clever technique to draw the text rotated
+ // by applying "skew" transformations to QPainter and using mCos
+ // and mSin as skew factors, but later the whole drawing routine
+ // was refactored and it switched to using QPainter::rotate() and
+ // degrees to describe the rotation angle.
  //
- // There were only four combinations of these values
- // and here we convert them to their human-readable
- // equivalents
- if (mCos == 0.0) {
- if (mSin == 1.0) {
- return 270;
- }
- return 90;
- }
-
- if (mCos == -1.0 && mSin == 0.0) {
- return 180;
- }
-
- return 0;
+ // Many other parts of the codebase still depend on mCos and mSin,
+ // for example rotating and mirroring of a component and more than
+ // 200 component constructors. It is a piece of work to get rid
+ // of mCos and mSin completely, so they're kept as is and their
+ // "degrees" equivalent is calculated when the text needs to be drawn.
+
+ const double radians = std::acos(mCos);
+ // convert from radians to degrees and normalize
+ const double degrees = std::remainder(
+ (radians * 180.0) / 3.14159265 /* Pi */, 360.0 /* Full circle */);
+
+ // Above we've found the angle in degrees from a cosinus value.
+ // A single cosinus value corresponds to two angles. If sinus is positive
+ // the angle is in upper half of a circle. If sinus in negative, then
+ // in lower half.
+ //
+ // At the same time QPainter::rotate() rotates *clockwise*, so if you
+ // want a text to have rotation angle of 45° (towards up-right direction),
+ // then the -45° has to be passed to QPainter::rotate().
+ //
+ // QPainter::rotate() is called in Text::draw
+ return mSin < 0 ? degrees : -degrees;
 }