partial line drawing for smith/polar charts

Software/PC_Application/Traces/tracepolar.cpp

@@ -13,6 +13,7 @@ TracePolar::TracePolar(TraceModel &model, QWidget *parent)
     limitToSpan = true;
     limitToEdge = true;
     edgeReflection = 1.0;
+    dx = 0;
     initializeTraceInfo();
 }
 
@@ -236,6 +237,71 @@ void TracePolar::updateContextMenu()
     finishContextMenu();
 }
 
+bool TracePolar::constrainLineToCircle(QPointF &a, QPointF &b, QPointF center, double radius)
+{
+    auto distance = [](const QPointF &a, const QPointF &b) {
+        auto dx = b.x() - a.x();
+        auto dy = b.y() - a.y();
+        return sqrt(dx*dx + dy*dy);
+    };
+
+    if(distance(a, center) <= radius && distance(b, center) <= radius) {
+        // both points are completely contained within the circle, no adjustment necessary
+        return true;
+    }
+
+    // shift points, the formulas assume center = (0,0)
+    a -= center;
+    b -= center;
+
+    // according to https://mathworld.wolfram.com/Circle-LineIntersection.html
+    auto dx = b.x() - a.x();
+    auto dy = b.y() - a.y();
+    auto dr = sqrt(dx*dx+dy*dy);
+    auto D = a.x()*b.y() - b.x()*a.y();
+    // check intersection
+    auto delta = radius*radius * dr*dr - D*D;
+    if(delta <= 0) {
+        // line does not intersect the circle
+        return false;
+    }
+    // line intersects the circle, calculate intersection points
+    auto x1 = (D*dy+copysign(1.0, dy) * dx*sqrt(delta)) / (dr*dr);
+    auto x2 = (D*dy-copysign(1.0, dy) * dx*sqrt(delta)) / (dr*dr);
+    auto y1 = (-D*dx+abs(dy)*sqrt(delta)) / (dr*dr);
+    auto y2 = (-D*dx-abs(dy)*sqrt(delta)) / (dr*dr);
+
+    auto inter1 = QPointF(x1, y1);
+    auto inter2 = QPointF(x2, y2);
+
+    bool inter1betweenPoints = false;
+    bool inter2betweenPoints = false;
+    if(abs(distance(a, inter1) + distance(b, inter1) - distance(a, b)) < 0.000001) {
+        inter1betweenPoints = true;
+    }
+    if(abs(distance(a, inter2) + distance(b, inter2) - distance(a, b)) < 0.000001) {
+        inter2betweenPoints = true;
+    }
+    if(inter1betweenPoints && inter2betweenPoints) {
+        // adjust both points, order does not matter
+        a = inter1;
+        b = inter2;
+    } else {
+        // exactly one intersection point must lie between the two line points, otherwise we would have returned already
+        auto inter = inter1betweenPoints ? inter1 : inter2;
+        if(distance(a, QPointF(0,0)) < radius) {
+            // point is in the circle and can remain unchanged. Use inter as new point b
+            b = inter;
+        } else {
+            // the other way around
+            a = inter;
+        }
+    }
+    a += center;
+    b += center;
+    return true;
+}
+
 PolarArc::PolarArc(QPointF center, double radius,  double startAngle, double spanAngle)
     : center(center),
       radius(radius),

Software/PC_Application/Traces/tracepolar.h

@@ -43,6 +43,11 @@ protected:
     virtual void updateContextMenu() override;
     virtual bool supported(Trace *t) override {Q_UNUSED(t) return false;};
 
+    // given two points and a circle, the two points are adjusted in such a way that the line they describe
+    // is constrained within the circle. Returns true if there is a remaining line segment in the circle, false
+    // if the line lies completely outside of the circle (or is tangent to the circle)
+    static bool constrainLineToCircle(QPointF &a, QPointF &b, QPointF center, double radius);
+
     bool limitToSpan;
     bool limitToEdge;
     double edgeReflection; // magnitude of reflection coefficient at the edge of the polar chart (zoom factor)

Software/PC_Application/Traces/tracepolarchart.cpp

@@ -157,13 +157,18 @@ void TracePolarChart::draw(QPainter &p) {
             last = dataAddDx(last);
             now = dataAddDx(now);
 
+            // scale to size of smith diagram
+            QPointF p1 = dataToPixel(last);
+            QPointF p2 = dataToPixel(now);
+
             if(limitToEdge && (abs(last.y) > edgeReflection || abs(now.y) > edgeReflection)) {
-                // outside of visible area
+                // partially outside of visible area, constrain
+                if(!TracePolar::constrainLineToCircle(p1, p2, transform.map(QPointF(0,0)), polarCoordMax * scale)) {
+                    // completely out of visible area
                     continue;
                 }
-            // scale to size of diagram
+            }
-            auto p1 = dataToPixel(last);
+
-            auto p2 = dataToPixel(now);
             // draw line
             p.drawLine(p1, p2);
         }
@@ -215,9 +220,6 @@ void TracePolarChart::draw(QPainter &p) {
 
 bool TracePolarChart::dropSupported(Trace *t)
 {
-    if(!t->isReflection()) {
-        return false;
-    }
     switch(t->outputType()) {
     case Trace::DataType::Frequency:
         return true;

Software/PC_Application/Traces/tracesmithchart.cpp

@@ -247,13 +247,18 @@ void TraceSmithChart::draw(QPainter &p) {
             last = dataAddDx(last);
             now = dataAddDx(now);
 
+            // scale to size of smith diagram
+            QPointF p1 = dataToPixel(last);
+            QPointF p2 = dataToPixel(now);
+
             if(limitToEdge && (abs(last.y) > edgeReflection || abs(now.y) > edgeReflection)) {
-                // outside of visible area
+                // partially outside of visible area, constrain
+                if(!TracePolar::constrainLineToCircle(p1, p2, transform.map(QPointF(0,0)), polarCoordMax * scale)) {
+                    // completely out of visible area
                     continue;
                 }
-            // scale to size of smith diagram
+            }
-            auto p1 = dataToPixel(last);
+
-            auto p2 = dataToPixel(now);
             // draw line
             p.drawLine(p1, p2);
         }