[apps/regression] Fix selection problem when 2 regressions are equal

When going down, the cursor would loop between the 2 equal regressions
without going to lower regressions

apps/regression/store.cpp

@@ -44,25 +44,53 @@ void Store::setSeriesRegressionType(int series, Model::Type type) {
 }
 
 int Store::closestVerticalRegression(int direction, double x, double y, int currentRegressionSeries, Poincare::Context * globalContext) {
-  int regressionSeries = -1;
-  float closestDistance = INFINITY;
   /* The conditions to test on all the regressions are in this order:
    * - the current regression is not the current regression
    * - the next regression point should be within the window abscissa bounds
    * - it is the closest one in abscissa to x
    * - it is above y if direction > 0 and below otherwise */
-  for (int series = 0; series < k_numberOfSeries; series ++) {
-    if (!seriesIsEmpty(series) && series != currentRegressionSeries) {
-      double regressionY = yValueForXValue(series, x, globalContext);
-      if ((m_yMin <= regressionY && regressionY <= m_yMax)
-          && (std::fabs(regressionY - y) < closestDistance)
-          && (regressionY - y > 0) == (direction > 0)) {
-        closestDistance = std::fabs(regressionY - y);
-        regressionSeries = series;
+
+  int nextRegressionSeries = -1;
+  float nextY = direction > 0 ? FLT_MAX : -FLT_MAX;
+
+  for (int i = 0; i < k_numberOfSeries; i ++) {
+    if (i == currentRegressionSeries || seriesIsEmpty(i)) {
+      continue;
+    }
+    double newY = yValueForXValue(i, x, globalContext);
+    if (newY < m_yMin || newY > m_yMax) {
+      continue;
+    }
+    bool isNextRegression = false;
+    /* Choosing the next regression to select quite complex because we need to
+     * take care of regressions that have the same values at the current x. When
+     * moving up, if several regressions have the same value, we select the
+     * regression of higher index. When going down, we select the regression of
+     * lower index. */
+    if (direction > 0) {
+      if (newY > y && newY < nextY) {
+        isNextRegression = true;
+      } else if (newY == nextY) {
+        assert(i > nextRegressionSeries);
+        isNextRegression = true;
+      } else if (newY == y && i < currentRegressionSeries) {
+        isNextRegression = true;
+      }
+    } else {
+      if (newY < y && newY > nextY) {
+        isNextRegression = true;
+      } else if (newY == nextY) {
+        assert(i > nextRegressionSeries);
+      } else if (newY == y && i > currentRegressionSeries) {
+        isNextRegression = true;
       }
     }
+    if (isNextRegression) {
+      nextY = newY;
+      nextRegressionSeries = i;
+    }
   }
-  return regressionSeries;
+  return nextRegressionSeries;
 }
 
 /* Dots */