[apps/graph_ctrlr] Reload range if no previous model is present

We memoize the checksum of the x first models, and we check that one of
these models is still present when the graph view appears. If so, we do
not reload the range, other wise we reload it.

Scenario:
f(t) = [t^2  t+1] in parametric
Display the graph
f(x) = 1 on ]-inf;0]
g(x) = 2 on [0;inf[
Display the graph -> the range did not change

apps/shared/interactive_curve_view_controller.cpp

@@ -133,11 +133,43 @@ Responder * InteractiveCurveViewController::defaultController() {
   return tabController();
 }
 
+bool InteractiveCurveViewController::previousModelsWereAllDeleted() {
+  bool result = true;
+  const int modelsCount = numberOfCurves();
+  const int memoizationCount = numberOfMemoizedVersions();
+
+  // Look for a current model that is the same as in the previous version
+  for (int i = 0; i < modelsCount; i++) {
+    uint32_t currentVersion = modelVersionAtIndex(i);
+    for (int j = 0; j < memoizationCount; j++) {
+      uint32_t * previousVersion = m_previousModelsVersions + j;
+      if (currentVersion == *previousVersion) {
+        result = false;
+        break;
+      }
+    }
+    if (!result) {
+      break;
+    }
+  }
+
+  // Update the memoization
+  for (int i = 0; i < memoizationCount; i++) {
+    uint32_t * previousVersion = m_previousModelsVersions + i;
+    uint32_t newVersion = modelVersionAtIndex(i);
+    if (*previousVersion != newVersion) {
+      *previousVersion = newVersion;
+    }
+  }
+  return result;
+}
+
 void InteractiveCurveViewController::viewWillAppear() {
   SimpleInteractiveCurveViewController::viewWillAppear();
   uint32_t newModelVersion = modelVersion();
   if (*m_modelVersion != newModelVersion) {
-    if (*m_modelVersion == 0 || numberOfCurves() == 1 || shouldSetDefaultOnModelChange()) {
+    // Put previousModelsWereAllDeleted first to update the model versions
+    if (previousModelsWereAllDeleted() || *m_modelVersion == 0 || numberOfCurves() == 1 || shouldSetDefaultOnModelChange()) {
       interactiveCurveViewRange()->setDefault();
     }
     *m_modelVersion = newModelVersion;