[apps/graph/test] Fix caching test

Change-Id: I536d1422ca6c9ecded66f7876ae019aaf5742005

apps/graph/graph/graph_view.cpp

@@ -41,9 +41,7 @@ void GraphView::drawRect(KDContext * ctx, KDRect rect) const {
     float tmin = f->tMin();
     float tmax = f->tMax();
 
-    float tstep = (tmax-tmin) / k_graphStepDenominator;
-
-    float tCacheMin, tCacheStep;
+    float tCacheMin, tCacheStep, tStepNonCartesian;
     if (type == ContinuousFunction::PlotType::Cartesian) {
       float rectLeft = pixelToFloat(Axis::Horizontal, rect.left() - k_externRectMargin);
       /* Here, tCacheMin can depend on rect (and change as the user move)
@@ -53,7 +51,8 @@ void GraphView::drawRect(KDContext * ctx, KDRect rect) const {
       tCacheStep = pixelWidth();
     } else {
       tCacheMin = tmin;
-      tCacheStep = int(k_graphStepDenominator) * tstep / ContinuousFunctionCache::k_numberOfParametricCacheablePoints;
+      // Compute tCacheStep and tStepNonCartesian
+      ContinuousFunctionCache::ComputeNonCartesianSteps(&tStepNonCartesian, &tCacheStep, tmax, tmin);
     }
     ContinuousFunctionCache::PrepareForCaching(f.operator->(), cch, tCacheMin, tCacheStep);
 
@@ -80,7 +79,7 @@ void GraphView::drawRect(KDContext * ctx, KDRect rect) const {
       }
     } else if (type == Shared::ContinuousFunction::PlotType::Polar) {
       // Polar
-      drawPolarCurve(ctx, rect, tmin, tmax, tstep, [](float t, void * model, void * context) {
+      drawPolarCurve(ctx, rect, tmin, tmax, tStepNonCartesian, [](float t, void * model, void * context) {
             ContinuousFunction * f = (ContinuousFunction *)model;
             Poincare::Context * c = (Poincare::Context *)context;
             return f->evaluateXYAtParameter(t, c);
@@ -88,7 +87,7 @@ void GraphView::drawRect(KDContext * ctx, KDRect rect) const {
     } else {
       // Parametric
       assert(type == Shared::ContinuousFunction::PlotType::Parametric);
-      drawCurve(ctx, rect, tmin, tmax, tstep, [](float t, void * model, void * context) {
+      drawCurve(ctx, rect, tmin, tmax, tStepNonCartesian, [](float t, void * model, void * context) {
           ContinuousFunction * f = (ContinuousFunction *)model;
           Poincare::Context * c = (Poincare::Context *)context;
           return f->evaluateXYAtParameter(t, c);

apps/graph/test/caching.cpp

@@ -55,8 +55,11 @@ void assert_check_polar_cache_against_function(ContinuousFunction * function, Co
 
   float tMin = range->xMin();
   float tMax = range->xMax();
-  float tStep = ((tMax - tMin) / Graph::GraphView::k_graphStepDenominator) / ContinuousFunctionCache::k_parametricStepFactor;
-  ContinuousFunctionCache::PrepareForCaching(function, cache, tMin, tStep);
+
+  float tStep, tCacheStep;
+  ContinuousFunctionCache::ComputeNonCartesianSteps(&tStep, &tCacheStep, tMax, tMin);
+
+  ContinuousFunctionCache::PrepareForCaching(function, cache, tMin, tCacheStep);
 
   // Fill the cache
   float t;

apps/shared/continuous_function_cache.cpp

@@ -7,7 +7,6 @@ namespace Shared {
 constexpr int ContinuousFunctionCache::k_sizeOfCache;
 constexpr float ContinuousFunctionCache::k_cacheHitTolerance;
 constexpr int ContinuousFunctionCache::k_numberOfAvailableCaches;
-constexpr int ContinuousFunctionCache::k_numberOfParametricCacheablePoints;
 
 // public
 void ContinuousFunctionCache::PrepareForCaching(void * fun, ContinuousFunctionCache * cache, float tMin, float tStep) {
@@ -52,6 +51,26 @@ Poincare::Coordinate2D<float> ContinuousFunctionCache::valueForParameter(const C
   return valuesAtIndex(function, context, t, resIndex);
 }
 
+void ContinuousFunctionCache::ComputeNonCartesianSteps(float * tStep, float * tCacheStep, float tMax, float tMin) {
+  // Expected step length
+  *tStep = (tMax - tMin) / Graph::GraphView::k_graphStepDenominator;
+  /* Parametric and polar functions require caching both x and y values,
+   * with the same k_sizeOfCache. To cover the entire range,
+   * number of cacheable points is half the cache size. */
+  const int numberOfCacheablePoints = k_sizeOfCache / 2;
+  const int numberOfWholeSteps = static_cast<int>(Graph::GraphView::k_graphStepDenominator);
+  static_assert(numberOfCacheablePoints % numberOfWholeSteps == 0, "numberOfCacheablePoints should be a multiple of numberOfWholeSteps for optimal caching");
+  /* Define cacheStep such that every whole graph steps are equally divided
+   * For instance, with :
+   *    graphStepDenominator = 10.1
+   *    numberOfCacheablePoints = 160
+   * tMin [----------------|----------------| ... |----------------|**] tMax
+   *             step1           step2                  step10       step11
+   * There are 11 steps, the first 10 are whole and have an equal size (tStep).
+   * There are 16 cache points in the first 10 steps, 160 total cache points. */
+  *tCacheStep = *tStep * numberOfWholeSteps / numberOfCacheablePoints;
+}
+
 // private
 void ContinuousFunctionCache::invalidateBetween(int iInf, int iSup) {
   for (int i = iInf; i < iSup; i++) {

apps/shared/continuous_function_cache.h

@@ -11,16 +11,8 @@ namespace Shared {
 class ContinuousFunction;
 
 class ContinuousFunctionCache {
-private:
-  /* The size of the cache is chosen to optimize the display of cartesian
-   * functions */
-   static constexpr int k_sizeOfCache = Ion::Display::Width;
 public:
   static constexpr int k_numberOfAvailableCaches = 2;
-  /* Parametric and polar functions require caching both x and y values,
-   * with the same k_sizeOfCache. To cover the entire range,
-   * k_numberOfParametricCacheablePoints is halved. */
-  static constexpr int k_numberOfParametricCacheablePoints = k_sizeOfCache / 2;
 
   static void PrepareForCaching(void * fun, ContinuousFunctionCache * cache, float tMin, float tStep);
 
@@ -29,7 +21,12 @@ public:
   float step() const { return m_tStep; }
   void clear();
   Poincare::Coordinate2D<float> valueForParameter(const ContinuousFunction * function, Poincare::Context * context, float t);
+  // Sets step parameters for non-cartesian curves
+  static void ComputeNonCartesianSteps(float * tStep, float * tCacheStep, float tMax, float tMin);
 private:
+  /* The size of the cache is chosen to optimize the display of cartesian
+   * functions */
+  static constexpr int k_sizeOfCache = Ion::Display::Width;
   /* We need a certain amount of tolerance since we try to evaluate the
    * equality of floats. But the value has to be chosen carefully. Too high of
    * a tolerance causes false positives, which lead to errors in curves