From 09c061e871299394a7ec3333aea96ec5049e5ee3 Mon Sep 17 00:00:00 2001
From: Gabriel Ozouf <gabriel.ozouf@numworks.com>
Date: Mon, 12 Oct 2020 12:44:30 +0200
Subject: [PATCH] [poincare/zoom] Method RangeFromSingleValue

This method adds margins to a range whose bounds are equal.

Change-Id: I2b2fe26fe431deda112389060d401f738a75b1ae
---
 apps/shared/range_1D.h           |  2 +-
 poincare/include/poincare/zoom.h |  4 ++++
 poincare/src/zoom.cpp            | 17 +++++++++++++----
 3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/apps/shared/range_1D.h b/apps/shared/range_1D.h
index b89b316d8..bd1b7a3b9 100644
--- a/apps/shared/range_1D.h
+++ b/apps/shared/range_1D.h
@@ -19,7 +19,7 @@ class __attribute__((packed)) Range1D final {
 public:
   /* If m_min and m_max are too close, we cannot divide properly the range by
    * the number of pixels, which creates a drawing problem. */
-  constexpr static float k_minFloat = 1E-4f;
+  constexpr static float k_minFloat = Poincare::Zoom::k_minimalRangeLength;
   constexpr static float k_default = Poincare::Zoom::k_defaultHalfRange;
   Range1D(float min = -k_default, float max = k_default) :
     m_min(min),
diff --git a/poincare/include/poincare/zoom.h b/poincare/include/poincare/zoom.h
index a12c9f1d8..958c88756 100644
--- a/poincare/include/poincare/zoom.h
+++ b/poincare/include/poincare/zoom.h
@@ -12,6 +12,7 @@ public:
   static constexpr float k_smallUnitMantissa = 1.f;
   static constexpr float k_mediumUnitMantissa = 2.f;
   static constexpr float k_largeUnitMantissa = 5.f;
+  static constexpr float k_minimalRangeLength = 1e-4f;
 
   typedef float (*ValueAtAbscissa)(float abscissa, Context * context, const void * auxiliary);
 
@@ -25,6 +26,9 @@ public:
    * of the smallest axis. If it is true, the longest axis will be reduced.*/
   static void SetToRatio(float yxRatio, float * xMin, float * xMax, float * yMin, float * yMax, bool shrink = false);
 
+  /* Compute a default range so that boundMin < value < boundMax */
+  static void RangeFromSingleValue(float value, float * boundMin, float * boundMax);
+
 private:
   static constexpr int k_peakNumberOfPointsOfInterest = 3;
   static constexpr int k_sampleSize = Ion::Display::Width / 4;
diff --git a/poincare/src/zoom.cpp b/poincare/src/zoom.cpp
index b90198405..75e236401 100644
--- a/poincare/src/zoom.cpp
+++ b/poincare/src/zoom.cpp
@@ -18,7 +18,8 @@ constexpr float
   Zoom::k_maxRatioBetweenPointsOfInterest,
   Zoom::k_smallUnitMantissa,
   Zoom::k_mediumUnitMantissa,
-  Zoom::k_largeUnitMantissa;
+  Zoom::k_largeUnitMantissa,
+  Zoom::k_minimalRangeLength;
 
 bool Zoom::InterestingRangesForDisplay(ValueAtAbscissa evaluation, float * xMin, float * xMax, float * yMin, float * yMax, float tMin, float tMax, Context * context, const void * auxiliary) {
   assert(xMin && xMax && yMin && yMax);
@@ -191,9 +192,7 @@ void Zoom::RefinedYRangeForDisplay(ValueAtAbscissa evaluation, float xMin, float
   *yMin = std::min(*yMin, sampleYMin);
   *yMax = std::max(*yMax, sampleYMax);
   if (*yMin == *yMax) {
-    float d = (*yMin == 0.f) ? 1.f : *yMin * 0.2f;
-    *yMin -= d;
-    *yMax += d;
+    RangeFromSingleValue(*yMin, yMin, yMax);
   }
   /* Round out the smallest bound to 0 if it is negligible compare to the
    * other one. This way, we can display the X axis for positive functions such
@@ -263,6 +262,16 @@ void Zoom::RangeWithRatioForDisplay(ValueAtAbscissa evaluation, float yxRatio, f
   SetToRatio(yxRatio, xMin, xMax, yMin, yMax, true);
 }
 
+void Zoom::RangeFromSingleValue(float value, float * boundMin, float * boundMax) {
+  constexpr float margin = 0.2f;
+  float delta = margin * std::fabs(value);
+  if (delta < k_minimalRangeLength) {
+    delta = 1.f;
+  }
+  *boundMin = value - delta;
+  *boundMax = value + delta;
+}
+
 bool Zoom::IsConvexAroundExtremum(ValueAtAbscissa evaluation, float x1, float x2, float x3, float y1, float y2, float y3, Context * context, const void * auxiliary, int iterations) {
   if (iterations <= 0) {
     return false;