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[apps/graph] Changed cache tolerance

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This fixes a bug where, when drawing 1/x, a vertical bar would appear on
0, because of false positive cache hits.

Change-Id: I2eafeac5e254c8a556769a41c8edc532db44383a
This commit is contained in:
Gabriel Ozouf
2020-06-23 17:07:55 +02:00
committed by Émilie Feral
parent beb228fa78
commit b0533e6836
2 changed files with 17 additions and 1 deletions
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8
apps/shared/continuous_function_cache.cpp
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@@ -19,6 +19,14 @@ void ContinuousFunctionCache::PrepareForCaching(void * fun, ContinuousFunctionCa
}
ContinuousFunction * function = static_cast<ContinuousFunction *>(fun);
if (tStep < 3 * k_cacheHitTolerance) {
/* If tStep is lower than twice the tolerance, we risk shifting the index
* by 1 for cache hits. As an added safety, we add another buffer of
* k_cacheHitTolerance, raising the threshold for caching to three times
* the tolerance. */
function->clearCache();
return;
}
if (function->cache() != cache) {
cache->clear();
function->setCache(cache);

10
apps/shared/continuous_function_cache.h
View File

@@ -27,7 +27,15 @@ public:
void clear();
Poincare::Coordinate2D<float> valueForParameter(const ContinuousFunction * function, Poincare::Context * context, float t);
private:
static constexpr float k_cacheHitTolerance = 1e-3;
/* 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
* (ex : 1/x with a vertical line at 0). Too low of a tolerance causes false
* negatives, which slows down the drawing.
*
* The value 128*FLT_EPSILON has been found to be the lowest for which all
* indices verify indexForParameter(tMin + index * tStep) = index. */
static constexpr float k_cacheHitTolerance = 128 * FLT_EPSILON;
void invalidateBetween(int iInf, int iSup);
void setRange(ContinuousFunction * function, float tMin, float tStep);