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bezier: optimize setup of bezier curves (#8528)

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avoid reallocations by resizing and copy the pVec into the resized
m_dPoints, reduce the amount of calculations in baking to only do it
once per iteration instead of twice. precompute in getYforT and getXforT
return early in getYForPoint if x is equal or below 0. and use const
references where we can.

these changes we are now down to an average of "time to bake: 2.50µs."
on my machine compared to before average of "time to bake: 11.15µs"
This commit is contained in:
Tom Englund 2024-11-22 02:47:51 +01:00 committed by GitHub
parent 940f7aa990
commit 943b3d467b
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2 changed files with 29 additions and 18 deletions
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39
src/helpers/BezierCurve.cpp
View file

@ -6,24 +6,27 @@
#include <algorithm>
void CBezierCurve::setup(std::vector<Vector2D>* pVec) {
m_dPoints.clear();
const auto BEGIN = std::chrono::high_resolution_clock::now();
m_dPoints.emplace_back(Vector2D(0, 0));
for (auto const& p : *pVec) {
m_dPoints.push_back(p);
// Avoid reallocations by reserving enough memory upfront
m_dPoints.resize(pVec->size() + 2);
m_dPoints[0] = Vector2D(0, 0); // Start point
size_t index = 1; // Start after the first element
for (const auto& vec : *pVec) {
if (index < m_dPoints.size() - 1) { // Bounds check to ensure safety
m_dPoints[index] = vec;
++index;
}
}
m_dPoints.emplace_back(Vector2D(1, 1));
m_dPoints.back() = Vector2D(1, 1); // End point
RASSERT(m_dPoints.size() == 4, "CBezierCurve only supports cubic beziers! (points num: {})", m_dPoints.size());
// bake BAKEDPOINTS points for faster lookups
// T -> X ( / BAKEDPOINTS )
for (int i = 0; i < BAKEDPOINTS; ++i) {
m_aPointsBaked[i] = Vector2D(getXForT((i + 1) / (float)BAKEDPOINTS), getYForT((i + 1) / (float)BAKEDPOINTS));
float const t = (i + 1) / (float)BAKEDPOINTS;
m_aPointsBaked[i] = Vector2D(getXForT(t), getYForT(t));
}
const auto ELAPSEDUS = std::chrono::duration_cast<std::chrono::nanoseconds>(std::chrono::high_resolution_clock::now() - BEGIN).count() / 1000.f;
@ -40,18 +43,26 @@ void CBezierCurve::setup(std::vector<Vector2D>* pVec) {
ELAPSEDUS, ELAPSEDCALCAVG);
}
float CBezierCurve::getYForT(float t) {
return 3 * t * pow(1 - t, 2) * m_dPoints[1].y + 3 * pow(t, 2) * (1 - t) * m_dPoints[2].y + pow(t, 3);
float CBezierCurve::getXForT(float const& t) {
float t2 = t * t;
float t3 = t2 * t;
return 3 * t * (1 - t) * (1 - t) * m_dPoints[1].x + 3 * t2 * (1 - t) * m_dPoints[2].x + t3 * m_dPoints[3].x;
}
float CBezierCurve::getXForT(float t) {
return 3 * t * pow(1 - t, 2) * m_dPoints[1].x + 3 * pow(t, 2) * (1 - t) * m_dPoints[2].x + pow(t, 3);
float CBezierCurve::getYForT(float const& t) {
float t2 = t * t;
float t3 = t2 * t;
return 3 * t * (1 - t) * (1 - t) * m_dPoints[1].y + 3 * t2 * (1 - t) * m_dPoints[2].y + t3 * m_dPoints[3].y;
}
// Todo: this probably can be done better and faster
float CBezierCurve::getYForPoint(float x) {
float CBezierCurve::getYForPoint(float const& x) {
if (x >= 1.f)
return 1.f;
if (x <= 0.f)
return 0.f;
int index = 0;
bool below = true;

8
src/helpers/BezierCurve.hpp
View file

@ -16,13 +16,13 @@ class CBezierCurve {
// this EXCLUDES the 0,0 and 1,1 points,
void setup(std::vector<Vector2D>* points);
float getYForT(float t);
float getXForT(float t);
float getYForPoint(float x);
float getYForT(float const& t);
float getXForT(float const& t);
float getYForPoint(float const& x);
private:
// this INCLUDES the 0,0 and 1,1 points.
std::deque<Vector2D> m_dPoints;
std::vector<Vector2D> m_dPoints;
std::array<Vector2D, BAKEDPOINTS> m_aPointsBaked;
};