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common bezier: Add a function that returns the position.

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A utility for common use of the Bezier curve.
This commit is contained in:
Hermet Park 2023-07-11 17:01:43 +09:00 • committed by Hermet Park
parent 81afba5035
commit def6393d82
2 changed files with 28 additions and 10 deletions
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35
src/lib/tvgBezier.cpp
View file

@ -20,8 +20,7 @@
* SOFTWARE. * SOFTWARE.
*/ */
#include <float.h> #include "tvgMath.h"
#include <math.h>
#include "tvgBezier.h" #include "tvgBezier.h"
/************************************************************************/ /************************************************************************/
@ -75,7 +74,7 @@ float bezLength(const Bezier& cur)
auto len = _lineLength(cur.start, cur.ctrl1) + _lineLength(cur.ctrl1, cur.ctrl2) + _lineLength(cur.ctrl2, cur.end); auto len = _lineLength(cur.start, cur.ctrl1) + _lineLength(cur.ctrl1, cur.ctrl2) + _lineLength(cur.ctrl2, cur.end);
auto chord = _lineLength(cur.start, cur.end); auto chord = _lineLength(cur.start, cur.end);
if (fabsf(len - chord) > BEZIER_EPSILON) { if (!mathEqual(len, chord)) {
bezSplit(cur, left, right); bezSplit(cur, left, right);
return bezLength(left) + bezLength(right); return bezLength(left) + bezLength(right);
} }
@ -116,19 +115,16 @@ float bezAt(const Bezier& bz, float at)
//just in case to prevent an infinite loop //just in case to prevent an infinite loop
if (at <= 0) return 0.0f; if (at <= 0) return 0.0f;
if (at >= len) return len;
if (at >= len) return 1.0f;
while (true) { while (true) {
auto right = bz; auto right = bz;
Bezier left; Bezier left;
bezSplitLeft(right, t, left); bezSplitLeft(right, t, left);
len = bezLength(left); len = bezLength(left);
if (mathEqual(len, at) || mathEqual(smallest, biggest)) {
if (fabsf(len - at) < BEZIER_EPSILON || fabsf(smallest - biggest) < BEZIER_EPSILON) {
break; break;
} }
if (len < at) { if (len < at) {
smallest = t; smallest = t;
t = (t + biggest) * 0.5f; t = (t + biggest) * 0.5f;
@ -148,4 +144,27 @@ void bezSplitAt(const Bezier& cur, float at, Bezier& left, Bezier& right)
bezSplitLeft(right, t, left); bezSplitLeft(right, t, left);
} }
Point bezPointAt(const Bezier& bz, float t)
{
Point cur;
auto it = 1.0f - t;
auto ax = bz.start.x * it + bz.ctrl1.x * t;
auto bx = bz.ctrl1.x * it + bz.ctrl2.x * t;
auto cx = bz.ctrl2.x * it + bz.end.x * t;
ax = ax * it + bx * t;
bx = bx * it + cx * t;
cur.x = ax * it + bx * t;
float ay = bz.start.y * it + bz.ctrl1.y * t;
float by = bz.ctrl1.y * it + bz.ctrl2.y * t;
float cy = bz.ctrl2.y * it + bz.end.y * t;
ay = ay * it + by * t;
by = by * it + cy * t;
cur.y = ay * it + by * t;
return cur;
} }
}

3
src/lib/tvgBezier.h
View file

@ -28,8 +28,6 @@
namespace tvg namespace tvg
{ {
#define BEZIER_EPSILON 1e-4f
struct Bezier struct Bezier
{ {
Point start; Point start;
@ -43,6 +41,7 @@ float bezLength(const Bezier& cur);
void bezSplitLeft(Bezier& cur, float at, Bezier& left); void bezSplitLeft(Bezier& cur, float at, Bezier& left);
float bezAt(const Bezier& bz, float at); float bezAt(const Bezier& bz, float at);
void bezSplitAt(const Bezier& cur, float at, Bezier& left, Bezier& right); void bezSplitAt(const Bezier& cur, float at, Bezier& left, Bezier& right);
Point bezPointAt(const Bezier& bz, float t);
} }