SkCubicMap.cpp File Reference

#include "include/core/SkCubicMap.h"
#include "include/private/base/SkTPin.h"
#include "src/base/SkVx.h"
#include <algorithm>
#include <cmath>

Go to the source code of this file.

Functions
static float	eval_poly (float t, float b)
template<typename... Rest>
static float	eval_poly (float t, float m, float b, Rest... rest)
static float	cubic_solver (float A, float B, float C, float D)
static bool	nearly_zero (SkScalar x)
static float	compute_t_from_x (float A, float B, float C, float x)
static bool	coeff_nearly_zero (float delta)

Function Documentation

coeff_nearly_zero()

static bool coeff_nearly_zero ( float  delta )

inlinestatic

Definition at line 84 of file SkCubicMap.cpp.

                                                  {
    return std::fabs(delta) <= 0.0000001f;
}

compute_t_from_x()

static float compute_t_from_x ( float  A, float  B, float  C, float  x  )

static

Definition at line 57 of file SkCubicMap.cpp.

                                                                  {
    return cubic_solver(A, B, C, -x);
}

cubic_solver()

static float cubic_solver ( float  A, float  B, float  C, float  D  )

static

Definition at line 23 of file SkCubicMap.cpp.

                                                              {
#ifdef SK_DEBUG
    auto valid = [](float t) { return t >= 0 && t <= 1; };
#endif
 
    auto guess_nice_cubic_root = [](float a, float b, float c, float d) { return -d; };
    float t = guess_nice_cubic_root(A, B, C, D);
 
    int iters = 0;
    const int MAX_ITERS = 8;
    for (; iters < MAX_ITERS; ++iters) {
        SkASSERT(valid(t));
        float f = eval_poly(t, A, B, C, D);        // f   = At^3 + Bt^2 + Ct + D
        if (std::fabs(f) <= 0.00005f) {
            break;
        }
        float fp = eval_poly(t, 3*A, 2*B, C);      // f'  = 3At^2 + 2Bt + C
        float fpp = eval_poly(t, 3*A + 3*A, 2*B);  // f'' = 6At + 2B
 
        float numer = 2 * fp * f;
        float denom = std::fma(2 * fp, fp, -(f * fpp));
 
        t -= numer / denom;
    }
 
    SkASSERT(valid(t));
    return t;
}

eval_poly() [1/2]

static float eval_poly ( float  t, float  b  )

static

Definition at line 16 of file SkCubicMap.cpp.

{ return b; }

eval_poly() [2/2]

template<typename... Rest>

static float eval_poly ( float  t, float  m, float  b, Rest...  rest  )

static

Definition at line 19 of file SkCubicMap.cpp.

                                                                {
    return eval_poly(t, std::fma(m, t, b), rest...);
}

nearly_zero()

static bool nearly_zero ( SkScalar  x )

inlinestatic

Definition at line 52 of file SkCubicMap.cpp.

                                           {
    SkASSERT(x >= 0);
    return x <= 0.0000000001f;
}