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LinearInterpolation.cpp
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// LinearInterpolation.cpp
// Implements methods for linear interpolation over 1D, 2D and 3D arrays
#include "Globals.h"
#include "LinearInterpolation.h"
/*
// Perform an automatic test upon program start (use breakpoints to debug):
extern void Debug3DNoise(float * a_Noise, int a_SizeX, int a_SizeY, int a_SizeZ, const AString & a_FileNameBase);
class Test
{
public:
Test(void)
{
// DoTest1();
DoTest2();
}
void DoTest1(void)
{
float In[8] = {0, 1, 2, 3, 1, 2, 2, 2};
float Out[3 * 3 * 3];
LinearInterpolate1DArray(In, 4, Out, 9);
LinearInterpolate2DArray(In, 2, 2, Out, 3, 3);
LinearInterpolate3DArray(In, 2, 2, 2, Out, 3, 3, 3);
LOGD("Out[0]: %f", Out[0]);
}
void DoTest2(void)
{
float In[3 * 3 * 3];
for (size_t i = 0; i < ARRAYCOUNT(In); i++)
{
In[i] = (float)(i % 5);
}
float Out[15 * 16 * 17];
LinearInterpolate3DArray(In, 3, 3, 3, Out, 15, 16, 17);
Debug3DNoise(Out, 15, 16, 17, "LERP test");
}
} gTest;
//*/
// Puts linearly interpolated values from one array into another array. 1D version
void LinearInterpolate1DArray(
float * a_Src,
int a_SrcSizeX,
float * a_Dst,
int a_DstSizeX
)
{
a_Dst[0] = a_Src[0];
int DstSizeXm1 = a_DstSizeX - 1;
int SrcSizeXm1 = a_SrcSizeX - 1;
float fDstSizeXm1 = static_cast<float>(DstSizeXm1);
float fSrcSizeXm1 = static_cast<float>(SrcSizeXm1);
for (int x = 1; x < DstSizeXm1; x++)
{
int SrcIdx = x * SrcSizeXm1 / DstSizeXm1;
float ValLo = a_Src[SrcIdx];
float ValHi = a_Src[SrcIdx + 1];
float Ratio = static_cast<float>(x) * fSrcSizeXm1 / fDstSizeXm1 - SrcIdx;
a_Dst[x] = ValLo + (ValHi - ValLo) * Ratio;
}
a_Dst[a_DstSizeX - 1] = a_Src[a_SrcSizeX - 1];
}
// Puts linearly interpolated values from one array into another array. 2D version
void LinearInterpolate2DArray(
float * a_Src,
int a_SrcSizeX, int a_SrcSizeY,
float * a_Dst,
int a_DstSizeX, int a_DstSizeY
)
{
ASSERT(a_DstSizeX > 0);
ASSERT(a_DstSizeX < MAX_INTERPOL_SIZEX);
ASSERT(a_DstSizeY > 0);
ASSERT(a_DstSizeY < MAX_INTERPOL_SIZEY);
// Calculate interpolation ratios and src indices along each axis:
float RatioX[MAX_INTERPOL_SIZEX];
float RatioY[MAX_INTERPOL_SIZEY];
int SrcIdxX[MAX_INTERPOL_SIZEX];
int SrcIdxY[MAX_INTERPOL_SIZEY];
for (int x = 1; x < a_DstSizeX; x++)
{
SrcIdxX[x] = x * (a_SrcSizeX - 1) / (a_DstSizeX - 1);
RatioX[x] = (static_cast<float>(x * (a_SrcSizeX - 1)) / (a_DstSizeX - 1)) - SrcIdxX[x];
}
for (int y = 1; y < a_DstSizeY; y++)
{
SrcIdxY[y] = y * (a_SrcSizeY - 1) / (a_DstSizeY - 1);
RatioY[y] = (static_cast<float>(y * (a_SrcSizeY - 1)) / (a_DstSizeY - 1)) - SrcIdxY[y];
}
// Special values at the ends. Notice especially the last indices being (size - 2) with ratio set to 1, to avoid index overflow:
SrcIdxX[0] = 0;
RatioX[0] = 0;
SrcIdxY[0] = 0;
RatioY[0] = 0;
SrcIdxX[a_DstSizeX - 1] = a_SrcSizeX - 2;
RatioX[a_DstSizeX - 1] = 1;
SrcIdxY[a_DstSizeY - 1] = a_SrcSizeY - 2;
RatioY[a_DstSizeY - 1] = 1;
// Output all the dst array values using the indices and ratios:
int idx = 0;
for (int y = 0; y < a_DstSizeY; y++)
{
int idxLoY = a_SrcSizeX * SrcIdxY[y];
int idxHiY = a_SrcSizeX * (SrcIdxY[y] + 1);
float ry = RatioY[y];
for (int x = 0; x < a_DstSizeX; x++)
{
// The four src corners of the current "cell":
float LoXLoY = a_Src[SrcIdxX[x] + idxLoY];
float HiXLoY = a_Src[SrcIdxX[x] + 1 + idxLoY];
float LoXHiY = a_Src[SrcIdxX[x] + idxHiY];
float HiXHiY = a_Src[SrcIdxX[x] + 1 + idxHiY];
// Linear interpolation along the X axis:
float InterpXLoY = LoXLoY + (HiXLoY - LoXLoY) * RatioX[x];
float InterpXHiY = LoXHiY + (HiXHiY - LoXHiY) * RatioX[x];
// Linear interpolation along the Y axis:
a_Dst[idx] = InterpXLoY + (InterpXHiY - InterpXLoY) * ry;
idx += 1;
}
}
}
void LinearInterpolate3DArray(
float * a_Src,
int a_SrcSizeX, int a_SrcSizeY, int a_SrcSizeZ,
float * a_Dst,
int a_DstSizeX, int a_DstSizeY, int a_DstSizeZ
)
{
ASSERT(a_DstSizeX > 0);
ASSERT(a_DstSizeX < MAX_INTERPOL_SIZEX);
ASSERT(a_DstSizeY > 0);
ASSERT(a_DstSizeY < MAX_INTERPOL_SIZEY);
ASSERT(a_DstSizeZ > 0);
ASSERT(a_DstSizeZ < MAX_INTERPOL_SIZEZ);
// Calculate interpolation ratios and src indices along each axis:
float RatioX[MAX_INTERPOL_SIZEX];
float RatioY[MAX_INTERPOL_SIZEY];
float RatioZ[MAX_INTERPOL_SIZEZ];
int SrcIdxX[MAX_INTERPOL_SIZEX];
int SrcIdxY[MAX_INTERPOL_SIZEY];
int SrcIdxZ[MAX_INTERPOL_SIZEZ];
for (int x = 1; x < a_DstSizeX; x++)
{
SrcIdxX[x] = x * (a_SrcSizeX - 1) / (a_DstSizeX - 1);
RatioX[x] = (static_cast<float>(x * (a_SrcSizeX - 1)) / (a_DstSizeX - 1)) - SrcIdxX[x];
}
for (int y = 1; y < a_DstSizeY; y++)
{
SrcIdxY[y] = y * (a_SrcSizeY - 1) / (a_DstSizeY - 1);
RatioY[y] = (static_cast<float>(y * (a_SrcSizeY - 1)) / (a_DstSizeY - 1)) - SrcIdxY[y];
}
for (int z = 1; z < a_DstSizeZ; z++)
{
SrcIdxZ[z] = z * (a_SrcSizeZ - 1) / (a_DstSizeZ - 1);
RatioZ[z] = (static_cast<float>(z * (a_SrcSizeZ - 1)) / (a_DstSizeZ - 1)) - SrcIdxZ[z];
}
// Special values at the ends. Notice especially the last indices being (size - 2) with ratio set to 1, to avoid index overflow:
SrcIdxX[0] = 0;
RatioX[0] = 0;
SrcIdxY[0] = 0;
RatioY[0] = 0;
SrcIdxZ[0] = 0;
RatioZ[0] = 0;
SrcIdxX[a_DstSizeX - 1] = a_SrcSizeX - 2;
RatioX[a_DstSizeX - 1] = 1;
SrcIdxY[a_DstSizeY - 1] = a_SrcSizeY - 2;
RatioY[a_DstSizeY - 1] = 1;
SrcIdxZ[a_DstSizeZ - 1] = a_SrcSizeZ - 2;
RatioZ[a_DstSizeZ - 1] = 1;
// Output all the dst array values using the indices and ratios:
int idx = 0;
for (int z = 0; z < a_DstSizeZ; z++)
{
int idxLoZ = a_SrcSizeX * a_SrcSizeY * SrcIdxZ[z];
int idxHiZ = a_SrcSizeX * a_SrcSizeY * (SrcIdxZ[z] + 1);
float rz = RatioZ[z];
for (int y = 0; y < a_DstSizeY; y++)
{
int idxLoY = a_SrcSizeX * SrcIdxY[y];
int idxHiY = a_SrcSizeX * (SrcIdxY[y] + 1);
float ry = RatioY[y];
for (int x = 0; x < a_DstSizeX; x++)
{
// The eight src corners of the current "cell":
float LoXLoYLoZ = a_Src[SrcIdxX[x] + idxLoY + idxLoZ];
float HiXLoYLoZ = a_Src[SrcIdxX[x] + 1 + idxLoY + idxLoZ];
float LoXHiYLoZ = a_Src[SrcIdxX[x] + idxHiY + idxLoZ];
float HiXHiYLoZ = a_Src[SrcIdxX[x] + 1 + idxHiY + idxLoZ];
float LoXLoYHiZ = a_Src[SrcIdxX[x] + idxLoY + idxHiZ];
float HiXLoYHiZ = a_Src[SrcIdxX[x] + 1 + idxLoY + idxHiZ];
float LoXHiYHiZ = a_Src[SrcIdxX[x] + idxHiY + idxHiZ];
float HiXHiYHiZ = a_Src[SrcIdxX[x] + 1 + idxHiY + idxHiZ];
// Linear interpolation along the Z axis:
float LoXLoYInZ = LoXLoYLoZ + (LoXLoYHiZ - LoXLoYLoZ) * rz;
float HiXLoYInZ = HiXLoYLoZ + (HiXLoYHiZ - HiXLoYLoZ) * rz;
float LoXHiYInZ = LoXHiYLoZ + (LoXHiYHiZ - LoXHiYLoZ) * rz;
float HiXHiYInZ = HiXHiYLoZ + (HiXHiYHiZ - HiXHiYLoZ) * rz;
// Linear interpolation along the Y axis:
float LoXInYInZ = LoXLoYInZ + (LoXHiYInZ - LoXLoYInZ) * ry;
float HiXInYInZ = HiXLoYInZ + (HiXHiYInZ - HiXLoYInZ) * ry;
// Linear interpolation along the X axis:
a_Dst[idx] = LoXInYInZ + (HiXInYInZ - LoXInYInZ) * RatioX[x];
idx += 1;
} // for x
} // for y
} // for z
}