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#include <math.h>
#include "float.h"
#include "segment-transfer.h"
/* Straight line interpolation (zero <= index <= one). */
f32
segment_transfer_interpolate_linear (f32 left,f32 right,f32 index)
{
return ((index * (right - left)) + left);
}
/* Logarithmic interpolation function (zero <= index <= one). This
works by translating `index' into a logarithmic space and making a
linear interpolation with the translated index.*/
f32
segment_transfer_interpolate_logarithmic (f32 left,f32 right,f32 index)
{
return ((log10 ((index * 9) + 1.0)) * (right - left)) + left;
}
/* `data' is a pointer to a `size' samples that define a valid
transfer function. `x' is a normalized lookup index between zero
and one. `size' must be a multiple of two, and `data' is
interpreted as a series of x/y co-ordinates. `data' is searched
left to right for two x co-ordinates that span `x', these are then
interpolated to calculate the corresponding y value. A single data
point covers all possible x values. Out of range indexes are
truncated left and right. Other cases are looked up in left to
right order. */
#define SEGMENT_TRANSFER_X(index) (data[((index)*2)])
#define SEGMENT_TRANSFER_Y(index) (data[((index)*2)+1])
f32
segment_transfer_lookup_linear (f32 *data,int size,f32 x)
{
int size_2 = size / 2;
if (size_2 == 1) {
return SEGMENT_TRANSFER_Y (0);
} else if (x <= 0.0) {
return SEGMENT_TRANSFER_Y (0);
} else if (x >= 1.0) {
return SEGMENT_TRANSFER_Y (size_2 - 1);
} else {
f32 x_left = SEGMENT_TRANSFER_X (0);
f32 x_right;
f32 z;
int i;
for (i = 1; i < size_2; i++) {
x_right = SEGMENT_TRANSFER_X (i);
if (x >= x_left && x <= x_right) {
f32 y_left = SEGMENT_TRANSFER_Y (i - 1);
f32 y_right = SEGMENT_TRANSFER_Y (i);
z = (x - x_left) / (x_right - x_left);
return segment_transfer_interpolate_linear (y_left,y_right,z);
}
x_left = x_right;
}
}
/* If the transfer function is corrupt return zero. */
return 0.0;
}
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