// Compute Perlin noise at coordinates x, y
float Perlin::getPerlin(float x, float y) {
// Determine grid cell coordinates
int x0 = (x >= 0.0 ? (int)x : (int)x - 1);
int x1 = x0 + 1;
int y0 = (y >= 0.0 ? (int)y : (int)y - 1);
int y1 = y0 + 1;
// Determine interpolation weights
float sx = x - (float)x0;
float sy = y - (float)y0;
// Interpolate between grid point gradients
float n0, n1, ix0, ix1, value;
n0 = dotGridGradient(x0, y0, x, y);
n1 = dotGridGradient(x1, y0, x, y);
ix0 = lerp(n0, n1, sx);
n0 = dotGridGradient(x0, y1, x, y);
n1 = dotGridGradient(x1, y1, x, y);
ix1 = lerp(n0, n1, sx);
value = lerp(ix0, ix1, sy);
float ret = value;
return ret;
}
// https://en.wikipedia.org/wiki/Perlin_noise
// here the input floats are fractions we must find the closest sample for
float Terrain::getHeight(float x, float y) {
// Determine grid cell coordinates
// send to full grid
float unfloored_x = (x * (bounds.xmax - bounds.xmin)) + (bounds.xmin);
float unfloored_y = (y * (bounds.ymax - bounds.ymin)) + (bounds.ymin);
int x0 = clamp(floor(unfloored_x), bounds.xmin, bounds.xmax - 1);
int y0 = clamp(floor(unfloored_y), bounds.ymin, bounds.ymax - 1);
int x1 = clamp(floor(x0 + 1), bounds.xmin, bounds.xmax - 1);
int y1 = clamp(floor(y0 + 1), bounds.ymin, bounds.ymax - 1);
float sx = unfloored_x - (float) x0;
float sy = unfloored_y - (float) y0;
float n0, n1, ix0, ix1, value;
n0 = dotGridGradient(x0, y0, x, y);
n1 = dotGridGradient(x1, y0, x, y);
ix0 = lerp(n0, n1, sx);
n0 = dotGridGradient(x0, y1, x, y);
n1 = dotGridGradient(x1, y1, x, y);
ix1 = lerp(n0, n1, sx);
value = lerp(ix0, ix1, sy);
return value;
}
