Looks like need some threshold to eliminate small noise bug as the right photo...
...
//Randomize the sample as input
int v = (int)random(-40, 40);
a+=0.2; A = (int) (80 + sin(a) * (v+50)); //add sine wave
stroke(100, 100, 100);
line(lastXPos, lastA, xPos, A); //draw gray samples------------------------------------
//smooth it
B = smooth(A, 0.9, B);
//get 1st derivative
C = B - lastB; // f''(x) = f(x) - f(x-1);
C = (C + lastC) >> 1; // some easy smooth
stroke(250, 100, 100);
line(lastXPos, 100+lastB, xPos, 100+B); //draw smoothed samples-------------
line(lastXPos+1, 100+lastB, xPos+1, 100+B);
stroke(100, 100, 250);
line(lastXPos, 400+(lastC*8), xPos, 400+(C*8));//draw 1st derivatives --------------
if ((C*lastC) <= 0) {
//f'(x) changed; when (f'(x)>0, f'(x-1)<0) or (f'(x)<0, f'(x-1)>0) or f'(x)=0 or f'x(x-1)=0
if (lastC >0) {//found valley, draw line------
stroke(40,40, 60);
line(xPos, 400, xPos, 200);
}
if (lastC <0) {//found peak, draw line-------
stroke(80,80, 120);
line(xPos, 400, xPos, 150);
}
}
lastA = A; //store current value for next iteration
lastB = B;
lastC = C;
lastXPos = xPos; //move forward
...
 |
| Change random samples into Perlin noise |
