# How should I use this 1D perlin noise function?

I'm trying to create a terraria like terrain with SDL2 and C++. For generating the terrain I'm trying to use the 1D noise function from here: https://github.com/SRombauts/SimplexNoise

It's pretty basic and only takes a x value. I've been messing around with it for a while but can't work out what to pass into the function as the x value. I first tried passing just the x value of the column I'm finding the noise for. This just returned 0 every time. Next I tried passing a value between 0 and 1, so I passed it x / width. This sort of worked, but the wider I made the terrain, the more spaced out it became.

Hope you understand, what I do give the function for the x value? Thanks in advance.

What Pikalek said is absolutely true about the return value, but the workaround he suggest is not very good.

Instead of adding a random offset, you should divide the current x position with a cobstant value. Let's call this value "smoothness". Higher smoothness means smokther terrain:

float smoothness = 20;
float height = 20; // Max height of terrain
for (float x = 0; x < COLUMN_MAX; x++) {
float val = SimplexNoise::noise(x / smoothness) * height;
// Stuff
}

• Thanks, it works nicely :) Is it possible I could also add the random value to get random results everytime? Oct 6, 2016 at 8:14
• @IHazza Do you mean to make it more "realistic" or to make it more random? Oct 6, 2016 at 8:50
• Make it random. The result is the same everytime, and I'm wondering if I add a random offset will it be random everytime? Oct 6, 2016 at 9:07
• @IHazza you should really read something about pseudo random noises. Take every integer between 0 abd 255 inclusively and insert them in the perm table randomly Oct 6, 2016 at 10:01
• What specifically is not very good about my solution? The constructor for SimplexNoise already has parameters to control frequency, amplitude, lacunarity & persistence. If OP wants smoother noise, the library already supports that without applying transforms to the input. Oct 6, 2016 at 14:38

The function documentation explicitly says:

@return Noise value in the range[-1; 1], value of 0 on all integer coordinates

Since the column number is an integer coord, passing it as input will always give 0 as output. An easy way around that is to add a constant decimal offset to the column number:

// seed RNG however you need
randomOffset = ((float) rand() / (RAND_MAX));

// do other setup as needed

// iterate over columns getting a noise value for each
for(int a=0; a<COLUMN_MAX; a++){
float noiseValue = SimplexNoise::noise(a + randomOffset);

// use noise value for the current column
}

• Ok I tried it, but the output seems weird, heres the output: postimg.org/image/9ahh9ro2l, and the code: gist.github.com/anonymous/856f2644d08995822392412eeaebf70f Oct 6, 2016 at 4:14
• I don't think so. The noise function is static and the constructor/object is for the fractal noise. But correct me if I'm wrong. Oct 6, 2016 at 23:26
• No, you are correct; I'm the one who didn't read the doc comments closely enough. If want to use the static function, you'll need to adjust for smoothness by scaling the input value as @Bálint suggested. Oct 7, 2016 at 2:44