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Following this lesson for implementing mid-point displacement algorithm for terrain generation. I aim at generating a wavefront(obj) file of the terrain

I have an array of dimension (2^n + 1) x (2^n + 1). The corners of the 2d array is initialized with random numbers.

n = plug_in_n arr = Array.new(2**n + 1) { Array.new(2**n +1) { 0 } } n_augmented = 2**n arr[0][0] = rand(10 + 1) arr[0][n_augmented] = rand(10 + 1) arr[n_augmented][0] = rand(10 + 1) arr[n_augmented][n_augmented] = rand(10 + 1)

This is the script I have written for generating a terrain.

a = arr n_augmented_copy = n_augmented while n_augmented > 1 puts "n_augmented = " + n_augmented.to_s i = 0 while(i < n_augmented_copy) j = 0 while(j < n_augmented_copy) a[i][j+(n_augmented)/2] = (a[i][j] + a[i][j+n_augmented]) / 2.0 + (rand 0.0..1.0) a[i + (n_augmented) / 2][j + n_augmented] = (a[i][j + n_augmented] + a[i + n_augmented][j + n_augmented]) / 2.0 + (rand 0.0..1.0) a[i + n_augmented][j +( n_augmented) / 2] = (a[i + n_augmented][j] + a[i + n_augmented][j + n_augmented] )/ 2.0 + (rand 0.0..1.0) a[i + (n_augmented) / 2][j] = (a[i + n_augmented][j] + a[i][j] )/ 2.0 + (rand 0.0..1.0) a[i + (n_augmented) / 2][j +( n_augmented) / 2] = ((a[i][j+(n_augmented)/2] + a[i + (n_augmented) / 2][j + n_augmented] + a[i + n_augmented][j +( n_augmented) / 2] + a[i + (n_augmented) / 2][j]))/ 4.0 + (rand 0.0..1.0) j = j + n_augmented end i = i + n_augmented end # binding.pry # p_arr(a) n_augmented = n_augmented / 2

end

Demonstrating a case for n = 2: I have omitted the random-displacement rand 0.0..1.0to check if the heightmap chucks are getting calculated fine.

Here is how the iterations look like

n_augmented = 4 9 0 5.5 0 2 0 0 0 0 0 6.5 0 5.5 0 4.5 0 0 0 0 0 4 0 5.5 0 7 n_augmented = 2 9 7.25 5.5 3.75 2 7.75 6.625 5.5 4.375 3.25 6.5 6.0 5.5 5.0 4.5 5.25 5.375 5.5 5.625 5.75 4 4.75 5.5 6.25 7

If I form a mesh using this alone, it results in a plane like: enter image description here

Considering the random displacement for this case, it results in : enter image description here

For n = 5, It looks like : enter image description here

This is not desirable since I cannot see any peaks and slopes.

Here is the ruby script : CODE

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2 Answers 2

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The magnitude of your random displacement is not changing appropriately. For your initial points, you're using a random value between 0 and 10. But for the subdivisions you're only using a random value between 0 and 1.

What you probably want to do is to start with a random value between 0 and 10, and then cut the range in half on each iteration. So on the 2nd iteration, the range of random values would only be between 0 and 5. On the 3rd iteration it would be between 0 and 2.5, etc. That should get you something with peaks and valleys.

Once you have that, you can increase the Y scale to make the peaks taller or valleys deeper, or decrease it to reduce the range.

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  • \$\begingroup\$ Thanks. Got it working and also posted the updated code in my answer. Y- scale in your answer referring to the initial upper range of the random value? \$\endgroup\$ Commented Apr 7, 2019 at 4:46
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    \$\begingroup\$ Yes, you can either increase the first random values, or scale all values afterwards. \$\endgroup\$ Commented Apr 7, 2019 at 5:17
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What you probably want to do is to start with a random value between 0 and 10, and then cut the range in half on each iteration. So on the 2nd iteration, the range of random values would only be between 0 and 5. On the 3rd iteration it would be between 0 and 2.5, etc. That should get you something with peaks and valleys.

Thanks for this step. Here is my updated source if it helps anyone and here is the result: Result

def p_arr(arr) width = arr.flatten.max.to_s.size+2 for i in (0..arr.length - 1) for j in (0..arr.length - 1) print arr[i][j].to_s.rjust(width + 2) + " " end puts "" end end def getrnd(range) rand -range.to_f..range.to_f end n = 8 arr = Array.new(2**n + 1) { Array.new(2**n +1) { 0 } } n_augmented = 2**n arr[0][0] = rand(10 + 1) arr[0][n_augmented] = rand(10 + 1) arr[n_augmented][0] = rand(10 + 1) arr[n_augmented][n_augmented] = rand(10 + 1) a = arr n_augmented_copy = n_augmented range = 50.0 while n_augmented > 1 i = 0 while(i < n_augmented_copy) j = 0 while(j < n_augmented_copy) a[i][j+(n_augmented)/2] = (a[i][j] + a[i][j+n_augmented]) / 2.0 + getrnd(range) a[i + (n_augmented) / 2][j + n_augmented] = (a[i][j + n_augmented] + a[i + n_augmented][j + n_augmented]) / 2.0 + getrnd(range) a[i + n_augmented][j +( n_augmented) / 2] = (a[i + n_augmented][j] + a[i + n_augmented][j + n_augmented] )/ 2.0 + getrnd(range) a[i + (n_augmented) / 2][j] = (a[i + n_augmented][j] + a[i][j] )/ 2.0 + getrnd(range) a[i + (n_augmented) / 2][j +( n_augmented) / 2] = ((a[i][j+(n_augmented)/2] + a[i + (n_augmented) / 2][j + n_augmented] + a[i + n_augmented][j +( n_augmented) / 2] + a[i + (n_augmented) / 2][j]))/ 4.0 + getrnd(range) j = j + n_augmented end i = i + n_augmented end range = range / 2 n_augmented = n_augmented / 2 end board = n_augmented_copy + 1 c = 0 k = board + 1 #Print vertices File.open("mountain.obj", 'w') { |file| for i in 0..a.length - 1 for j in 0..a.length - 1 file.write("v " + j.to_f.to_s + " " + a[i][j].to_f.to_s + " " + i.to_f.to_s+ "\n") end end for i in 0..a.length - 2 for i in 0..a.length - 2 file.write("f " + (c + i + 1).to_s + " " + k.to_s + " " + (c + i + 2).to_s + "\n") file.write("f " + (c + i + 2).to_s + " " + (k).to_s + " " + (k+1).to_s + "\n") k=k+1 end k = k +1 c += board end }
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