generateTerrain = { function smallestPowerOfTwoAfter(n) { var ret = 1; while (ret < n) { ret <<= 1; } return ret; } /** * Generate a square matrix * @param {number} size - Width and length of the square. * @return {Array.>} The vertices matrix of the square */ function generateMatrix(size) { var matrix = []; for (var i = 0; i < size; i++) { var row = []; for (var j = 0; j < size; ++j) { row.push(0); } matrix.push(row); }; return matrix; } /** * Diamond step of iteration. * @param {Array.>} matrix - Matrix to iterate on. * @param {number} depth - Depth of current iteration(starts from 1). * @param {number} smoothness - Smoothness of terrain. */ function diamond(matrix, depth, smoothness) { var len = matrix.length; var terrainSize = len - 1; var numSegs = 1 << (depth - 1); var span = terrainSize / numSegs; var half = span / 2; // enumerate sub-squares // for each sub-square, the height of the center is caculated // by averaging the height of its four vertices plus a random offset. for (var x = 0; x < terrainSize; x += span) { for (var y = 0; y < terrainSize; y += span) { // (x, y) // \ // a---b---c // | | | // d---e---f // | | | // g---h---i // // \___ ___/ // V // span // var va = [x, y]; var vc = [x + span, y]; var ve = [x + half, y + half]; var vg = [x, y + span]; var vi = [x + span, y + span]; // heights of vertices var heights = [va, vc, vg, vi].map(function(v) { return matrix[v[1]][v[0]]; }); // average height var avg = average(heights); // random offset var offset = getH(smoothness, depth); // set center height matrix[ve[1]][ve[0]] = avg + offset; } } } /** * Get a random offset. * @param {number} smoothness - Higher the value, smoother the terrain. * recommended value is 1. * @param {number} depth - Depth of current iteration(starts from 1). */ function getH(smoothness, depth) { var sign = Math.random() > 0.5 ? 1 : -1; var reduce = 1; for (var i = 0; i < depth; ++i) { reduce *= Math.pow(2, -smoothness); } return sign * Math.random() * reduce; } function average(numbers) { var sum = 0; numbers.forEach(function(v) { sum += v; }); return sum / numbers.length; } function squareHelper(matrix, depth, smoothness, a, b, c, d, t) { var heights = [a, b, c, d].map(function(v) { return matrix[v[1]][v[0]]; }); var avg = average(heights); var offset = getH(smoothness, depth); matrix[t[1]][t[0]] = avg + offset; } /** * Square step of iteration. * @param {Array.>} matrix - Matrix to iterate on. * @param {number} depth - Depth of current iteration(starts from 1). * @param {number} smoothness - Smoothness of terrain. */ function square(matrix, depth, smoothness) { var len = matrix.length var terrainSize = len - 1; var numSegs = 1 << (depth - 1); var span = terrainSize / numSegs; var half = span / 2; // enumerate sub-dimaonds for (var x = 0; x < terrainSize; x += span) { for (var y = 0; y < terrainSize; y += span) { // for each sub-square, the height of the center is caculated // by averaging the height of its four vertices plus a random offset. // for example, // h = avg(g, c, i, m) + random; // f = avg(a, g, k, i) + random; // j = f; // // (x, y) // \ // a---b---c---d---e // | \ | / | \ | / | // f---g---h---i---j // | / | \ | / | \ | // k---l---m---n---o // | \ | / | \ | / | // p---q---r---s---t // | / | \ | / | \ | // u---v---w---x---y // // \___ ___/ // V // span // var va = [x, y]; var vb = [x + half, y]; var vc = [x + span, y]; var vf = [x, y + half]; var vg = [x + half, y + half]; var vh = [x + span, y + half]; var vk = [x, y + span]; var vl = [x + half, y + span]; var vm = [x + span, y + span]; // right of h var vhr = [x + half * 3, y + half]; if (vhr[0] > terrainSize) vhr[0] = half; // left of f var vfl = [x - half, y + half] if (vfl[0] < 0) vfl[0] = terrainSize - half; // under l var vlu = [x + half, y + half * 3]; if (vlu[1] > terrainSize) vlu[1] = half; // above b var vba = [x + half, y - half] if (vba[1] < 0) vba[1] = terrainSize - half; squareHelper(matrix, depth, smoothness, va, vg, vk, vfl, vf); squareHelper(matrix, depth, smoothness, va, vba, vc, vg, vb); squareHelper(matrix, depth, smoothness, vc, vhr, vm, vg, vh); squareHelper(matrix, depth, smoothness, vk, vg, vm, vlu, vl); } } // set the elevations of the rightmost and bottom vertices to // equal the leftmost and topmost ones'. for (var y = 0; y < terrainSize; y += span) { matrix[y][terrainSize] = matrix[y][0]; } for (var x = 0; x < terrainSize; x += span) { matrix[terrainSize][x] = matrix[0][x]; } } /** * Iterate on the matrix using Diamond-Square algorithm. * @param {Array.>} matrix - Matrix to be iterated on. * @param {number} smoothness - Smoothness of terrain. */ function iterate(matrix, smoothness) { // the count of iterations applied so far var counter = 0; // the total number of iterations to apply is log_2^(size of matrix) var numIteration = Math.log(matrix.length - 1) / Math.LN2; while (counter++ < numIteration) { diamond(matrix, counter, smoothness); square(matrix, counter, smoothness); } } /** * Generate a square fractal terrain. * @param {number} size - Size of terrain, MUST be a power of 2. * @param {number} smoothness - Higher this value, smoother the terrain. * recommended value is 1. * @return {Array.>} A two-dimensional array holding the elevations * of the vertices of the terrain. Each elevation will be between -1 and 1. */ function generateSquareTerrain(size, smoothness) { // throw error if size is not a power of two. if (size & (size - 1)) { throw new Error('Expected terrain size to be a power of 2, received ' + size + ' instead.'); } // generate a square matrix var mat = generateMatrix(size + 1); // iterate on the matrix using the square-diamond algorithm iterate(mat, smoothness); return mat; } /** * Generate fractal terrain. * @param {number} width - Width of rectangle. * @param {number} height - Height of rectangle. * @param {number} smoothness - Higher this value, smoother the terrain. * recommended value is 1. * @return {Array.>} A two-dimensional array holding the elevations * of the vertices of the terrain. */ return (width, height, smoothness) => { var smoothness = typeof smoothness === 'undefined' ? 1 : smoothness; var size = smallestPowerOfTwoAfter(Math.max(width, height)); var squareTerrain = generateSquareTerrain(size, smoothness); // console.log(squareTerrain); var terrain = []; // terrain is a matrix of size (width + 1) x (height + 1) for (var i = 0; i <= height; ++i) { terrain.push(squareTerrain[i].slice(0, width + 1)); } return terrain; } }

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