javascript - 手写 asm.js

Question

我正在尝试向 perlin 单纯形噪声函数添加 asm.js 注释:

"use strict";

// Ported from Stefan Gustavson's java implementation
// http://staffwww.itn.liu.se/~stegu/simplexnoise/simplexnoise.pdf
// Read Stefan's excellent paper for details on how this code works.
//
// Sean McCullough banksean@gmail.com

function SimplexNoise(stdlib,foreign,heap) {
    "use asm";
    // heap should be at least 1024*4+12*3*4 bytes long
    var floor = stdlib.Math.floor,
        sqrt = stdlib.Math.sqrt,
        random = new stdlib.Float32Array(heap),
        buf = new stdlib.Int32Array(heap),
        F2 = 0.0, F3 = 0.0,
        G2 = 0.0, G3 = 0.0;
    F2 = (sqrt(3.0)-1.0)*0.5; F3 = 1.0/3.0;
    G2 = (3.0-sqrt(3.0))/6.0; G3 = 1.0/6.0;
    function init() {
        // before calling this function, set the first 256 floats in the heap to be random numbers between 0..1
        // the heap gets rewritten, but if you record the IV separately, the noise is reproducable
        for(var i=0; i<256; i++) {
            buf[i] = buf[i+256] = floor(random[i]*256.0) & 0xff;
            buf[i+512] = buf[i+512+256] = (buf[i] % 12) * 3 + 1024;
        }
        i = 1024;
        buf[i++] = 1;  buf[i++] = 1;  buf[i++] = 0;
        buf[i++] = -1; buf[i++] = 1;  buf[i++] = 0;
        buf[i++] = 1;  buf[i++] = -1; buf[i++] = 0;
        buf[i++] = -1; buf[i++] = -1; buf[i++] = 0;
        buf[i++] = 1;  buf[i++] = 0;  buf[i++] = 1;
        buf[i++] = -1; buf[i++] = 0;  buf[i++] = 1; 
        buf[i++] = 1;  buf[i++] = 0;  buf[i++] = -1;
        buf[i++] = -1; buf[i++] = 0;  buf[i++] = -1;
        buf[i++] = 0;  buf[i++] = 1;  buf[i++] = 1;
        buf[i++] = 0;  buf[i++] = -1; buf[i++] = 1;
        buf[i++] = 0;  buf[i++] = 1;  buf[i++] = -1;
        buf[i++] = 0;  buf[i++] = -1; buf[i++] = -1;
    }
    function noise2D(xin,yin) {
        xin = +xin; yin = +yin;
        var s = 0.0, i = 0, j = 0,
            t = 0.0,
            X0 = 0.0, Y0 = 0.0,
            x0 = 0.0, y0 = 0.0,
            i1 = 0, j1 = 0,
            x1 = 0.0, y1 = 0.0,
            x2 = 0.0, y2 = 0.0,
            ii = 0, jj = 0,
            gi0 = 0, gi1 = 0, gi2 = 0,
            t0 = 0.0, t1 = 0.0, t2 = 0.0,
            n0 = 0.0, n1 = 0.0, n2 = 0.0;
        // Skew the input space to determine which simplex cell we're in 
        s = (xin+yin)*F2; // Hairy factor for 2D 
        i = floor(xin+s); j = floor(yin+s);
        t = (i+j)*G2;
        X0 = i-t; Y0 = j-t; // Unskew the cell origin back to (x;y) space 
        x0 = xin-X0; y0 = yin-Y0; // The x;y distances from the cell origin 
        // For the 2D case; the simplex shape is an equilateral triangle. 
        // Determine which simplex we are in. 
        i1 = (x0>y0?1:0); j1 = (x0>y0?0:1); // Offsets for second (middle) corner of simplex in (i;j) coords 
        // A step of (1;0) in (i;j) means a step of (1-c;-c) in (x;y); and 
        // a step of (0;1) in (i;j) means a step of (-c;1-c) in (x;y); where 
        // c = (3-sqrt(3))/6 
        x1 = x0-i1+G2; y1 = y0-j1+G2; // Offsets for middle corner in (x;y) unskewed coords 
        x2 = x0-1+2*G2; y2 = y0-1+2*G2; // Offsets for last corner in (x;y) unskewed coords 
        // Work out the hashed gradient indices of the three simplex corners 
        ii = i & 255; jj = j & 255;
        gi0 = buf[ii+buf[jj]+512];
        gi1 = buf[ii+i1+buf[jj+j1]+512]; 
        gi2 = buf[ii+1+buf[jj+1]+512];
        // Calculate the contribution from the three corners 
        t0 = 0.5-x0*x0-y0*y0; t1 = 0.5-x1*x1-y1*y1; t2 = 0.5-x2*x2-y2*y2;
        n0 = t0<0.0? 0.0: t0*t0*t0*t0*(buf[gi0]*x0+buf[gi0+1]*y0);  // (x;y) of buf used for 2D gradient 
        n1 = t1<0.0? 0.0: t1*t1*t1*t1*(buf[gi1]*x1+buf[gi1+1]*y1);
        n2 = t2<0.0? 0.0: t2*t2*t2*t2*(buf[gi2]*x2+buf[gi2+1]*y2); 
        // Add contributions from each corner to get the final noise value. 
        // The result is scaled to return values in the interval [-1,1]. 
        return 70.0 * (n0 + n1 + n2);
    }
    return {
        init: init,
        noise2D: noise2D
    };
};

Firefox Javascript 错误控制台仅显示:

Warning: TypeError: asm.js type error: asm.js must end with a return export statement Source File: perlin_simplex.js Line: 9

我已经搜索了有关错误可能是什么的帮助，但只找到了 https://github.com/zbjornson/human-asmjs这通常非常有用，但在这种特定情况下没有帮助。

我做错了什么？这个 perlin 噪声函数如何由人类 asm.js 处理？

Answer 1

问题出在以下几行:

F2 = (sqrt(3.0)-1.0)*0.5; F3 = 1.0/3.0;
G2 = (3.0-sqrt(3.0))/6.0; G3 = 1.0/6.0;

在 asm.js 模块的顶级范围内只允许声明。不允许在顶级范围内定义变量。

根据spec您只能将文字值分配给全局变量(以及其他导入语句)。因此，您也不能执行以下操作，因为 F2、F3、G2 和 G3 未被分配文字值(value)观:

var floor = stdlib.Math.floor,
    sqrt = stdlib.Math.sqrt,
    random = new stdlib.Float32Array(heap),
    buf = new stdlib.Int32Array(heap),
    F2 = (sqrt(3.0)-1.0)*0.5, F3 = 1.0/3.0,
    G2 = (3.0-sqrt(3.0))/6.0, G3 = 1.0/6.0;

因此，您需要将 F2、F3、G2 和 G3 的定义移动到一个函数中(可能是 init 函数)。因此你的代码应该是这样的:

function SimplexNoise(stdlib,foreign,heap) {
    "use asm";

    var floor = stdlib.Math.floor,
        sqrt = stdlib.Math.sqrt,
        random = new stdlib.Float32Array(heap),
        buf = new stdlib.Int32Array(heap),
        F2 = 0.0, F3 = 0.0,
        G2 = 0.0, G3 = 0.0;

    function init() {
        F2 = (sqrt(3.0)-1.0)*0.5; F3 = 1.0/3.0;
        G2 = (3.0-sqrt(3.0))/6.0; G3 = 1.0/6.0;
        // rest of init
    }

    function noise2D(xin,yin) {
        // function body
    }

    return {
        init: init,
        noise2D: noise2D
    };
};

Human asm.js 确实告诉你这个问题，但他们给你的例子是一个数组而不是一个简单的变量:

Note that these typed arrays cannot be modified outside of a function:

function MyModule(stdlib, foreign, heap) {
  var arr = new stdlib.Int8Array(heap);
  arr[0] = 1; // "asm.js must end with a return export statement"
  // ...
}

Instead do something like this:

function MyModule(stdlib, foreign, heap) {
  var arr = new stdlib.Int8Array(heap);
  function init() {
    arr[0] = 1;
  }

  return {
    init: init
  };
}

给你。 asm.js 不是很痛苦吗？