使用帧缓冲区渲染为立方体贴图纹理

"use strict";

function log() {
  var pre = document.createElement("pre");
  pre.appendChild(document.createTextNode(Array.prototype.join.call(arguments, " ")));
  document.body.appendChild(pre);
}

function glEnumToString(gl, value) {
  for(var key in gl) {
    if (gl[key] === value) {
      return key;
    }
  }
  return "0x" + value.toString(16);
}

var INSCATTER_RESOLUTION = 64;

var gl = document.createElement("canvas").getContext("webgl");
var ext = gl.getExtension("OES_texture_float");
if (!ext) { log("need OES_texture_float"); }
ext = gl.getExtension("OES_texture_float_linear");
if (!ext) { log("need OES_texture_float_linear"); }
           
var o = {};
(function() {
  this.inscatterFrameBuffers_ = [];
  this.inscatterDepthBuffers_ = [];
  this.inscatterTexture_ = gl.createTexture();
  gl.bindTexture(gl.TEXTURE_CUBE_MAP, this.inscatterTexture_);

  gl.texParameteri(gl.TEXTURE_CUBE_MAP, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
  gl.texParameteri(gl.TEXTURE_CUBE_MAP, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
  gl.texParameteri(gl.TEXTURE_CUBE_MAP, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
  gl.texParameteri(gl.TEXTURE_CUBE_MAP, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);       
  for (let i = 0; i < 6; i++) {
    gl.texImage2D(gl.TEXTURE_CUBE_MAP_POSITIVE_X + i, 0, gl.RGBA, INSCATTER_RESOLUTION, INSCATTER_RESOLUTION, 0, gl.RGBA, gl.FLOAT, null);
  }

  for (let i = 0; i < 6; i++) {
    // Create framebuffer
    this.inscatterFrameBuffers_[i] = gl.createFramebuffer();
    gl.bindFramebuffer(gl.FRAMEBUFFER, this.inscatterFrameBuffers_[i]);

    // Create and attach depth buffer
    this.inscatterDepthBuffers_[i] = gl.createRenderbuffer();
    gl.bindRenderbuffer(gl.RENDERBUFFER, this.inscatterDepthBuffers_[i]);
    gl.renderbufferStorage(gl.RENDERBUFFER, gl.DEPTH_COMPONENT16, INSCATTER_RESOLUTION, INSCATTER_RESOLUTION);
    gl.framebufferRenderbuffer(gl.FRAMEBUFFER, gl.DEPTH_ATTACHMENT, gl.RENDERBUFFER, this.inscatterDepthBuffers_[i]);
    gl.bindRenderbuffer(gl.RENDERBUFFER, null);

    // Attach one face of cube map
    gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_CUBE_MAP_POSITIVE_X + i, this.inscatterTexture_, 0);

    if (gl.checkFramebufferStatus(gl.FRAMEBUFFER) != gl.FRAMEBUFFER_COMPLETE) {
      let status_code = gl.checkFramebufferStatus(gl.FRAMEBUFFER);
      log("Inscatter frame buffer, " + i + ", is not complete: " + glEnumToString(gl, status_code));
    } else {
      log("success");
    }

  }
}).call(o);