WebGL全向阴影映射问题

首先，我想说的是，我已经阅读了很多有关使用深度图和立方体贴图进行阴影贴图的文章，我了解它们是如何工作的，并且我在使用OpenGL时也有使用它们的工作经验，但是，实现时遇到了问题全向阴影贴图技术在我的3D图形引擎“ EZ3”中使用单点光源。我的引擎使用WebGL作为3D图形API，并使用JavaScript作为编程语言，这是我的计算机科学学士学位论文的目的。

基本上，这就是我实现阴影贴图算法的方式，但是我只关注点光源的情况，因为有了它们，我可以归档全向阴影贴图。

首先，我像这样积极进行正面剔除：

if (this.state.faceCulling !== Material.FRONT) {
    if (this.state.faceCulling === Material.NONE)
      gl.enable(gl.CULL_FACE);

    gl.cullFace(gl.FRONT);
    this.state.faceCulling = Material.FRONT;
  }

其次，我创建一个深度程序以记录每个立方体贴图面的深度值，这是我在GLSL 1.0中的深度程序代码：

顶点着色器：

precision highp float;

attribute vec3 position;

uniform mat4 uModelView;
uniform mat4 uProjection;

void main() {
  gl_Position = uProjection * uModelView * vec4(position, 1.0);
}

片段着色器：

precision highp float;

vec4 packDepth(const in float depth) {
  const vec4 bitShift = vec4(256.0 * 256.0 * 256.0, 256.0 * 256.0, 256.0, 1.0);
  const vec4 bitMask = vec4(0.0, 1.0 / 256.0, 1.0 / 256.0, 1.0 / 256.0);
  vec4 res = mod(depth * bitShift * vec4(255), vec4(256)) / vec4(255);
  res -= res.xxyz * bitMask;
  return res;
}

void main() {
  gl_FragData[0] = packDepth(gl_FragCoord.z);
}

第三，这是我的JavaScript函数的主体，可“归档”全向阴影映射

program.bind(gl);

  for (i = 0; i < lights.length; i++) {
    light = lights[i];

    // Updates pointlight's projection matrix

    light.updateProjection();

    // Binds point light's depth framebuffer

    light.depthFramebuffer.bind(gl);

    // Updates point light's framebuffer in order to create it 
    // or if it's resolution changes, it'll be created again.

    light.depthFramebuffer.update(gl);

    // Sets viewport dimensions with depth framebuffer's dimensions

    this.viewport(new Vector2(), light.depthFramebuffer.size);

    if (light instanceof PointLight) {

      up = new Vector3();
      view = new Matrix4();
      origin = new Vector3();
      target = new Vector3();

      for (j = 0; j < 6; j++) {

    // Check in which cubemap's face we are ...

        switch (j) {
          case Cubemap.POSITIVE_X:
            target.set(1, 0, 0);
            up.set(0, -1, 0);
            break;
          case Cubemap.NEGATIVE_X:
            target.set(-1, 0, 0);
            up.set(0, -1, 0);
            break;
          case Cubemap.POSITIVE_Y:
            target.set(0, 1, 0);
            up.set(0, 0, 1);
            break;
          case Cubemap.NEGATIVE_Y:
            target.set(0, -1, 0);
            up.set(0, 0, -1);
            break;
          case Cubemap.POSITIVE_Z:
            target.set(0, 0, 1);
            up.set(0, -1, 0);
            break;
          case Cubemap.NEGATIVE_Z:
            target.set(0, 0, -1);
            up.set(0, -1, 0);
            break;
        }

    // Creates a view matrix using target and up vectors according to each face of pointlight's
    // cubemap. Furthermore, I translate it in minus light position in order to place
    // the point light in the world's origin and render each cubemap's face at this 
    // point of view

        view.lookAt(origin, target, up);
        view.mul(new EZ3.Matrix4().translate(light.position.clone().negate()));

    // Flips the Y-coordinate of each cubemap face
    // scaling the projection matrix by (1, -1, 1).

    // This is a perspective projection matrix which has:
    // 90 degress of FOV.
    // 1.0 of aspect ratio.
    // Near clipping plane at 0.01.
    // Far clipping plane at 2000.0.

        projection = light.projection.clone();
        projection.scale(new EZ3.Vector3(1, -1, 1));

    // Attaches a cubemap face to current framebuffer in order to record depth values for the face with this line
    // gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_CUBE_MAP_POSITIVE_X + j, id, 0);

        light.depthFramebuffer.texture.attach(gl, j);

    // Clears current framebuffer's color with these lines:
    // gl.clearColor(1.0,1.0,1.0,1.0);
    // gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

        this.clear(color);

    // Renders shadow caster meshes using the depth program

        for (k = 0; k < shadowCasters.length; k++)
          this._renderShadowCaster(shadowCasters[k], program, view, projection);
      }
    } else {
       // Directional light & Spotlight case ...
    }
  }

第四，这是我在主顶点着色器和片段着色器中使用深度立方体贴图计算全向阴影贴图的方式：

顶点着色器：

precision highp float;

attribute vec3 position;

uniform mat4 uModel;
uniform mat4 uModelView;
uniform mat4 uProjection;

varying vec3 vPosition;

void main() {
  vPosition = vec3(uModel * vec4(position, 1.0));

  gl_Position = uProjection * uModelView * vec4(position, 1.0);
}

片段着色器：

float unpackDepth(in vec4 color) {
    return dot(color, vec4(1.0 / (256.0 * 256.0 * 256.0), 1.0 / (256.0 * 256.0), 1.0 / 256.0, 1.0 ));
}

float pointShadow(const in PointLight light, const in samplerCube shadowSampler) {
    vec3 direction = vPosition - light.position;
    float vertexDepth = clamp(length(direction), 0.0, 1.0);
    float shadowMapDepth = unpackDepth(textureCube(shadowSampler, direction));

    return (vertexDepth > shadowMapDepth) ? light.shadowDarkness : 1.0;
}

最后，这就是我得到的结果，我的场景有一个平面，一个立方体和一个球体。此外，红色亮球是点光源：

如您所见，我似乎像点光源深度帧缓冲区的立方体贴图在它们的脸部之间做得不好。

到目前为止，我还不知道如何解决这个问题。

解

几天后，我意识到我正在使用FOV角度（以度为单位）计算投影矩阵，并且应以弧度为单位。我进行了转换，现在一切正常。现在，深度帧缓冲区的立方体贴图的各个面之间的插值非常完美。因此，以弧度为单位处理每个三角函数的角度非常重要。

此外，我意识到您可以按照我在问题中所说的那样来计算视图矩阵：

view.lookAt(position, target.add(position.clone()), up);

这种方法意味着您的视点位于pointlight的中心，并且仅在立方体贴图的每个方向上进行渲染，但是这些方向是哪些？好的，这些方向是通过将我在切换块中的每个目标（根据每个立方体贴图的面）与您的点光源的位置相加得出的。

此外，不必翻转投影矩阵的Y坐标，在这种情况下，可以将Pointlight的透视投影矩阵分派到您的GLSL着色器，而无需按（1，-1，1）缩放它，因为我正在使用没有翻转的Y坐标的纹理，我认为只有在使用翻转的纹理的Y坐标时，才应该翻转点光源投影矩阵的Y坐标，这样才能获得正确的全向阴影贴图效果。

最后，我将在CPU / GPU端保留全向阴影映射算法的最终版本。在CPU方面，我将解释为每个立方体贴图的面孔计算正确的阴影贴图所必须执行的每个步骤。另一方面，在GPU方面，我将在我的主要片段着色器中解释深度程序的顶点/片段着色器和全向阴影映射功能，以帮助可能正在学习该技术的人，或解决对此算法的未来疑虑。 ：

中央处理器

  // Disable blending and enable front face culling.

  this.state.disable(gl.BLEND);

  this.state.enable(gl.CULL_FACE);
  this.state.cullFace(gl.FRONT);

  // Binds depth program

  program.bind(gl);

  // For each pointlight source do

  for (i = 0; i < lights.length; i++) {
    light = lights[i];

    // Get each pointlight's world position

    position = light.worldPosition();

    // Binds pointlight's depth framebuffer. Besides, in this function,
    // viewport's dimensions are set according to depth framebuffer's dimension.

    light.depthFramebuffer.bind(gl, this.state);

    // Updates point light's framebuffer in order to create it 
    // or if it's resolution have changed, it'll be created again.

    light.depthFramebuffer.update(gl);

    // Check in which cubemap's face we are ...

    for (j = 0; j < 6; j++) {
      switch (j) {
        case Cubemap.POSITIVE_X:
          target.set(1, 0, 0);
          up.set(0, -1, 0);
          break;
        case Cubemap.NEGATIVE_X:
          target.set(-1, 0, 0);
          up.set(0, -1, 0);
          break;
        case Cubemap.POSITIVE_Y:
          target.set(0, 1, 0);
          up.set(0, 0, 1);
          break;
        case Cubemap.NEGATIVE_Y:
          target.set(0, -1, 0);
          up.set(0, 0, -1);
          break;
        case Cubemap.POSITIVE_Z:
          target.set(0, 0, 1);
          up.set(0, -1, 0);
          break;
        case Cubemap.NEGATIVE_Z:
          target.set(0, 0, -1);
          up.set(0, -1, 0);
          break;
      }

      // Creates a view matrix using target and up vectors 
      // according to each face of pointlight's cubemap.

      view.lookAt(position, target.add(position.clone()), up);

      // Attaches cubemap's face to current framebuffer 
      // in order to record depth values in that direction.

      light.depthFramebuffer.texture.attach(gl, j);

      // Clears color & depth buffers of your current framebuffer

      this.clear();

      // Render each shadow caster mesh using your depth program

      for (k = 0; k < meshes.length; k++)
        this._renderMeshDepth(program, meshes[k], view, light.projection);
    }
  }

在renderMeshDepth函数上，我已经：

  // Computes pointlight's model-view matrix 

  modelView.mul(view, mesh.world);

  // Dispatch each matrix to the GLSL depth program

  program.loadUniformMatrix(gl, 'uModelView', modelView);
  program.loadUniformMatrix(gl, 'uProjection', projection);

  // Renders a mesh using vertex buffer objects (VBO)

  mesh.render(gl, program.attributes, this.state, this.extensions);

显卡

深度程序顶点着色器：

precision highp float;

attribute vec3 position;

uniform mat4 uModelView;
uniform mat4 uProjection;

void main() {
  gl_Position = uProjection * uModelView * vec4(position, 1.0);
}

深度程序片段着色器：

precision highp float;

// The pack function distributes fragment's depth precision storing 
// it throughout (R,G,B,A) color channels and not just R color channel 
// as usual in shadow mapping algorithms. This is because I'm working
// with 8-bit textures and one color channel hasn't enough precision 
// to store a depth value.

vec4 pack(const in float depth) {
  const vec4 bitShift = vec4(255.0 * 255.0 * 255.0, 255.0 * 255.0, 255.0, 1.0);
  const vec4 bitMask = vec4(0.0, 1.0 / 255.0, 1.0 / 255.0, 1.0 / 255.0);

  vec4 res = fract(depth * bitShift);
  res -= res.xxyz * bitMask;

  return res;
}

void main() {
  // Packs normalized fragment's Z-Coordinate which is in [0,1] interval.

  gl_FragColor = pack(gl_FragCoord.z);
}

我的主要片段着色器中的全方位阴影映射功能：

// Unpacks fragment's Z-Coordinate which was packed 
// on the depth program's fragment shader.

float unpack(in vec4 color) {
   const vec4 bitShift = vec4(1.0 / (255.0 * 255.0 * 255.0), 1.0 / (255.0 * 255.0), 1.0 / 255.0, 1.0);
   return dot(color, bitShift);
}

// Computes Omnidirectional Shadow Mapping technique using a samplerCube
// vec3 lightPosition is your pointlight's position in world coordinates.
// vec3 vPosition is your vertex's position in world coordinates, in code
// I mean this -> vPosition = vec3(uModel * vec4(position, 1.0));
// where uModel is your World/Model matrix.

float omnidirectionalShadow(in vec3 lightPosition, in float bias, in float darkness, in samplerCube sampler) {
    vec3 direction = vPosition - lightPosition;
    float vertexDepth = clamp(length(direction), 0.0, 1.0);
    float shadowMapDepth = unpack(textureCube(sampler, direction)) + bias;

    return (vertexDepth > shadowMapDepth) ? darkness : 1.0;
}

这是算法的最终渲染

玩得开心编码美丽的图形，祝您好运:)

CZ