Opengl es 2.0中带有立方体贴图的阴影贴图

我是OpenGL ES的新手，我正在尝试为当前场景添加一些阴影。我决定在立方体贴图的帮助下做这件事。我使用的是OpenGL es 2.0，所以几何着色器或gl_FragDepth变量对我来说不可用(http://www.cg.tuwien.ac.at/courses/Realtime/repetitorium/2010/OmnidirShadows.pdf)事实证明非常有用。基本上我依赖这个链接的文档。

但我的代码有问题，因为在渲染的场景中，每个像素都在阴影下。我认为这个问题可以在我的着色器中找到，但我将所有相关代码粘贴到这里，以清楚地看到所有内容。

设置帧缓冲区并创建立方体映射：

GLuint FBO;
GLuint cubeTexture;
glGenFramebuffers(1, &FBO);
glBindFramebuffer(GL_FRAMEBUFFER, FBO);
// Depth texture
glGenTextures(1, &cubeTexture);
glBindTexture(GL_TEXTURE_CUBE_MAP, cubeTexture);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
//glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE); // no GL_TEXTURE_WRAP_R
// right, left, top, bottom, front, back
for (int face = 0; face < 6; ++face) {
// create space for the textures, content need not to be specified (last parameter is 0)
glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + face, 0, GL_DEPTH_COMPONENT16, 1024, 768, 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0);
}
glBindTexture(GL_TEXTURE_CUBE_MAP, 0);
glBindFramebuffer(GL_FRAMEBUFFER, 0);

在Display函数中，我尝试实现6个渲染过程来填充阴影贴图(立方体的6条边)。

渲染：

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClearDepthf(1.0f);
glm::vec3 camPos = ... // position of the camera, it is in world space
glm::vec4 lightPos = ... // position of the light source, it is in world space
// 1. render into texture
float zNear = 0.1f;
float zFar = 100.0f;
// or should I use ortho instead of perspective?
glm::mat4 projMatrix = glm::perspective(90.0f, (float)esContext->width / esContext->height, zNear, zFar);
// The 6 cameras have to be placed to the light source and they need the proper view matrices 
glm::mat4 cubeMapMatrices[6]; // contains six basic and defined rotation matrices for the six directions 
cubeMapMatrices[0] = glm::make_mat4(rotPositiveX);
cubeMapMatrices[1] = glm::make_mat4(rotNegativeX);
cubeMapMatrices[2] = glm::make_mat4(rotPositiveY);
cubeMapMatrices[3] = glm::make_mat4(rotNegativeY);
cubeMapMatrices[4] = glm::make_mat4(rotPositiveZ);
cubeMapMatrices[5] = glm::make_mat4(rotNegativeZ);
glm::vec4 translation = lightPos;
glBindTexture(GL_TEXTURE_CUBE_MAP, cubeTexture);
glBindFramebuffer(GL_FRAMEBUFFER, FBO);
for (int face = 0; face < 6; ++face) {
glClear(GL_DEPTH_BUFFER_BIT); // do I need this here?
cubeMapMatrices[face][3] = translation; // the translation part is the same for all
cubeMapMatrices[face] = projMatrix * cubeMapMatrices[face]; // now it's an mvp matrix
glUniformMatrix4fv(cubeProjectionMatrixID, 1, GL_FALSE, glm::value_ptr(cubeMapMatrices[face]));
// Attach depth cubemap texture to FBO's depth attachment point
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_CUBE_MAP_POSITIVE_X + face, cubeTexture, 0);
int err = glCheckFramebufferStatus(GL_FRAMEBUFFER);
if (err != GL_FRAMEBUFFER_COMPLETE) {
std::cout << "Framebuffer error, status: " << err << std::endl;
}
RenderScene(); // do the drawing 
}
glBindFramebuffer(GL_FRAMEBUFFER, 0);
// 2. render into screen
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
RenderScene(); // do the drawing
// swap the buffers

所以不同的着色器来了。我有一个顶点着色器和一个片段着色器用于深度计算，一个顶点着色和一个碎片着色器用于屏幕渲染。我的问题是，我不知道如何写入立方体映射，如果帧缓冲区正在使用，那么gl_Position会决定给定立方体面的坐标吗？

用于深度计算的顶点着色器：

in vec3 vPosition;
uniform mat4 mModel;
uniform mat4 mCubeProjection;
uniform vec4 vLight;
out vec4 vFrag Position; // world space
out vec4 vLightPosition; // mvp transformed
void main()
{
vec4 position = vec4(vPosition, 1.0);
vFragPosition  = mModel* position;
vLightPosition = vLight;
gl_Position = mCubeProjection * vFragPosition;
}

用于深度计算的片段着色器：

in vec4 vFragPosition; // world space
in vec4 vLightPosition; // world space
out float depthValue;
void main()
{
depthValue = distance(vFragPosition.xyz, vLightPosition.xyz); // need normalization?
}

用于渲染到屏幕的顶点着色器：

uniform mat4 mModel;
uniform mat4 mView;
uniform mat4 mProjection;
uniform vec4 vLight; // it is in world space
out vec3 lw; // light position in world space
out vec3 pw; // pixel position in world space
void main()
{
vec4 position = vec4(vPosition, 1.0);
lw = vLight.xyz;
pw = (mModel* position).xyz;
gl_Position  = mProjection* mView * mModel* position;
}

用于渲染到屏幕的片段着色器：

in vec3 lw;
in vec3 pw;
uniform samplerCube cubeMap;
out vec4 outputColor;
void main()
{
vec3 lookup = pw - lw;
float smValue = texture(cubeMap, lookup).r; // retrieves texels from a texture (d, d, d, 1.0)
float distance = length(lookup); // dist from the fragment to the light
float eps = 0.1;
float shadowVal = 1.0;
if (smValue + eps < distance) {
shadowVal = 0.1; // in shadow
}
// here comes the lighting stuff
// ...
outputColor =  outputColor * shadowVal;
}

因此，问题再次出现，每个像素都处于阴影之下。从代码中，我排除了一些到着色器的统一过程，但它们还可以。你能给我一个建议吗？我应该在代码中修复什么？我的着色器(尤其是第一次)正确吗？我是否正确设置了立方体贴图的变换？非常感谢。

p.S：这是我在这里的第一个问题，我希望它足够清楚，并满足正确张贴问题的要求。