具有深度立方体贴图的全向阴影贴图 [英] Omnidirectional shadow mapping with depth cubemap
问题描述
我正在使用全向点光源.我已经使用立方体贴图纹理作为6个帧缓冲区的颜色附加实现了阴影贴图，并在其每个像素中对光到片段的距离进行了编码.
现在，如果可能的话，我想以这种方式更改我的实现:
- 1)将深度立方体贴图纹理附加到我的帧缓冲区的深度缓冲区上，而不是颜色上.
- 2)仅渲染深度，请勿在此过程中书写颜色
- 3)在主遍中，从立方体贴图纹理读取深度，将其转换为距离，然后检查当前片段是否被灯光遮挡.
将立方体图的深度值转换回距离时出现我的问题.我使用光到碎片矢量(在世界空间中)在立方体贴图中获取我的深度值.在这一点上，我不知道正在使用六个面中的哪一个，也不知道什么2D纹理坐标与我正在读取的深度值相匹配.那么如何将深度值转换为距离呢?
以下是我的代码段，以说明:
深度纹理:
glGenTextures(1, &TextureHandle);
glBindTexture(GL_TEXTURE_CUBE_MAP, TextureHandle);
for (int i = 0; i < 6; ++i)
glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, 0, GL_DEPTH_COMPONENT,
Width, Height, 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
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);
帧缓冲区构造:
for (int i = 0; i < 6; ++i)
{
glGenFramebuffers(1, &FBO->FrameBufferID);
glBindFramebuffer(GL_FRAMEBUFFER, FBO->FrameBufferID);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT,
GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, TextureHandle, 0);
glDrawBuffer(GL_NONE);
}
我正在尝试为实现代码而编写的片段着色器:
float ComputeShadowFactor(samplerCubeShadow ShadowCubeMap, vec3 VertToLightWS)
{
float ShadowVec = texture(ShadowCubeMap, vec4(VertToLightWS, 1.0));
ShadowVec = DepthValueToDistance(ShadowVec);
if (ShadowVec * ShadowVec > dot(VertToLightWS, VertToLightWS))
return 1.0;
return 0.0;
}
DepthValueToDistance函数是我的实际问题.
因此，解决方案是将光到碎片矢量转换为深度值，而不是将从立方体贴图读取的深度转换为距离. /p>
这是修改后的着色器代码:
float VectorToDepthValue(vec3 Vec)
{
vec3 AbsVec = abs(Vec);
float LocalZcomp = max(AbsVec.x, max(AbsVec.y, AbsVec.z));
const float f = 2048.0;
const float n = 1.0;
float NormZComp = (f+n) / (f-n) - (2*f*n)/(f-n)/LocalZcomp;
return (NormZComp + 1.0) * 0.5;
}
float ComputeShadowFactor(samplerCubeShadow ShadowCubeMap, vec3 VertToLightWS)
{
float ShadowVec = texture(ShadowCubeMap, vec4(VertToLightWS, 1.0));
if (ShadowVec + 0.0001 > VectorToDepthValue(VertToLightWS))
return 1.0;
return 0.0;
}
关于VectorToDepthValue(vec3 Vec)的解释:
LocalZComp对应于给定的Vec的Z分量到匹配的立方图视锥中.实际上，它是Vec的最大组成部分(例如，如果Vec.y是最大的组成部分，我们将在立方体贴图的Y +或Y-面上查看).
如果您看这篇 wikipedia文章，您将在理解数学之后(我保留了它)以理解的正式形式)，只需将LocalZComp转换为归一化的Z值(在[-1..1]之间)，然后将其映射到[0..1]，即深度缓冲区的实际范围价值观. (假设您没有更改它). n和f是用于生成立方体贴图的视锥的近和远值.
ComputeShadowFactor然后只需将立方体贴图的深度值与从片段到光向量(此处命名为VertToLightWS)计算出的深度值进行比较，还添加一个小的深度偏差(问题中就没有了) ，如果片段没有被光遮挡，则返回1.
I'm working with omnidirectional point lights. I already implemented shadow mapping using a cubemap texture as color attachement of 6 framebuffers, and encoding the light-to-fragment distance in each pixel of it.
Now I would like, if this is possible, to change my implementation this way:
- 1) attach a depth cubemap texture to the depth buffer of my framebuffers, instead of colors.
- 2) render depth only, do not write color in this pass
- 3) in the main pass, read the depth from the cubemap texture, convert it to a distance, and check whether the current fragment is occluded by the light or not.
My problem comes when converting back a depth value from the cubemap into a distance. I use the light-to-fragment vector (in world space) to fetch my depth value in the cubemap. At this point, I don't know which of the six faces is being used, nor what 2D texture coordinates match the depth value I'm reading. Then how can I convert that depth value to a distance?
Here are snippets of my code to illustrate:
Depth texture:
glGenTextures(1, &TextureHandle);
glBindTexture(GL_TEXTURE_CUBE_MAP, TextureHandle);
for (int i = 0; i < 6; ++i)
glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, 0, GL_DEPTH_COMPONENT,
Width, Height, 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
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);
Framebuffers construction:
for (int i = 0; i < 6; ++i)
{
glGenFramebuffers(1, &FBO->FrameBufferID);
glBindFramebuffer(GL_FRAMEBUFFER, FBO->FrameBufferID);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT,
GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, TextureHandle, 0);
glDrawBuffer(GL_NONE);
}
The piece of fragment shader I'm trying to write to achieve my code:
float ComputeShadowFactor(samplerCubeShadow ShadowCubeMap, vec3 VertToLightWS)
{
float ShadowVec = texture(ShadowCubeMap, vec4(VertToLightWS, 1.0));
ShadowVec = DepthValueToDistance(ShadowVec);
if (ShadowVec * ShadowVec > dot(VertToLightWS, VertToLightWS))
return 1.0;
return 0.0;
}
The DepthValueToDistance function being my actual problem.
So, the solution was to convert the light-to-fragment vector to a depth value, instead of converting the depth read from the cubemap into a distance.
Here is the modified shader code:
float VectorToDepthValue(vec3 Vec)
{
vec3 AbsVec = abs(Vec);
float LocalZcomp = max(AbsVec.x, max(AbsVec.y, AbsVec.z));
const float f = 2048.0;
const float n = 1.0;
float NormZComp = (f+n) / (f-n) - (2*f*n)/(f-n)/LocalZcomp;
return (NormZComp + 1.0) * 0.5;
}
float ComputeShadowFactor(samplerCubeShadow ShadowCubeMap, vec3 VertToLightWS)
{
float ShadowVec = texture(ShadowCubeMap, vec4(VertToLightWS, 1.0));
if (ShadowVec + 0.0001 > VectorToDepthValue(VertToLightWS))
return 1.0;
return 0.0;
}
Explaination on VectorToDepthValue(vec3 Vec) :
LocalZComp corresponds to what would be the Z-component of the given Vec into the matching frustum of the cubemap. It's actually the largest component of Vec (for instance if Vec.y is the biggest component, we will look either on the Y+ or the Y- face of the cubemap).
If you look at this wikipedia article, you will understand the math just after (I kept it in a formal form for understanding), which simply convert the LocalZComp into a normalized Z value (between in [-1..1]) and then map it into [0..1] which is the actual range for depth buffer values. (assuming you didn't change it). n and f are the near and far values of the frustums used to generate the cubemap.
ComputeShadowFactor then just compare the depth value from the cubemap with the depth value computed from the fragment-to-light vector (named VertToLightWS here), also add a small depth bias (which was missing in the question), and returns 1 if the fragment is not occluded by the light.
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