c++ - 从深度纹理采样总是结果为 0

Question

我正在尝试使用 opengl 和定向光实现阴影贴图。

我已确认深度纹理已正确渲染，如下所示:

为了进行视觉检查，我还输出了世界空间坐标，转换为光透视:

又一次，似乎没问题。

但是，当我对深度纹理进行采样时，使用:

vec3 coord = vec3(shadowCoords.xy,shadowCoords.z/shadowCoords.w);
float depth = texture( shadowMap, coord);

我发现比较总是失败。如果我将 uniform sampler2DShadow shadowMap; 更改为 uniform sampler2D shadowMap;，并使用 texture(shadowMap, coord.xy).r 直接对纹理进行采样, 通过将此结果输出到屏幕，我发现采样值始终为零。

我像这样创建了深度纹理:

glGenTextures(1, &m_DepthTexture);
glBindTexture(GL_TEXTURE_2D, m_DepthTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT16, width, height, 0, GL_DEPTH_COMPONENT, GL_FLOAT, NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_FUNC, GL_LEQUAL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_COMPARE_REF_TO_TEXTURE);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, m_DepthTexture, 0);

我的着色器代码如下(顶点):

#version 430
// Some drivers require the following
precision highp float;
layout (location = 0)in vec3 MSVertex;
layout (location = 4)in vec2 MSTexCoord;

out xferBlock
{
    vec3 VSVertex;
    vec2 VSTexCoord;
} outdata;

void main()
{
    outdata.VSVertex = MSVertex;
    outdata.VSTexCoord = MSTexCoord;
    gl_Position = vec4(MSVertex,1.0);
}

和片段着色器:

#version 430 core
// Some drivers require the following
precision highp float;

layout (location = 0) uniform sampler2D positionMap;
layout (location = 1) uniform sampler2D normalMap;
layout (location = 2) uniform sampler2D colourMap;
layout (location = 3) uniform sampler2D specularMap;
layout (location = 4) uniform sampler2DShadow shadowMap;

struct DirLightData
{
    vec4 colour;
    float intensity;
    vec4 direction;
};
uniform mat4 ShadowTransform;
uniform DirLightData dirLight;
out vec4 colour;
uniform vec3 WSCamPos;
in xferBlock
{
    vec3 VSVertex;
    vec2 VSTexCoord;
} indata;

vec3 computeLight(vec3 Ldirection, vec3 Vdirection, vec3 Lcolour, vec3 normal, float Lintensity, float specular)
{
    vec3 diffCol = Lcolour * max(0.0,dot(normalize(normal),-Ldirection));
    vec3 reflectVec = normalize(reflect(Ldirection,normal));
    float specFactor = max(dot(reflectVec,Vdirection),0);
    float specPow = pow(specFactor,specular*255.0);
    vec3 specCol = Lcolour * specPow;
    return (diffCol+specCol)*Lintensity;;
}
float computeOcclusion(vec4 shadowCoords)
{
    float vis = 1.0;
    vec3 coord = vec3(shadowCoords.xyz/shadowCoords.w);
    float depth = texture( shadowMap, vec3(coord.xy,coord.z+0.05));
    if (  depth < coord.z);
    {
        vis = 0.5;
    }
    return vis;
}
void main()
{
    vec4 pcolour = texture(positionMap, indata.VSTexCoord).rgba;
    vec4 ncolour = texture(normalMap, indata.VSTexCoord).rgba;
    vec4 dcolour = texture(colourMap, indata.VSTexCoord).rgba;
    vec4 scolour = texture(specularMap, indata.VSTexCoord).rgba;

    vec4 shadowCoord = ShadowTransform * pcolour;
    float visibility = computeOcclusion( shadowCoord );
    //float depth = texture(shadowMap, shadowCoord.xy).z;
    vec3 vToEye = WSCamPos - pcolour.xyz;
    vToEye = normalize(vToEye);
    vec3 outColour = vec3(0.0,0.0,0.0);

    outColour = computeLight(dirLight.direction.xyz,vToEye,dirLight.colour.rgb,ncolour.rgb,dirLight.intensity,scolour.r);
    colour = vec4(visibility*(dcolour.rgb*outColour),1.0);

}

谁能找出哪里出了问题？

Answer 1

事实证明，我的采样返回了正确的值。

真正的问题是由于在渲染深度贴图时剔除几何体的背面以及错误地处理深度纹理采样返回值而导致的非常细粒度的阴影痤疮。

我将采样函数更改为:

float computeOcclusion(vec4 shadowCoords)
{
    vec3 coord = vec3(shadowCoords.xyz/shadowCoords.w);
    float depth = texture( shadowMap, vec3(coord.xy,coord.z+0.001));
    return depth;
}

并更改了我的深度渲染 gl 客户端代码以包括:

glCullFace(GL_FRONT); 

在将几何图形渲染到 shadowMap 之前。

完成后，我得到了以下结果:

还有一些彼得平移问题，但这是我可以单独处理的问题。