大气散射着色器中的伪像

Question

我正在尝试实现此处的大气散射着色器：https://lightshaderdevlog.wordpress.com/

我已经在GLSL中实现了算法并且它看起来不错，但由于某种原因，黑色工件呈现： https://imgur.com/a/CDrLt

看起来只有在查看特定摄像机角度和那些特定顶点时才会出现伪影。

这是我的代码：

顶点着色器

 #version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec2 aTexCoord;
layout (location = 2) in vec3 aNormal;

// Vertex
uniform vec3 star_pos;      // point light source position (Sun) [GCS]
uniform vec3 planet_pos;    // planet center position [GCS]
uniform float overglow;     // cos(angle) of terminator propagation\

uniform mat4 modelView;
uniform mat4 projection;
uniform float og_farPlaneDistance;
uniform float u_logarithmicDepthConstant;

out vec3 lpos;          // point light source position (Sun) [camera space]
out vec3 ppos;          // planet center position [camera space]
out vec3 pixel_pos;     // fragment position [camera space]
out vec3 pixel_nor;     // fragment surface normal
out vec2 pixel_txy;     // fragment surface texture coord
out float angleIncidence;
out vec4 colAtmosphere;
out vec3 lightDir;

const float PI = 3.14159265f;
const float transitionWidth = 0.1f;
const float fresnelExponent = 20f;


vec4 modelToClipCoordinates(vec4 position, mat4 modelViewPerspectiveMatrix, float depthConstant, float farPlaneDistance){
    vec4 clip = modelViewPerspectiveMatrix * position;

    clip.z = ((2.0 * log(depthConstant * clip.z + 1.0) / log(depthConstant * farPlaneDistance + 1.0)) - 1.0) * clip.w;
    return clip;
}

void main()
    {


    lpos=(modelView*vec4(star_pos,1.0)).xyz;
    ppos=(modelView*vec4(planet_pos,1.0)).xyz;

    lightDir =normalize(lpos-ppos);

    pixel_pos=vec3(modelView*vec4(aPos,1.0));
    pixel_nor=mat3(transpose(inverse(modelView))) * aNormal;
    pixel_txy=aTexCoord;

    vec3 viewDir = normalize(-pixel_pos);


    angleIncidence = acos(dot(lightDir, pixel_nor)) / PI;

    float shadeFactor = 0.1 * (1 - angleIncidence) + 0.9 * (1 - (clamp(angleIncidence, 0.5, 0.5 + transitionWidth) - 0.5) / transitionWidth);

    float angleToViewer = sin(acos(dot(pixel_nor, viewDir)));

    float perspectiveFactor = 0.3 + 0.2 * pow(angleToViewer, fresnelExponent) + 0.5 * pow(angleToViewer, fresnelExponent * 20);

    colAtmosphere = vec4(perspectiveFactor*shadeFactor);

    gl_Position = modelToClipCoordinates(vec4(aPos, 1.0), projection * modelView, u_logarithmicDepthConstant, og_farPlaneDistance);
    }

片段着色器

#version 330 core
out vec4 FragColor;

// Fragment
uniform vec3 star_pos;      // point light source position (Sun) [GCS]
uniform vec3 planet_pos;    // planet center position [GCS]
//uniform vec3 planet_r;        // planet radius
uniform float overglow;     // cos(angle) of terminator propagation

uniform sampler2D diffuseTex;
uniform sampler2D txratm;
in vec3 lpos;           // point light source position (Sun) [camera space]
in vec3 ppos;           // planet center position [camera space]
in vec3 pixel_pos;      // fragment position [camera space]
in vec3 pixel_nor;      // fragment surface normal
in vec2 pixel_txy;      // fragment surface texture coord
in float angleIncidence;
in vec4 colAtmosphere;
in vec3 lightDir;

void main()
    {
    float li;
    vec3 c,lt_dir,c0;
    vec4 c1;
    lt_dir=lightDir; // vector from fragment to point light source
    li=dot(pixel_nor,lt_dir)+overglow;
    if (li<0.0) {
        li=0.0;
    }
    if (li>1.0) {
        li=1.0;
    }

    vec2 gradientLevel = vec2(angleIncidence, 0.5);
    c1 = colAtmosphere * texture(txratm, gradientLevel) * 1.4;

    c0=texture(diffuseTex,pixel_txy).rgb * li;

    c = c1.a * c1.rgb + (vec3(1.0, 1.0, 1.0) - c1.a) * c0;;


    FragColor=vec4(c,1.0);
//  gl_FragDepth=0.0;
    }

Answer 1

我已经解决了我的问题。问题出在顶点着色器的acos函数中。由于某种原因，正常和光线之间的点积和视图方向的值大于1（我不确定为什么会发生这种情况，因为所有这些值都应该标准化）。

通过检查点积返回的值，并选择它与值1之间的最小值，可以简单地解决这个问题。

这是更新的顶点着色器代码：

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec2 aTexCoord;
layout (location = 2) in vec3 aNormal;

// Vertex
uniform vec3 star_pos;      // point light source position (Sun) [GCS]
uniform vec3 planet_pos;    // planet center position [GCS]
uniform float overglow;     // cos(angle) of terminator propagation\

uniform mat4 modelView;
uniform mat4 projection;
uniform float og_farPlaneDistance;
uniform float u_logarithmicDepthConstant;

out vec3 lpos;          // point light source position (Sun) [camera space]
out vec3 ppos;          // planet center position [camera space]
out vec3 pixel_pos;     // fragment position [camera space]
out vec3 pixel_nor;     // fragment surface normal
out vec2 pixel_txy;     // fragment surface texture coord
out float angleIncidence;
out vec4 colAtmosphere; //color of the atmosphere
out vec3 lightDir; //direction of light in camera space

const float PI = 3.14159265;
const float transitionWidth = 0.1; //How prominent the atmosphere is
const float fresnelExponent = 20;


vec4 modelToClipCoordinates(vec4 position, mat4 modelViewPerspectiveMatrix, float depthConstant, float farPlaneDistance){
    vec4 clip = modelViewPerspectiveMatrix * position;

    clip.z = ((2.0 * log(depthConstant * clip.z + 1.0) / log(depthConstant * farPlaneDistance + 1.0)) - 1.0) * clip.w;
    return clip;
}

void main()
    {


    lpos=(modelView*vec4(star_pos,1.0)).xyz;
    ppos=(modelView*vec4(planet_pos,1.0)).xyz;

    lightDir =normalize(lpos-ppos);

    pixel_pos=vec3(modelView*vec4(aPos,1.0));
    pixel_nor=normalize(mat3(transpose(inverse(modelView))) * aNormal);
    pixel_txy=aTexCoord;

    vec3 viewDir = normalize(-pixel_pos);

    float dotProd = dot(lightDir, pixel_nor);
    dotProd = min(dotProd,1.0);

    angleIncidence = acos(dotProd) / PI;

    float shadeFactor = 0.1 * (1 - angleIncidence) + 0.9 * (1 - (clamp(angleIncidence, 0.5, 0.5 + transitionWidth) - 0.5) / transitionWidth);

    float dotProd2 = dot(pixel_nor, viewDir);
    dotProd2 = min(dotProd2,1.0);

    float angleToViewer = sin(acos(dotProd2));

    float perspectiveFactor = 0.3 + 0.2 * pow(angleToViewer, fresnelExponent) + 0.5 * pow(angleToViewer, fresnelExponent * 20);

    colAtmosphere = vec4(perspectiveFactor*shadeFactor);

    gl_Position = modelToClipCoordinates(vec4(aPos, 1.0), projection * modelView, u_logarithmicDepthConstant, og_farPlaneDistance);
    }