Question

我正在尝试在GLSL 4.10版中实现大气散射。我正在调整Shadertoy着色器https://www.shadertoy.com/view/lslXDr中的着色器。我的程序中的氛围是从行星球体的缩放版本创建的。

我的实际散射方程有效，但对于大多数摄像机位置，大气的内半径与球体的外半径不对齐。我知道这是从大气层的半径大于行星球体，但我似乎无法将其缩小。

我的问题最好在这里说明。该模型在这些图片中放大。可以看出，大气内半径与行星半径（深蓝色球体）不匹配。

此处模型被缩放和翻译。气氛偏离了摄像机的中心，内部的气氛仍然没有与行星对齐。

这是顶点着色器，它实质上是一个直通着色器

#version 410

in vec4 vPosition;
in vec3 vNormal;

out vec3 fPosition;
out mat3 m;

uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;

void main()
{   
    fPosition = vec3(vPosition);
    m = mat3(model);

    gl_Position = projection*view*model*vPosition;
}

片段着色器。

#version 410

uniform float time;
uniform vec3 camPosition;
uniform float fInnerRadius;
uniform float fOuterRadius;

in vec3 fPosition;
in mat3 m;

out vec4 FragColor;

const float PI = 3.14159265359;
const float degToRad = PI / 180.0;
const float MAX = 10000.0;

float K_R = 0.166;
const float K_M = 0.0025;
const float E = 14.3;
const vec3 C_R = vec3(0.3, 0.7, 1.0);
const float G_M = -0.85;

float SCALE_H = 4.0 / (fOuterRadius - fInnerRadius);
float SCALE_L = 1.0 / (fOuterRadius - fInnerRadius);

const int numOutScatter = 10;
const float fNumOutScatter = 10.0;
const int numInScatter = 10;
const float fNumInScatter = 10.0;

vec3 rayDirection(vec3 camPosition) {
    vec3 ray = m*fPosition - camPosition;
    float far = length(ray);
    return ray /= far;
}

vec2 rayIntersection(vec3 p, vec3 dir, float radius ) {
    float b = dot( p, dir );
    float c = dot( p, p ) - radius * radius;

    float d = b * b - c;
    if ( d < 0.0 ) {
        return vec2( MAX, -MAX );
    }
    d = sqrt( d );

    float near = -b - d;
    float far = -b + d;

    return vec2(near, far);
 }

// Mie
// g : ( -0.75, -0.999 )
//      3 * ( 1 - g^2 )               1 + c^2
// F = ----------------- * -------------------------------
//      2 * ( 2 + g^2 )     ( 1 + g^2 - 2 * g * c )^(3/2)
float miePhase( float g, float c, float cc ) {
    float gg = g * g;

    float a = ( 1.0 - gg ) * ( 1.0 + cc );

    float b = 1.0 + gg - 2.0 * g * c;
    b *= sqrt( b );
    b *= 2.0 + gg;  

    return 1.5 * a / b;
}

// Reyleigh
// g : 0
// F = 3/4 * ( 1 + c^2 )
float rayleighPhase( float cc ) {
    return 0.75 * ( 1.0 + cc );
}


float density(vec3 p) {
    return exp(-(length(p) - fInnerRadius) * SCALE_H);
}

float optic(vec3 p, vec3 q) {
    vec3 step = (q - p) / fNumOutScatter;
    vec3 v = p + step * 0.5;

    float sum = 0.0;
    for(int i = 0; i < numOutScatter; i++) {
        sum += density(v);
        v += step;
    }
    sum *= length(step)*SCALE_L;
    return sum;
}

vec3 inScatter(vec3 o, vec3 dir, vec2 e, vec3 l) {
    float len = (e.y - e.x) / fNumInScatter;
    vec3 step = dir * len;
    vec3 p = o + dir * e.x;
    vec3 v = p + dir * (len * 0.5);

    vec3 sum = vec3(0.0);
    for(int i = 0; i < numInScatter; i++) {
        vec2 f = rayIntersection(v, l, fOuterRadius);
        vec3 u = v + l * f.y;
        float n = (optic(p, v) + optic(v, u))*(PI * 4.0);
        sum += density(v)* exp(-n * ( K_R * C_R + K_M ));
        v += step;
    }
    sum *= len * SCALE_L;
    float c = dot(dir, -l);
    float cc = c * c;
    return sum * ( K_R * C_R * rayleighPhase( cc ) + K_M * miePhase( G_M, c, cc ) ) * E;
}

void main (void)
{
    vec3 dir = rayDirection(vec3(camPosition.x, 0.0, camPosition.z));
    vec3 eye = vec3(camPosition.x, 0.0, camPosition.z);

    vec3 l = normalize(vec3(0.0, 0.0, 1.0));

    vec2 e = rayIntersection(eye, dir, fOuterRadius);
    if ( e.x > e.y ) {
        discard;
    }
    vec2 f = rayIntersection(eye, dir, fInnerRadius);
    e.y = min(e.y, f.x);

    vec3 I = inScatter(eye, dir, e, l);

    FragColor = vec4(I, 1.0);
}

如果需要，这里是吸引大气的代码。绘制行星的代码与scaleFactor具有基本相同的转换。

void drawAtmosphere()
{
    glUseProgram(atmosphereShader);

    v = getViewMatrix();
    vec3 Position = getCameraPosition();

    float scaleFactor = 1.25;
    m = multiplymat4(translate(0.0, 0.0, -10), scale(fScale*scaleFactor));
    float fOuter = (fScale*scaleFactor);
    float fInner = fScale;

    glUniform1f(glGetUniformLocation(atmosphereShader, "fInnerRadius"), fInner);
    glUniform1f(glGetUniformLocation(atmosphereShader, "fOuterRadius"), fOuter);
    glUniform3f(glGetUniformLocation(atmosphereShader, "camPosition"), Position.x, Position.y, Position.z);
    glUniform1f(glGetUniformLocation(atmosphereShader, "time"), glfwGetTime());

    initMVP(atmosphereShader, m, v);

    glBindVertexArray (atmosphereVAO);
    glDrawArrays( GL_TRIANGLES, 0, planet.vertexNumber);
    glBindVertexArray(0);

}

任何帮助，或任何可以指引我朝正确方向发展的事情都表示赞赏。

Answer 1

发现问题是由于摄像机位置计算不正确而未考虑对象的模型空间造成的。我上传了代码here的精简版。

希望这有助于任何试图实施肖恩·奥尼尔气氛代码的人。

GLSL大气散射不随变换而变化

1 个答案: