GLSL简易光线追踪代码编译通过但输出全黑问题求解

我正在学习基于GLSL的简易光线追踪技术，参考了Inigo Quilez的教程。编写的代码编译无任何报错，但无法输出预期的球体渲染效果，最终输出图像完全为黑色，暂无法定位问题根源，寻求解决方案。

问题代码 #

#ifdef GL_ES
precision highp float;
#endif

uniform vec3 unResolution;
uniform float time;
uniform sampler2D tex0;
uniform sampler2D tex1;
uniform sampler2D fft;
uniform vec4 unPar;
uniform vec4 unPos;
uniform vec4 unBeatBassFFT;

float iSphere( in vec3 ro, in vec3 rd, in vec4 sph )
{
    // 球心在原点的求交公式
    // |ro|^2 + t^2 + 2<ro,rd>t - r^2 = 0
    vec3 oc = ro - sph.xyz;
    float b = 2.0*dot( oc,rd );
    float c = 2.0*dot( oc,oc );
    float h = b*b - sph.w*sph.w;
    if ( h<0.0 ) return -1.0;
    float t = (-b - sqrt(h))/2.0;
    return t; 
}
vec3 nSphere( in vec3 pos, in vec4 sph )
{
    return (pos-sph.xyz)/sph.w;
}

float iPlane( in vec3 ro, in vec3 rd )
{
    return -ro.y/rd.y;
}

vec3 nPlane( in vec3 pos ) 
{
    return vec3(0.0,1.0,0.0);
}

vec4 sph1 = vec4( 0.0, 1.0, 0.0, 1.0 );
float intersect( in vec3 ro, in vec3 rd, out float resT )
{
    resT = 1000.0;
    float id = -1.0;
    float tsph = iSphere( ro, rd, sph1 );
    float tpla = iPlane( ro, rd );
    if ( tsph>0.0 )
    {
        id = 1.0;
        resT = tsph;
    }
    if (tpla>0.0 && tpla<resT)
    {
        id = 2.0;
        resT = tpla;
    }
    return id;
}

void main(void) 
{
    vec3 light = normalize( vec3( 0.57703 ));
    vec2 uv = (gl_FragCoord.xy/unResolution.xy)*vec2(1.78,1.0);

    //sph1.x = 0.5*cos(time);
    //sph1.z = 0.5*sin(time);

    vec3 ro = vec3( 0.0, 0.5, 3.0 );
    vec3 rd = normalize( vec3( (-1.0+2.0+uv)*vec2(1.78,1.0), 1.0 ) );

    float t;
    float id = intersect( ro, rd, t );

    vec3 col = vec3(0.0);
    if( id>0.5 && id<1.5 )
    {
        vec3 pos = ro + t*rd; 
        vec3 nor = nSphere( pos, sph1 );
        float dif = clamp(dot( nor, light ), 0.0, 1.0);
        float ao = 0.5 + 0.5*nor.y;
        float amb = 0.5 + 0.5*nor.y;
        col = vec3( 0.9, 0.8, 0.6 )*dif+amb*vec3(0.5,0.6,0.7);
    }
    else if( id>1.5 )
    {
        vec3 pos = ro + t*rd;
        vec3 nor = nPlane( pos );
        float dif = clamp( dot(nor, light), 0.0, 1.0 );
        float amb = smoothstep( 0.0, 2.0*sph1.w, length(pos.xz-sph1.xz) );
        col = vec3(amb*0.7);
        //col = vec3( 1.0, 0.0, 0.0 )*dif + amb*vec3(0.5,0.6,0.7);
    }
    col = sqrt(col);

    gl_FragColor = vec4(col,1.0);
}

修复后可运行代码 #

目前球体的着色还未完全优化，但代码已经可以正常运行：

#ifdef GL_ES
precision highp float;
#endif

uniform vec2 resolution;
#define unResolution resolution
uniform float time;
uniform sampler2D tex0;
uniform sampler2D tex1;
uniform sampler2D fft;
uniform vec4 unPar;
uniform vec4 unPos;
uniform vec4 unBeatBassFFT;

float iSphere( in vec3 ro, in vec3 rd, in vec4 sph )
{
    // 球心在原点的求交公式
    // |ro|^2 + t^2 + 2<ro,rd>t - r^2 = 0
    vec3 oc = ro - sph.xyz;
    float b = 2.0*dot( oc,rd );
    float c = 2.0*dot( oc,oc );
    float h = b*b - sph.w*sph.w;
    if ( h<0.0 ) return -1.0;
    float t = (-b - sqrt(h))/2.0;
    return t; 
}
vec3 nSphere( in vec3 pos, in vec4 sph )
{
    return (pos-sph.xyz)/sph.w;
}

float iPlane( in vec3 ro, in vec3 rd )
{
    return -ro.y/rd.y;
}

vec3 nPlane( in vec3 pos ) 
{
    return vec3(0.0,1.0,0.0);
}

vec4 sph1 = vec4( 0.0, 1.0, 0.0, 1.0 );
float intersect( in vec3 ro, in vec3 rd, out float resT )
{
    resT = 1000.0;
    float id = -1.0;
    float tsph = iSphere( ro, rd, sph1 );
    float tpla = iPlane( ro, rd );
    if ( tsph>0.0 )
    {
        id = 1.0;
        resT = tsph;
    }
    if (tpla>0.0 && tpla<resT)
    {
        id = 2.0;
        resT = tpla;
    }
    return id;
}

void main(void) 
{
    vec3 light = normalize( vec3( 0.57703 ));
    vec2 uv = (gl_FragCoord.xy/unResolution.xy);
    vec2 p = uv * 2.0 - 1.0;
    p.x*=unResolution.x/unResolution.y;

    //sph1.x = 0.5*cos(time);
    //sph1.z = 0.5*sin(time);

    vec3 ro = vec3( 0.0, 1.0, -1.0 );
    vec3 rd = normalize( vec3(p,0.2) );

    float t;
    float id = intersect( ro, rd, t );

    vec3 col = vec3(0.0);
    if( id>0.5 && id<1.5 )
    {
        vec3 pos = ro + t*rd; 
        vec3 nor = nSphere( pos, sph1 );
        float dif = clamp(dot( nor, light ), 0.0, 1.0);
        float ao = 0.1 + 0.5*nor.y;
        float amb = 0.5 + 0.5*nor.y;
        col = vec3( 1.0, 0.0, 0.0 )*dif + amb*vec3(0.5,0.6,0.7);
    }
    else if( id>1.5 )
    {
        vec3 pos = ro + t*rd;
        vec3 nor = nPlane( pos );
        float dif = clamp( dot(nor, light), 0.5, 1.0 );
        float amb = smoothstep( 0.5, 2.0*sph1.w, length(pos.xz-sph1.xz) );
        col = vec3(amb*0.9);
        //col = vec3( 1.0, 0.0, 0.0 )*dif + amb*vec3(0.5,0.6,0.7);
    }
    col = sqrt(col);

    gl_FragColor = vec4(col,1.0);
}

内容的提问来源于stack exchange，提问作者user7428090