Phong Lighting 在我的地形的某些部分偶尔会太亮（OpenGL）

Question

使用 Triangle_Strips 和高度图我制作了一个山区地形，并使用 3D 平面投影进行纹理处理。对于 3D 平面投影，我遵循以下链接的第 1.5 节。 https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch01.html

这是 Phong Lighting 之前的样子。 Unitl贴图，没问题。

https://imgur.com/3WZUiDR

这就是它在 Phong Lighting 之后的样子。请注意，我假设了定向光，所以我假设光的方向朝向 -y 轴方向。我设置为shader.setVec3("light.direction", 0.0f, -0.1f, 0.0f);

https://imgur.com/wPWtrHA

地形的某些部分突然变得更亮了，好像只有这些部分的光线才变强。

我检查了法线向量是否正确。所以我通过几何着色器将它们可视化。结果如下。

https://imgur.com/y9Ej8cU

如您所见，法线向量实际上是正确的。所以我的着色器程序一定有问题。这是代码。首先是顶点着色器。

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

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

float scale = 0.5;

out vec2 TexX;
out vec2 TexY;
out vec2 TexZ;
out vec3 blend_weights;
out vec3 FragPos;
out vec3 wNormal;

void main()
{
    FragPos = vec3(model * vec4(aPos, 1.0));    
    blend_weights = abs(aNormal.xyz);
    blend_weights = (blend_weights - 0.2) * 0.7;
    blend_weights = max(blend_weights, 0);
    blend_weights /= (blend_weights.x + blend_weights.y + blend_weights.z);

    TexX = aPos.yz * scale;
    TexY = aPos.zx * scale; 
    TexZ = aPos.xy * scale;

    wNormal = mat3(transpose(inverse(model))) * aNormal;

    gl_Position = projection * view * vec4(FragPos, 1.0);
}

这是我的片段着色器。

#version 330 core
out vec4 FragColor;

struct Material{

    //aka terrainTexture;
    sampler2D diffuse;
    sampler2D specular;
    float shininess;
};

struct Light {
    // Direction has to be in world coordinates.
    vec3 direction;
    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
};

uniform Light light;
uniform Material material;
uniform vec3 viewPos;

in vec3 FragPos;    //world Coordinate!
in vec2 TexX;
in vec2 TexY;
in vec2 TexZ;

in vec3 wNormal;

in vec3 blend_weights;

void main()
{
    vec4 ColorNoLighting = texture(material.diffuse, TexX)*blend_weights.x + texture(material.diffuse, TexY)*blend_weights.y + texture(material.diffuse, TexZ)*blend_weights.z;

    vec3 ambient = light.ambient * ColorNoLighting.xyz; 

    vec3 norm = normalize(wNormal);
    vec3 lightDir = normalize(-light.direction);
    float diff = max(dot(norm, lightDir), 0.0);
    vec3 diffuse = light.diffuse * diff * ColorNoLighting.xyz;

    vec3 viewDir = normalize(viewPos - FragPos);
    vec3 reflectDir = reflect(-lightDir, norm);
    float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);
    vec3 specular = light.specular * spec * ColorNoLighting.xyz;

    vec3 result = ambient + diffuse + specular;
    FragColor = vec4(result, 1.0);
}

最后，这就是我设置所有制服的方式。

shader.use();
shader.setInt("material.diffuse", 0);
shader.setInt("material.specular", 1);
shader.setVec3("light.direction", 0.0f, -0.1f, 0.0f);
shader.setVec3("viewPos", camera.Position);
shader.setVec3("light.ambient", 0.2f, 0.2f, 0.2f);
shader.setVec3("light.diffuse", 0.5f, 0.5f, 0.5f);
shader.setVec3("light.specular", 1.0f, 1.0f, 1.0f);
shader.setFloat("material.shininess", 32.0f);
shader.setMat4("model", model);
shader.setMat4("view", view);
shader.setMat4("projection", projection);

我不明白为什么我的地形的某些部分在 phong 照明后突然变得如此明亮。任何帮助，将不胜感激。提前致谢！

Answer 1

与 Phong 镜面高光相比，光的 Lambertian 漫反射分量较弱。

在您的着色器代码中，漫反射分量的强度由参数light.diffuse 设置：

float diff = max(dot(norm, lightDir), 0.0);
vec3 diffuse = light.diffuse * diff * ColorNoLighting.xyz;

高光成分的强度和大小分别由light.specular设置material.shininess：

float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);
vec3 specular = light.specular * spec * ColorNoLighting.xyz;

注意，如果 shininess 参数减小，镜面高光的大小会增加，但会变得更平滑。

更改参数以解决您的问题。

例如

shader.setVec3("light.diffuse", 1.0f, 1.0f, 1.0f);
shader.setVec3("light.specular", 0.5f, 0.5f, 0.5f);
shader.setFloat("material.shininess", 10.0f);

看例子，演示了参数的效果：

(function loadscene() {

var sliderScale = 100.0
var gl;
var canvas;
var vp_size;
var progDraw;
var bufTorus = {};

function render(deltaMS){

    var ambient = document.getElementById( "ambient" ).value / sliderScale;
    var diffuse = document.getElementById( "diffuse" ).value / sliderScale;
    var specular = document.getElementById( "specular" ).value / sliderScale;
    var shininess = Math.max(1, document.getElementById( "shininess" ).value / 2);
    document.getElementById( "ambient_val" ).innerHTML = ambient;
    document.getElementById( "diffuse_val" ).innerHTML = diffuse;
    document.getElementById( "specular_val" ).innerHTML = specular;
    document.getElementById( "shininess_val" ).innerHTML = shininess;

    Camera.create();
    Camera.vp = [canvas.width, canvas.height];
        
    gl.viewport( 0, 0, canvas.width, canvas.height );
    gl.enable( gl.DEPTH_TEST );
    gl.clearColor( 0.0, 0.0, 0.0, 1.0 );
    gl.clear( gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT );

    // set up draw shader
    ShaderProgram.Use( progDraw );
    ShaderProgram.SetUniformMat44( progDraw, "u_projectionMat44", Camera.Perspective() );
    ShaderProgram.SetUniformMat44( progDraw, "u_viewMat44", Camera.LookAt() );
    ShaderProgram.SetUniform3f( progDraw, "u_lightDir", [-1.0, -0.5, -2.0] )
    ShaderProgram.SetUniformFloat( progDraw, "u_ambient", ambient )
    ShaderProgram.SetUniformFloat( progDraw, "u_diffuse", diffuse )
    ShaderProgram.SetUniformFloat( progDraw, "u_specular", specular )
    ShaderProgram.SetUniformFloat( progDraw, "u_shininess", shininess )
    var modelMat = IdentityMat44()
    modelMat = RotateAxis( modelMat, CalcAng( deltaMS, 13.0 ), 0 );
    modelMat = RotateAxis( modelMat, CalcAng( deltaMS, 17.0 ), 1 );
    ShaderProgram.SetUniformMat44( progDraw, "u_modelMat44", modelMat );

    // draw scene
    VertexBuffer.Draw( bufTorus );

    requestAnimationFrame(render);
}

function initScene() {

    document.getElementById( "ambient" ).value = 0.2 * sliderScale;
    document.getElementById( "diffuse" ).value = 0.75 * sliderScale;
    document.getElementById( "specular" ).value = 0.75 * sliderScale;
    document.getElementById( "shininess" ).value = 20.0;
    
    canvas = document.getElementById( "phong-canvas");
    vp_size = [canvas.width, canvas.height];
    gl = canvas.getContext( "experimental-webgl" );
    if ( !gl )
      return;

    progDraw = ShaderProgram.Create( 
      [ { source : "draw-shader-vs", stage : gl.VERTEX_SHADER },
        { source : "draw-shader-fs", stage : gl.FRAGMENT_SHADER }
      ],
      [ "u_projectionMat44", "u_viewMat44", "u_modelMat44", 
        "u_lightDir", "u_ambient", "u_diffuse", "u_specular", "u_shininess", ] );
    progDraw.inPos = gl.getAttribLocation( progDraw, "inPos" );
    progDraw.inNV  = gl.getAttribLocation( progDraw, "inNV" );
    progDraw.inCol = gl.getAttribLocation( progDraw, "inCol" );
    if ( progDraw == 0 )
        return;

    // create torus
    var circum_size = 32, tube_size = 32;
    var rad_circum = 1.0;
    var rad_tube = 0.5;
    var torus_pts = [];
    var torus_nv = [];
    var torus_col = [];
    var torus_inx = [];
    var col = [1, 0.5, 0.0];
    for ( var i_c = 0; i_c < circum_size; ++ i_c ) {
        var center = [
            Math.cos(2 * Math.PI * i_c / circum_size),
            Math.sin(2 * Math.PI * i_c / circum_size) ]
        for ( var i_t = 0; i_t < tube_size; ++ i_t ) {
            var tubeX = Math.cos(2 * Math.PI * i_t / tube_size)
            var tubeY = Math.sin(2 * Math.PI * i_t / tube_size)
            var pt = [
                center[0] * ( rad_circum + tubeX * rad_tube ),
                center[1] * ( rad_circum + tubeX * rad_tube ),
                tubeY * rad_tube ]
            var nv = [ pt[0] - center[0] * rad_tube, pt[1] - center[1] * rad_tube, tubeY * rad_tube ]
            torus_pts.push( pt[0], pt[1], pt[2] );
            torus_nv.push( nv[0], nv[1], nv[2] );
            torus_col.push( col[0], col[1], col[2] );
            var i_cn = (i_c+1) % circum_size
            var i_tn = (i_t+1) % tube_size
            var i_c0 = i_c * tube_size; 
            var i_c1 = i_cn * tube_size; 
            torus_inx.push( i_c0+i_t, i_c0+i_tn, i_c1+i_t, i_c0+i_tn, i_c1+i_t, i_c1+i_tn )
        }
    }
    bufTorus = VertexBuffer.Create(
      [ { data : torus_pts, attrSize : 3, attrLoc : progDraw.inPos },
        { data : torus_nv,  attrSize : 3, attrLoc : progDraw.inNV },
        { data : torus_col, attrSize : 3, attrLoc : progDraw.inCol } ],
        torus_inx
    );

    window.onresize = resize;
    resize();
    requestAnimationFrame(render);
}

function resize() {
    //vp_size = [gl.drawingBufferWidth, gl.drawingBufferHeight];
    vp_size = [window.innerWidth, window.innerHeight]
    canvas.width = vp_size[0];
    canvas.height = vp_size[1];
}

function Fract( val ) { 
return val - Math.trunc( val );
}
function CalcAng( deltaMS, intervall ) {
return Fract( deltaMS / (1000*intervall) ) * 2.0 * Math.PI;
}
function CalcMove( deltaMS, intervall, range ) {
var pos = self.Fract( deltaMS / (1000*intervall) ) * 2.0
var pos = pos < 1.0 ? pos : (2.0-pos)
return range[0] + (range[1] - range[0]) * pos;
}    
function EllipticalPosition( a, b, angRag ) {
var a_b = a * a - b * b
var ea = (a_b <= 0) ? 0 : Math.sqrt( a_b );
var eb = (a_b >= 0) ? 0 : Math.sqrt( -a_b );
return [ a * Math.sin( angRag ) - ea, b * Math.cos( angRag ) - eb, 0 ];
}

function IdentityMat44() { return [1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1]; }

function RotateAxis(matA, angRad, axis) {
    var aMap = [ [1, 2], [2, 0], [0, 1] ];
    var a0 = aMap[axis][0], a1 = aMap[axis][1]; 
    var sinAng = Math.sin(angRad), cosAng = Math.cos(angRad);
    var matB = matA.slice(0);
    for ( var i = 0; i < 16; ++ i ) matB[i] = matA[i];
    for ( var i = 0; i < 3; ++ i ) {
        matB[a0*4+i] = matA[a0*4+i] * cosAng + matA[a1*4+i] * sinAng;
        matB[a1*4+i] = matA[a0*4+i] * -sinAng + matA[a1*4+i] * cosAng;
    }
    return matB;
}

function Cross( a, b ) { return [ a[1] * b[2] - a[2] * b[1], a[2] * b[0] - a[0] * b[2], a[0] * b[1] - a[1] * b[0], 0.0 ]; }
function Dot( a, b ) { return a[0]*b[0] + a[1]*b[1] + a[2]*b[2]; }
function Normalize( v ) {
    var len = Math.sqrt( v[0] * v[0] + v[1] * v[1] + v[2] * v[2] );
    return [ v[0] / len, v[1] / len, v[2] / len ];
}

var Camera = {};
Camera.create = function() {
    this.pos    = [0, 3, 0.0];
    this.target = [0, 0, 0];
    this.up     = [0, 0, 1];
    this.fov_y  = 90;
    this.vp     = [800, 600];
    this.near   = 0.5;
    this.far    = 100.0;
}
Camera.Perspective = function() {
    var fn = this.far + this.near;
    var f_n = this.far - this.near;
    var r = this.vp[0] / this.vp[1];
    var t = 1 / Math.tan( Math.PI * this.fov_y / 360 );
    var m = IdentityMat44();
    m[0]  = t/r; m[1]  = 0; m[2]  =  0;                              m[3]  = 0;
    m[4]  = 0;   m[5]  = t; m[6]  =  0;                              m[7]  = 0;
    m[8]  = 0;   m[9]  = 0; m[10] = -fn / f_n;                       m[11] = -1;
    m[12] = 0;   m[13] = 0; m[14] = -2 * this.far * this.near / f_n; m[15] =  0;
    return m;
}
Camera.LookAt = function() {
    var mz = Normalize( [ this.pos[0]-this.target[0], this.pos[1]-this.target[1], this.pos[2]-this.target[2] ] );
    var mx = Normalize( Cross( this.up, mz ) );
    var my = Normalize( Cross( mz, mx ) );
    var tx = Dot( mx, this.pos );
    var ty = Dot( my, this.pos );
    var tz = Dot( [-mz[0], -mz[1], -mz[2]], this.pos ); 
    var m = IdentityMat44();
    m[0]  = mx[0]; m[1]  = my[0]; m[2]  = mz[0]; m[3]  = 0;
    m[4]  = mx[1]; m[5]  = my[1]; m[6]  = mz[1]; m[7]  = 0;
    m[8]  = mx[2]; m[9]  = my[2]; m[10] = mz[2]; m[11] = 0;
    m[12] = tx;    m[13] = ty;    m[14] = tz;    m[15] = 1; 
    return m;
} 

// shader program object
var ShaderProgram = {};
ShaderProgram.Create = function( shaderList, uniformNames ) {
    var shaderObjs = [];
    for ( var i_sh = 0; i_sh < shaderList.length; ++ i_sh ) {
        var shderObj = this.CompileShader( shaderList[i_sh].source, shaderList[i_sh].stage );
        if ( shderObj == 0 )
            return 0;
        shaderObjs.push( shderObj );
    }
    var progObj = this.LinkProgram( shaderObjs )
    if ( progObj != 0 ) {
        progObj.unifomLocation = {};
        for ( var i_n = 0; i_n < uniformNames.length; ++ i_n ) {
            var name = uniformNames[i_n];
            progObj.unifomLocation[name] = gl.getUniformLocation( progObj, name );
        }
    }
    return progObj;
}
ShaderProgram.Use = function( progObj ) { gl.useProgram( progObj ); } 
ShaderProgram.SetUniformInt = function( progObj, name, val ) { gl.uniform1i( progObj.unifomLocation[name], val ); }
ShaderProgram.SetUniformFloat = function( progObj, name, val ) { gl.uniform1f( progObj.unifomLocation[name], val ); }
ShaderProgram.SetUniform2f = function( progObj, name, arr ) { gl.uniform2fv( progObj.unifomLocation[name], arr ); }
ShaderProgram.SetUniform3f = function( progObj, name, arr ) { gl.uniform3fv( progObj.unifomLocation[name], arr ); }
ShaderProgram.SetUniformMat44 = function( progObj, name, mat ) { gl.uniformMatrix4fv( progObj.unifomLocation[name], false, mat ); }
ShaderProgram.CompileShader = function( source, shaderStage ) {
    var shaderScript = document.getElementById(source);
    if (shaderScript) {
      source = "";
      var node = shaderScript.firstChild;
      while (node) {
        if (node.nodeType == 3) source += node.textContent;
        node = node.nextSibling;
      }
    }
    var shaderObj = gl.createShader( shaderStage );
    gl.shaderSource( shaderObj, source );
    gl.compileShader( shaderObj );
    var status = gl.getShaderParameter( shaderObj, gl.COMPILE_STATUS );
    if ( !status ) alert(gl.getShaderInfoLog(shaderObj));
    return status ? shaderObj : 0;
} 
ShaderProgram.LinkProgram = function( shaderObjs ) {
    var prog = gl.createProgram();
    for ( var i_sh = 0; i_sh < shaderObjs.length; ++ i_sh )
        gl.attachShader( prog, shaderObjs[i_sh] );
    gl.linkProgram( prog );
    status = gl.getProgramParameter( prog, gl.LINK_STATUS );
    if ( !status ) alert("Could not initialise shaders");
    gl.useProgram( null );
    return status ? prog : 0;
}

var VertexBuffer = {};
VertexBuffer.Create = function( attributes, indices ) {
    var buffer = {};
    buffer.buf = [];
    buffer.attr = []
    for ( var i = 0; i < attributes.length; ++ i ) {
        buffer.buf.push( gl.createBuffer() );
        buffer.attr.push( { size : attributes[i].attrSize, loc : attributes[i].attrLoc } );
        gl.bindBuffer( gl.ARRAY_BUFFER, buffer.buf[i] );
        gl.bufferData( gl.ARRAY_BUFFER, new Float32Array( attributes[i].data ), gl.STATIC_DRAW );
    }
    buffer.inx = gl.createBuffer();
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, buffer.inx );
    gl.bufferData( gl.ELEMENT_ARRAY_BUFFER, new Uint16Array( indices ), gl.STATIC_DRAW );
    buffer.inxLen = indices.length;
    gl.bindBuffer( gl.ARRAY_BUFFER, null );
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, null );
    return buffer;
}
VertexBuffer.Draw = function( bufObj ) {
  for ( var i = 0; i < bufObj.buf.length; ++ i ) {
        gl.bindBuffer( gl.ARRAY_BUFFER, bufObj.buf[i] );
        gl.vertexAttribPointer( bufObj.attr[i].loc, bufObj.attr[i].size, gl.FLOAT, false, 0, 0 );
        gl.enableVertexAttribArray( bufObj.attr[i].loc );
    }
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, bufObj.inx );
    gl.drawElements( gl.TRIANGLES, bufObj.inxLen, gl.UNSIGNED_SHORT, 0 );
    for ( var i = 0; i < bufObj.buf.length; ++ i )
       gl.disableVertexAttribArray( bufObj.attr[i].loc );
    gl.bindBuffer( gl.ARRAY_BUFFER, null );
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, null );
}

initScene();

})();

html,body { margin: 0; overflow: hidden; }
#gui { position : absolute; top : 0; left : 0; }

<script id="draw-shader-vs" type="x-shader/x-vertex">
precision mediump float;

attribute vec3 inPos;
attribute vec3 inNV;
attribute vec3 inCol;

varying vec3 vertPos;
varying vec3 vertNV;
varying vec3 vertCol;

uniform mat4 u_projectionMat44;
uniform mat4 u_viewMat44;
uniform mat4 u_modelMat44;

void main()
{
    vec3 modelNV  = mat3( u_modelMat44 ) * normalize( inNV );
    vertNV        = mat3( u_viewMat44 ) * modelNV;
    vertCol       = inCol;
    vec4 modelPos = u_modelMat44 * vec4( inPos, 1.0 );
    vec4 viewPos  = u_viewMat44 * modelPos;
    vertPos       = viewPos.xyz / viewPos.w;
    gl_Position   = u_projectionMat44 * viewPos;
}
</script>

<script id="draw-shader-fs" type="x-shader/x-fragment">
precision mediump float;

varying vec3 vertPos;
varying vec3 vertNV;
varying vec3 vertCol;

uniform vec3  u_lightDir;
uniform float u_ambient;
uniform float u_diffuse;
uniform float u_specular;
uniform float u_shininess;

void main()
{
    vec3 color      = vertCol;
    vec3 lightCol   = u_ambient * color;
    vec3  normalV   = normalize( vertNV );
    vec3  lightV    = normalize( -u_lightDir );
    vec3  eyeV      = normalize( -vertPos );
    
    // Lambertian
    float NdotL     = max( 0.0, dot( normalV, lightV ) );
    lightCol       += NdotL * u_diffuse * color;
    
    // Phong
    vec3  reflectV  = reflect(-lightV, normalV);
    float VdotR     = max( 0.0, dot( eyeV, reflectV ) );
    float kSpecular = ( u_shininess + 2.0 ) * pow( VdotR, u_shininess ) / ( 2.0 * 3.14159265 );
    
    lightCol       += kSpecular * u_specular * color;
    gl_FragColor    = vec4( lightCol.rgb, 1.0 );
}
</script>

<form id="gui" name="inputs">
    <table>
        <tr> <td> <font color=#40f040>ambient</font> </td> 
                <td> <input type="range" id="ambient" min="0" max="100" value="0"/></td> <td> <font color= #CCF><span id="ambient_val">0</span></font> </td> </tr>
        <tr> <td> <font color=#40f040>diffuse</font> </td> 
                <td> <input type="range" id="diffuse" min="0" max="100" value="0"/></td> <td> <font color= #CCF><span id="diffuse_val">0</span></font> </td></tr>
        <tr> <td> <font color=#40f040>specular</font> </td> 
                <td> <input type="range" id="specular" min="0" max="100" value="0"/></td> <td> <font color= #CCF><span id="specular_val">0</span></font> </td></tr>
        <tr> <td> <font color=#40f040>shininess</font> </td> 
                <td> <input type="range" id="shininess" min="0" max="100" value="0"/></td> <td> <font color= #CCF><span id="shininess_val">0</span></font> </td></tr>
    </table>
</form>

<canvas id="phong-canvas" style="border: none;"></canvas>