法线贴图根据方向而不同
我正在尝试使用法线贴图而不是顶点法线，我无法弄清楚哪个步骤我做错了。我想将光线方向转换为切线空间并从那里进行计算。 首先，我将矢量法线和切线转换为视图空间。
vec3 norm_viewsp = mat3(view) * normalize(norm);
vec3 tangent_viewsp = mat3(view) * normalize(tangent);
vec3 bitangent_viewsp = cross(tangent_viewsp, norm_viewsp);
接下来，我构建了一个矩阵，它应该执行从视图空间到切线空间的变换，并使用它来计算切线空间中光线的距离。
mat3 tbn = transpose(mat3(tangent_viewsp, bitangent_viewsp, norm_viewsp));
vec3 light_dir = light_pos - pos.xyz;
vec3 light_dir_viewsp = mat3(view) * light_dir;
v_light_dir_tansp = tbn * light_dir_viewsp;
在片段着色器中，我然后从法线贴图中采样法线并将其与光线方向相乘。
vec3 norm = texture(normal_map, v_tex_pos).rgb * 2.0 - 1.0;
float diffuse = dot(normalize(norm), normalize(v_light_dir_tansp));
法线贴图肯定能正确加载。
结果左上角太暗，左下角太亮 我认为问题出在光线方向的某处，但我无法发现错误。
Nore，在上面的图片中，值介于-1和1之间，这就是为什么，例如法线贴图看起来太暗了。
编辑：灯光位于模型的中心。 如果使用顶点法线，则照明工作正常。 在视图空间而不是切线空间中进行计算没有任何区别。
2 个答案:
答案 0 :(得分：4)
首先，您必须计算切线空间矩阵，在右侧系统中这样做：
vec3 norm_viewsp = mat3(view) * normalize(norm);
vec3 tangent_viewsp = mat3(view) * normalize(tangent);
vec3 bitangent_viewsp = cross(norm_viewsp, tangent_viewsp);
mat3 tbn = mat3(tangent_viewsp, bitangent_viewsp, norm_viewsp));
当然，您需要切线空间中法线贴图的法线矢量和视图空间中光源的矢量：
vec3 norm_map_tbn = normalize(texture(normal_map, v_tex_pos).xyz * 2.0 - 1.0);
vec3 light_dir_viewsp = normalize(mat3(view) * (light_pos - pos.xyz));
之后你有两种可能性。由于来自法线贴图的法线矢量在切线空间中，因此光矢量也可以转换为切线空间，并且光计算可以在切线空间中。为此，光矢量必须由反正切空间矩阵变换。逆矩阵可以通过GLSL函数inverse计算，而不是transpose计算（参见What is the difference between "matrix inverse" and "matrix transpose"?）。
vec3 light_dir_tbn = inverse(tbn) * light_dir_viewsp;
float diffuse = max(0.0, dot(norm_map_tbn, light_dir_tbn);
但你也可以反过来做。来自法线贴图的法线矢量可以转换为视图空间，并且光计算可以在视图空间中完成。为此，法向量必须由切线空间矩阵进行变换。这样可以避免昂贵的inverse操作。
将法向量替换为tbn[2]（切线空间矩阵的Z轴），以在不受法线贴图影响的情况下显示效果。
vec3 norm_map_viewsp = tbn * norm_map_tbn;
float diffuse = max(0.0, dot(norm_map_viewsp, light_dir_viewsp);
请注意，Lambertian diffuse灯光模型通常按如下方式计算：
f_lambertian = max( 0.0, dot(N, L ))
如果光源非常靠近物体，那么光矢量和面的法向矢量之间的角度可以在左上边缘和下右边缘之间大规模地不同。这将导致更暗和更亮的区域，因为朗伯漫射光模型线性地取决于角度的余弦。
将法向量替换为tbn[2]（切线空间矩阵的Z轴），以在不受法线贴图影响的情况下显示效果。
注意，您必须确保所有法向矢量指向相同方向，而切线指向相同方向。请参阅示例，该示例演示了如果其中一个法线向量被反转会发生什么：
＆＃13;
＆＃13;
＆＃13;
＆＃13;
glArrayType = typeof Float32Array !="undefined" ? Float32Array : ( typeof WebGLFloatArray != "undefined" ? WebGLFloatArray : Array );
function IdentityMat44() {
var m = new glArrayType(16);
m[0] = 1; m[1] = 0; m[2] = 0; m[3] = 0;
m[4] = 0; m[5] = 1; m[6] = 0; m[7] = 0;
m[8] = 0; m[9] = 0; m[10] = 1; m[11] = 0;
m[12] = 0; m[13] = 0; m[14] = 0; m[15] = 1;
return m;
};
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 = new glArrayType(16);
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, 1.5, 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;
}
var ShaderProgram = {};
ShaderProgram.Create = function( shaderList ) {
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.attribIndex = {};
var noOfAttributes = gl.getProgramParameter( progObj, gl.ACTIVE_ATTRIBUTES );
for ( var i_n = 0; i_n < noOfAttributes; ++ i_n ) {
var name = gl.getActiveAttrib( progObj, i_n ).name;
progObj.attribIndex[name] = gl.getAttribLocation( progObj, name );
}
progObj.unifomLocation = {};
var noOfUniforms = gl.getProgramParameter( progObj, gl.ACTIVE_UNIFORMS );
for ( var i_n = 0; i_n < noOfUniforms; ++ i_n ) {
var name = gl.getActiveUniform( progObj, i_n ).name;
progObj.unifomLocation[name] = gl.getUniformLocation( progObj, name );
}
}
return progObj;
}
ShaderProgram.AttributeIndex = function( progObj, name ) { return progObj.attribIndex[name]; }
ShaderProgram.UniformLocation = function( progObj, name ) { return progObj.unifomLocation[name]; }
ShaderProgram.Use = function( progObj ) { gl.useProgram( progObj ); }
ShaderProgram.SetUniformI1 = function( progObj, name, val ) { if(progObj.unifomLocation[name]) gl.uniform1i( progObj.unifomLocation[name], val ); }
ShaderProgram.SetUniformF1 = function( progObj, name, val ) { if(progObj.unifomLocation[name]) gl.uniform1f( progObj.unifomLocation[name], val ); }
ShaderProgram.SetUniformF2 = function( progObj, name, arr ) { if(progObj.unifomLocation[name]) gl.uniform2fv( progObj.unifomLocation[name], arr ); }
ShaderProgram.SetUniformF3 = function( progObj, name, arr ) { if(progObj.unifomLocation[name]) gl.uniform3fv( progObj.unifomLocation[name], arr ); }
ShaderProgram.SetUniformF4 = function( progObj, name, arr ) { if(progObj.unifomLocation[name]) gl.uniform4fv( progObj.unifomLocation[name], arr ); }
ShaderProgram.SetUniformM33 = function( progObj, name, mat ) { if(progObj.unifomLocation[name]) gl.uniformMatrix3fv( progObj.unifomLocation[name], false, mat ); }
ShaderProgram.SetUniformM44 = function( progObj, name, mat ) { if(progObj.unifomLocation[name]) 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 );
}
function drawScene(){
var canvas = document.getElementById( "camera-canvas" );
Camera.create();
Camera.vp = [canvas.width, canvas.height];
var currentTime = Date.now();
var deltaMS = currentTime - startTime;
var texUnit = 0;
gl.activeTexture( gl.TEXTURE0 + texUnit );
gl.bindTexture( gl.TEXTURE_2D, textureObj );
var mapUnit = 1;
gl.activeTexture( gl.TEXTURE0 + mapUnit );
gl.bindTexture( gl.TEXTURE_2D, normalMapObj );
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.SetUniformM44( progDraw, "u_projectionMat44", Camera.Perspective() );
ShaderProgram.SetUniformM44( progDraw, "u_viewMat44", Camera.LookAt() );
var modelMat = IdentityMat44()
modelMat = RotateAxis( modelMat, 105.0 * Math.PI / 180.0, 0 );
ShaderProgram.SetUniformM44( progDraw, "u_modelMat44", modelMat );
ShaderProgram.SetUniformI1( progDraw, "tex", texUnit );
ShaderProgram.SetUniformI1( progDraw, "normal_map", mapUnit );
// draw scene
var chg_tang = document.getElementById( "change_tangent" ).checked;
if ( chg_tang )
VertexBuffer.Draw( bufPlane2 );
else
VertexBuffer.Draw( bufPlane );
}
var Texture = {};
Texture.HandleLoadedTexture2D = function( image, texture, flipY ) {
gl.activeTexture( gl.TEXTURE0 );
gl.bindTexture( gl.TEXTURE_2D, texture );
gl.texImage2D( gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, image );
if ( flipY != undefined && flipY == true )
gl.pixelStorei( gl.UNPACK_FLIP_Y_WEBGL, true );
gl.texParameteri( gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR );
gl.texParameteri( gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR );
gl.texParameteri( gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.REPEAT );
gl.texParameteri( gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.REPEAT );
gl.bindTexture( gl.TEXTURE_2D, null );
return texture;
}
Texture.LoadTexture2D = function( name ) {
var texture = gl.createTexture();
texture.image = new Image();
texture.image.setAttribute('crossorigin', 'anonymous');
texture.image.onload = function () {
Texture.HandleLoadedTexture2D( texture.image, texture, true )
}
texture.image.src = name;
return texture;
}
var gl;
var progDraw;
var bufCube = {};
var bufTorus = {};
function sceneStart() {
var canvas = document.getElementById( "camera-canvas");
var vp = [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 }
] );
progDraw.inPos = gl.getAttribLocation( progDraw, "pos" );
progDraw.inNV = gl.getAttribLocation( progDraw, "norm" );
progDraw.inTV = gl.getAttribLocation( progDraw, "tangent" );
progDraw.inTex = gl.getAttribLocation( progDraw, "tex_pos" );
if ( progDraw == 0 )
return;
var planPosData = [-1.0, -1.0, 0.0, 1.0, -1.0, 0.0, 1.0, 1.0, 0.0, -1.0, 1.0, 0.0];
var planNVData = [ 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0];
var planTVData = [ 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0];
var planTexData = [ 0.0, 0.0, 0.0, 1.0, 1.0, 1.0, 1.0, 0.0 ];
var planInxData = [0,1,2,0,2,3];
bufPlane = VertexBuffer.Create(
[ { data : planPosData, attrSize : 3, attrLoc : progDraw.inPos },
{ data : planNVData, attrSize : 3, attrLoc : progDraw.inNV },
{ data : planTVData, attrSize : 3, attrLoc : progDraw.inTV },
{ data : planTexData, attrSize : 2, attrLoc : progDraw.inTex } ],
planInxData );
var planPosData2 = [-1.0, -1.0, 0.0, 1.0, -1.0, 0.0, 1.0, 1.0, 0.0, -1.0, 1.0, 0.0];
var planNVData2 = [ 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, -1.0, 0.0, 0.0, 1.0];
//var planTVData2 = [ 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0];
var planTVData2 = [ 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0];
var planTexData2 = [ 0.0, 0.0, 0.0, 1.0, 1.0, 1.0, 1.0, 0.0 ];
var planInxData2 = [0,1,2,0,2,3];
bufPlane2 = VertexBuffer.Create(
[ { data : planPosData2, attrSize : 3, attrLoc : progDraw.inPos },
{ data : planNVData2, attrSize : 3, attrLoc : progDraw.inNV },
{ data : planTVData2, attrSize : 3, attrLoc : progDraw.inTV },
{ data : planTexData2, attrSize : 2, attrLoc : progDraw.inTex } ],
planInxData2 );
textureObj = Texture.LoadTexture2D( "https://raw.githubusercontent.com/Rabbid76/graphics-snippets/master/resource/texture/Gominolas.png" );
normalMapObj = Texture.LoadTexture2D( "https://raw.githubusercontent.com/Rabbid76/graphics-snippets/master/resource/texture/GominolasBump.png" );
startTime = Date.now();
setInterval(drawScene, 50);
}<script id="draw-shader-vs" type="x-shader/x-vertex">
precision mediump float;
attribute vec4 pos;
attribute vec3 norm;
attribute vec3 tangent;
attribute vec2 tex_pos;
varying vec2 v_tex_pos;
varying vec3 v_light_dir_tansp;
// ADDED -----
varying vec3 v_tangent_vsp;
varying vec3 v_binoraml_vsp;
varying vec3 v_norm_vsp;
// ADDED -----
//uniform mat4 view;
//uniform mat4 view_projection;
// ADDED -----
uniform mat4 u_projectionMat44;
uniform mat4 u_viewMat44;
uniform mat4 u_modelMat44;
// ADDED -----
//const vec3 light_pos = vec3(50.0, 25.0, 50.0);
// ADDED -----
const vec3 light_pos = vec3(0.0, 0.0, 0.25);
// ADDED -----
// ADDED -----
mat3 transpose(mat3 m)
{
mat3 tm = m;
for(int i = 0; i < 3; ++i)
{
for(int j = 0; j < 3; ++j)
tm[j][i]=m[i][j];
}
return tm;
}
// ADDED -----
void main() {
// ADDED -----
mat4 view = u_viewMat44 * u_modelMat44;
mat4 view_projection = u_projectionMat44 * view;
// ADDED -----
vec3 norm_viewsp = mat3(view) * normalize(norm);
vec3 tangent_viewsp = mat3(view) * normalize(tangent);
vec3 bitangent_viewsp = cross(tangent_viewsp, norm_viewsp);
mat3 tbn = transpose(mat3(tangent_viewsp, bitangent_viewsp, norm_viewsp));
vec3 light_dir = light_pos - pos.xyz;
vec3 light_dir_viewsp = mat3(view) * light_dir;
v_tex_pos = tex_pos;
v_light_dir_tansp = tbn * light_dir_viewsp;
gl_Position = view_projection * pos;
// ADDED -----
v_tangent_vsp = tangent_viewsp;
v_binoraml_vsp = bitangent_viewsp;
v_norm_vsp = norm_viewsp;
// ADDED -----
}
</script>
<script id="draw-shader-fs" type="x-shader/x-fragment">
precision mediump float;
varying vec2 v_tex_pos;
varying vec3 v_light_dir_tansp;
// ADDED -----
varying vec3 v_tangent_vsp;
varying vec3 v_binoraml_vsp;
varying vec3 v_norm_vsp;
// ADDED -----
uniform sampler2D tex;
uniform sampler2D normal_map;
void main() {
vec3 norm = texture2D(normal_map, v_tex_pos).rgb * 2.0 - 1.0;
float diffuse = dot(normalize(norm), normalize(v_light_dir_tansp));
diffuse = clamp(diffuse, 0.0, 1.0);
gl_FragColor = texture2D(tex, v_tex_pos) * diffuse;
// ADDED -----
vec4 texColor = texture2D(tex, v_tex_pos);
gl_FragColor = vec4( texColor.rgb * diffuse * 2.0, 1.0 );
//gl_FragColor = vec4(abs(v_tangent_vsp), 1.0);
//gl_FragColor = vec4(abs(v_binoraml_vsp), 1.0);
//gl_FragColor = vec4(abs(v_norm_vsp), 1.0);
//gl_FragColor = vec4(texture2D(tex, v_tex_pos).rgb, 1.0);
//gl_FragColor = vec4(texture2D(normal_map, v_tex_pos).rgb, 1.0);
// ADDED -----
}
</script>
<body onload="sceneStart();">
<div style="margin-left: 520px;">
<div style="float: right; width: 100%; background-color: #CCF;">
<form name="inputs">
<table>
<tr> <td> change tangent </td>
<td> <input type="checkbox" id="change_tangent"/>
</td> </tr>
</table>
</form>
</div>
<div style="float: right; width: 520px; margin-left: -520px;">
<canvas id="camera-canvas" style="border: none;" width="512" height="512"></canvas>
</div>
<div style="clear: both;"></div>
</div>
</body>
答案 1 :(得分：1)
IMO不需要矩阵伏都教：
v_light_dir_tansp = vec3(
dot(tangent_viewsp, light_dir_viewsp),
dot(bitangent_viewsp, light_dir_viewsp),
dot(norm_viewsp, light_dir_viewsp)
);
顺便说一句，由于内插， v_light_dir_tansp 不准确。
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