javascript - 如何在模型 View 投影广告牌顶点着色器中保留旋转和缩放变换？

Question

我正在寻找 GLSL 广告牌顶点着色器解决方案。我正在渲染一个带有纹理的四边形。我目前有一个顶点着色器，看起来像:

precision mediump float;

attribute vec3 position;
attribute vec2 uvs;

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

varying vec2 uv;

void main() {
  uv = uvs;

  gl_Position = projection * view * model * vec4(position, 1);
}

我的模型矩阵是在别处从旋转、平移和缩放变换矩阵构建的。

我尝试过的一些解决方案已经奏效并提供了广告牌(面向相机)效果。不幸的是，他们放弃了对原始模型矩阵的原始旋转和缩放变换。我尝试过的最接近的解决方案来自:http://www.geeks3d.com/20140807/billboarding-vertex-shader-glsl/

更新:

这是当前设置的 MVCE http://requirebin.com/?gist=9491aa294f11b31af639910cfeff7140

有一个旋转四边形的相机。四边形应用了缩放和旋转。纹理上写着“玩家姓名”。四边形应始终面向相机，就像一个广告牌，上面写着“玩家姓名”，而不丢弃比例或 x 旋转。

Answer 1

要将对象定向到视口(viewport)，您必须忽略 View 矩阵的方向。方向是矩阵的归一化左上角 3*3。由于您的模型是翻转的，因此您必须通过反转 X 轴来补偿这一点:

precision mediump float;
attribute vec3 position;
attribute vec2 uvs;

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

varying vec2 uv;

void main() {
    uv = uvs;

    mat4 bbView = mat4(
        vec4(-1.0,0.0,0.0,0.0),
        vec4(0.0,1.0,0.0,0.0),
        vec4(0.0,0.0,1.0,0.0),
        view[3] );

    gl_Position = projection * bbView * model * vec4(position, 1);
}

请注意，转换矩阵(模型和 View 矩阵)如下所示:

( X-axis.x, X-axis.y, X-axis.z, 0 )
( Y-axis.x, Y-axis.y, Y-axis.z, 0 )
( Z-axis.x, Z-axis.y, Z-axis.z, 0 )
( trans.x,  trans.y,  trans.z,  1 ) 

广告牌矩阵 bbView 使用 View (相机)位置，但它忽略了 View 矩阵提供的旋转。这会导致对象看起来像是从正面看。

在透视投影中，物体的大小随到相机的距离线性变化。

这意味着如果您希望对象保持其大小和在视口(viewport)中的位置，则必须按到相机的距离缩放对象:

precision mediump float;
attribute vec3 position;
attribute vec2 uvs;

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

varying vec2 uv;

void main() {
    uv = uvs;

    float scale = length(view[3].xyz);
    mat4 scaleMat = mat4(
        vec4(scale,0.0,0.0,0.0),
        vec4(0.0,scale,0.0,0.0),
        vec4(0.0,0.0,1.0,0.0),
        vec4(0.0,0.0,0.0,1.0) );

    mat4 bbView = mat4(
        vec4(-1.0,0.0,0.0,0.0),
        vec4(0.0,1.0,0.0,0.0),
        vec4(0.0,0.0,1.0,0.0),
        view[3] );

    gl_Position = projection * bbView * model * scaleMat * vec4(position, 1);
}

查看代码片段:

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, 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;
} 

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.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( "billboard-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 );

    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 );
    
    var rotMat = IdentityMat44();
    rotMat = RotateAxis( rotMat, CalcAng( currentTime, 13.0 ), 0 );
    rotMat = RotateAxis( rotMat, CalcAng( currentTime, 17.0 ), 1 );
    var d = 1.0 + 0.7*Math.sin( CalcAng( currentTime, 25.0 ) )
    Camera.pos = [d*rotMat[0], d*rotMat[1], d*rotMat[2]];
    var viewMat = Camera.LookAt();

    // set up draw shader
    ShaderProgram.Use( progDraw );
    ShaderProgram.SetUniformM44( progDraw, "u_projectionMat44", Camera.Perspective() );
    ShaderProgram.SetUniformM44( progDraw, "u_viewMat44", viewMat );
    ShaderProgram.SetUniformI1( progDraw, "u_texture", texUnit );
    var modelMat = IdentityMat44();
    modelMat[0] = 0.5; modelMat[5] = 0.5;
    modelMat[12] = -0.55;
    ShaderProgram.SetUniformM44( progDraw, "u_modelMat44", modelMat );
    ShaderProgram.SetUniformF1( progDraw, "u_billboard", 0.0 );
    VertexBuffer.Draw( bufPlane );

    modelMat[12] = 0.55
    ShaderProgram.SetUniformM44( progDraw, "u_modelMat44", modelMat );
    ShaderProgram.SetUniformF1( progDraw, "u_billboard", 1.0 );
    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 startTime;
function Fract( val ) { 
    return val - Math.trunc( val );
}
function CalcAng( currentTime, intervall ) {
    return Fract( (currentTime - startTime) / (1000*intervall) ) * 2.0 * Math.PI;
}
function CalcMove( currentTime, intervall, range ) {
    var pos = self.Fract( (currentTime - startTime) / (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 ];
}

var sliderScale = 100.0
var gl;
var progDraw;
var bufCube = {};
function sceneStart() {

    var canvas = document.getElementById( "billboard-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, "inPos" );
    progDraw.inTex = gl.getAttribLocation( progDraw, "inTex" );
    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 planTexData = [ 0.0,  1.0,          1.0,  1.0,          1.0,  0.0,          0.0, 0.0     ];
    var planInxData = [0,1,2,0,2,3];
    bufPlane = VertexBuffer.Create(
    [ { data : planPosData, attrSize : 3, attrLoc : progDraw.inPos },
      { data : planTexData, attrSize : 2, attrLoc : progDraw.inTex } ],
      planInxData );

    textureObj = Texture.LoadTexture2D( "https://raw.githubusercontent.com/Rabbid76/graphics-snippets/master/resource/texture/tree.jpg" );
    
    startTime = Date.now();
    setInterval(drawScene, 50);
}

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

attribute vec3 inPos;
attribute vec2 inTex;

varying vec2 vertTex;

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

uniform float u_billboard;

void main()
{
    vertTex       = inTex;

    float scale = u_billboard > 0.5 ? length(u_viewMat44[3].xyz) : 1.0;
    mat4 scaleMat = mat4(
        vec4(scale,0.0,0.0,0.0),
        vec4(0.0,scale,0.0,0.0),
        vec4(0.0,0.0,1.0,0.0),
        vec4(0.0,0.0,0.0,1.0) );

    mat4 bbView = mat4(
        vec4(1.0,0.0,0.0,0.0),
        vec4(0.0,1.0,0.0,0.0),
        vec4(0.0,0.0,1.0,0.0),
        u_viewMat44[3] );

    mat4 view = u_billboard > 0.5 ? bbView : u_viewMat44;

    gl_Position  = u_projectionMat44 * view * scaleMat * u_modelMat44 * vec4( inPos, 1.0 );
}
</script>

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

varying vec2 vertTex;

uniform sampler2D u_texture;
uniform sampler2D u_normalMap;

void main()
{
    vec3 texColor = texture2D( u_texture, vertTex.st ).rgb;
    gl_FragColor = vec4( texColor.rgb, 1.0 );
}
</script>

<body onload="sceneStart();">
    <canvas id="billboard-canvas" style="border: none;" width="512" height="512"></canvas>
</body>