将抗锯齿圆与 regl 混合

Question

我正在使用 regl 渲染圆圈，并且有三个目标：

1. 画布应该是透明的，在其后面显示 HTML 内容。
2. 圆应该平滑地消除锯齿。
3. 重叠的圆圈看起来应该是合理的（混合颜色，不显示角）

到目前为止，我有这个：Glitch code 和 demo。

更新：演示链接现在反映了有效的、可接受的答案。下面的代码没有改变。

index.js

const regl = require('regl');
const glsl = require('glslify');
const vertexShader = glsl.file('../shaders/vertex.glsl');
const fragmentShader = glsl.file('../shaders/fragment.glsl');

// Create webgl context and clear.
const canvasEl = document.querySelector('canvas');
const app = regl({
  canvas: canvasEl,
  extensions: ['OES_standard_derivatives']
});
app.clear({color: [0, 0, 0, 0], depth: 1});

// Generate random points and colors.
const attributes = {position: [], color: []};
for (let i = 0; i < 100; i++) {
  attributes.position.push(Math.random() * 2 - 1, Math.random() * 2 - 1);
  attributes.color.push(Math.random(), Math.random(), Math.random());
}

// Define draw instructions.
const draw = app({
  vert: vertexShader,
  frag: fragmentShader,
  attributes: attributes,
  count: 100,
  primitive: 'points',
  depth: {enable: true},
  blend: {
    enable: true
  }
});

// Draw the points.
draw();

vertex.glsl

// vertex.glsl
precision mediump float;

attribute vec2 position;
attribute vec3 color;

varying vec3 vColor;

void main() {
  vColor = color;
  gl_Position = vec4(position, 0, 1);
  gl_PointSize = 40.;
}

fragment.glsl

// fragment.glsl
#ifdef GL_OES_standard_derivatives
#extension GL_OES_standard_derivatives : enable
#endif

precision mediump float;

varying vec3 vColor;

void main() {

  float r = 0.0, delta = 0.0, alpha = 1.0;
  vec2 cxy = 2.0 * gl_PointCoord - 1.0;
  r = dot(cxy, cxy);

#ifdef GL_OES_standard_derivatives
  delta = fwidth(r);
  alpha = 1.0 - smoothstep(1.0 - delta, 1.0 + delta, r);
#endif

  gl_FragColor = vec4(vColor, alpha);
}

但是，结果看起来不太好。角落是可见的，并且圆圈没有正确混合。

我还尝试添加以下混合术语：

func: {
  srcRGB: 'src alpha',
  srcAlpha: 'one minus src alpha',
  dstRGB: 'one minus src alpha',
  dstAlpha: 'src alpha'
}

这样看起来好一点，但是边角还在，而且背景是白色的时候有问题。

您能建议对此进行改进吗？ （如果这就是我在这里所缺少的，也许可以向我指出有关混合的更好信息）谢谢！

Answer 1

你应该像这样设置你的混合参数：

func: {
    srcRGB:   'src alpha',
    srcAlpha: 'src alpha',
    dstRGB:   'one minus src alpha',
    dstAlpha: 'one minus src alpha'
}

这意味着您的目标颜色和源颜色会像这样混合：

红、绿、蓝（srcRGB: 'src alpha'、dstRGB: 'one minus src alpha'）：

R_dest = R_dest * (1 - Alpha_src) + R_src * Alpha_src
G_dest = G_dest * (1 - Alpha_src) + G_src * Alpha_src
B_dest = R_dest * (1 - Alpha_src) + R_src * Alpha_src

Alpha 通道（srcAlpha: 'src alpha'、dstAlpha: 'one minus src alpha'）：

Alpha_dest = Alpha_dest * (1 - Alpha_src) + Alpha_src * Alpha_src

另见glBlendFunc和glBlendFuncSeparate

您还必须确保禁用深度测试

参见上面的 WebGL 示例（用 Firefox、Chrome、Edge、Opera 测试）：

<script type="text/javascript">

back_vert =
"precision mediump float; \n" +
"attribute vec2 inPos; \n" +
"varying vec2 pos; \n" +
"uniform   mat4 u_projectionMat44;" +
"uniform   mat4 u_modelViewMat44;" +
"void main()" +
"{" +
"    pos           = inPos.xy;" +
"    vec4 viewPos  = u_modelViewMat44 * vec4( inPos.xy, 0.0, 1.0 );" +
"    gl_Position   = u_projectionMat44 * viewPos;" +
"}";

back_frag =
"precision mediump float; \n" +
"varying vec2 pos; \n" +
"void main() \n" +
"{ \n" +
"    vec2 coord = pos * 0.5 + 0.5; \n" +
"    float gray = smoothstep( 0.3, 0.7, (coord.x + coord.y) * 0.5 ); \n" +
"    gl_FragColor = vec4( vec3( gray ), 1.0 ); \n" +
"}";

draw_vert =
"precision mediump float; \n" +
"attribute vec2 inPos; \n" +
"varying vec2 pos; \n" +
"uniform   mat4 u_projectionMat44;" +
"uniform   mat4 u_modelViewMat44;" +
"void main()" +
"{" +
"    pos           = inPos.xy;" +
"    vec4 viewPos  = u_modelViewMat44 * vec4( inPos.xy, 0.0, 1.0 );" +
"    gl_Position   = u_projectionMat44 * viewPos;" +
"}";

draw_frag =
"precision mediump float; \n" +
"varying vec2 pos; \n" +
"uniform vec4 u_color;" +
"uniform vec2 u_vp;" +
"void main()" +
"{" +
"    float r = length( pos );" +
"    float d = 4.0 * length( 1.0 / u_vp ); \n" +
"    float a = 1.0 - smoothstep( 1.0 - d, 1.0 + d, r ); \n" +
"    gl_FragColor = vec4( u_color.rgb, u_color.a * a );" +
"}";

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 Translate( matA, trans ) {
    var matB = new glArrayType(16);
    for ( var i = 0; i < 16; ++ i ) matB[i] = matA[i];
    for ( var i = 0; i < 3; ++ i )
        matB[12+i] = matA[i] * trans[0] + matA[4+i] * trans[1] + matA[8+i] * trans[2] + matA[12+i];
    return matB;
}

function Scale( matA, scale ) {
    var matB = new glArrayType(16);
    for ( var i = 0; i < 16; ++ i ) matB[i] = matA[i];
    for ( var a = 0; a < 4; ++ a )
        for ( var i = 0; i < 3; ++ i )
            matB[a*4+i] = matA[a*4+i] * scale[0];
    return matB;
}

Ortho = function( l, r, t, b, n, f ) {
    var fn  = f + n;
    var f_n = f - n;
    var m = IdentityMat44();
    m[0]  = 2/(r-l); m[1]  = 0;       m[2]  =  0;       m[3]  = 0;
    m[4]  = 0;       m[5]  = 2/(t-b); m[6]  =  0;       m[7]  = 0;
    m[8]  = 0;       m[9]  = 0;       m[10] = -2 / f_n; m[11] = -fn / f_n;
    m[12] = 0;       m[13] = 0;       m[14] = 0;        m[15] = 1;
    return m;
}

vec4_add = function( a, b ) { return [ a[0]+b[0], a[1]+b[1], a[2]+b[2], a[3]+b[3] ]; }
vec4_sub = function( a, b ) { return [ a[0]-b[0], a[1]-b[1], a[2]-b[2], a[3]-b[3] ]; }
vec4_mul = function( a, b ) { return [ a[0]*b[0], a[1]*b[1], a[2]*b[2], a[3]*b[3] ]; }
vec4_scale = function( a, s ) { return [ a[0]*s, a[1]*s, a[2]*s, a[3]*s ]; }

// 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.SetUniform2f = function( progObj, name, arr ) { gl.uniform2fv( progObj.unifomLocation[name], arr ); }
ShaderProgram.SetUniform3f = function( progObj, name, arr ) { gl.uniform3fv( progObj.unifomLocation[name], arr ); }
ShaderProgram.SetUniform4f = function( progObj, name, arr ) { gl.uniform4fv( progObj.unifomLocation[name], arr ); }
ShaderProgram.SetUniformMat44 = function( progObj, name, mat ) { gl.uniformMatrix4fv( progObj.unifomLocation[name], false, mat ); }
ShaderProgram.CompileShader = function( source, shaderStage ) {
    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;
}
        

function drawScene(){

    var canvas = document.getElementById( "camera-canvas" );
    var vp = [canvas.width, canvas.height];
    var currentTime = Date.now();   
    var deltaMS = currentTime - startTime;
    var aspect =  canvas.width / canvas.height;
    var matOrtho = Ortho( -aspect, aspect, 1, -1, -1, 1 );
    var alpha = document.getElementById( "alpha" ).value / 100;
        
    gl.viewport( 0, 0, canvas.width, canvas.height );
    gl.disable( gl.DEPTH_TEST );
    gl.clearColor( 0.0, 0.0, 0.0, 1.0 );
    gl.clear( gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT );
    gl.disable( gl.BLEND );
    ShaderProgram.Use( progBack );
    ShaderProgram.SetUniformMat44( progBack, "u_projectionMat44",  matOrtho );
    ShaderProgram.SetUniformMat44( progBack, "u_modelViewMat44", IdentityMat44() );
    gl.enableVertexAttribArray( progBack.inPos );
    gl.bindBuffer( gl.ARRAY_BUFFER, bufObj.pos );
    gl.vertexAttribPointer( progBack.inPos, 2, gl.FLOAT, false, 0, 0 ); 
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, bufObj.inx );
    gl.drawElements( gl.TRIANGLES, bufObj.inx.len, gl.UNSIGNED_SHORT, 0 );
    gl.disableVertexAttribArray( progBack.pos ); 

    gl.enable( gl.BLEND );
    gl.blendFunc( gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA );
    ShaderProgram.Use( progDraw );
    gl.enableVertexAttribArray( progDraw.inPos );
    gl.bindBuffer( gl.ARRAY_BUFFER, bufObj.pos );
    gl.vertexAttribPointer( progDraw.inPos, 2, gl.FLOAT, false, 0, 0 ); 
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, bufObj.inx );
    ShaderProgram.SetUniformMat44( progDraw, "u_projectionMat44",  matOrtho );
    ShaderProgram.SetUniform2f( progDraw, "u_vp",  vp );
        
    var col = [ [1.0,0.0,0.0], [1.0,1.0,0.0], [0.0,0.0,1.0] ];
    var time = [ 7.0, 11.0, 13.0 ];
    for ( var i = 0; i < 3; ++ i ) {    
        var modelMat = Scale( IdentityMat44(), [ 0.3, 0.3, 0.3] );
        var angRad = CalcAng( currentTime, time[i] ) + i * Math.PI * 2 / 3;
        var sinAng = Math.sin(angRad), cosAng = Math.cos(angRad);
        modelMat[12] = cosAng * 0.3 + i * 0.2;
        modelMat[13] = sinAng * 0.3 + i * 0.2;
        
        ShaderProgram.SetUniformMat44( progDraw, "u_modelViewMat44", modelMat );
        var color = col[i];
        color.push( alpha );
        ShaderProgram.SetUniform4f( progDraw, "u_color", color );
        gl.drawElements( gl.TRIANGLES, bufObj.inx.len, gl.UNSIGNED_SHORT, 0 );
    }
    gl.disableVertexAttribArray( progDraw.pos ); 
}

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;
}    

var mousePos = [-1, -1];
var gl;
var prog;
var bufObj = {};
function cameraStart() {

    var canvas = document.getElementById( "camera-canvas");
    gl = canvas.getContext( "experimental-webgl" );
    if ( !gl )
      return;
    var vp = [canvas.width, canvas.height];

    progBack = ShaderProgram.Create( 
      [ { source : back_vert, stage : gl.VERTEX_SHADER },
        { source : back_frag, stage : gl.FRAGMENT_SHADER }
      ],
      [ "u_projectionMat44", "u_modelViewMat44"] );
    progBack.inPos = gl.getAttribLocation( progBack, "inPos" );
    if ( progBack == 0 )
        return;

    progDraw = ShaderProgram.Create( 
      [ { source : draw_vert, stage : gl.VERTEX_SHADER },
        { source : draw_frag, stage : gl.FRAGMENT_SHADER }
      ],
      [ "u_projectionMat44", "u_modelViewMat44", "u_color", "u_alpha", "u_vp"] );
    progDraw.inPos = gl.getAttribLocation( progDraw, "inPos" );
    if ( progDraw == 0 )
        return;

    var pos = [ -1, -1, 1, -1, 1, 1, -1, 1 ];
    var inx = [ 0, 1, 2, 0, 2, 3 ];
    bufObj.pos = gl.createBuffer();
    gl.bindBuffer( gl.ARRAY_BUFFER, bufObj.pos );
    gl.bufferData( gl.ARRAY_BUFFER, new Float32Array( pos ), gl.STATIC_DRAW );
    bufObj.inx = gl.createBuffer();
    bufObj.inx.len = inx.length;
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, bufObj.inx );
    gl.bufferData( gl.ELEMENT_ARRAY_BUFFER, new Uint16Array( inx ), gl.STATIC_DRAW );

    startTime = Date.now();
    setInterval(drawScene, 50);
}

</script>

<body onload="cameraStart();">
    <div style="margin-left: 260px;">
        <div style="float: right; width: 100%; background-color: #CCF;">
            <form name="inputs">
                <table>
                    <tr> <td> alpha </td> 
                         <td> <input type="range" id="alpha" min="0" max="100" value="50"/></td> </tr>
                </table>
            </form>
        </div>
        <div style="float: right; width: 260px; margin-left: -260px;">
            <canvas id="camera-canvas" style="border: none;" width="256" height="256"></canvas>
        </div>
        <div style="clear: both;"></div>
    </div>
</body>

Answer 2

除非您特别要求，否则 Canvas 需要预乘 alpha，所以问题 #1 是您的混合函数应该是

  blend: {
    enable: true,
    func: {
      srcRGB: 'one',
      srcAlpha: 'one',
      dstRGB: 'one minus src alpha',
      dstAlpha: 'one minus src alpha',
    },
  },

您还需要从着色器返回预乘值

  gl_FragColor = vec4(vColor, alpha);
  gl_FragColor.rgb *= gl_FragColor.a;   // premultiply by alpha
}

另一个问题是您进行了深度测试。默认深度函数为LESS。这意味着不会绘制新像素，除非它们的 Z 值小于现有 Z 值。由于您所有的圆圈都以相同的深度绘制，因此不会在任何先前绘制的圆圈处绘制新的圆圈。

最简单的解决方法是关闭深度测试

  depth: {enable: false},

结果：

至于为什么预乘alpha见

https://developer.nvidia.com/content/alpha-blending-pre-or-not-pre