将抗锯齿圆圈与 regl 混合
Blending anti-aliased circles with regl
我正在使用 regl 渲染圆圈，并且有三个目标：
- canvas 应该是透明的，显示后面的 HTML 内容。
- 圆应该平滑地消除锯齿。
- 重叠的圆应该看起来合理（混合颜色，不显示角）
UPDATE: The demo links now reflect the working, accepted answer. Code below is unchanged.
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);
}
然而，结果看起来不太好。角是可见的，圆圈没有正确混合。
我还尝试添加以下混合项：
func: {
srcRGB: 'src alpha',
srcAlpha: 'one minus src alpha',
dstRGB: 'one minus src alpha',
dstAlpha: 'src alpha'
}
这看起来好多了，但是角落仍然存在，当背景是白色时有些不对劲。
你能对此提出改进建议吗？ （如果这是我在这里所缺少的，也许可以指出有关混合的更好信息）谢谢！
您应该像这样设置混合参数：
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
也看到了glBlendFunc and glBlendFuncSeparate
此外，您必须确保禁用深度测试
参见上面的 WebGL 示例（使用 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>
Canvas 需要预乘 alpha，除非您特别要求否则问题 #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 return 来自着色器的预乘值
gl_FragColor = vec4(vColor, alpha);
gl_FragColor.rgb *= gl_FragColor.a; // premultiply by alpha
}
另一个问题是你开启了深度测试。默认的深度函数是 LESS。这意味着除非新像素的 Z 值小于现有 Z 值，否则不会绘制新像素。由于您的所有圆圈都以相同的深度绘制，因此不会在先前绘制的圆圈的任何位置绘制新的圆圈。
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
我正在使用 regl 渲染圆圈，并且有三个目标：
- canvas 应该是透明的，显示后面的 HTML 内容。
- 圆应该平滑地消除锯齿。
- 重叠的圆应该看起来合理（混合颜色，不显示角）
UPDATE: The demo links now reflect the working, accepted answer. Code below is unchanged.
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);
}
然而，结果看起来不太好。角是可见的，圆圈没有正确混合。
我还尝试添加以下混合项：
func: {
srcRGB: 'src alpha',
srcAlpha: 'one minus src alpha',
dstRGB: 'one minus src alpha',
dstAlpha: 'src alpha'
}
这看起来好多了，但是角落仍然存在，当背景是白色时有些不对劲。
你能对此提出改进建议吗？ （如果这是我在这里所缺少的，也许可以指出有关混合的更好信息）谢谢！
您应该像这样设置混合参数：
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
也看到了glBlendFunc and glBlendFuncSeparate
此外，您必须确保禁用深度测试
参见上面的 WebGL 示例（使用 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>
Canvas 需要预乘 alpha，除非您特别要求否则问题 #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 return 来自着色器的预乘值
gl_FragColor = vec4(vColor, alpha);
gl_FragColor.rgb *= gl_FragColor.a; // premultiply by alpha
}
另一个问题是你开启了深度测试。默认的深度函数是 LESS。这意味着除非新像素的 Z 值小于现有 Z 值，否则不会绘制新像素。由于您的所有圆圈都以相同的深度绘制，因此不会在先前绘制的圆圈的任何位置绘制新的圆圈。
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