我在一个情况下,我有两个画布,我想在两个画布中显示相同的对象(事实上我必须在每个画布中显示不同的对象,但我想从两个中显示相同的对象开始),但我我不能这样做,
有人可以请我这样做吗？
我尝试这样做是:(我有两个灰色的画布(帆布和帆布2),它在两者中都显示多个方块,但它只显示一个),如何在两者中显示.
我的代码是：
<!DOCTYPE html>
<html lang="en" xmlns="http://www.w3.org/1999/xhtml">
<head>
<script class="WebGL">
var gl,gl2;
function createProgram(gl, vertexShader, fragmentShader)
{
var vs = gl.createShader(gl.VERTEX_SHADER);
gl.shaderSource(vs, vertexShader);
gl.compileShader(vs);
if (!gl.getShaderParameter(vs, gl.COMPILE_STATUS))
alert(gl.getShaderInfoLog(vs));
//////
var fs = gl.createShader(gl.FRAGMENT_SHADER);
gl.shaderSource(fs, fragmentShader);
gl.compileShader(fs);
if (!gl.getShaderParameter(fs, gl.COMPILE_STATUS))
alert(gl.getShaderInfoLog(fs));
program = gl.createProgram();
gl.attachShader(program, vs);
gl.attachShader(program, fs);
gl.linkProgram(program);
if (!gl.getProgramParameter(program, gl.LINK_STATUS))
alert(gl.getProgramInfoLog(program));
return program;
}
function createShaderFromScriptElement(gl , shaderName)
{
var Shader = document.getElementById(shaderName).firstChild.nodeValue;
return Shader;
}
function start()
{
var canvas = document.getElementById("canvas");
canvas2 = document.getElementById("canvas2");
gl = canvas.getContext("experimental-webgl");
gl2 = canvas2.getContext("experimental-webgl");
if (!gl) { alert("error while GL load"); }
if (!gl2) { alert("error while GL load"); }
// var vertexShader2 = createShaderFromScriptElement(gl, "2d-vertex-shader");
// var fragmentShader2 = createShaderFromScriptElement(gl, "2d-fragment-shader");
var vertexShader = createShaderFromScriptElement(gl, "2d-vertex-shader");
var fragmentShader = createShaderFromScriptElement(gl, "2d-fragment-shader");
var program = createProgram(gl, vertexShader, fragmentShader);
gl.useProgram(program);
var positionLocation = gl.getAttribLocation(program, "a_position");
var colorLocation = gl.getUniformLocation(program, "u_color");
var resolutionLocation = gl.getUniformLocation(program, "u_resolution");
var buffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
gl.uniform2f(resolutionLocation, 200, 200);
gl.enableVertexAttribArray(positionLocation);
gl.vertexAttribPointer(positionLocation, 2, gl.FLOAT, false, 0, 0);
for (var ii = 0; ii < 5005; ++ii)
{
// Setup a random rectangle
setRectangle(gl, randomInt(300), randomInt(300), 50, 50);
// Set a random color.
gl.uniform4f(colorLocation, Math.random(), Math.random(), Math.random(), 1);
// Draw the rectangle.
gl.drawArrays(gl.TRIANGLES, 0, 3);
gl2.drawArrays(gl2.TRIANGLES, 0, 3);
}
function randomInt(range)
{
return Math.floor(Math.random() * range);
}
// Fills the buffer with the values that define a rectangle.
function setRectangle(gl, x, y, width, height)
{
var x1 = x;
var x2 = x + width;
var y1 = y;
var y2 = y + height;
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
x1, y1,
x1, -y1,
-x1, y1,
]), gl.STATIC_DRAW);
}
}
</script>
<script id="2d-vertex-shader" type="x-shader/x-vertex">
attribute vec2 a_position;
uniform vec2 u_resolution;
void main() {
// convert the rectangle from pixels to 0.0 to 1.0
vec2 zeroToOne = a_position / u_resolution;
// convert from 0->1 to 0->2
vec2 zeroToTwo = zeroToOne * 2.0;
// convert from 0->2 to -1->+1 (clipspace)
vec2 clipSpace = zeroToTwo - 1.0;
gl_Position = vec4(clipSpace* vec2(1, -1), 0, 1);
}
</script>
<script id="2d-fragment-shader" type="x-shader/x-fragment">
precision mediump float;
uniform vec4 u_color;
void main()
{
gl_FragColor = u_color; // green
}
</script>
</head>
<body onl oad="start()">
<div style="text-align: center">
</div>
<table style="width:100%; height: 10%;">
<tr>
<td style="width:200px; max-width:200px; background-color:gray ">
<canvas id="canvas" width="300" height="300"></canvas>
</td>
<td style="width:200px; max-width:200px; background-color:gray; ">
<canvas id="canvas2" width="300" height="300"></canvas>
</td>
</tr>
</table>
</body>
</html>
解决方法:
不,遗憾的是,您无法在WebGL 1.0中跨画布共享WebGL对象
你想达到什么目的？
一些解决方案
>拆分1帆布
如果您需要多个视图,例如许多3D建模程序,您可以使用gl.enable(gl.SCISSOR_TEST),gl.scissor和gl.viewport拆分单个画布. Here’s one example
>绘制到一个画布,然后复制到其他画布
在这种情况下,您使用WebGL渲染到屏幕外的画布
使用多个可见画布2d画布来显示
drawImage方法.
gl = offscreenCanvas.getContext("webgl");
ctx1 = onscreenCanvas1.getContext("2d");
ctx2 = onscreenCanvas2.getContext("2d");
// render whatever you want to appear in onscreenCanvas1
renderScene(scene1Settings, gl);
// copy the result to offscreenCanvas1
ctx1.drawImage(gl.canvas, ...);
// render whatever you want to appear in onscreenCanvas2
renderScene(scene2Settings, gl);
// copy the result to offsceenCanvas2
ctx2.drawImage(gl,canvas, ...);
>将1个画布设置为窗口大小,将其放在背景中,使用第一个技术(剪刀,视口)和getBoundingClientRect来精确渲染其他元素的位置.
在这种情况下,您可以创建一个与窗口大小相同的WebGL画布
并使用CSS将其放在后台.然后创建一个占位符
< DIV>或其他元素来表示您想要画布的位置
出现.
然后,您可以向浏览器询问该元素的确切位置
使用该信息设置视口和剪刀,然后渲染到
该区域看起来像是一个画布