我们正在构建一个WebGL应用程序,其中包含一些高渲染负载的对象。有什么方法可以在浏览器绘制时间之外(即在后台)渲染那些对象?我们不希望FPS下降,并且可以分解渲染过程(在帧之间拆分)。
想到三个主意。
const gl = document.querySelector('canvas').getContext('webgl');
const vs = `
attribute vec4 position;
attribute vec2 texcoord;
varying vec2 v_texcoord;
void main() {
gl_Position = position;
v_texcoord = texcoord;
}
`;
const fs = `
precision highp float;
uniform sampler2D tex;
varying vec2 v_texcoord;
void main() {
gl_FragColor = texture2D(tex, v_texcoord);
}
`;
// compile shader, link program, look up locations
const programInfo = twgl.createProgramInfo(gl, [vs, fs]);
// gl.createBuffer, gl.bindBuffer, gl.bufferData
const bufferInfo = twgl.createBufferInfoFromArrays(gl, {
position: {
numComponents: 2,
data: [
-1, -1,
1, -1,
-1, 1,
-1, 1,
1, -1,
1, 1,
],
},
texcoord: {
numComponents: 2,
data: [
0, 0,
1, 0,
0, 1,
0, 1,
1, 0,
1, 1,
],
},
});
// create a framebuffer with a texture and depth buffer
// same size as canvas
// gl.createTexture, gl.texImage2D, gl.createFramebuffer
// gl.framebufferTexture2D
const framebufferInfo = twgl.createFramebufferInfo(gl);
const infoElem = document.querySelector('#info');
const numDrawSteps = 16;
let drawStep = 0;
let time = 0;
// draw over several frames. Return true when ready
function draw() {
// draw to texture
// gl.bindFrambuffer, gl.viewport
twgl.bindFramebufferInfo(gl, framebufferInfo);
if (drawStep == 0) {
// on the first step clear and record time
gl.disable(gl.SCISSOR_TEST);
gl.clearColor(0, 0, 0, 0);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
time = performance.now() * 0.001;
}
// this represents drawing something.
gl.enable(gl.SCISSOR_TEST);
const halfWidth = framebufferInfo.width / 2;
const halfHeight = framebufferInfo.height / 2;
const a = time * 0.1 + drawStep
const x = Math.cos(a ) * halfWidth + halfWidth;
const y = Math.sin(a * 1.3) * halfHeight + halfHeight;
gl.scissor(x, y, 16, 16);
gl.clearColor(
drawStep / 16,
drawStep / 6 % 1,
drawStep / 3 % 1,
1);
gl.clear(gl.COLOR_BUFFER_BIT);
drawStep = (drawStep + 1) % numDrawSteps;
return drawStep === 0;
}
let frameCount = 0;
function render() {
++frameCount;
infoElem.textContent = frameCount;
if (draw()) {
// draw to canvas
// gl.bindFramebuffer, gl.viewport
twgl.bindFramebufferInfo(gl, null);
gl.disable(gl.DEPTH_TEST);
gl.disable(gl.BLEND);
gl.disable(gl.SCISSOR_TEST);
gl.useProgram(programInfo.program);
// gl.bindBuffer, gl.enableVertexAttribArray, gl.vertexAttribPointer
twgl.setBuffersAndAttributes(gl, programInfo, bufferInfo);
// gl.uniform...
twgl.setUniformsAndBindTextures(programInfo, {
tex: framebufferInfo.attachments[0],
});
// draw the quad
gl.drawArrays(gl.TRIANGLES, 0, 6);
}
requestAnimationFrame(render);
}
requestAnimationFrame(render);
<canvas></canvas>
<div id="info"></div>
<script src="https://twgljs.org/dist/4.x/twgl.min.js"></script>
ctx.drawImage(webglCanvas, ...)
将其绘制到2D画布上。这与#1基本相同,不同之处在于您让浏览器“将纹理渲染到画布上”部分const ctx = document.querySelector('canvas').getContext('2d');
const gl = document.createElement('canvas').getContext('webgl');
const vs = `
attribute vec4 position;
attribute vec2 texcoord;
varying vec2 v_texcoord;
void main() {
gl_Position = position;
v_texcoord = texcoord;
}
`;
const fs = `
precision highp float;
uniform sampler2D tex;
varying vec2 v_texcoord;
void main() {
gl_FragColor = texture2D(tex, v_texcoord);
}
`;
// compile shader, link program, look up locations
const programInfo = twgl.createProgramInfo(gl, [vs, fs]);
const infoElem = document.querySelector('#info');
const numDrawSteps = 16;
let drawStep = 0;
let time = 0;
// draw over several frames. Return true when ready
function draw() {
if (drawStep == 0) {
// on the first step clear and record time
gl.disable(gl.SCISSOR_TEST);
gl.clearColor(0, 0, 0, 0);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
time = performance.now() * 0.001;
}
// this represents drawing something.
gl.enable(gl.SCISSOR_TEST);
const halfWidth = gl.canvas.width / 2;
const halfHeight = gl.canvas.height / 2;
const a = time * 0.1 + drawStep
const x = Math.cos(a ) * halfWidth + halfWidth;
const y = Math.sin(a * 1.3) * halfHeight + halfHeight;
gl.scissor(x, y, 16, 16);
gl.clearColor(
drawStep / 16,
drawStep / 6 % 1,
drawStep / 3 % 1,
1);
gl.clear(gl.COLOR_BUFFER_BIT);
drawStep = (drawStep + 1) % numDrawSteps;
return drawStep === 0;
}
let frameCount = 0;
function render() {
++frameCount;
infoElem.textContent = frameCount;
if (draw()) {
// draw to canvas
ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
ctx.drawImage(gl.canvas, 0, 0);
}
requestAnimationFrame(render);
}
requestAnimationFrame(render);
<canvas></canvas>
<div id="info"></div>
<script src="https://twgljs.org/dist/4.x/twgl.min.js"></script>
请注意,如果您使用DOS的GPU(给GPU过多的工作),您仍然可以影响主线程的响应能力,因为大多数GPU不支持抢先式多任务处理。因此,如果您有很多真正繁重的工作,则将其分解为较小的任务。
例如,如果您从shadertoy.com中获取了最重的着色器之一,以1920x1080渲染时,其运行速度为0.5 fps,即使在屏幕外,也会迫使整个机器以0.5 fps的速度运行。要解决此问题,您需要在几帧上渲染较小的部分。如果它以0.5 fps的速度运行,则表明您需要将其分成至少120个较小的部分(也许更多),以保持主线程的响应速度,而在120个较小的部分中,您将仅每2秒查看一次结果。
实际上尝试显示一些问题。 Here's Iq's Happy Jumping Example drawn over 960 frames。即使我的2018年末Macbook Air每帧仅渲染2160像素(1920x1080画布的2列),仍然无法保持60fps。问题可能是场景的某些部分必须深入进行,并且无法事先知道场景的哪些部分。使用签名距离字段的阴影样式着色器更多是toy(因此,shaderTOY)而不是生产样式技术的原因之一。
无论如何,关键是如果您给GPU过多的工作,您仍然会获得无响应的计算机。