在移动设备上全屏、全 dpi WebGL canvas

Question

有什么方法可以使 canvas 在移动设备上的大小与设备屏幕的实际像素大小成一比？

这对于 google 直接从站点支持纸板 (VR) 应用程序很重要。（在这种情况下 dpi 真的很重要）

目前使用视口 target-densitydpi 的唯一方法已被弃用，并且不适用于现代浏览器。

Answer 1

最简单的方法是使用 CSS 来决定您想要 canvas 的尺寸。然后使用 canvas.clientWidth 和 canvas.clientHeight 查看浏览器以 CSS 像素显示的 canvas 的大小。现在将其乘以 window.devicePixelRatio 以获得那些 CSS 像素代表的设备像素数，并设置 canvas 的 content/drawingbuffer 大小以匹配。

示例：

制作canvas
```
<canvas id="c"></canvas>  
```
使用 CSS
设置其大小
在这里，我将 canvas 设为视口的大小（window）。
```
body {
  margin: 0;
}
canvas {
  width: 100vw;
  height: 100vh; 
  display: block;
}
```

查找显示的大小并匹配其绘图缓冲区大小。

function resizeToMatchDisplaySize(canvas) {
  var displayWidth  = canvas.clientWidth  * window.devicePixelRatio;
  var displayHeight = canvas.clientHeight * window.devicePixelRatio;
  if (canvas.width !== displayWidth || canvas.height !== displayHeight) {
    canvas.width  = displayWidth;
    canvas.height = displayHeight;
    return true;
  }
  return false;
}

在渲染每一帧之前调整大小

function render() {
  // resize before rendering in case of resizing or rotation
  if (resizeToMatchDisplaySize(gl.canvas)) {
    gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight); 
  }


  // render scene

  requestAnimationFrame(render);
}
requestAnimationFrame(render);

下面是一个画线的例子

var gl = document.querySelector("#c").getContext("webgl", { alpha: false });
var programInfo = twgl.createProgramInfo(gl, ['vs', 'fs']);
var ids = [];
for (var i = 0; i < 500; ++i) {
  ids.push(i);
}
var arrays = {
  vertexId: { size:1, data: ids},
};
var bufferInfo = twgl.createBufferInfoFromArrays(gl, arrays);

var uniforms = {
  time: 0,
  numIds: ids.length,
  resolution: [0, 0],
};

function resizeToMatchDisplaySize(canvas) {
  var displayWidth  = canvas.clientWidth  * window.devicePixelRatio;
  var displayHeight = canvas.clientHeight * window.devicePixelRatio;
  if (canvas.width !== displayWidth || canvas.height !== displayHeight) {
    canvas.width  = displayWidth;
    canvas.height = displayHeight;
    return true;
  }
  return false;
}

function render(time) {
  // resize before rendering in case of resizing or rotation
  if (resizeToMatchDisplaySize(gl.canvas)) {
    gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight);
  }
  
  // render scene
  gl.useProgram(programInfo.program);
  uniforms.time = time * 0.001;
  uniforms.resolution[0] = gl.drawingBufferWidth;
  uniforms.resolution[1] = gl.drawingBufferHeight;
  twgl.setBuffersAndAttributes(gl, programInfo, bufferInfo);
  twgl.setUniforms(programInfo, uniforms);
  twgl.drawBufferInfo(gl, gl.LINES, bufferInfo);
  
  requestAnimationFrame(render);
}
requestAnimationFrame(render);

body {
  margin: 0;
}
canvas {
  width: 100vw;
  height: 100vh;
  display: block;
}

<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
<canvas id="c"></canvas>
  <script id="vs" type="notjs">
attribute float vertexId;

varying vec4 v_color;

uniform float numIds;
uniform float time;
uniform vec2 resolution;

#define PI radians(180.0)

vec3 hsv2rgb(vec3 c) {
  c = vec3(c.x, clamp(c.yz, 0.0, 1.0));
  vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
  vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
  return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
}


void main() {
  vec4 offsets = vec4(
    sin(time), 
    sin(time * .13) * PI * 2.,
    sin(time * .43) * .5 + 1.,
    cos(time * .17) * .5 + .5);

  vec4 centers = vec4(
    sin(time * .163) * .5,
    cos(time * .267) * .5,
    sin(time * .367) * .5,
    cos(time * .497) * .5);

  vec4 mult = vec4(
    1.,
    (sin(time * .1) * .5 + .5) * 3.,
    0.,
    0.);

  vec2 position = vec2(vertexId / numIds, mod(vertexId, 2.));
  vec2 offset = mix(offsets.xz, offsets.yw, position.y);
  float a = mult.x * position.x * PI * 2.0 + offset.x;//mix(u_offsets.x, u_offsets.y, a_position.y);
  float c = cos(a * mult.y);
  vec2 xy = vec2(
    cos(a),
    sin(a)) * c * offset.y +
    mix(centers.xy, centers.zw, position.y);
  vec2 aspect = vec2(resolution.y / resolution.x, 1);
  gl_Position = vec4(xy * aspect, 0, 1);
  
  float hue = position.x;
  float sat = 1.;
  float val = 1.;
  v_color = vec4(hsv2rgb(vec3(hue, sat, val)), 1);
}
  </script>
  <script id="fs" type="notjs">
precision mediump float;
varying vec4 v_color;
void main() {
  gl_FragColor = v_color;
}
  </script>
  <script src="https://twgljs.org/dist/twgl-full.min.js"></script>

请注意，您问了 2 个问题。如何获得原生 1x1 像素以及如何进入全屏。全屏更难。 iOS Safari 不支持 fullscreen API。 Chrome for android 可以，但它需要您的网站从 HTTPS 提供服务。

你也应该把这个放在你的<head>部分

<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">

并根据需要将user-scalable设置为yes或no

在移动设备上全屏、全 dpi WebGL canvas

Fullscreen, full dpi WebGL canvas on mobile device

mobile

android

webgl

ios

webvr