Question

我正在尝试在webgl中将画布渲染为纹理。

这是代码：

gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, texture);
// gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 1, 1, 0, gl.RGBA, gl.UNSIGNED_BYTE,
                 new Uint8Array([0, 0, 255, 255]));

第一行，texture是一个画布dom元素，用红色填充，如果我将其附加到document.body上，它可以很好地呈现。但是此行不会在webgl上呈现任何内容。

如果我取消注释第二行，它将呈现蓝色。

const fShaderSource = `#version 300 es

precision mediump float;

out vec4 outColor;

uniform sampler2D u_texture;

void main() {
  outColor = texture(u_texture, vec2(0.0));
}

`;

const vShaderSource = `#version 300 es

precision mediump float;

in vec2 a_position;

void main() {
  gl_Position = vec4(a_position, 0, 1);
}
`;

main(document.getElementById('app'));

function main(element) {
  
  const canvas = document.createElement('canvas'),
        gl = canvas.getContext('webgl2');
  element.append(canvas);
  const displayWidth = canvas.clientWidth,
        displayHeight = canvas.clientHeight;
  canvas.width = displayWidth;
  canvas.height = displayHeight;


  let graphics = new Graphics({width: displayWidth, height: displayHeight}, gl);
  
  new Loop(() => {
     graphics.render();
  }).start();
}

function Graphics(state, gl) {

  const { width, height } = state;

  let vShader = createShader(gl, gl.VERTEX_SHADER, vShaderSource);
  let fShader = createShader(gl, gl.FRAGMENT_SHADER, fShaderSource);

  let program = createProgram(gl, vShader, fShader);

  let posAttrLocation = gl.getAttribLocation(program, "a_position");
  let posBuffer = gl.createBuffer();

  gl.bindBuffer(gl.ARRAY_BUFFER, posBuffer);


  /*
    (-1, 1).( 1, 1)
        .
    (-1,-1).( 1,-1)
   */
  let positions = [
    -1, 1,
    -1, -1,
    1, -1,
    -1, 1,
    1,-1,
    1, 1
  ];

  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW);


  let vao = gl.createVertexArray();
  gl.bindVertexArray(vao);

  gl.enableVertexAttribArray(posAttrLocation);

  let size = 2,
      type = gl.FLOAT,
      normalize = false,
      stride = 0,
      offset = 0;

  gl.vertexAttribPointer(posAttrLocation,
                         size,
                         type,
                         normalize,
                         stride,
                         offset);

  let glTexture = gl.createTexture();
  gl.bindTexture(gl.TEXTURE_2D, glTexture);
  
  gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, canvasTexture());
  //gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 1, 1, 0, gl.RGBA, gl.UNSIGNED_BYTE, new Uint8Array([0, 0, 255, 255]));




  let resUniformLocation = gl.getUniformLocation(program, "u_resolution");

  let texUniformLocation = gl.getUniformLocation(program, "u_texture");




  gl.clearColor(0, 0, 0, 0);

  this.render = () => {
    gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
    gl.clear(gl.COLOR_BUFFER_BIT);

    gl.useProgram(program);

    gl.uniform2f(resUniformLocation, gl.canvas.width, gl.canvas.height);
    
    gl.activeTexture(gl.TEXTURE0);
    gl.bindTexture(gl.TEXTURE_2D, glTexture);

    gl.bindVertexArray(vao);
    gl.drawArrays(gl.TRIANGLES, 0, 6);


  };

}

function canvasTexture() {
 
 return withCanvasTexture(256, 256, (w, h, canvas, ctx) => {
    ctx.fillStyle = 'red';
    ctx.fillRect(0, 0, w, h);
    ctx.font = '50pt Comic Sans';
    ctx.fillStyle = 'white';
    ctx.textAlign = 'center';
    ctx.textBaseline = 'middle';
    ctx.fillText('label', w / 2, 50);

    return canvas;
 });
 
function withCanvasTexture(width, height, f) {
  var canvas = document.createElement('canvas');
  canvas.width = width;
  canvas.height = height;
  f(width, height, canvas, canvas.getContext('2d'));
  const texture = canvas;
  document.body.append(canvas);
  return texture;
}
}

function createShader(gl, type, source) {
  let shader = gl.createShader(type);
  gl.shaderSource(shader, source);
  gl.compileShader(shader);
  let success = gl.getShaderParameter(shader, gl.COMPILE_STATUS);

  if (success) {
    return shader;
  }

  console.error(gl.getShaderInfoLog(shader));
  gl.deleteShader(shader);
  return null;
};

function createProgram(gl, vShader, fShader) {
  let program = gl.createProgram();
  gl.attachShader(program, vShader);
  gl.attachShader(program, fShader);
  gl.linkProgram(program);
  let success = gl.getProgramParameter(program, gl.LINK_STATUS);
  if (success) {
    return program;
  }

  console.error(gl.getProgramInfoLog(program));
  gl.deleteProgram(program);
  return null;
}


// Loop Library
function Loop(fn) {

const perf = window.performance !== undefined ? window.performance : Date;

const now = () => perf.now();

const raf = window.requestAnimationFrame;

  let running = false,
      lastUpdate = now(),
      frame = 0;

  this.start = () => {
    if (running) {
      return this;
    }

    running = true;
    lastUpdate = now();
    frame = raf(tick);
    return this;
  };

  this.stop = () => {
    running = false;

    if (frame != 0) {
      raf.cancel(frame);
    }

    frame = 0;
    return this;
  };

  const tick = () => {
    frame = raf(tick);
    const time = now();
    const dt = time - lastUpdate;
    fn(dt);
    lastUpdate = time;
  };
}

#app canvas {
  position: fixed;
  top: 50%;
  bottom: 0;
  left: 50%;
  right: 0;

  width: 100vmin;
  height: 70vmin;

  transform: translate(-50%, -25%);

  image-rendering: optimizeSpeed;
  cursor: none;
  margin: auto;
}

<div id="app">
</div>

Answer 1

您没有正确设置过滤条件。

要渲染不带mips的纹理，您必须将min滤镜设置为LINEAR或NEAREST，因为那些不尝试使用mips的模式

 gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);

要么，要么您需要提供mips

 gl.generateMipmap(gl.TEXTURE_2D);

不能在webgl中将画布渲染为纹理，但是蓝色可以渲染

1 个答案: