WebGL 重置顶点位置

Question

我正在创建一个简单的 webgl 程序，它在画布上放置 3 个随机顶点并将它们连接成一个三角形。我尝试添加平移以将三角形向右移动（增加每个顶点的 X 值），但当然，如果它永远消失，三角形就会离开画布。有谁知道如何检测顶点的 x 值是否大于 1，如果是，则重置给定顶点的位置，因为我的解决方案似乎没有做任何事情，它甚至没有触发

var canvas = document.getElementById("canvas");
var gl = canvas.getContext("webgl");

gl.clearColor(0.1, 0.2, 0.2, 1.0);
gl.clear(gl.DEPTH_BUFFER_BIT | gl.COLOR_BUFFER_BIT);

var indices = [0, 0, 0, 0, 0, 0];
for (var points = 0; points < 6; points++) {
  indices[points] = (Math.random() * 2) - 1;
  //indices[points + 1] = Math.random() < 0.5 ? -1 : 1;
}

var buf = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, buf);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(indices),
  gl.STATIC_DRAW);

var vert = gl.createShader(gl.VERTEX_SHADER);
gl.shaderSource(vert, `
      precision mediump float;

      attribute vec2 position;
      uniform vec2 translation;

      void main(){
        gl_Position = vec4(position + translation, 0.0, 1.0);
      }
      `);
gl.compileShader(vert);
var success1 = gl.getShaderParameter(vert, gl.COMPILE_STATUS);
if (!success1) {
  // Something went wrong during compilation; get the error
  throw gl.getShaderInfoLog(vert);
}

var frag = gl.createShader(gl.FRAGMENT_SHADER);
gl.shaderSource(frag, `
      precision mediump float;
      void main(){
        gl_FragColor = vec4(0.3, 0.6, 0.4, 1.0);
      }
      `);
gl.compileShader(frag);
var success2 = gl.getShaderParameter(frag, gl.COMPILE_STATUS);
if (!success2) {
  // Something went wrong during compilation; get the error
  throw gl.getShaderInfoLog(frag);
}




var program = gl.createProgram();
gl.attachShader(program, vert);
gl.attachShader(program, frag);
gl.linkProgram(program);

var vertLoc = gl.getAttribLocation(program, "position");
gl.vertexAttribPointer(vertLoc, 2, gl.FLOAT, gl.FALSE, 0, 0);
gl.enableVertexAttribArray(vertLoc);

gl.useProgram(program);

var trans = gl.getUniformLocation(program, "translation");
var translation = [0.0, 0.0];
gl.uniform2fv(trans, translation);


gl.drawArrays(gl.TRIANGLES, 0, 3);

function loop() {
  gl.clearColor(0.1, 0.2, 0.2, 1.0);
  gl.clear(gl.DEPTH_BUFFER_BIT | gl.COLOR_BUFFER_BIT);
  translation[0] += 0.01;
  gl.uniform2fv(trans, translation);



  gl.drawArrays(gl.TRIANGLES, 0, 3);

  for (var points = 0; points < 6; points++) {
    if (indices[points] % 2 == 0) {
      if (indices[points] + translation[0] > 1) {
        indices[points] = (Math.random() * 2) - 1;
      }
    }
    //indices[points + 1] = Math.random() < 0.5 ? -1 : 1;
  }
  requestAnimationFrame(loop);
}
loop();

<canvas id="canvas"></canvas>

Answer 1

要实现这一点，请考虑对您的代码进行以下更改：

• 在您的顶点着色器中通过translation 删除顶点的放置，以便您“按顶点”控制几何体的放置（translation 实际上意味着“对象级”放置，这不是什么你想要的）

• 当您在 loop() 中迭代 points 时，您会检查顶点坐标上的模数。您应该像这样对迭代索引执行检查：if (points % 2 == 0)

• 现在translation 的概念消失了，更新顶点坐标的位置，而不是模检查后的translation 数组：indices[points] += 0.01;

• 最后，看到您正在更新 indices 顶点数据，您需要更新 webgl buf 以确保在渲染下一帧时反映您的更改：

  gl.bindBuffer(gl.ARRAY_BUFFER, buf);
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(indices), gl.STATIC_DRAW);
  

这是完整的更新脚本：

var canvas = document.getElementById("canvas");
var gl = canvas.getContext("webgl");

gl.clearColor(0.1, 0.2, 0.2, 1.0);
gl.clear(gl.DEPTH_BUFFER_BIT | gl.COLOR_BUFFER_BIT);

var indices = [0, 0, 0, 0, 0, 0];
for (var points = 0; points < 6; points++) {
  indices[points] = (Math.random() * 2) - 1;
}

var buf = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, buf);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(indices),
  gl.STATIC_DRAW);

var vert = gl.createShader(gl.VERTEX_SHADER);
gl.shaderSource(vert, `
          precision mediump float;

          attribute vec2 position;

          void main(){
            gl_Position = vec4(position, 0.0, 1.0);
          }
          `);
gl.compileShader(vert);
var success1 = gl.getShaderParameter(vert, gl.COMPILE_STATUS);
if (!success1) {
  throw gl.getShaderInfoLog(vert);
}

var frag = gl.createShader(gl.FRAGMENT_SHADER);
gl.shaderSource(frag, `
          precision mediump float;
          void main(){
            gl_FragColor = vec4(0.3, 0.6, 0.4, 1.0);
          }
          `);
gl.compileShader(frag);
var success2 = gl.getShaderParameter(frag, gl.COMPILE_STATUS);
if (!success2) {
  throw gl.getShaderInfoLog(frag);
}

var program = gl.createProgram();
gl.attachShader(program, vert);
gl.attachShader(program, frag);
gl.linkProgram(program);

var vertLoc = gl.getAttribLocation(program, "position");
gl.vertexAttribPointer(vertLoc, 2, gl.FLOAT, gl.FALSE, 0, 0);
gl.enableVertexAttribArray(vertLoc);

gl.useProgram(program);
gl.drawArrays(gl.TRIANGLES, 0, 3);

function loop() {
  gl.clearColor(0.1, 0.2, 0.2, 1.0);
  gl.clear(gl.DEPTH_BUFFER_BIT | gl.COLOR_BUFFER_BIT);

  gl.drawArrays(gl.TRIANGLES, 0, 3);

  // Update the vertex data, causing the vertex x coordinate to increase per-frame
  for (var points = 0; points < 6; points++) {

    // Only process x coordinate
    if (points % 2 == 0) {

      // Increase x coordinate per-frame
      indices[points] += 0.01;

      // If x position > 1 reset it to a new random value
      if (indices[points] > 1) {
        indices[points] = (Math.random() * 2) - 1;
      }
    }
  }

  // Update webgl vertex buffer so that updated indices data is rendered
  gl.bindBuffer(gl.ARRAY_BUFFER, buf);
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(indices), gl.STATIC_DRAW);

  requestAnimationFrame(loop);
}
loop();

<canvas id="canvas"><canvas>