Question

我正在尝试使用两个缓冲区渲染两个三角形，我已经看过一些教程并尝试两次调用glDrawArrays函数。但是，只渲染了最新的缓冲区数据，即只渲染了一个三角形。请提前帮助我解决和理解绘制多个对象的概念。

这是代码

// HelloTriangle.js (c) 2012 matsuda
// Vertex shader program
var VSHADER_SOURCE =
  'attribute vec4 a_Position;\n' +
  'void main() {\n' +
  '  gl_Position = a_Position;\n' +
  '}\n';

// Fragment shader program
var FSHADER_SOURCE =
  'void main() {\n' +
  '  gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);\n' +
  '}\n';

function main() {
  // Retrieve <canvas> element
  var canvas = document.getElementById('webgl');

  // Get the rendering context for WebGL
  var gl = getWebGLContext(canvas);
  if (!gl) {
    console.log('Failed to get the rendering context for WebGL');
    return;
  }

  // Initialize shaders
  if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {
    console.log('Failed to intialize shaders.');
    return;
  }

  // Write the positions of vertices to a vertex shader
  var n = initVertexBuffers(gl);
  if (n < 0) {
    console.log('Failed to set the positions of the vertices');
    return;
  }

  // Specify the color for clearing <canvas>
  gl.clearColor(0, 0, 0, 1);

  // Clear <canvas>
  gl.clear(gl.COLOR_BUFFER_BIT);

  // Draw the rectangle
  gl.drawArrays(gl.TRIANGLES, 0, n);

   gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0);
     gl.drawArrays(gl.TRIANGLES, 0, n);
}

function initVertexBuffers(gl) {
  var vertices = new Float32Array([
    0, 0.5,   -0.5, -0.5,   0.5, -0.5,
  ]);

    var verticesOne = new Float32Array([
     0.5, -0.5,   0, 0.5,   0.5, 2.0
  ]);
  var n = 3; // The number of vertices

  // Create a buffer object
  var vertexBuffer = gl.createBuffer();
  if (!vertexBuffer) {
    console.log('Failed to create the buffer object');
    return -1;
  }
var vertexBufferO = gl.createBuffer();
  // Bind the buffer object to target
  gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
  // Write date into the buffer object
  gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);

    gl.bindBuffer(gl.ARRAY_BUFFER, vertexBufferOne);
  // Write date into the buffer object
  gl.bufferData(gl.ARRAY_BUFFER, verticesOne, gl.STATIC_DRAW);

  var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
  if (a_Position < 0) {
    console.log('Failed to get the storage location of a_Position');
    return -1;
  }
  // Assign the buffer object to a_Position variable
  gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0);

  // Enable the assignment to a_Position variable
  gl.enableVertexAttribArray(a_Position);

  return n;
}

Answer 1

WebGL基本上只有2个“真实”功能。 <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script> <li style="display: block;"><input type="checkbox">Lead1 <br> <ul> <li style="display: block;"><input type="checkbox"> All Leads <br></li> <li style="display: block;"><input type="checkbox"> Recent Leads <br></li> <li style="display: block;"><input type="checkbox"> My Leads <br></li> </ul> </li> <li style="display: block;"><input type="checkbox">Lead2 <br> <ul> <li style="display: block;"><input type="checkbox"> first <br></li> <li style="display: block;"><input type="checkbox"> second <br></li> <li style="display: block;"><input type="checkbox"> third <br></li> </ul> </li>和gl.drawArrays几乎所有WebGL API的其余部分都只是为这两个函数设置状态。

因此，对于您绘制的每件事，您需要设置所需的所有状态。

gl.drawElements

在初始化期间，您只执行了两次步骤1。在你画出那个特定的东西之前，它需要发生。

Here's one tutorial that might help以及another answer和another question

使用两个缓冲区尝试渲染两个三角形WebGL

1 个答案: