在 WebGL 中绘制许多形状

我正在阅读教程here.

<script class = "WebGL">
var gl;
function initGL() {
  // Get A WebGL context
  var canvas = document.getElementById("canvas");
  gl = getWebGLContext(canvas);
  if (!gl) {
    return;
  }
}
var positionLocation;
var resolutionLocation;
var colorLocation;
var translationLocation;
var rotationLocation;
var translation = [50,50];
var rotation = [0, 1];
var angle = 0;
function initShaders() {
  // setup GLSL program
  vertexShader = createShaderFromScriptElement(gl, "2d-vertex-shader");
  fragmentShader = createShaderFromScriptElement(gl, "2d-fragment-shader");
  program = createProgram(gl, [vertexShader, fragmentShader]);
  gl.useProgram(program);

  // look up where the vertex data needs to go.
  positionLocation = gl.getAttribLocation(program, "a_position");

  // lookup uniforms
  resolutionLocation = gl.getUniformLocation(program, "u_resolution");
  colorLocation = gl.getUniformLocation(program, "u_color");
  translationLocation = gl.getUniformLocation(program, "u_translation");
    rotationLocation = gl.getUniformLocation(program, "u_rotation");

  // set the resolution
  gl.uniform2f(resolutionLocation, canvas.width, canvas.height);
}
function initBuffers() {
  // Create a buffer.
  var buffer = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
  gl.enableVertexAttribArray(positionLocation);
  gl.vertexAttribPointer(positionLocation, 2, gl.FLOAT, false, 0, 0);

  // Set Geometry.
  setGeometry(gl);
}

function setColor(red, green, blue) {
    gl.uniform4f(colorLocation, red, green, blue, 1);
}
// Draw the scene.
function drawScene() {
    // Clear the canvas.
    gl.clear(gl.COLOR_BUFFER_BIT);

    // Set the translation.
    gl.uniform2fv(translationLocation, translation);
    // Set the rotation.
    gl.uniform2fv(rotationLocation, rotation);

    // Draw the geometry.
    gl.drawArrays(gl.TRIANGLES, 0, 6);
}


// Fill the buffer with the values that define a letter 'F'.
function setGeometry(gl) {
/*Assume size1 is declared*/
    var vertices = [
         -size1/2, -size1/2,
         -size1/2, size1/2,
         size1/2, size1/2,
         size1/2, size1/2,
         size1/2, -size1/2,
         -size1/2, -size1/2 ];
      gl.bufferData(
         gl.ARRAY_BUFFER,
         new Float32Array(vertices),
         gl.STATIC_DRAW);
}
function animate() {
    translation[0] += 0.01;
    translation[1] += 0.01;
    angle += 0.01;
    rotation[0] = Math.cos(angle);
    rotation[1] = Math.sin(angle);
}
function tick() {
    requestAnimFrame(tick);
    drawScene();
    animate();
}
function start() {

    initGL();
    initShaders();
    initBuffers();
    setColor(0.2, 0.5, 0.5);
    tick();
}

</script>

<!-- vertex shader -->
<script id="2d-vertex-shader" type="x-shader/x-vertex">
    attribute vec2 a_position;

    uniform vec2 u_resolution;
    uniform vec2 u_translation;
    uniform vec2 u_rotation;
    void main() {
        vec2 rotatedPosition = vec2(
        a_position.x * u_rotation.y + a_position.y * u_rotation.x,
        a_position.y * u_rotation.y - a_position.x * u_rotation.x);

       // Add in the translation.
       vec2 position = rotatedPosition + u_translation;

       // convert the position from pixels to 0.0 to 1.0
       vec2 zeroToOne = position / u_resolution;

       // convert from 0->1 to 0->2
       vec2 zeroToTwo = zeroToOne * 2.0;

       // convert from 0->2 to -1->+1 (clipspace)
       vec2 clipSpace = zeroToTwo - 1.0;

       gl_Position = vec4(clipSpace, 0, 1);
    }
</script>
<!-- fragment shader -->
<script id="2d-fragment-shader" type="x-shader/x-fragment">
    precision mediump float;

    uniform vec4 u_color;

    void main() {
       gl_FragColor = u_color;
    }
</script>

我的 1 个形状的 WebGL 程序的工作原理如下：

1. 从 canvas 元素获取上下文 (gl)。
2. 用我的对象的形状初始化缓冲区
3. drawScene(): 打电话给gl.drawArrays()
4. 如果有动画，更新函数，它会更新我的形状的角度、位置， 进而drawScene()同时在tick()，以便它被重复调用。

现在，当我需要超过 1 个形状时，我是否应该立即用许多对象填充单个缓冲区，然后使用它来稍后调用drawScene()一次绘制所有对象[OR]我应该重复打电话吗initBuffer and drawScene() from requestAnimFrame().

在伪代码中

在初始化时

• 从 canvas 元素获取上下文 (gl)。
• for each shader
  • 创建着色器
  • 查找属性和统一位置
• for each shape
  • 使用形状初始化缓冲区
• for each texture
  • 创建纹理和/或用数据填充它们。

抽奖时

• for each shape
  • 如果最后使用的着色器与此形状调用所需的着色器不同gl.useProgram
  • For each attribute needed by shader
    • call gl.enableVertexAttribArray, gl.bindBuffer and gl.vertexAttribPointer对于形状所需的每个属性以及当前着色器的属性位置。
  • For each uniform needed by shader
    • call gl.uniformXXX使用当前着色器的位置与所需的值
  • call gl.drawArrays或者如果数据被索引称为gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, bufferOfIndicesForCurrentShape)其次是gl.drawElements

常见优化

1）通常你不需要设置每件制服。例如，如果您使用以下命令绘制 10 个形状same着色器并且该着色器采用viewMatrix或cameraMatrix，viewMatrix制服或cameraMatrix制服很可能对于每个形状都是相同的，因此只需设置一次。

2) 您通常可以将呼叫转移至gl.enableVertexAttribArray到初始化时间。