const canvas = document.getElementById('myCanvas');
const gl = canvas.getContext('webgl');

if (!gl) {
  alert('你的浏览器不支持WebGL');
}

// 顶点着色器源码
const vertexShaderSource = `
  attribute vec4 a_position;
  void main() {
    gl_Position = a_position;
  }
`;

// 片段着色器源码
const fragmentShaderSource = `
  precision mediump float;
  void main() {
    gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0); // 红色
  }
`;

function createShader(gl, type, source) {
  const shader = gl.createShader(type);
  gl.shaderSource(shader, source);
  gl.compileShader(shader);
  if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
    console.error('Shader编译失败:', gl.getShaderInfoLog(shader));
    gl.deleteShader(shader);
    return null;
  }
  return shader;
}

function createProgram(gl, vertexShader, fragmentShader) {
  const program = gl.createProgram();
  gl.attachShader(program, vertexShader);
  gl.attachShader(program, fragmentShader);
  gl.linkProgram(program);
  if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
    console.error('Program链接失败:', gl.getProgramInfoLog(program));
    return null;
  }
  return program;
}

// 使用方式
const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource);
const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource);
const program = createProgram(gl, vertexShader, fragmentShader);
gl.useProgram(program);

const positions = [
  -0.5, -0.5,
   0.5, -0.5,
   0.0,  0.5
];

const positionBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW);

const positionAttributeLocation = gl.getAttribLocation(program, 'a_position');
gl.enableVertexAttribArray(positionAttributeLocation);
gl.vertexAttribPointer(positionAttributeLocation, 2, gl.FLOAT, false, 0, 0);

gl.drawArrays(gl.TRIANGLES, 0, 3); // 绘制三角形

gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);