如何使用直线webgl (无THREE.js)将网格线添加到函数中？

// 步骤1：创建Canvas元素
const canvas = document.createElement('canvas');
document.body.appendChild(canvas);

// 步骤2：获取WebGL上下文
const gl = canvas.getContext('webgl');

// 步骤3：创建顶点着色器和片段着色器
const vertexShaderSource = `
    attribute vec2 a_position;
    void main() {
        gl_Position = vec4(a_position, 0, 1);
    }
`;

const fragmentShaderSource = `
    precision mediump float;
    uniform vec4 u_color;
    void main() {
        gl_FragColor = u_color;
    }
`;

// 步骤4：编译和链接着色器
const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource);
const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource);
const program = createProgram(gl, vertexShader, fragmentShader);

// 步骤5：创建缓冲区对象
const buffer = gl.createBuffer();

// 步骤6：定义顶点数据
const vertices = [
    -1, 0,
    1, 0,
    0, -1,
    0, 1
];

// 步骤7：将顶点数据存储到缓冲区对象中
gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);

// 步骤8：启用attribute变量并指定顶点数据布局
const positionAttributeLocation = gl.getAttribLocation(program, 'a_position');
gl.enableVertexAttribArray(positionAttributeLocation);
gl.vertexAttribPointer(positionAttributeLocation, 2, gl.FLOAT, false, 0, 0);

// 步骤9：设置视口和清除画布
gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
gl.clearColor(0, 0, 0, 1);
gl.clear(gl.COLOR_BUFFER_BIT);

// 步骤10：使用着色器程序
gl.useProgram(program);

// 步骤11：绘制网格线
gl.uniform4fv(gl.getUniformLocation(program, 'u_color'), [1, 1, 1, 1]);
gl.drawArrays(gl.LINES, 0, 2);

gl.uniform4fv(gl.getUniformLocation(program, 'u_color'), [1, 0, 0, 1]);
gl.drawArrays(gl.LINES, 2, 2);

// 步骤12：结束渲染循环

// 创建着色器函数
function createShader(gl, type, source) {
    const shader = gl.createShader(type);
    gl.shaderSource(shader, source);
    gl.compileShader(shader);
    const success = gl.getShaderParameter(shader, gl.COMPILE_STATUS);
    if (success) {
        return shader;
    }
    console.log(gl.getShaderInfoLog(shader));
    gl.deleteShader(shader);
}

// 创建着色器程序函数
function createProgram(gl, vertexShader, fragmentShader) {
    const program = gl.createProgram();
    gl.attachShader(program, vertexShader);
    gl.attachShader(program, fragmentShader);
    gl.linkProgram(program);
    const success = gl.getProgramParameter(program, gl.LINK_STATUS);
    if (success) {
        return program;
    }
    console.log(gl.getProgramInfoLog(program));
    gl.deleteProgram(program);
}