const VSHADER_SOURCE = `
  attribute vec4 a_position;
  uniform mat4 u_xformMatrix;
  void main(void){
    gl_Position=u_xformMatrix *  a_position;
  }
`

let angle = 60
const radian = Math.PI * angle / 180
const cosB = Math.cos(radian)
const sinB = Math.sin(radian)
const xformMatrix = new Float32Array([
  cosB, sinB, 0.0, 0.0,
  -sinB, cosB, 0.0, 0.0,
  0.0, 0.0, 1.0, 0.0,
  0.0, 0.0, 0.0, 1.0,
])
const u_xformMatrix = webgl.getUniformLocation(webgl.program, 'u_xformMatrix')
webgl.uniformMatrix4fv(u_xformMatrix, false, xformMatrix)

const render = () => {
  const matrixUniformLocation = webgl.getUniformLocation(webgl.program, "matrix")
  // 計(jì)算旋轉(zhuǎn)矩陣
  const angle = performance.now() / 2000 * Math.PI
  const rotationMatrix = mat3.fromRotation(mat3.create(), angle)
  // 將矩陣傳遞給著色器程序
  webgl.useProgram(webgl.program)
  webgl.uniformMatrix3fv(matrixUniformLocation, false, rotationMatrix)
  // 繪制三角形
  webgl.clear(webgl.COLOR_BUFFER_BIT)
  webgl.drawArrays(webgl.TRIANGLES, 0, 3)
  // 循環(huán)調(diào)用渲染函數(shù)以實(shí)現(xiàn)動(dòng)態(tài)旋轉(zhuǎn)
  requestAnimationFrame(render)
}

const vertexShaderSource = `
  attribute vec3 aPosition;
  attribute vec3 aColor;
  varying vec3 vColor;
  uniform mat4 uModelMatrix;
  void main() {
    gl_Position = uModelMatrix * vec4(aPosition, 1.0);
    vColor = aColor;
  }
`

const render = () => {
  webgl.clear(webgl.COLOR_BUFFER_BIT)
  const rotation = Date.now() * rotationSpeed / 10
  // 設(shè)置放縮變換矩陣
  let scaleMatrix = mat4.create()
  mat4.scale(scaleMatrix, scaleMatrix, [scale, scale, scale])
  // 設(shè)置旋轉(zhuǎn)變換矩陣
  let rotationMatrix = mat4.create()
  mat4.rotateZ(rotationMatrix, rotationMatrix, rotation)
  // 將旋轉(zhuǎn)和放縮變換矩陣相乘
  let transformMatrix = mat4.create()
  mat4.multiply(transformMatrix, rotationMatrix, scaleMatrix)
  // 將變換矩陣傳遞給uniform變量
  webgl.uniformMatrix4fv(matrixUniformLocation, false, transformMatrix)
  // 繪制正方形
  webgl.clearColor(0.0, 1.0, 1.0, 1.0)
  webgl.drawArrays(webgl.TRIANGLE_STRIP, 0, 4)
  // 更新放縮因子
  updateScale()
  // 循環(huán)調(diào)用渲染函數(shù)以實(shí)現(xiàn)動(dòng)態(tài)旋轉(zhuǎn)
  requestAnimationFrame(render)
}

const matrixUniformLocation = webgl.getUniformLocation(webgl.program, "uModelMatrix")
const rotationSpeed = 0.005
let scale = 1.0
let delta = 0.005
let direction = 1
const updateScale = () => {
  scale += delta * direction;
  if (scale >= 1.2 || scale <= 0.5) {
    direction = -direction;
  }
}