图像位移

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位移原理

与在普通的坐标系中一样，只需在需要位移的坐标位置加入相应的矢量即可。
(x1, y1, z1, w1) + (x2, y2, z2, w2) -> (x1 + x2, y1 + y2, z1 + z2, w1 + w2)
平移矩阵：

$$
\begin{bmatrix}
x’ \
y’ \
z’ \
1
\end{bmatrix} =
\begin{bmatrix}
1 & 0 & 0 & Tx \
0 & 1 & 0 & Ty \
0 & 0 & 1 & Tz \
0 & 0 & 0 & 1 \
\end{bmatrix} ×
\begin{bmatrix}
x \
y \
z \
1 \
\end{bmatrix}
$$

代码实现

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// position = P + ▲P
const vShaderSource = `
    attribute vec4 a_Position;
    uniform vec4 u_Translation;
    void main() {
        gl_Position = a_Position + u_Translation;
    }
`

const fShaderSource = `
    void main() {
        gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
    }
`

// Displacement
const Tx = 0.4,
  Ty = -0.2,
  Tz = 0.3
Tw = 0.0

function main() {
  const gl = document.querySelector('#canvas').getContext('webgl')

  if (!initShaders(gl, vShaderSource, fShaderSource)) return

  let n = initVertexBuffers(gl)
  if (n < 0) return

  let u_Translation = gl.getUniformLocation(gl.program, 'u_Translation')
  gl.uniform4f(u_Translation, Tx, Ty, Tz, Tw)

  gl.clearColor(0.0, 0.0, 0.0, 1.0)
  gl.clear(gl.COLOR_BUFFER_BIT)

  gl.drawArrays(gl.TRIANGLES, 0, n)
}

function initVertexBuffers(gl) {
  let vertices = new Float32Array([0.0, 0.5, -0.5, -0.5, 0.5, -0.5])
  let n = vertices.length / 2

  let vertexBuffer = gl.createBuffer()
  if (!vertexBuffer) {
    console.log('failed to create buffer')
    return -1
  }

  gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer)
  gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW)

  let a_Position = gl.getAttribLocation(gl.program, 'a_Position')

  gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0)
  gl.enableVertexAttribArray(a_Position)

  return n
}