gl_Position =
      vec4(a.x * (0.5 - b.x) * v -
               a.y * b.y * u - offset * offsetMul * u,
           0, 0) +
      transform * vec4(position, 0, 1);

attribute vec4 position;    // your data
attribute float a_count;    // count 0, 1, 2, 3
uniform vec2 u_resolution;  // resolution of output texture

// vertex shader
varying vec4 v_position;

void main() {
  v_position =
      vec4(a.x * (0.5 - b.x) * v -
               a.y * b.y * u - offset * offsetMul * u,
           0, 0) +
      transform * vec4(position, 0, 1);
  vec2 pixelCoord = vec2(
      mod(a_count, resolution.x);
      floor(a_count / resolution.x));
  vec2 clipSpaceCoord = (pixelCoord + 0.5) / resolution * 2.0 - 1.0;

  gl_Position = vec4(clipSpaceCoord, 0, 1);
}

// fragment shdaer
precision highp float
varying vec4 v_position;
void main() {
  gl_FragColor = v_position;
}