attribute vec2 a_position;
attribute vec4 a_color;

uniform mat3 u_matrix;

varying vec4 v_color;

const float bias = 255.0 / 254.0;

void main() {
  // Scale from [[-1 1] [-1 1]] to the container:
  gl_Position = vec4(
    (u_matrix * vec3(a_position, 1)).xy,
    0,
    1
  );

  // Extract the color:
  v_color = a_color;
  v_color.a *= bias;
}