attribute vec2 a_position;
attribute float a_size;
attribute float a_angle;
attribute vec4 a_color;

uniform mat3 u_matrix;
uniform float u_sqrtZoomRatio;
uniform float u_correctionRatio;

varying vec4 v_color;
varying vec2 v_diffVector;
varying float v_radius;
varying float v_border;

const float bias = 255.0 / 254.0;
const float marginRatio = 1.05;

void main() {
  float size = a_size * u_correctionRatio * u_sqrtZoomRatio * 4.0;
  vec2 diffVector = size * vec2(cos(a_angle), sin(a_angle));
  vec2 position = a_position + diffVector * marginRatio;
  gl_Position = vec4(
    (u_matrix * vec3(position, 1)).xy,
    0,
    1
  );

  v_border = u_correctionRatio * u_sqrtZoomRatio * u_sqrtZoomRatio;
  v_diffVector = diffVector;
  v_radius = size / 2.0 / marginRatio;

  v_color = a_color;
  v_color.a *= bias;
}