void main()

in modules/layers/src/arc-layer/arc-layer-vertex.glsl.js [130:216]
72 lines of code
12 McCabe index (conditional complexity)

void main(void) {
  geometry.worldPosition = instanceSourcePositions;
  geometry.worldPositionAlt = instanceTargetPositions;

  float segmentIndex = positions.x;
  float segmentRatio = getSegmentRatio(segmentIndex);
  // if it's the first point, use next - current as direction
  // otherwise use current - prev
  float indexDir = mix(-1.0, 1.0, step(segmentIndex, 0.0));
  isValid = 1.0;

  uv = vec2(segmentRatio, positions.y);
  geometry.uv = uv;
  geometry.pickingColor = instancePickingColors;

  vec4 curr;
  vec4 next;
  vec3 source;
  vec3 target;

  if ((greatCircle || project_uProjectionMode == PROJECTION_MODE_GLOBE) && project_uCoordinateSystem == COORDINATE_SYSTEM_LNGLAT) {
    source = project_globe_(vec3(instanceSourcePositions.xy, 0.0));
    target = project_globe_(vec3(instanceTargetPositions.xy, 0.0));
    float angularDist = getAngularDist(instanceSourcePositions.xy, instanceTargetPositions.xy);
  
    float prevSegmentRatio = getSegmentRatio(max(0.0, segmentIndex - 1.0));
    float nextSegmentRatio = getSegmentRatio(min(numSegments, segmentIndex + 1.0));

    vec3 prevPos = interpolateGreatCircle(instanceSourcePositions, instanceTargetPositions, source, target, angularDist, prevSegmentRatio);
    vec3 currPos = interpolateGreatCircle(instanceSourcePositions, instanceTargetPositions, source, target, angularDist, segmentRatio);
    vec3 nextPos = interpolateGreatCircle(instanceSourcePositions, instanceTargetPositions, source, target, angularDist, nextSegmentRatio);

    if (abs(currPos.x - prevPos.x) > 180.0) {
      indexDir = -1.0;
      isValid = 0.0;
    } else if (abs(currPos.x - nextPos.x) > 180.0) {
      indexDir = 1.0;
      isValid = 0.0;
    }
    nextPos = indexDir < 0.0 ? prevPos : nextPos;
    nextSegmentRatio = indexDir < 0.0 ? prevSegmentRatio : nextSegmentRatio;

    if (isValid == 0.0) {
      // split at the 180th meridian
      nextPos.x += nextPos.x > 0.0 ? -360.0 : 360.0;
      float t = ((currPos.x > 0.0 ? 180.0 : -180.0) - currPos.x) / (nextPos.x - currPos.x);
      currPos = mix(currPos, nextPos, t);
      segmentRatio = mix(segmentRatio, nextSegmentRatio, t);
    }

    vec3 currPos64Low = mix(instanceSourcePositions64Low, instanceTargetPositions64Low, segmentRatio);
    vec3 nextPos64Low = mix(instanceSourcePositions64Low, instanceTargetPositions64Low, nextSegmentRatio);
  
    curr = project_position_to_clipspace(currPos, currPos64Low, vec3(0.0), geometry.position);
    next = project_position_to_clipspace(nextPos, nextPos64Low, vec3(0.0));
  
  } else {
    source = project_position(instanceSourcePositions, instanceSourcePositions64Low);
    target = project_position(instanceTargetPositions, instanceTargetPositions64Low);

    float nextSegmentRatio = getSegmentRatio(segmentIndex + indexDir);
    vec3 currPos = interpolateFlat(source, target, segmentRatio);
    vec3 nextPos = interpolateFlat(source, target, nextSegmentRatio);
    curr = project_common_position_to_clipspace(vec4(currPos, 1.0));
    next = project_common_position_to_clipspace(vec4(nextPos, 1.0));
    geometry.position = vec4(currPos, 1.0);
  }

  // Multiply out width and clamp to limits
  // mercator pixels are interpreted as screen pixels
  float widthPixels = clamp(
    project_size_to_pixel(instanceWidths * widthScale),
    widthMinPixels, widthMaxPixels
  );

  // extrude
  vec3 offset = vec3(
    getExtrusionOffset((next.xy - curr.xy) * indexDir, positions.y, widthPixels),
    0.0);
  DECKGL_FILTER_SIZE(offset, geometry);
  gl_Position = curr + vec4(project_pixel_size_to_clipspace(offset.xy), 0.0, 0.0);
  DECKGL_FILTER_GL_POSITION(gl_Position, geometry);

  vec4 color = mix(instanceSourceColors, instanceTargetColors, segmentRatio);
  vColor = vec4(color.rgb, color.a * opacity);
  DECKGL_FILTER_COLOR(vColor, geometry);
}