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Revision Cloud Generation

About 2 min

Revision Cloud Generation

Generate AutoCAD REVCLOUD-style revision clouds from path coordinates. The result is a polyline with semicircular arc bulges.

Online Example

Online Demo{target="_blank"}

Overview

A revision cloud is a common CAD markup style used to highlight areas that need changes or attention in a drawing. The algorithm divides each path segment into equal parts according to the specified arc length and assigns each subsegment a semicircular bulge value (bulge = 1) to produce a continuous scalloped outline.

Typical application scenarios:

  • Drawing review markup
  • Change-area marking
  • Highlighting important regions

Usage

Method 1: Command Panel

In the menu bar, choose Create -> Revision Cloud, click Revision Cloud in the Ribbon Draw group, or enter the command REVCLOUD (alias RC).

Method 2: Call in Code

const { PolylineEnt, Engine, generateRevcloudBulgePoints } = vjcad;

// Define path
const path = [[0, 0], [200, 0], [200, 100], [0, 100]];

// Generate bulge points for the revision cloud
const bulgePoints = generateRevcloudBulgePoints(path, {
    arcLength: 30,   // Chord length of each arc segment
    isClosed: true,  // Closed path
});

// Create polyline entity
const cloud = new PolylineEnt(bulgePoints);
cloud.isClosed = true;
cloud.setDefaults();
Engine.addEntities(cloud);

API Reference

generateRevcloudBulgePoints

function generateRevcloudBulgePoints(
    pathPoints: PointInput[],
    options?: RevcloudOptions
): BulgePoints

Generates cloud-style BulgePoints from a path vertex array. The result can be passed directly into new PolylineEnt(bulgePoints).

Parameters

ParameterTypeDescription
pathPointsPointInput[]Path vertex array, at least 2 points. Supports [x, y], Point2D, and other formats
optionsRevcloudOptionsOptional configuration

RevcloudOptions

PropertyTypeDefaultDescription
arcLengthnumber50Chord length of each arc segment
bulgenumber1Bulge value. 1 = semicircle, 0.5 ≈ 90° arc, negative values reverse the arc direction
isClosedbooleanfalseWhether the path is closed. When true, the last vertex automatically connects to the first

Return Value

BulgePoints — a bulged point collection that can be used directly to construct a PolylineEnt.

Algorithm

Input: path point array + arc length parameter
    ↓
For each adjacent point pair:
    ↓
    1. Calculate distance d between the two points
    ↓
    2. Number of arc segments n = max(1, round(d / arcLength))
    ↓
    3. Divide the line segment into n equal parts
    ↓
    4. Set bulge = 1 for each division point
    ↓
Concatenate all division points
(remove duplicate points at joints between adjacent segments)
    ↓
Output: BulgePoints (usable to construct PolylineEnt)

Bulge and Arc Shape

The bulge value determines arc curvature:

bulgeArc ShapeSweep Angle
0Straight line0°
0.5Shallow arc≈ 90°
1Semicircle180°
-1Reverse semicircle180° in the opposite direction

Tips

Revision clouds use bulge = 1 by default, which matches the visual effect of AutoCAD REVCLOUD. You can change the arc curvature by adjusting the bulge parameter.

Examples

Closed Rectangular Revision Cloud

const path = [[0, 0], [200, 0], [200, 100], [0, 100]];
const bp = generateRevcloudBulgePoints(path, {
    arcLength: 20,
    isClosed: true,
});
const cloud = new PolylineEnt(bp);
cloud.isClosed = true;
cloud.setDefaults();
Engine.addEntities(cloud);

Open-Path Revision Cloud

const path = [[0, 0], [80, 30], [160, 0], [240, 30]];
const bp = generateRevcloudBulgePoints(path, {
    arcLength: 15,
    isClosed: false,
});
const cloud = new PolylineEnt(bp);
cloud.setDefaults();
Engine.addEntities(cloud);

Compare Different Arc Lengths

[10, 25, 50].forEach((arcLen, i) => {
    const bp = generateRevcloudBulgePoints(
        [[0, i * 40], [300, i * 40]],
        { arcLength: arcLen }
    );
    const pline = new PolylineEnt(bp);
    pline.setDefaults();
    pline.color = i + 1;
    Engine.addEntities(pline);
});