Acad Hatches

AutoCAD Hatches and Gradient Fills

Use this skill when creating or modifying hatch patterns, solid fills, or gradient fills in drawings.

Creating a Hatch Pattern

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTableRecord btr = (BlockTableRecord)tr.GetObject(
        db.CurrentSpaceId, OpenMode.ForWrite);

    Hatch hatch = new Hatch();
    hatch.SetDatabaseDefaults();
    hatch.Normal = Vector3d.ZAxis;
    hatch.Elevation = 0.0;

    // Step 1: Add to database FIRST (required before SetHatchPattern and AppendLoop)
    btr.AppendEntity(hatch);
    tr.AddNewlyCreatedDBObject(hatch, true);

    // Step 2: Set pattern AFTER AppendEntity, BEFORE AppendLoop
    hatch.SetHatchPattern(HatchPatternType.PreDefined, "ANSI31");
    hatch.PatternScale = 1.0;
    hatch.PatternAngle = 0.0;

    // Step 3: Set Associative BEFORE AppendLoop
    hatch.Associative = true;

    // Step 4: Add boundary loop
    ObjectIdCollection boundaryIds = new ObjectIdCollection();
    boundaryIds.Add(polylineId);  // closed polyline as boundary
    hatch.AppendLoop(HatchLoopTypes.External, boundaryIds);

    // Evaluate to generate hatch lines
    hatch.EvaluateHatch(true);

    tr.Commit();
}

Boundary Loop Types

From Entity IDs (most common)

ObjectIdCollection outerBoundary = new ObjectIdCollection();
outerBoundary.Add(outerPolylineId);
hatch.AppendLoop(HatchLoopTypes.External, outerBoundary);

// Add island (inner boundary)
ObjectIdCollection innerBoundary = new ObjectIdCollection();
innerBoundary.Add(innerCircleId);
hatch.AppendLoop(HatchLoopTypes.Default, innerBoundary);

From Polyline Vertices (with bulge)

Point2dCollection vertices = new Point2dCollection();
vertices.Add(new Point2d(0, 0));
vertices.Add(new Point2d(100, 0));
vertices.Add(new Point2d(100, 100));
vertices.Add(new Point2d(0, 100));

DoubleCollection bulges = new DoubleCollection();
bulges.Add(0); bulges.Add(0); bulges.Add(0); bulges.Add(0);

hatch.AppendLoop(HatchLoopTypes.External | HatchLoopTypes.Polyline,
    vertices, bulges);

From 2D Curve Edges

Curve2dCollection edges = new Curve2dCollection();
IntegerCollection edgeTypes = new IntegerCollection();

edges.Add(new LineSegment2d(new Point2d(0, 0), new Point2d(100, 0)));
edgeTypes.Add((int)HatchEdgeType.Line);  // 1

edges.Add(new CircularArc2d(
    new Point2d(100, 0), new Point2d(100, 50), new Point2d(100, 100)));
edgeTypes.Add((int)HatchEdgeType.CircularArc);  // 2

edges.Add(new LineSegment2d(new Point2d(100, 100), new Point2d(0, 0)));
edgeTypes.Add((int)HatchEdgeType.Line);

hatch.AppendLoop(HatchLoopTypes.External, edges, edgeTypes);

Using HatchLoop Object

HatchLoop loop = new HatchLoop(HatchLoopTypes.External);
// loop is read-only after construction; use for inspection:
// loop.Curves, loop.Polyline, loop.LoopType, loop.IsPolyline

hatch.AppendLoop(loop);

Loop Management

int loopCount = hatch.NumberOfLoops;
HatchLoopTypes loopType = hatch.LoopTypeAt(0);
HatchLoop loop = hatch.GetLoopAt(0);

// Insert loop at specific position
hatch.InsertLoopAt(1, HatchLoopTypes.Default, boundaryIds);
hatch.InsertLoopAt(1, hatchLoop);

// Remove loop
hatch.RemoveLoopAt(0);

// Get associated objects for a loop
ObjectIdCollection assocIds = hatch.GetAssociatedObjectIdsAt(0);
ObjectIdCollection allAssocIds = hatch.GetAssociatedObjectIds();
hatch.RemoveAssociatedObjectIds();

Solid Fill

Hatch hatch = new Hatch();
hatch.SetDatabaseDefaults();
hatch.Normal = Vector3d.ZAxis;
hatch.SetHatchPattern(HatchPatternType.PreDefined, "SOLID");
// IsSolidFill will be true

Gradient Fills

Hatch gradient = new Hatch();
gradient.SetDatabaseDefaults();
gradient.Normal = Vector3d.ZAxis;
gradient.HatchObjectType = HatchObjectType.GradientObject;

// Set gradient type
gradient.SetGradient(GradientPatternType.PreDefinedGradient, "LINEAR");
// Other names: "CYLINDER", "INVCYLINDER", "SPHERICAL", "INVSPHERICAL",
//              "HEMISPHERICAL", "INVHEMISPHERICAL", "CURVED", "INVCURVED"

gradient.GradientAngle = Math.PI / 4;  // 45 degrees

// Two-color gradient
gradient.GradientOneColorMode = false;
GradientColor[] colors = new GradientColor[2];
colors[0] = new GradientColor(Color.FromRgb(255, 0, 0), 0.0f);   // start
colors[1] = new GradientColor(Color.FromRgb(0, 0, 255), 1.0f);   // end
gradient.SetGradientColors(colors);

// One-color gradient (single color with tint)
gradient.GradientOneColorMode = true;
gradient.ShadeTintValue = 0.5f;  // 0 = dark, 1 = light
gradient.GradientShift = 0.0f;

// Add boundary and evaluate
btr.AppendEntity(gradient);
tr.AddNewlyCreatedDBObject(gradient, true);
gradient.AppendLoop(HatchLoopTypes.External, boundaryIds);
gradient.EvaluateHatch(true);

Gradient methods:

• SetGradient(GradientPatternType type, string name) - set gradient pattern
• GetGradientColors() -> GradientColor[] - get color stops
• SetGradientColors(GradientColor[] colors) - set color stops
• EvaluateGradientColorAt(float value) -> Color - sample color at position (0-1)

Enums

HatchLoopTypes (flags): Default=0x0, External=0x1, Polyline=0x2, Derived=0x4, Textbox=0x8, Outermost=0x10, NotClosed=0x20, SelfIntersecting=0x40, TextIsland=0x80, Duplicate=0x100

HatchEdgeType: Line=1, CircularArc=2, EllipticalArc=3, Spline=4

HatchStyle: Normal=0 (fills between nested boundaries), Outer=1 (outermost boundary only), Ignore=2 (ignores internal boundaries)

HatchPatternType: UserDefined=0, PreDefined=1, CustomDefined=2

HatchObjectType: HatchObject=0, GradientObject=1

GradientPatternType: PreDefinedGradient=0, UserDefinedGradient=1

Gotchas

• Set the pattern type/name BEFORE adding loops and BEFORE calling EvaluateHatch
• AppendLoop must be called AFTER AppendEntity and AddNewlyCreatedDBObject - the hatch must be in the database first
• EvaluateHatch(true) underestimates line count (faster); EvaluateHatch(false) is accurate but slower
• For user-defined patterns, use PatternSpace instead of PatternScale; set PatternDouble = true for crosshatch
• Associative must be set to true BEFORE adding boundary loops for associativity to work
• Boundary loops must be closed - open boundaries cause EvaluateHatch to fail silently
• The outer boundary should use HatchLoopTypes.External; inner islands should use HatchLoopTypes.Default
• HatchStyle.Normal alternates fill between nested boundaries; Outer fills only the outermost; Ignore fills everything
• For gradients, set HatchObjectType = HatchObjectType.GradientObject before calling SetGradient
• PatternName and PatternType are read-only - use SetHatchPattern() to change them
• After changing PatternScale, PatternAngle, or PatternSpace, you must re-call SetHatchPattern(type, name) before calling EvaluateHatch() — otherwise the change has no visual effect
• BulgeVertex Bulge value: 0 = straight segment, positive = counterclockwise arc, negative = clockwise arc; tan(includedAngle/4)

Related Skills

• acad-polylines — polylines as hatch boundaries; vertex+bulge loop construction
• acad-layers — layer assignment for hatch entities