create transparent hatch with Python

[Danielm103]

import traceback
from pyrx import Ap, Db, Ed, Ge

_index = 1

def makeBoundary(db: Db.Database, pnt: Ge.Point3d, tr: Db.Transparency):
    ids = []
    plines = Ed.Editor.traceBoundary(pnt, False)
    for pline in plines:
        pline.setColorIndex(_index) # Uses the global integer
        pline.setTransparency(tr)
        ids.append(db.addToModelspace(pline))
    return ids

@Ap.Command()
def doit():
    global _index
    try:
        db = Db.curDb()
        tr = Db.Transparency(0.5) #50%
        
        ps, pnt = Ed.Editor.getPoint("\nSelect internal point: ")
        if ps != Ed.PromptStatus.eOk:
            return
        
        # 1. Generate the boundary polylines
        ids = makeBoundary(db, pnt, tr)
        if not ids:
            print("\nNo boundary found.")
            return
        
        # 2. Create and configure the Hatch object
        hat = Db.Hatch()
        hat.setPattern(Db.HatchPatternType.kPreDefined, "SOLID")
        hat.setColorIndex(_index)
        hat.setTransparency(tr)
        
        # 3. Add hatch to model space BEFORE appending loops (AutoCAD requirement)
        db.addToModelspace(hat)
        
        # 4. Establish associativity and evaluate
        hat.setAssociative(True)
        hat.appendLoop(Db.HatchLoopType.kDefault, ids)
        hat.evaluateHatch(True)
        
        print(f"\nCreated boundary and hatch with Color Index: {_index}")
        
        # 5. Increment color index (Cycle back to 1 if it exceeds standard ACI 255)
        _index += 1
        if _index > 255:
            _index = 1
            
    except Exception as e:
        print("Error encountered:")
        traceback.print_exc()

 

[indiancad]

The key is to make the Hatch entity itself see-through not the boundary lines that get drawn. The hatch must also be checked after each boundary loop is added.

The main fix is the transparency value. For 50% see‑through use an alpha value 127 instead of 0.5 because Db.Transparency uses a 0–255 scale. Set it directly on the hatch for example: hat.setTransparency(Db.Transparency(127)). Also if traceBoundary returns loops find the outer loop and any inner islands separately before you call appendLoop. If you do not do this the hatch might fill spots that should stay open.

[Danielm103]

Db.Transparency in ARX (and Python) is overloaded to take an alpha 0-255 or alphaPercent 0.0 – 1.0, so you can use either.  0.5 is the same as 127 in this case. In this case traceBoundary was called with detect islands = False. Of course one might like to have a different transparency between the boundary and hatch, this just illustrates one