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Andrea Boriani

A C# polygon library for Boolean operations

A C# polygon library for Boolean operations

Today I was looking for a library for Boolean and offsetting operations on polygons and I stumbled upon this little library called Clipper by
Angus Johnson.

It is distributed in source form in various languages including C# and is freeware both for opensource and commercial applications.

I needed to solve this problem:

  • Offset a rectangular polygon by a fixed amount, rounding corners.
  • Intersect the previous polygon with a second polygon.
  • Compute area and perimeter of resulting polygon.


This is needed to solve a problem in civil engineering about punching of columns through slabs in case of corner or border columns.


I put together this small demo app in Vb.Net to test this library. You can check it out at:
https://github.com/andreaboriani/clipper_test

.Net, Programming

Use PubNub in VB.Net

Use PubNub in VB.Net

I made some experiments using PubNub in VB.NET, as the examples on the site are only in C#. If you still don't know PubNub is a real-time messaging service based on channels with a  publish-subscribe protocol (similar to Telegram). The base plan is free till 1M transactions and 1GB of data persistence. At first, you have to register, create an app and give it a name. Two keys will be created, one to publish (pub-.....) and one to subscribe to a channel (sub-.....).

  1. Create a  VB.NET project with a form
  2. In Visual Studio go to Tools-> NuGet Packages and import  PubNub package.

Now we can write our code: I put everything in  form_shown

Private Sub FrmMAIN_Shown(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Shown   
  Dim pnConfiguration As New PubnubApi.PNConfiguration()  
  'insert key here   
  pnConfiguration.SubscribeKey = "sub-xxxxxxxxxxxxx"   
  pnConfiguration.Secure = False   
  PubNub = New PubnubApi.Pubnub(pnConfiguration)   
  'prepare call back   
  Dim IncomingMessages As Action(Of PubnubApi.Pubnub, 
  PubnubApi.PNMessageResult(Of Object)) = AddressOf IncomingMessagesCB   
  Dim IncomingPresence As Action(Of PubnubApi.Pubnub, PubnubApi.PNPresenceEventResult) = AddressOf IncomingPresenceCB   
  Dim IncomingStatus As Action(Of PubnubApi.Pubnub, PubnubApi.PNStatus) = AddressOf IncomingStatusCB   
  Dim sc As New PubnubApi.SubscribeCallbackExt(IncomingMessages, IncomingPresence, IncomingStatus)   
  'set up listener   
  PubNub.AddListener(sc)   
  PubNub.Subscribe(Of String).Channels(New String() {"my_channel"}).Execute()  
End Sub  
'callback for messaes  
Private Sub IncomingMessagesCB(pn As PubnubApi.Pubnub, messageResult As PubnubApi.PNMessageResult(Of Object))         
  If messageResult IsNot Nothing Then             
    Debug.Print("In Example, SubscribeCallback received PNMessageResult")             
    Debug.Print("In Example, SubscribeCallback messsage channel = " + 
  messageResult.Channel)             
    Debug.Print("In Example, SubscribeCallback messsage channelGroup = " + messageResult.Subscription)             
    Debug.Print("In Example, SubscribeCallback messsage publishTimetoken = " + messageResult.Timetoken.ToString)            
    Debug.Print("In Example, SubscribeCallback messsage publisher = " + messageResult.Publisher)             
    Dim jsonString = messageResult.Message.ToString()             
    Dim msg As Dictionary(Of String, String) = 
    Newtonsoft.Json.JsonConvert.DeserializeObject(Of Dictionary(Of String, String))(jsonString)             
    Debug.Print("msg: " + msg("msg"))         
  End if     
End Sub    
'callback for presence 
Private Sub IncomingPresenceCB(pn As PubnubApi.Pubnub, presencResult As PubnubApi.PNPresenceEventResult)         
  If presencResult IsNot Nothing Then             
    Debug.Print("In Example, SubscribeCallback received PNPresenceEventResult")             
    Debug.Print(presencResult.Channel + " " + presencResult.Occupancy + " " + presencResult.Event)         
  End If     
End Sub     
'callback for status     
Private Sub IncomingStatusCB(pn As PubnubApi.Pubnub, statusResult As PubnubApi.PNStatus)         
  If statusResult.Category = bnubApi.PNStatusCategory.PNConnectedCategory Then             
    Debug.Print(statusResult.Category.ToString)         
  End If     
End Sub
.Net, Programming