Show HN: A virtual whiteboard for working or teaching remotely

Re:Show HN: A virtual whiteboard for working or teaching rem... by MarkMc on Thursday August 21, 2014 @08:39AM (#8207027)

The drawing is basically a list of strokes, and a stroke is a list of points - that is, (x, y) coordinates. So the database is mostly a huge table of (x,y) coordinates.

Uploading the entire canvas would far too inefficient - I simply upload the points.

The transfer between two clients uses a technique called 'long polling'. That is, the client sends an HTTP request to the server, and the server doesn't respond until it has received a message (ie. stroke) from another client.

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Re:Show HN: A virtual whiteboard for working or teaching rem... by henningo on Thursday August 21, 2014 @01:03PM (#8208354)

Did you consider doing spline fits to the x,y coordinates and then just saving the spline coefficients instead?

The fit process could likely be done client-side, and could offer some subtle smoothing if wanted?

Anyhow, really nice execution!

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Re:Show HN: A virtual whiteboard for working or teaching rem... by byoung2 on Thursday August 21, 2014 @03:51PM (#8209214)

paper.js has a nice method to do this. I actually used it in a whiteboard app I made as a proof of concept. Rather than saving every X,Y coordinate, it uses a configurable number of points and handles and makes bezier curves. http://paperjs.org/examples/path-simplification/

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Re:Show HN: A virtual whiteboard for working or teaching rem... by dceddia on Thursday August 21, 2014 @09:35AM (#8207244)

Did you end up using any libraries for the communication, such as socket.io? (http://socket.io/)

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Re:Show HN: A virtual whiteboard for working or teaching rem... by MarkMc on Thursday August 21, 2014 @10:18AM (#8207443)

No just the standard async Java servlet calls. To be honest I didn't find out about socket.io until half way through the project.

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