### XNA and Farseer Physics Engine 3.3 Presentation at Nokia

The slides and demos from the presentation at Nokia can be found here.

Thanks to everyone that showed up!

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The slides and demos from the presentation at Nokia can be found here.

Thanks to everyone that showed up!

- Get link
- Google+
- Other Apps

I often find myself needing a compression library in a software development project, and after a few tests with disappointing results I usually fall back to spawning 7Zip as an external process. This time however, the application specification prohibits any data written to disk, which 7Zip needs to do in order to work correctly. I needed to do everything in memory, and so I had to test some of the C# libraries available for compression as well as the different compression algorithms.

Here is a full list of the tested libraries:

.NET DeflateStreamICSharpCode SharpZipZlib.NETDotNetZipManaged LZMALZMA SDKQuickLZ Compression 101 Before I get to the results of the benchmark, I think it is important to understand the different archive formats and compression algorithms in order to compare the results with other benchmarks/and or tests. Lets get to it!

A compression algorithm can be compared to a small machine that takes in some data, do some math on it and transform it to some new data -…

Here is a full list of the tested libraries:

.NET DeflateStreamICSharpCode SharpZipZlib.NETDotNetZipManaged LZMALZMA SDKQuickLZ Compression 101 Before I get to the results of the benchmark, I think it is important to understand the different archive formats and compression algorithms in order to compare the results with other benchmarks/and or tests. Lets get to it!

A compression algorithm can be compared to a small machine that takes in some data, do some math on it and transform it to some new data -…

If you don’t know about the big O notation, I recommend you read about it here first. This post gives you an idea of what broad and narrow phase algorithms are and how they are used in physics engines.**Broad Phase Collision Detection**Performance is an essential part of a physics engine. You can get away with just implementing a few algorithms that detect collisions using a O(n^2) algorithm, but when you add more and more objects to the simulator It becomes quite expensive (CPU wise). Not very good for performance.We can reduce the amount of tests by implementing a broad phase into our collision system. It is responsible of eliminating tests and thus reducing the number of tests needed (We obviously don't need to test objects far away from the player). We could for example have an algorithm that tests the distance using the X and Y axis of the screen, if the objects are too far away from each other, we can eliminate them as potential collisions. There are many algorithms that can eli…

A lot of people have asked me: Why use a convex polygon only engine like Box2D? In this post I will provide some info on why convex polygons is the optimal polygon type to use.What does convex mean?Convex polygons needs to satisfy the following requirements:All internal angles must be below 180 degreesEvery line segment between two vertices can be contained fully inside or at the edge the polygonA non-convex polygon is called a concave polygon and it must have an internal angle measuring greater than 180 degrees. As you might have thought about yourself; concave polygons can be quite handy. Convex-only engines can’t represent a simple player polygon like Pac-Man.Why use convex-only?There are really only one big juicy reason: **performance**Physics engines are able to take quite a few shortcuts and use cheap algorithms to determine the closest vertex, shortest distance and a lot more. An algorithm like Separating Axis Theorem and the Gilbert – Johnson – Keerthi (GJK) (pdf) algorithm both o…

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You had a tough crowd, but it was a great presentation !

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