Olhovsky

Miscellaneous Coding

Fields vs. properties performance on the Xbox 360.

Apr 17

Posted by olhovsky in Coding, XNA | No Comments

I took Sam Allen’s performance test and ran a similar test (below) on the Xbox 360 with XNA.

static string _backing; // Backing store for property
static string Property // Getter and setter
{
get
{
return _backing;
}
[...]

Occurences of one string in another.

Dec 30

Posted by olhovsky in Coding, Misc | No Comments

The string “ABC” occurs in “ABBC” twice, if you remove any characters you wish from “ABBC”.
The following algorithm finds such occurences in O(n) time given any two strings.
One assumption worth noting for the O(n) time bound is that the size of the alphabet is limited to some constant size.
Nested loops in this algorithm scream O(n^2)!! [...]

Extract Longest Non-Decreasing Sequence From Any Sequence

Nov 10

Posted by olhovsky in Coding, Misc | 5 Comments

I wrote some python code that extracts the longest non-decreasing subsequence from any given sequence.
This runs in O(n log n) time, and uses O(n) memory.
”’ An item in the final sequence, used to form a linked list. ”’
class SeqItem():
val = 0 # This item’s value.
[...]

Foreach through non-primitive types creates garbage.

Sep 19

Posted by olhovsky in Coding, XNA | No Comments

Time and again I have seen code like this used in XNA tutorials.

effectDrawBlock.Begin();
foreach (EffectPass pass in effectDrawBlock.CurrentTechnique.Passes)
{
pass.Begin();

gd.DrawIndexedPrimitives(PrimitiveType.TriangleStrip, 0, 0, 35, 0, 70);

pass.End();
}
effectDrawBlock.End();

When you use a foreach over an array of ints, you will not create garbage, and it’s fast, so that’s [...]

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ToString Garbage Creation in C#

Sep 17

Posted by olhovsky in Coding, XNA | 1 Comment

I profiled my XNA game project today using the XNA Framework Remote Perf Monitor and discovered that I was generating about 8000 more manage objects per second than I was expecting to.
It turns out that this code was generating 7400 managed objects per second:
[...]

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Convert greyscale images to Alpha8 format with a Custom Content Processor in XNA 3.1.

Sep 14

Posted by olhovsky in Coding, XNA | No Comments

I noticed that at least two terrain engine examples in XNA are reading heightmap images into 4 channel textures instead of single channel textures.
To create a custom content processor that will permit you to convert any Texture2D compatible input format into an Alpha8 format texture, do the following:
Right click your game solution -> add new [...]

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2D CDF 9/7 Wavelet Transform in Python

Mar 17

Posted by olhovsky in Coding | 4 Comments

As promised, here is an implementation of the Cohen-Daubechies-Feauveau 9 tap / 7 tap wavelet transform on a 2D signal in Python. This is the same transform used in the JPEG2000 codec.
”’
2D CDF 9/7 Wavelet Forward and Inverse Transform (lifting implementation)

This code is provided “as is” and is given for educational purposes.
2008 – Kris Olhovsky – code.inquiries@olhovsky.com
”’

from PIL [...]

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