Category Archives: Programming
Understanding Memory: Part 1
This article is meant for programmers who have some familiarity with writing and compiling simple code in C/C++. It assumes the reader knows basic data types like int and double and how to define and use variables and functions. This article will then expose the reader to a basic memory model, explain how the use of variables interacts with this memory, and introduce addresses and pointers. On a modern platform, memory is presented to a program as byte-addressable blocks. Each … Continue reading
When you need std::remove_const
I ran across an interesting case where I needed to use std::remove_const to ensure a template parameter wasn’t const by default. I had something like this: const Matrix<4> m4 = Identity; Vector<3> v3 = project(m4[3]); With the library I was using, TooN 2.0.0 beta8, this resulted in a compile error. The error stated that when the vector returned from project() was being created, the compiler couldn’t invoke assign to a read only location. A simplified declaration of project() looks as … Continue reading
Cubic Spline Interpolation
Cubic spline interpolation is a simple way to obtain a smooth curve from a set of discrete points (knots). It has both C1 (first derivative) and C2 (second derivative) continuity, enabling it to produce a continuous piecewise function given a set of data points. From the algorithm detailed here I have implemented a clamped cubic spline class in C++. It is templated on the type of X and Y, allowing for use of scalar or vector types. It requires only … Continue reading
Houses in Minecraft
So I’ve been playing Minecraft, focusing mainly on the creative aspect, although I play the new Beta client and run my own server locally so I get the features added post-classic. I’ve turned off monster spawning and set the difficulty to Peaceful, so I can focus on bringing creations to life instead of running from scary monsters in the night. The first time I played with monsters, I found the sound of a zombie’s “murrrrrrrr” in a dark, endless cavern … Continue reading
Units of mach_absolute_time()
As programmers on OS X are well aware, the units of mach_absolute_time() have been nanoseconds since 10.2, although this was only documented since 10.5. As the iPhone runs a slimmed down version of OS X, I thought it reasonable that the units would remain the same on the device. [Update] As Justin points out below, this was never the case. A complete misread of the documentation on my part. I managed to work on only machines for which the units … Continue reading
Key Value Observing Improvements v1.2.2
Quick bug fix update: 1.2.2 Fixes a crash due to a missing implementation of __KVOAdditions__dealloc__original__ on NSObject. 1.2.1 now runs on the iPhone. The new updates are in SVN at http://svn.shiftedbits.org/public/KVOAdditions/trunk and tagged at http://svn.shiftedbits.org/public/KVOAdditions/tags/1.2.2
Key Value Observing Improvements v1.2
Hot on the heels of the 1.1 bug fix release comes version a freshly rewritten 1.2 with API cleanup, bug fixes, and a great new feature. Lately, I’ve been using observers to allow an object to observe changes to its own properties. This means I don’t have to override the setter method (I’m using synthesized properties) and the observation is managed the same way that it would be externally. The current KVO implementation (at least, in non-GC land,) however, doesn’t … Continue reading
Key Value Observing Improvements
Key value observing is quite a useful tool, no doubt about it. But it has a singularly annoying manner of informing the observer of a change. The -[NSObject observeValueForKeyPath:ofObject:change:context:] method is sent to the observer when a change occurs. It’s up to the implementor to parse the `change’ dictionary to figure out what changed. When I use observers, I usually want a method called on my class when a change occurs, similar to target/action with UI elements. So my -[NSObject … Continue reading
SSE Optimized Compositing
As part of a graphics API I’ve been working on (for my own use, it’s hardly ready for production,) I decided to try learning SSE optimization by making the compositing routine faster. I came up with an implementation which, according to my tests, is 3-5X faster than the non-optimized version. The optimized version below composites a single color starting at a destination pixel buffer for a specified run of pixels. It uses source over compositing on a RGBA, 8bpc, integer … Continue reading
Transparency Layer Slowdowns
As the documentation mentions, a transparency layer allows subsequent drawing to be rendered in a separate, fully transparent buffer before being composited to the destination context. In the absence of a clipping region, this buffer is the same size as the destination context, requiring a context-sized buffer regardless of the actual drawing bounds. Creating a transparency layer for a small section of content, then drawing this layer in a window, for example, results in a window-sized buffer for the layer. … Continue reading