Edit: Seriously, these are all personal pictures of people clearly visible. Isn't that question legitimate?
The reason for this is so that the OS could move around memory allocations to make efficient use. (This was obviously before Macs had virtual memory.)
There were some rules in these early versions of MacOS about which MacOS system calls could cause the pointers to change.
If you ALWAYS used the double pointer (and used the 'volatile' keyword or its Pascal equivalent appropriately), you were always safe. But if you kept a single-pointer version of a double-pointer from the OS, and then used certain OS calls, you might find that the OS moved your allocations around you behind your back.
As a seasoned system software engineer, this completely makes sense to me. But as a teenager trying to understand software, this completely blew my mind and I wrote a lot of code that crashed in strange ways.
The find-the-closest-finger algorithm was taken from another project we did, where we needed much more speed. We use a voronoi diagram with a distinct color for each point.. then we can get the pixel color at the position of the cursor and find the related pointer..
This is actually much faster than what you see happening on Pointer Pointer. We introduced a pause to force people to wait, thus making it a more rewarding experience when the image finally shows up. A touch of magic, you could say.
[1] http://www.pointerpointer.com/gridPositions.json
Try moving your pointer around to different positions very close to the top right corner. This triggers a picture with a wristwatch and water bottle. The pointing is done by the right hand, which if your pointer is too far right is cut out of the frame, but becomes visible as you move towards the left.
From there on it's a matter of finding the pointer in javascript and a Voronoi search to the matching photo. I'm not seeing an ajax call in the logs so there's probably a bit more magic going on clientside.
Edit: Terminology
For a small number of photos (up to a few thousand), a linear search (i.e. check against each one) would be quick enough. You could compare the distance of the pointed spot to the cursor (using Euclidean distance), pick the best one, maybe add in a random factor.
EDIT: Somehow the author is putting Voronoi diagrams into use. Take a look at the source.
A small glitch? Some points outside the right border don't load any image, though it still shows "Pointer located. Pointing...". Anybody else going through same problem, or am I the only one.
Thanks for the fun :)
Try the top-right corner: I get an image without a pointer (someone looking at his watch).
Prime example of use-after-free ;)
edit: ignore. just saw the cropped hand pointing.
Same solution is also useful for other more serious applications: https://www.youtube.com/watch?v=90NsjKvz9Ns
Edit: Sorry, I missed the "me" in your "entertain me".
