Another Pixel Bender bug

For those interested I've created a test app to demonstrate a Pixel Bender bug (or at least a very strange behaviour) I encountered this week:


http://wonderfl.net/c/dLHH


And started a thread on Adobe's forums about it:


http://forums.adobe.com/thread/1003124

Two more screenshots

I took a bit of a break this week for the bank holiday, but otherwise have kept working on the game. The front end is in, though not working, and I've been adding code to handle starting and restarting the game without it falling over or running out of memory.


Mostly though I've been working on graphics, trying to fix a glitch in the way the gradient shaded circles are drawn. This was a subtle glitch in game but rather more obvious in the front end so it was time to fix it.


I tried creating two new shaders for it but that didn't work as expected, because of some oddity in how Pixel Bender shaders handle alpha in Flash. So I decided used a different approach relying on an existing shader and some BitmapData API calls, especially copyPixels.


It was a subtle glitch, probably only visible to me as I knew it was there, but it's now hopefully fixed. The rendering code becomes a little more complex but it's not code that runs every frame or few frames; at most it runs a few times a game.

Shader bug update

I made another shader today. Nothing that interesting as it's a variation on one I'd done before, but as I added it I uncommented out a line in the game which I must have disabled while trying to fix the shader bug two weeks ago. And the bug re-appeared. Thankfully as I knew it was a shader bug and knew the last change I'd done it was easy to undo, but it was surprising as I thought I'd fixed it in the shader code.

Two more screenshots

Two more screenshots, showing two different levels, in the much improved inverted colour scheme. I still haven't decided how to use this, so am alternating between it and the normal, light lines on a dark background, mode to make sure it works as well and get some idea of how to fit it in. Currently they are the second and fourth levels; early levels which accounts for the simple colour schemes.

Update, new screenshot

I've been quiet on my game for a week (except for discussing a shader I made for it) but I've still been busy, on two main things. One is a graphical overhaul, involving the shader but also a new way of drawing filled rings and a lot of tweaks to make it work, which I finished last week.

Pixel Bender bug

The circular gradient fill shader I wrote yesterday took more time than expected as for a while it would not work: more specifically it worked fine in Pixel Bender Toolkit but not in Flash. And it failed in a particular way: on use it would instantly lock up rather than fail with an error or produce the wrong result.

Circular gradient shader

This is something I started coding today before I realised it wasn't available in the BitmapData APIs: the gradient fill available comes in two varieties, linear and radial. But the latter is always based on the distance from the centre, never the bearing from the centre as I wanted. So I wrote a shader for it, to generate a result like this:

Quaternion rotation shader

After writing yesterday's post I wondered how easy it would be to use the mathematics in a shader. This would be a natural way to extend my cross product shader, replacing the simple product in that with a more general geometric product.

Multiplying two vectors

In mathematics there are a number of ways to multiply two vectors. The most common is the dot product, which works for any two vectors of the same size. In three dimensions there's the cross product, while in two dimensions there's the perp dot product, sort of equivalent to the cross product.

But they all have the weakness that they are not invertible. Given the cross product

and knowing c and another vector it isn't possible to calculate the third vector (c × c = 0, so given a solution all points on a line through this solution parallel to c are also solutions).

Oops

I've been working on the front end, which also means I've been deciding how many levels, what distinguishes them etc. It's very different from Bug Tunnel Defense where every level was designed individually. Here the levels are mostly numbers. But at the same time I've been changing and adding things to make it easier to introduce elements progressively, and make for a more varied experience.

While testing some of these changes I generated the above screenshot, which is a really bad way to start a game (hence the title), but is also more aesthetically pleasing than the usual cluttered mess of the screenshots the game produces. It shows off some elements of the game much more clearly than usual, although they really need to be seen in motion to appreciate.