BlitzMax - generating 2D neon glowing line effect to png file

I'm looking to create a glowing line effect in BlitzMax, something like a Star Wars lightsaber or laserbeam. Doesn't have to be realtime, but just to TImage objects and then maybe saved to PNG for later use in animation. I'm happy to use 3D features, but it will be for use in a 2D game.

Since it will be on black/space background, my strategy is to draw a series of white blurred lines with color and high transparency, then eventually central lines less blurred and more white. What I want to draw is actually bezier curved lines. Drawing curved lines is easy enough, but I can't use the technique above to create a good laser/neon effect because it comes out looking very segmented. So, I think it may be better to use a blur effect/shader on what does render well, which is a 1-pixel bezier curve.

The problems I've been having are:

• Applying a shader to just a certain area of the screen where lines are drawn. If there's a way to do draw lines to a texture and then blur that texture and save the png, that would be great to hear about. There's got to be a way to do this, but I just haven't gotten the right elements working together yet. Any help from someone familiar with this stuff would be greatly appreciated.
• Using just 2D calls could be advantageous, simpler to understand and re-use.
• It would be very nice to know how to save a PNG that preserves the transparency/alpha stuff.

p.s. I've reviewed this post (and others), have the samples working, and even developed my own 5x5 shader. But, it's 3D and a scene-wide thing that doesn't seem to convert to 2D or just a certain area very well. 开发者_如何学JAVAhttp://www.blitzbasic.com/Community/posts.php?topic=85263

Ok, well I don't know about BlitzMax, so I can't go into much detail regarding implementation, but to give you some pointers:

• For applying shaders to specific parts of the image only, you will probably want to use multiple rendering passes to compose your scene.
• If you have pixel access, doing the same things that fragment shaders do is, of course, possible "the oldskool way" in 2D, ie. something like getpixel/setpixel. However, you'll have much poorer performance this way.
• If you have a texture with an alpha channel intact, saving in PNG with an alpha channel should Just Work (sorry, once again no idea how to do this in BlitzMax specifically). Just make sure you're using RGBA modes all along.