Archive for the ‘screen-aligned’ tag

Snow (i.e. Point Sprites)

without comments

I added a quick, cheap attempt at snow to Tutorial 5. The primary purpose is to demonstrate point sprites.

Below is a quick vimeo clip of the results:

What and What’s Next

The effect is achieved by sending point list (GL_POINTS) of about size 800 and using a geometry shader to create a screen-aligned, texture-mapped, alpha-blended quad for each point.

A extremely simple particle system is in effect here that resets the z position of the sprite when it falls below 0 (I feel like it’s almost an abuse of language in general to use a specialized term like “particle system” for as simple an update loop as that!). The point sprite shader derives directly from the code provided in OpenGL 4.0 Shading Language Cookbook by David Wolff (which I recommend, by the way – it’s a pretty decent book if you’re like me and hadn’t paid a lot of attention to what’s been happening since GLSL first was introduced).

Next it’d be great get the “Utah sky model” working in the tutorial, if I still had my copy of More OpenGL Game Programming around (which is a pretty good book, but I don’t endorse too highly – too much API reference material or other information easily found on the web is needlessly listed) or still had link to the web page that describes the sky shader code that was later included in the book. Or maybe I could just do a little reading here to add some nice sky effects…

Oh, and adding some first-person navigation and physics would be pretty nice as well if I get back into working with Bullet (I’m not sure I really liked the design I used with the LxMorrowind sample to implement physics – and there were some bugs in there that I never quite understood).

Another minor OpenGL lesson learned during the implementation: glDepthMask() affects calls to glClear(). That makes sense, but I wish I had thought of it before spending a while in the debugger wondering why my shader wasn’t working :)

Written by arthur

April 6th, 2012 at 5:26 pm