I am blown away. Almost 4,000 downloads of my Frustum Culling tutorial in 4 days! I figured there''d be maybe a hundred tops :-) Lot''s of email too - more than I really have time to reply to unfortunately. So "thank you!" to everyone for your comments. You''ve inspired me to work on more OpenGL tutorials (whether I actually complete more is another matter entirely of course). In case anyone is interested, my current (and somewhat ambitious) project is to build a realistic sky dome. Given any location on earth and any date & time (within a few centuries either way of January 2000), it accurately calulates the position of the sun, moon, and stars. The sun and moon rise and set, the moon cycles through its phases (using a series of 29 texture maps), the stars are real ones and have varying brightnesses, etc. This is all working now. So far it hasn''t decreased my frame rate (over 120, my monitor''s refresh). It transitions nicely from day colours to night colours, based on the altitude of the sun. Right now I''m working on the sunrise/sunset colouring. The colouring will eventually take into consideration the haziness of the atmosphere, meaning sunrises and sunsets should vary in colour and intensity, and it should be able to simulate anything from clear to overcast days. When the colouring is done I''d like to do a decent cloud system. I was thinking of using both textured planes and polygon models so that clouds would have that cool colouring they get during sunrises and sunsets. After that I may try my hand at simulating weather including rain, snow, lightening, and fog. I''m also thinking about a lens flare effect to round it out. What other effects would be cool in a sky dome? Hmmm... wonder how I''d simulate the northern and southern lights... that would be cool. Probably too slow though. Maybe with pre-rendered animated plasma textures or something. And rainbows would be good too. Any other ideas? I know it sounds like a lot of work, but most of the hard stuff is already done (I hope, but something always pops up). I''ve learned more about astronomy in the past two days than I ever wanted to know, that''s for sure! Hope to make a demo available soon. I don''t have a specific game or simulation in mind for this yet, just tinkering with things that interest me right now. Ack - it''s after 2 am. Sorry for rambling... ''night. Toom

This would be great! If you get all that working it will be an awesome tutorial...

Pete

forget the lens flares UUUGGGHH
try some fractal procedural clouds. i have a simple demo on me site of procedural textures. IMO they look so much better than textured stuff JUST because of the randonis!!

http://members.xoom.com/myBollux

No, no, keep in the lens flare. I think its cool! I agree with the fractal clouds idea, however, it would be nice to have clouds which vary from day to day. If your skydome is going to be used in virtual worlds, it should of course give a very low fps as all that worldly geometry is going to be the real bottleneck any way. Fantastic idea, keep it up!

Lens flare is actually pretty cool if you want to simulate looking through a lens (telescopes, binoculars, cameras, even some windshields and glasses). I think most (all?) glass will generate hexogonal shaped flares though, not these perfectly round disks I see in most implementations. I could be wrong. I''ll have to research it a bit more. I agree that lens flares look out of place in simulations and games where the viewer isn''t actually looking through a lens (most FPS games for example). In my sky dome engine it will be something that can be turned on/off depending on the situation. Assuming I even get that far.

As for the clouds, I think you are right about using a texture that is generated on the fly, but I imagine that might be expensive computationally (more so than the astronomy calcs even). Guess it depends on the algorithm. I''ll have to research this too.

I''d like to use 3D clouds as well though, so that they can actually be shaded by the current sunlight (which wouldn''t really look right with a simple textured cloud plane I think). But maybe if the cloud plane was "bumpy", like a water surface... hmm... It would be cool for the clouds to take on purple, red, orange, and yellow tints during sunrises and sets, and to be whiter during clear days and grayer during overcast ones. Probably a combination of a cloud plane and polygonal clouds would work...

Toom

What would be REALLY cool would be simulation Aurora Borealis (Northern Lights)

That would be sweet.

Jason A.

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I write code.
DelphiGL (http://delphigl.cfxweb.net)

Looked up some info on the Northern and Southern lights. I think the only tricky part would be to find a fractal algorithm that generates a pattern similar to the real thing, and does it fast enough. Ah well, it''ll be a while before I get to that one anyway.

In the meantime, I realized today that I didn''t recognise any of the stars in my sky dome. Tracked down a couple of calculation errors and now my virtual night sky looks pretty much like it does in real life (from my lat/long anyway). Kinda cool to be able to pick out real constellations!

Toom