To explain how to create the over-used, totally hyped "Lens Flare" effect that everyone seems to be talking about these days.
"Did you see the screenshots for , they had the coolest Lens Flares!!!"
I assume that you are familiar with 2d coordinate systems.
I assume that you are capable of using blit to compose the image.
[size="5"]Explanation of the Concepts
The basic idea is that when a bright light passes in front of a camera in real life, it typically creates a glare on each of the lenses within your camera. The physics of why and how the optics of lens flares work are irrelevant to achieving a believable effect.
Now, in your typical polygon-based 3d engine, you don't actually use multiple lenses in your calculations so we need to find a way to "fake" the illusion that the light is glaring off of several lenses within your virtual camera.
The position of the center of the screen in screen coordinates(cx,cy).[/bquote]
// find the direction vector from the center to the light
vx = cx - lx;
vy = cy - ly;
NOTE: STORE THE LENGTH OF THE VECTOR...we'll call ours "length"
You'll also need several images to use as components of the effect. One of these images is typically a star-burst type of image. The others are usually halo type images. See below.
OK, so now we have three vectors:
lx,ly = position of the light
vx,vy = normalized direction vector from the center to the light[/bquote]
Here comes the easy part...
Simply scale the normalized direction vector by the length to get the center coordinate of where to draw the primary "star-burst" image.
vx = vx * distance;
vy = vy * distance;
top = vy - 64 + cy;
left = vx - 64 + cx;
right = vx + 64 + cx;
bottom = vy + 64 + cy;
// NOTE: MAKE SURE TO OFFSET BY THE CENTER POINT
I've found the following values to work quite well...
|Flare||Length Scale||Image Scale|
Below you can see a shot of the effect at work...Notice the lack of proper alpha-blending, this was due to the fact that I slapped the lens flare test project together with C++ Builder using straight SRCAND-style "blits"...gets the point across and only took about a half-hour to code...
For an actual high-quality example of this algorithm at work, be sure to download the Venom demo on March 2, 1998.
I hope you have enjoyed this short tutorial, if you have any questions or would like the source code to the C++ Builder project that this screen shot is from, send me an email.
Reprinted with Permission