How to create fast and easy scene-independent shadows w/o shaders in OpenGL

Question

Let i have some mesh (for ex. sphere) in the center of room, full of cubes and one light source. How can i make fast and easy shadow-casting in OpenGL, using "standard" (fixed) functions only? Note: the result must contain cube and sphere shadows as well.

Answer 1

If you can generate a silhouette of the sphere then you could use shadow volumes. nVidia hardware has also supported fixed function shadow mapping for a fair while as well.

Shadow volumes have the disadvantage of very high fill rate requirements. Shadow maps can be better but require an extra pass.

If you are projecting on to a single plane it may well be easier to just project the object on to a plane.

Answer 2

There is no fast and easy way. There are lots of differnt techiques, that each have their own pros and cons. You can look at a project I host on github, that uses very simple code to create a shadow, using the shadow volume technique (http://iuiz.github.com/VolumeShadow/). However it is written in Java, but it should not be hard to port it to any other language.

The most important ways to create shadows are the so called "shadow mapping" method, where you render your scene (with the camera at the light source, directed to each shadow casting object) to a texture. And the second technique is the shadow voulume method (made famous with Doom3).

Answer 3

I've found one way using StencilBuffers. Being a little confused for a while, i finally got the idea - whith this the most hard thing would be looping through each light source and projecting all scene objects. This one looks more pretty than texture shadowing and works faster than volumeric shadows. here and here are some resources, which helped me to understand matrix multiplication step (it confused me a bit when i was looking through dino demo). As for me, this method is most easy to understand and use. The only question left to solve is how to calculate multiplication matrix.

Although this method could be changed a bit using textures as shown here.

Thanks everybody! =)