I don't know shaders, but I have a basic idea of their concept.
I need to implement depth peeling and so I would like to know if first I should go deeper into the shader world or it could be implemented without shaders, just using smartly the glDepthFunc..
Depth peeling needs to perform this test on each pixel:
[source]
if( pixel_depth < depth_buffer_value || pixel_depth > peeled_depth_value )
{
discard;
}
[/source]
With the old FF style rendering, you could only ever do a single depth query (i.e. glDepthFunc, GL_LEQUAL, GL_LESS, etc). The test you need for depth peeling has two depth queries per pixel, which means there isn't any way to shoehorn it into a single glDepthFunc param. You will need to do this in a shader.
You can grab sample code for Dual Depth peeling from Nvidia: http://developer.download.nvidia.com/SDK/10.5/opengl/screenshots/samples/dual_depth_peeling.html
