Is there a known projection shader for a panini projection?

jokoon · May 16, 2018, 11:58pm

http://tksharpless.net/vedutismo/Pannini/

Basically a panini projection is projecting vertices onto a cylinder (if I get it right), which is then unrolled on screen.

Here is how blinky, a quake mode, is doing is, using some LUA script:

github.com

shaunlebron/blinky/blob/master/game/lua-scripts/lenses/panini.lua

d = 1

max_fov = 360
max_vfov = 180

onload = "f_fov 180"

function lens_inverse(x,y)
   local k = x*x/((d+1)*(d+1))
   local dscr = k*k*d*d - (k+1)*(k*d*d-1)
   local clon = (-k*d+sqrt(dscr))/(k+1)
   local S = (d+1)/(d+clon)
   local lon = atan2(x,S*clon)
   local lat = atan2(y,S)

   return latlon_to_ray(lat,lon)
end

function lens_forward(x,y,z)
   local lat,lon = ray_to_latlon(x,y,z)

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Not sure it’s a real projection since it’s using globes and lenses.

GClements · May 17, 2018, 2:58am

The thing about non-linear projections is that the projection of a straight line isn’t a straight line. So you can’t project a triangle simply by projecting the vertices. Typically, you’d either use tessellation to get a sufficient approximation, or project onto the faces of a cube map and then project the cube map as a post-processing step using a fragment shader.