Curved World Shader (code included)
The Animal Crossing Shader has an article on how to do it online by someone named Alastair.
I had never done anything with shaders before, but I wanted to give this a shot after seeing it in Four Warriors of Light, so here is his code in a manner that works for me in Godot:
If anyone was a noob like me, notice that in order for whatever code to take effect on the desired built-in, you need to set that built in to your manipulated variable, as in the last line VERTEX = v;
Also, it took forever for me to find this link, so here it is:
float curve = -.001; vec3 v = VERTEX; mat4 mv = MODELVIEW_MATRIX; mat4 wv = WORLD_MATRIX; mat4 cv = INV_CAMERA_MATRIX; //v*= vec3(1,1,1); vec4 vv = mv * vec4(v,0.0); vv -= cv.x; vv -= cv.y; vv -= cv.z; vv = vec4(0.0,pow(vv.z,2)*curve,0.0,0.0); vv*=wv; vec3 vvp = vv.xyz; v+=vvp; VERTEX = v;