Banded Lighting Shader (godot 3.x)
ported from Jordan Stevens
https://www.jordanstevenstechart.com/lighting-models
Shader code
shader_type spatial;
render_mode ambient_light_disabled;
uniform sampler2D _albedo:hint_albedo;
varying vec4 vector_ws;
varying vec4 vector_os;
uniform float _lightSteps:hint_range(0.0, 256.0, 2.0)=1.0;
void vertex()
{
vector_os.xyz = VERTEX;
vector_ws= WORLD_MATRIX* vec4(vector_os.xyz,1.0);
}
void light()
{
vec3 i = ATTENUATION;
vec3 l = LIGHT;
vec3 n = NORMAL;
vec3 viewDirection= normalize(CAMERA_MATRIX[3]-vector_ws).xyz;
float roughness=ROUGHNESS;
vec3 nDotL = max(0.0, dot(n, l)) * i;
vec3 vDotL = max(0.0, dot(viewDirection, l)) * i;
float lightBandsMultiplier = _lightSteps/256.0;
float lightBandAdditive = _lightSteps/2.0;
vec3 bandedNDotL=(floor((nDotL*256.0+lightBandAdditive)/_lightSteps))*lightBandsMultiplier;
vec3 lightingModel = bandedNDotL *ALBEDO;
vec3 attenuation = ATTENUATION;
vec3 attenColor = i * LIGHT_COLOR;
vec4 finalDiffuse = vec4(lightingModel*attenColor,1);
DIFFUSE_LIGHT += finalDiffuse.xyz;
SPECULAR_LIGHT +=finalDiffuse.xyz;
}