Being accurate:
	Ray Tracing is often favored
	New shader types available in Vulkan and DX12 for that
	What I'm about to teach will probably be a historical relic in a few years
		Sorry!
	But, it's the way things are done now, and will be until everyone has an RTX or equivalent
		How long?  Brief unscientific poll...
	We like to say technology moves along and everyone has to adapt
		This time we can see it coming

https://paroj.github.io/gltut/Illumination/Tutorial%2009.html

Ok, pretend it's still 2018:
	Simple model of light

Brief philisophical note:
	gravity
	We can land a space probe on Mars

Think about real light hitting a surface
	Partial and colored reflections

Photorealistic Rendering:
	Believe it or not, that's the name of the type we'll use!
	vs. cartoons and such

Lights and temperature and spectrum:
	"full spectrum"
	grow lights
	daylight, incandescent, sodium vapor, etc.
	Reflections have color
	RGB:  Trick of human visual processing!
		It's ok, we don't really care about non-humans anyway...

Light absorbtion:
	Pigments absorb the colors they're not
	Black absorbs everything, pure white nothing
		mirror vs. white:  white scatters, mirror does not
		Laser armor, and nothing is perfect

Light and angles:
	Why is the Winter sun weak?
		More than one reason, but the angle is one of them
	Angle between the light and the surface is critical
		That's why normal vectors come into play!
		A big triangle and apparent curves

Diffuse Lighting:
	Light hits at some angle (could be straight on) and scatters
	Even distribution in all directions
		No surface is actually like this, but it's a decent approximation

Diffuse Equation:
	R = D * I * cos(Theta)
	R is the diffuse lighting color
	D is the absorbtion (vec3)
	I is the light intensity (vec3)
	Theta is the angle between the light and the surface normal vector
		cos(0) is 1.0, cos(90) or cos(-90) is 0
		abs(Theta) > 90 shouldn't be lit, or it'd be negative
	Where to calculate it:
		Vertex shader:  Since the triangle is flat, it's mostly consistent over the whole thing!
			Angle to light source can vary
			Historical method, kind of
			Good if light is far away
			Facets, and approximation of curves
	 	Geometry Shader:  Less redundancy, once per triangle (nobody does this)
		Fragment Shader:  More invocations unless triangles are really small
			Allows re-calculation at each point
			Slower, especially for low-res models
			We've got the power, and it normally looks better
	How to do the cosine:
		Could just calculate it the normal way, but we don't need to
		dot product:  definition, actual calculation with just multiplication
		Magnitude when both vectors were unit vectors
		glsl dot function

Gouraud Shading:
	Diffuse, done in the vertex shader
	Interpolated over the whole triangle
	Very popular for a decade or so
	
Normals, and calculation in difference spaces
	The model is not actually in model space if we've scaled, etc.
	The normal vectors are in model space
	MVP and what happens to these
		Short answer:  Compute the inverse-transpose matrix, and multiply by that instead
		If you're really interested in 3D, take linear algebra.  It counts as an upper-division elective
		Do it once on the CPU instead of a whole bunch of times on the card
	This is only a problem if the object has had a non-uniform scale applied
		Can avoid overhead if you just make the models so they don't need a non-uniform scale
	
A very practical note about normal vectors and vertices:
	With the cube, we're storing each vertex once
	Each vertex has THREE normal vectors!
	obj file internals	
	Can manage this with a variety of buffers
	Don't sweat it too much.  In a curved mesh, each vertex just has one normal

Ambiant Light
	Doesn't exist
	Basically, we just add a little "bonus" light
	Can use diffuse colors
	Can set an ambiant color, for the extra light
	Diffuse gives us a term, R
	L = R + A
	Can't exceed 1.0 here - OpenGL will clamp the color at 1.0
	This'll cause the color to be washed out if it exceeds 1.0
	More terms will keep being added!
		Dynamic range

Point lighting:
	A directional light for diffuse lighting comes from some direction
	A point light comes from a point
	We can figure out a direction to a point, not a problem?
		More or less defeats gouraud shading
		Fragment shader:  Must preserve surface location and normal
	Attenuation:
		Decrease light power with distance!
		Real:  I / (1.0 + k*r^2)
		k constant:  Can use distance where half the light is lost
		Less attenuation:  I / (1.0 + k*r)
			Just take out the r, and lights work when further away
		Calculations happen in world-space distances
			Can compute from camera space, or preserve, or whatnot

Specular Reflection:
	Reflection in a specific direction!
		Comes with a different color
		Microfacets, roughness
		Angle to the camera matters!
		Phong:  dot product of V and R raised to the s power
		V is the viewing direction
		R is the reflection direction
		s is a term that represents roughness
		The Phong term is multiplied by the light intensity and the specular absorption
			Specular absorption might not be the same color as diffuse absorption
			Only works for angle less than 90
		Blinn term:  Use half angle vector
		Gaussian:  Probability distribution of microfaucets
	
Dynamic and HDR lights

Practice:  Add some kind of model into a lighting demo