Problem w/ the shader tutorials

Unity Engine
1

I’m trying to get through the shader tut #2

http://unity3d.com/support/documentation/Manual/ShaderTut2.html

It’s as though the tutorial is very thorough and then wham, hits you w/ a ton of crap that makes no sense under the premise that all is known. I wouldn’t be doing a tutorial if I already knew what all of this was. Can someone explain these elements?

First is a vertex color the area around the vertex and fragment color the color of the main body of the polygon? I’m not sure what’s what.

struct v2f {
float4 pos : SV_POSITION;
float3 color : COLOR0;
};
What is a struct? What’s a float3 vs. a float4? Where did SV_POSITION and COLOR0 come from? Are they inherit to Unity?

v2f vert (appdata_base v)
{
v2f o;
o.pos = mul (UNITY_MATRIX_MVP, v.vertex);
o.color = v.normal * 0.5 + 0.5;
return o;
}
I get that appdata_base is available because of UnityCg.cginc but what does it do? Why do I need it? I assume that the preceding code creates some sort of function but “v2f vert (appdata_base v)”?? What on earth is that? I’m guessing its similar to function vert(v2f,v) but aren’t really sure. v2f o; is this a way of declaring o as a variable of type v2f? Where did mul come from, what does it do?

half4 frag (v2f i) : COLOR
{
return half4 (i.color, 1);
}

Same questions as before on the first line except now there’s :COLOR added. I think I know what’s happening on the next line but I’m not sure what it’s returning. Does this loop through each polygon and update the color individually or all at once w/ an array?

2

That isn’t really a tutorial about CG code - it’s a tutorial on using CG code in Unity’s shader system. It assumes that if you’re playing with it, you already know what CG code is.

To learn what it all is, you’d be better off searching for CG (or HLSL - they’re similar enough to make very little difference) shader tutorials on Google.

3

nvidia’s cg tutorial is nice

4

Thanks everyone. I think I get it better now.