Introduction to the High-Level Shading Language - Introduction to 3D Game Programming with DirectX 9.0 - page 281

float —32-bit floating-point number
double —64-bit floating-point number
Note: Some platforms might not support int , half , and double .If
this is the case, these types are emulated using float .
16.3.2 Vector Types
HLSL has the following built-in vector types:
vector —A 4D vector where each component is of type float
vector<T, n> —An n -dimensional vector, where each component
is of scalar type T . The dimension n must be between 1 and 4. Here
is an example of a 2D double vector:
vector<double, 2> vec2;
We can access a component of a vector using an array subscript syntax.
For example, to set the i th component of a vector vec , we would write:
vec[i] = 2.0f;
In addition, we can access the components of a vector vec as we would
access the members of a structure, using the defined component names
x , y , z , w , r , g , b , and a .
vec.x = vec.r = 1.0f;
vec.y = vec.g = 2.0f;
vec.z = vec.b = 3.0f;
vec.w = vec.a = 4.0f;
The names r , g , b , and a refer to exactly the same component as the
names x , y , z , and w , respectively. When using vectors to represent col-
ors, the RGBA notation is more desirable since it reinforces the fact
that the vector is representing a color.
Alternatively, we can use these other predefined types that repre-
sent a 2D, 3D, and 4D vector, respectively:
float2 vec2;
float3 vec3;
float4 vec4;
Consider the vector u =( u x , u y , u z , u w ) and suppose we want to copy
the components of u to a vector v such that v =( u x , u y , u y , u w ). The
most immediate solution would be to individually copy each component
of u over to v as necessary. However, HLSL provides a special syntax
for doing these kinds of out-of-order copies called swizzles :
vector u = {1.0f, 2.0f, 3.0f, 4.0f};
vector v = {0.0f, 0.0f, 5.0f, 6.0f};
v = u.xyyw; // v = {1.0f, 2.0f, 2.0f, 4.0f}