Graphics Reference
In-Depth Information
The following shows some examples of constructing vectors:
vec4 myVec4 = vec4(1.0); // myVec4 = {1.0, 1.0, 1.0,
// 1.0}
vec3 myVec3 = vec3(1.0,0.0,0.5); // myVec3 = {1.0, 0.0, 0.5}
vec3 temp = vec3(myVec3); // temp = myVec3
vec2 myVec2 = vec2(myVec3); // myVec2 = {myVec3.x,
// myVec3.y}
myVec4 = vec4(myVec2, temp); // myVec4 = {myVec2.x,
// myVec2.y,
// temp.x, temp.y}
For matrix construction, the language is flexible. These basic rules describe
how matrices can be constructed:
• If only one scalar argument is provided to a matrix constructor, that
value is placed in the diagonal of the matrix. For example,
mat4
(1.0)
will create a 4 × 4 identity matrix.
• A matrix can be constructed from multiple vector arguments. For
example, a
mat2
can be constructed from two
vec2
s.
• A matrix can be constructed from multiple scalar arguments—one for
each value in the matrix, consumed from left to right.
The matrix construction is even more flexible than the basic rules just
stated, in that a matrix can basically be constructed from any combination
of scalars and vectors as long as enough components are provided to
initialize the matrix. Matrices in OpenGL ES are stored in column major
order. When using a matrix constructor, the arguments will be consumed
to fill the matrix by column. The comments in the following example
show how the matrix constructor arguments map into columns.
mat3 myMat3 = mat3(1.0, 0.0, 0.0, // First column
0.0, 1.0, 0.0, // Second column
0.0, 1.0, 1.0); // Third column
The individual components of a vector can be accessed in two ways:
by using the “.” operator or through array subscripting. Depending on
the number of components that make up a given vector, each of the
components can be accessed through the use of the swizzles {
x
,
y
,
z
,
w
},
{
r
,
g
,
b
,
a
}, or {
s
,
t
,
p
,
q
}
.
The reason for the three different naming schemes
