Graphics Reference
In-Depth Information
GLSL's built-in Boolean scalar and vector types are
bool
,
bvec2
,
bvec3
,
and
bvec4
. The main value in Boolean vectors is their ability to support logical
operations on vectors, and thus to parallelize some logical tests.
GLSL supports a number of matrix types. For square matrices,
mat2
,
mat3
,
and
mat4
can be used for square floating-point matrices of dimension 2 × 2,
3 × 3, or 4 × 4, respectively. Using explicit matrix types rather than simple arrays
lets you take advantage of GLSL's many matrix operations and functions.
There are also matrix types that define the dimensions explicitly by listing
both dimensions in the declaration. Thus, GLSL has
mat2x2
,
mat2x3
,
mat2x4
,
mat3x2
,
mat3x3
,
mat3x4
,
mat4x2
,
mat4x3
, and
mat4x4
floating-point matrix
types. When the two dimensions are equal, this is the same as the declarations
above (
mat2x2
is the same as
mat2
, for example). Using these matrix types lets
you use GLSL's matrix operations on non-square matrices. Note that there is
no declaration of
mat1xN
or
matNx1
arrays; when a one-dimensional array is
needed, you can usually use a simple
vecN
in its place.
Name Sets
GLSL supports some standard name sets for vector components that are used
for notational convenience. For a
vec4
variable, you can use (
x
,
y
,
z
,
w
) if you
want to refer to components for geometry, (
r
,
g
,
b
,
a
) if you want to refer to
components for color, or (
s
,
t
,
p
,
q
) if you want to refer to components for tex-
ture coordinates. The name set you choose need not depend on the context;
you can use (
x
,
y
,
z
,
w
) to refer to colors if you like, for example. (Note that the
leter
r
for texture coordinates has been replaced by
p
to avoid confusion with
the leter
r
for red.) In general, you should be careful to avoid name sets that
imply such meanings when choosing name sets for vectors other than geom-
etry, RGBA color, or texture.
The component selection syntax allows multiple components to be
selected by appending their names (which must be from the same name set)
after the period (
.
). So with a declaration
vec4 v4
, for example, we have the
examples given in the table below.
v4.rgba
Is a
vec4
and is the same as just using
v4
.
v4.rgb
Is a
vec3
made from the first three components of
v4
.
v4.b
Is a float whose value is the third component of
v4
; also
v4.z
or
v4.p
.
v4.xz
Is a
vec2
made from the first and third components of
v4
; also
v4.rb
or
v4.sp
.
v4.xgba
Is illegal because the component names do not come from the same set.
