GLSLANG Spec 4.0 - OpenGL

4 Variables and Types
If an instance name (instance-name) is not used, the names declared inside the block are scoped at the
global level and accessed as if they were declared outside the block. If an instance name (instance-name)
is used, then it puts all the members inside a scope within its own name space, accessed with the field
selector ( . ) operator (analogously to structures). For example,
in Light {
vec4 LightPos;
vec3 LightColor;
};
in ColoredTexture {
vec4 Color;
vec2 TexCoord;
} Material; // instance name
vec3 Color;
// different Color than Material.Color
vec4 LightPos;
// illegal, already defined
...
... = LightPos; // accessing LightPos
... = Material.Color; // accessing Color in ColoredTexture block
Outside the shading language (i.e., in the API), members are similarly identified except the block name is
always used in place of the instance name (API accesses are to interfaces, not to shaders). If there is no
instance name, then the API does not use the block name to access a member, just the member name.
out Vertex {
vec4 Position; // API transform/feedback will use “Vertex.Position”
vec2 Texture;
} Coords; // shader will use “Coords.Position”
out Vertex2 {
vec4 Color;
};
// API will use “Color”
For blocks declared as arrays, the array index must also be included when accessing members, as in this
example
uniform Transform { // API uses “Transform[2]” to refer to instance 2
mat4
ModelViewMatrix;
mat4
ModelViewProjectionMatrix;
float
Deformation;
} transforms[4];
...
... = transforms[2].ModelViewMatrix; // shader access of instance 2
// API uses “Transform.ModelViewMatrix” to query an offset or other query
For uniform blocks declared as an array, each individual array element corresponds to a separate buffer
object backing one instance of the block. As the array size indicates the number of buffer objects needed,
uniform block array declarations must specify an array size. Any integral expression can be used to index
a uniform block array, as per section 4.1.9 "Arrays".
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