GLSL 3.30 - OpenGL

4 Variables and Types
Types and declarators are the same as for other input, output, and uniform variable declarations outside
blocks, with these exceptions:
• initializers are not allowed
• sampler types are not allowed
• structure definitions cannot be nested inside a block
Otherwise, built-in types, previously declared structures, and arrays of these are allowed as the type of a
declarator in the same manner they are allowed outside a block.
If no optional qualifier is used in a member-declaration, the qualification of the variable is just in, out, or
uniform as determined by interface-qualifier. If optional qualifiers are used, they can include
interpolation and storage qualifiers and they must declare an input, output, or uniform variable consistent
with the interface qualifier of the block: Input variables, output variables, and uniform variables can only
be in in blocks, out blocks, and uniform blocks, respectively. Repeating the in, out, or uniform
interface qualifier for a member's storage qualifier is optional. Declarations using the deprecated
attribute and varying qualifiers are not allowed. For example,
in Material {
smooth in vec4 Color1; // legal, input inside in block
smooth vec4 Color2; // legal, 'in' inherited from 'in Material'
vec2 TexCoord;
// legal, TexCoord is an input
uniform float Atten; // illegal, mismatched interfaces
varying vec2 TexCoord2;//illegal, deprecated keywords don't get new uses
};
For this section, define an interface to be one of these
• All the uniforms of a program. This spans all compilation units linked together within one program.
• The boundary between adjacent programmable pipeline stages: This spans all the outputs in all
compilation units of the first stage and all the inputs in all compilation units of the second stage.
The block name (block-name) is used to match interfaces: an output block of one pipeline stage will be
matched to an input block with the same name in the subsequent pipeline stage. For uniform blocks, the
application uses the block name to identify the block. Block names have no other use within a shader
beyond interface matching; it is an error to use a block name at global scope for anything other than as a
block name (e.g., use of a block name for a global variable name or function name is currently reserved).
Matched block names within an interface (as defined above) must match in terms of having the same
number of declarations with the same sequence of types and the same sequence of member names, as well
as having the same member-wise layout qualification (see next section). Furthermore, if a matching block
is declared as an array, then the array sizes must also match (or follow array matching rules for the
interface between a vertex and a geometry shader). Any mismatch will generate a link error. A block
name is allowed to have different definitions in different interfaces within the same shader, allowing, for
example, an input block and output block to have the same name.
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