Shaders in GLSL Flashcards
What is not allowed in a fragment shader?
No access to adjacent fragments. Cannot change fragment position.
What are the conversion rules for GLSL?
There is no implicit conversion.
What are the basic types for GLSL?
void bool int float vec2 vec3 vec4 bvec2 bvec3 bvec4 ivec2 ivec3 ivec4 mat2 mat3 mat4 sampler2D samplerCube
What are the non-type keywords in GLSL?
attribute const uniform varying break continue do for while if else in out inout true false lowp mediump highp precision invariant discard return struct
What preprocessor directives are defined in GLSL?
# #define #undef #if #ifdef #ifndef #else #elif #endif #error #pragma #extension #version #line
What is the operator precedence for GLSL?
() defined + - ~ ! * / % \+ - << >> < > = == != & ^ | && ||
What is a sampler type?
Sampler2D and SamplerCube are opaque handlers to textures.
What are the usage restrictions on sampler types?
They can only be declared as function parameters or uniforms. Their use in expressions is limited. The cannot be used as out or inout function parameters.
What is an anonymous structure?
This:
struct S {
int i;
};
S myStruct;
// Illegal in GLSL, need "struct S myStruct"What is an embedded structure definition?
struct S {
struct T {
}
}
// Illegal in GLSL, but this is OK:
struct T {
}
struct S {
T foo;
}How are arrays initialized at declaration in GLSL?
This is impossible.
How are variables scoped in GLSL?
By a system of statically nested scopes, as in C or Java { { } }.
What is the only shared global allowed in GLSL?
uniform
How is const used in GLSL?
Compile-time constants and read-only function parameters.
What is a GLSL attribute?
A linkage between a vertex shader and OpenGL ES per-vertex data
What is a GLSL uniform?
Uniforms form the linkage between a fragment shader, OpenGL ES, and the application. This value does not change across the primitive being processed.
What is a GLSL varying?
A linkage between a vertex shader and a fragment shader through interpolation.
What are the storage qualifiers and the rules for when they are allowed?
default, const, attribute, varying, or uniform.
Local variables may only be default.
Function parameters can only use const.
Function return types and structures do not use qualifiers.
What kind of data is used to communicate between runs of a shader?
None are allowed. This would defeat the SIMD nature of the GPU.
What is “static use” of a variable?
It is when the code contains a compiled reference to the variable, even if the code is never executed.
What do precision qualifiers do?
Specify minimum storage requirements for variables.
What is the rule for precision of operations?
Operations preserve precision of their highest-precision operand, with the exception of a few computationally-intense built-in functions, such as atan().
What does the precision keyword do for GLSL?
Creates a default precision for a storage type.
What does variance refer to in shaders?
In general, the same expression may give different values in different shaders. Shaders are compiled independently, so different shaders may have different values for the same expression.
gl_Position
The ultimate job of a vertex shader is to set gl_Position, a vec4 final position of the vertex.
gl_FragColor
The ultimate job of a fragment shader is to set or discard gl_FragColor.
Which precisions are supported by which shaders?
Vertex shaders support highp, mediump, and lowp. Fragment shaders support mediump and lowp, with highp being optional.
What does this do?
vec3 foo = vec3(1.2);
This constructor initializes foo to (1.2, 1.2, 1.2).
What does this do?
mat3 foo = mat3(3.4);
This constructor initializes the diagonal of foo to 3.4, and all other entries to 0.0.
What does this do?
vec4 a = vec4(1.0,2.0,3.0,4.0);
vec3 b = vec3(a);
Shortens a by dropping 4.0 and assigns result to b.
What is a structure constructor?
A structure constructor is created at structure declaration time. It matches the order and type of members as such:
struct light {
float a;
vec3 b;
};
light newLight = light(1.0,(0.1,0.2,0.3));
Name all of the vector component aliases.
{x, y, z, w} // useful for vertex coordinates
{r, g, b, a} // useful for colors
{s, t, p, q} // useful for texture coordinates
What is the type of
v4.xy
vec2
Which element?
m[1][0]
e10, or the second row, first column.
How many bits (typically) in lowp?
10 bits
How many bits (typically) in medium?
16 bits
How many bits (typically) in high?
24 bits
How many uniforms are typically permitted in the system?
128
What is the intrinsic declaration of gl_Position?
highp vec4 gl_Position
What is the intrinsic declaration of gl_PointSize?
mediump float gl_Pointsize
VNT
Vertex, Normal, Texture Coordinate. A vertex buffer format.
What is the difference between static procedural deformation and dynamic procedural deformation?
Static procedural deformation creates time-independent effects, such as bumps on a metal surface from impact. Dynamic procedural deformation creates time-dependent effects, such as a flag waving or a creature breathing.
How can vertex shaders aid in implementing environmental effects?
Effects like smoke or fog which depend on location or elevation can be calculated in a vertex shader.
How is morphing implemented by a vertex shader?
Two different versions of an object are made available to the vertex shader. The shader blends the position of each vertex in these models.
