The Shader Language (GLSL)

• Very C like
• // for comments
• and /* */ as well
• Statements are terminated with a ;
• main is void.
• variables must be declared with an associated type before use
  • float, double (32 and 64 bit IEEE 754 Floating point numbers)
  • int, uint
  • bool
• Scoping rules
  • variables declared outside of a function are global.
  • Otherwise, within the codeblock where they are declared.
• May be initialized at declaration.
• standard C literal rules
  • 0n - octal
  • 0xn - hex
  • nu (342u) unsigned.
  • nf (123f) float
  • nl (2.34l) double
• Most coercion is not permitted
  • int f = false; is a syntax error.
  • Permitted:
    • int to uint
    • int, uint to float
    • int, uint, float to double
  • Others require explicit conversion float f; int i = int(f);
  • I have the feeling that everything is a class, and conversion is actually calling an overloaded constructor.
• Aggrigate Types
  • float: vec2, vec3, vec4, mat2, mat3, mat4, mat2x2, mat2x3, mat2x4, mat3x2 mat3x3, mat3x4, mat4x2, mat4x3, mat4x4
  • double: dvec2, dvec3, dvec4, dmat*
  • int: ivec2, ivec3, ivec4
  • uint: uvec2, uvec3, uvec4
  • bool: bvec2, bvec3, bvec4
• mat4x2 is a four column by 2 row matrix.
• Initialization
• vec3 velocity = vec3(0.0, 2.0, 3.0)
• Casting
• ivec3 steps = ivec3(velocity)
• Constructors can be used to lengthen k = vec4(3), or shorten vec3(k) a vector.
• And vec3 color=(1.0, 0.0, 1.0) ; vec4 translucent = vec4(color, 0.5);
• Matricies are initialized on the diagional mat3(1) gives the identity matrix.
• mat3(1,2,3,4,5,6,7,8,9), mat3(vec3(1,2,3),vec3(4,5,6), vec3(7,8,9))
• Components of a vector
  • addressed as an array
  • vec4 color[0] is the first component.
  • addressed as points (x,y,z,w) vec3 point, point.x
  • addressed as colors (r,g,b,a) vec4 color, color.a
  • or as textures (s,t,p,q)
  • python weirdness color.rrr returns a vec3(r,r,r)
  • color.gbra returns vec4(g,b,r,a)
  • But you may not mix groups
  • color.rgz is not allowed
  • or go outside of sizes
  • vec2 point; point.z is a syntax error.
• And of a matrix
  • mat4 m; m[2] gives back column 2, m[1][1]
• structs

  • struct Particles {
        float lifetime;
        vec3 position;
        vec3 velocity;
    }
    	 

  • Particle(10.0, pos, vel) is declared as a constructor automatically.
  • dereference: Particle p; p.position = vec3(1,0,0);
• Arrays are possible as well
  • Bounds are checked, no out of bounds access permitted.
  • float coeff[3];
  • but also float[3] coeff;
  • coeff.length() returns 3
  • multidimensional arrays are possible.
• Storage qualifiers
  • const
    • c++ constant
    • const float Pi=3.141529;
  • in/out
    • input/output value to/from a shader.
    • in float a;
    • out int b;
  • uniform
    • Specified by the application before a shader is executed
    • Will not change across the execution of the shader
    • Must be global variables
    • Available to all shaders.
    • Shaders can not change values of a uniform
  • buffer: for bidirectional shared data
  • shared: shared across shaders.