Shaderforth is a horrendously ugly experiment in making GLSL shaders using a Forth- and APL-inspired language.

The structure of Shaderforth files is a top-level main word, one or more globals words, any number of normal words, and macro words.

Here's a simple GLSL fragment shader:

uniform vec3 iResolution;
uniform float iGlobalTime;

void main() {
	vec2 pos = (gl_FragCoord.xy / iResolution.xy - 0.5) * 2.0;
	float temp = abs(sin(length(pos) * cos(iGlobalTime)));
	gl_FragColor = vec4(temp, temp, temp, 1.0);
}

And here's one terse ShaderForth equivalent:

:globals
	@vec3 uniform =iResolution
	@float uniform =iGlobalTime
;

gl_FragCoord .xy iResolution .xy / 0.5 - 2.0 *
length iGlobalTime cos * sin abs
dup dup 1.0 vec4 =gl_FragColor

Which compiles to:

uniform vec3 iResolution;
uniform float iGlobalTime;
void main() {
	float var_0 = abs(sin((length(((((gl_FragCoord).xy) / ((iResolution).xy)) - (0.5)) * (2.0))) * (cos(iGlobalTime))));
	gl_FragColor = vec4(var_0, var_0, var_0, 1.0);
}

And another:

:globals
	@vec3 uniform =iResolution
	@float uniform =iGlobalTime
;

gl_FragCoord .xy iResolution .xy / 0.5 - 2.0 * length =distance
distance iGlobalTime cos * sin abs =>color
color color color 1.0 vec4 =gl_FragColor

Which compiles to:

uniform vec3 iResolution;
uniform float iGlobalTime;
void main() {
	float distance = length(((((gl_FragCoord).xy) / ((iResolution).xy)) - (0.5)) * (2.0));
	gl_FragColor = vec4(abs(sin((distance) * (cos(iGlobalTime)))), abs(sin((distance) * (cos(iGlobalTime)))), abs(sin((distance) * (cos(iGlobalTime)))), 1.0);
}

• GLSL functions are all there as words (This isn't complete, but it's pretty straightforward to see how they are added)
• =name -- Assigns to a GLSL variable named name
• =>name -- Creates a local macro variable, whose value will be embedded literally wherever it's used
• : name ( argtype argtype argtype -> returntype ) atom atom atom ; -- Defines a word that will be created as a GLSL function
  • This can optionally take argument names, argname:argtype, which will become macro locals.
• :m name atom atom atom ; -- Defines a macro word whose contents will be inlined upon use
  • This can optionally take argument names, which will become macro locals. :m name ( arg1 arg2 ) atom atom atom ;
• ( ) -- Everything between parentheses (make sure you include spaces around them -- these are both words) will be ignored as a comment, with the exception of type specifiers on words
• [ atom atom atom ] -- Defines an array
• [ atom atom atom ]v -- Defines a vector. Equivalent to the same array followed by avec
• /word -- For each element of the array at the top of the stack, map against word -- this can take a macro word
• \word -- Performs a reduce operation with word against the array at the top of the stack -- this can take a macro word
• flatten -- Given an array at the top of the stack, this will turn the elements into native stack elements
• avec -- Takes an array from the top of the stack and generates a vector of the requisite size
• dup -- Duplicates the element at the top of the stack
• swap -- Swaps the top two elements of the stack
• Binary math operators -- They're used as expected
• Unary math operator negate -- Flips the sign on the topmost element
• &word -- Pushes a word reference to the stack
• call -- Executes a word reference
• *name -- Equivalent to name call