# The stocking of Nineveh

What a week. I’m a bit exhausted right now as I’ve been pushing a bit, but the results are fairly pleasing to me.

### GLSL Quality

First off I did a bunch of work in making the generated GLSL a bit nice to read. The most obvious issue was that, when I returned multiple values I would created a bunch of temporary variables. The code was all technically correct but it didn’t read well. So now like this:

```
(defun-g foo ((x :float))
(let ((sq (* x x)))
(values (v2! sq)
(v3! (* sq x)))))
```

can compile to glsl like this

```
vec2 FOO(float X, out vec3 return_1)
{
float SQ = (X * X);
vec2 g_G1075 = vec2(SQ);
return_1 = vec3((SQ * X));
return g_G1075;
}
```

Which is fairly readable. 1 temporary variable is still used, but that is to maintain the order of evaluation that was expected.

`return`

is one of areas of the compiler with the most magic as we generate different code based on the context the code is being compiled in. It could be a return from a regular function (like above), or it could be from a stage in which case we need to turn it into `out`

interface block assignments etc. This meant it took a bunch of testing to get it correct.

### Compiler cleanup

For a while I’ve been trying to clean up the code around how multiple return values are handled. I had a few false starts here (which ended in force-pushing away a day’s worth of work) but it’s done now. They are still plenty of scars in the codebase but the healing can at least begin :p

### Bugs in release

I then found a bug & a regression in the code I had prepped for the next release (into the common lisp package manager). As the releases are not made on a fixed cadence I wasn’t sure how long I had so I dived into that. It turned out one of those cases where even good type checking wouldn’t have helped. I had removed some code that looked redundant but was actually resolving the aliased name of a type.

### Compile in every direction

With that done I had sat down for some well earned farting around. Last week I had knocked up a simple shadertoy like thing[0] so I went back to working through that.

I got to this part where it was recommending going and implementing various curve functions from folks like IQ & Golan Levin. So dutifully I started.. but I was getting this nagging feeling that I should have more noise functions. So after porting some functions from the chaps above I found [this article] (https://briansharpe.wordpress.com/2011/10/01/gpu-texture-free-noise/) on texture-free noise.

Needless to say I got hooked on that, and then finding out out he had a whole library I decided that I needed it, all of it, in lisp :)

So that was the weekend. I polished up my naive GLSL -> Lisp translator and got cracking porting. Having this much code pouring in was a really good test-case for the compiler and so I got to clean up a few more bugs in the process.

One interesting addition to the compiler was to allow floating point numbers as strings in the lisp code. It looks like this: `(+ (v4! 1.5) (v4! "1.4142135623730950488016887242097"))`

the reason for this is that some floating point numbers used in shaders are used for their exact bit-pattern rather than strictly for the value itself. This optional string syntax avoid the risk of the host lisp using a different floating point representation a messing up the value in some way.

The first pass of the import is done. Next is cleanup and documentation but that is less critical. My standard library Nineveh is looking slightly better stocked now :)

### Validation

One thing that felt great was noticing that, in the naive GLSL -> Lisp translator and got cracking porting. Having this much code pouring in was a really GLSL noise library, there were cases where it would be nice to switch out the hashing function used in a noise function. In the GLSL it was done with comments but I realized this was a *PERFECT* place to use first class functions. So here it is:

```
(defun-g ctoy-quad-frag ((uv :vec2)
&uniform (now :float)
(mouse :vec2)
(mouse-norm :vec2)
(mouse-buttons :vec2)
(screen-res :vec2))
;; here is the hash function we pass in ↓↓↓↓↓↓
(v3! (+ 0.4 (* (perlin-noise #'sgim-qpp-hash-2-per-corner
(* uv 5))
0.5))))
```

In that code we call `perlin-noise`

passing in the hashing function we would like it to use. And here is the generated GLSL.

```
// vertex-stage
#version 450
uniform float NOW;
uniform vec2 MOUSE;
uniform vec2 MOUSE_NORM;
uniform vec2 MOUSE_BUTTONS;
uniform vec2 SCREEN_RES;
vec3 CTOY_QUAD_FRAG(vec2 UV);
float PERLIN_NOISE(vec2 P);
vec2 PERLIN_QUINTIC(vec2 X2);
vec4 SGIM_QPP_HASH_2_PER_CORNER(vec2 GRID_CELL, out vec4 return_1);
vec4 QPP_RESOLVE(vec4 X1);
vec4 QPP_PERMUTE(vec4 X0);
vec4 QPP_COORD_PREPARE(vec4 X);
vec4 QPP_COORD_PREPARE(vec4 X)
{
return (X - (floor((X * (1.0f / 289.0f))) * 289.0f));
}
vec4 QPP_PERMUTE(vec4 X0)
{
return (fract((X0 * (((34.0f / 289.0f) * X0) + vec4((1.0f / 289.0f))))) * 289.0f);
}
vec4 QPP_RESOLVE(vec4 X1)
{
return fract((X1 * (7.0f / 288.0f)));
}
vec4 SGIM_QPP_HASH_2_PER_CORNER(vec2 GRID_CELL, out vec4 return_1)
{
vec4 HASH_0;
vec4 HASH_1;
vec4 HASH_COORD = QPP_COORD_PREPARE(vec4(GRID_CELL.xy,(GRID_CELL.xy + vec2(1.0f))));
HASH_0 = QPP_PERMUTE((QPP_PERMUTE(HASH_COORD.xzxz) + HASH_COORD.yyww));
HASH_1 = QPP_RESOLVE(QPP_PERMUTE(HASH_0));
HASH_0 = QPP_RESOLVE(HASH_0);
vec4 g_G5388 = HASH_0;
return_1 = HASH_1;
return g_G5388;
}
vec2 PERLIN_QUINTIC(vec2 X2)
{
return (X2 * (X2 * (X2 * ((X2 * ((X2 * 6.0f) - vec2(15.0f))) + vec2(10.0f)))));
}
float PERLIN_NOISE(vec2 P)
{
vec2 PI = floor(P);
vec4 PF_PFMIN1 = (P.xyxy - vec4(PI,(PI + vec2(1.0f))));
vec4 MVB_0;
vec4 MVB_1;
//
// Here is that hashing function in the GLSL
// ↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓
MVB_0 = SGIM_QPP_HASH_2_PER_CORNER(PI,MVB_1);
vec4 GRAD_X = (MVB_0 - vec4(0.49999));
vec4 GRAD_Y = (MVB_1 - vec4(0.49999));
vec4 GRAD_RESULTS = (inversesqrt(((GRAD_X * GRAD_X) + (GRAD_Y * GRAD_Y))) * ((GRAD_X * PF_PFMIN1.xzxz) + (GRAD_Y * PF_PFMIN1.yyww)));
GRAD_RESULTS *= vec4(1.4142135623730950488016887242097);
vec2 BLEND = PERLIN_QUINTIC(PF_PFMIN1.xy);
vec4 BLEND2 = vec4(BLEND,(vec2(1.0f) - BLEND));
return dot(GRAD_RESULTS,(BLEND2.zxzx * BLEND2.wwyy));
}
vec3 CTOY_QUAD_FRAG(vec2 UV)
{
vec4(MOUSE_NORM.x,MOUSE_BUTTONS.x,MOUSE_NORM.y,float(1));
return vec3((0.4f + (PERLIN_NOISE((UV * float(5))) * 0.5f)));
}
void main()
{
CTOY_QUAD_FRAG(<dummy v-vec2>);
gl_Position = vec4(float(1),float(2),float(3),float(4));
return;
}
```

I’m stoked at how natural the function call looks in the resulting code. Also it’s extra func that the function passed in has 2 return values and everything just worked :)

For completeness here are a couple of the other functions involved

```
(defun-g perlin-noise ((hash-func (function (:vec2) (:vec4 :vec4)))
(p :vec2))
;; looks much better than revised noise in 2D, and with an efficent hash
;; function runs at about the same speed.
;;
;; requires 2 random numbers per point.
(let* ((pi (floor p))
(pf-pfmin1 (- (s~ p :xyxy) (v! pi (+ pi (v2! 1.0))))))
(multiple-value-bind (hash-x hash-y) (funcall hash-func pi)
(let* ((grad-x (- hash-x (v4! "0.49999")))
(grad-y (- hash-y (v4! "0.49999")))
(grad-results
(* (inversesqrt (+ (* grad-x grad-x) (* grad-y grad-y)))
(+ (* grad-x (s~ pf-pfmin1 :xzxz))
(* grad-y (s~ pf-pfmin1 :yyww))))))
(multf grad-results (v4! "1.4142135623730950488016887242097"))
(let* ((blend (perlin-quintic (s~ pf-pfmin1 :xy)))
(blend2 (v! blend (- (v2! 1.0) blend))))
(dot grad-results (* (s~ blend2 :zxzx) (s~ blend2 :wwyy))))))))
```

```
(defun-g sgim-qpp-hash-2-per-corner ((grid-cell :vec2))
(let (((hash-0 :vec4)) ((hash-1 :vec4)))
(let* ((hash-coord
(qpp-coord-prepare
(v! (s~ grid-cell :xy) (+ (s~ grid-cell :xy) (v2! 1.0))))))
(setf hash-0
(qpp-permute
(+ (qpp-permute (s~ hash-coord :xzxz)) (s~ hash-coord :yyww))))
(setf hash-1 (qpp-resolve (qpp-permute hash-0)))
(setf hash-0 (qpp-resolve hash-0)))
(values hash-0 hash-1)))
```

All credit of implementation goes to Brian Sharpe for this excellent noise library

### Peace

OK I’ll stop now and spare you more details. I’m just so happy to see this behaving.

Have a great week.

Ciao

[0] https://github.com/cbaggers/fraggle/blob/master/main.lisp