From: hgn <hgodden00@gmail.com>
Date: Mon, 27 Nov 2023 06:54:50 +0000 (+0000)
Subject: cone & disc distributions
X-Git-Url: https://harrygodden.com/git/?p=vg.git;a=commitdiff_plain;h=17dc0afed8913ce7756e86f1c69da4ada8ceda79

cone & disc distributions
---

diff --git a/vg_m.h b/vg_m.h
index 46cf38c..91071ff 100644
--- a/vg_m.h
+++ b/vg_m.h
@@ -2273,8 +2273,7 @@ struct {
 } 
 static vg_rand;
 
-static void vg_rand_seed( unsigned long seed ) 
-{
+static void vg_rand_seed( unsigned long seed ) {
    /* set initial seeds to mt[STATE_VECTOR_LENGTH] using the generator
     * from Line 25 of Table 1 in: Donald Knuth, "The Art of Computer
     * Programming," Vol. 2 (2nd Ed.) pp.102.
@@ -2289,8 +2288,7 @@ static void vg_rand_seed( unsigned long seed )
 /*
  * Generates a pseudo-randomly generated long.
  */
-static u32 vg_randu32(void) 
-{
+static u32 vg_randu32(void) {
    u32 y;
    /* mag[x] = x * 0x9908b0df for x = 0,1 */
    static u32 mag[2] = {0x0, 0x9908b0df}; 
@@ -2330,32 +2328,47 @@ static u32 vg_randu32(void)
 /*
  * Generates a pseudo-randomly generated f64 in the range [0..1].
  */
-static inline f64 vg_randf64(void)
-{
+static inline f64 vg_randf64(void){
    return (f64)vg_randu32()/(f64)0xffffffff;
 }
 
-static inline f64 vg_randf64_range( f64 min, f64 max )
-{
+static inline f64 vg_randf64_range( f64 min, f64 max ){
    return vg_lerp( min, max, (f64)vg_randf64() );
 }
 
-static inline void vg_rand_dir( v3f dir )
-{
+static inline void vg_rand_dir( v3f dir ){
    dir[0] = vg_randf64();
    dir[1] = vg_randf64();
    dir[2] = vg_randf64();
 
+   /* warning: *could* be 0 length.
+    * very unlikely.. 1 in (2^32)^3. but its mathematically wrong. */
+
    v3_muls( dir, 2.0f, dir );
    v3_sub( dir, (v3f){1.0f,1.0f,1.0f}, dir );
 
    v3_normalize( dir );
 }
 
-static inline void vg_rand_sphere( v3f co )
-{
+static inline void vg_rand_sphere( v3f co ){
    vg_rand_dir(co);
    v3_muls( co, cbrtf( vg_randf64() ), co );
 }
 
+static void vg_rand_disc( v2f co ){
+   f32 a = vg_randf64() * VG_TAUf;
+   co[0] = sinf(a);
+   co[1] = cosf(a); 
+   v2_muls( co, sqrtf( vg_randf64() ), co );
+}
+
+static void vg_rand_cone( v3f out_dir, f32 angle ){
+   f32 r = sqrtf(vg_randf64()) * angle * 0.5f,
+       a = vg_randf64() * VG_TAUf;
+
+   out_dir[0] = sinf(a) * sinf(r);
+   out_dir[1] = cosf(a) * sinf(r);
+   out_dir[2] = cosf(r);
+}
+
 #endif /* VG_M_H */