From ea6e267d983a34978606b2cedde383a1bd1fb53d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Robert=20M=C3=BCller?= <robytemueller@gmail.com>
Date: Mon, 13 Mar 2023 00:15:39 +0100
Subject: [PATCH] Add `random_angle` function

To generate a random angle in the range `[0.0f;2.0f * pi[`. This ensures that the random angle cannot be `2.0f * pi`, which would be identical to the angle `0.0f` and therefore cause the random angle to be less uniformly selected.

Note that this first casts `RAND_MAX` to a `float` and then uses `std::nextafter` to get the next larger `float`. Using `RAND_MAX + 1` would cause an integer overflow on systems where `RAND_MAX == INT_MAX` (e.g. Ubuntu and macOS).
---
 src/base/math.h                          |  9 +++++++--
 src/game/client/components/damageind.cpp |  2 +-
 src/game/client/components/effects.cpp   | 14 +++++++-------
 3 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/src/base/math.h b/src/base/math.h
index 91a19c80c..5c9bb7b50 100644
--- a/src/base/math.h
+++ b/src/base/math.h
@@ -9,6 +9,8 @@
 
 using std::clamp;
 
+constexpr float pi = 3.1415926535897932384626433f;
+
 constexpr inline int round_to_int(float f)
 {
 	return f > 0 ? (int)(f + 0.5f) : (int)(f - 0.5f);
@@ -30,6 +32,11 @@ inline float random_float()
 	return rand() / (float)(RAND_MAX);
 }
 
+inline float random_angle()
+{
+	return 2.0f * pi * (rand() / std::nextafter((float)RAND_MAX, std::numeric_limits<float>::max()));
+}
+
 constexpr int fxpscale = 1 << 10;
 
 // float to fixed
@@ -85,8 +92,6 @@ public:
 	}
 };
 
-constexpr float pi = 3.1415926535897932384626433f;
-
 template<typename T>
 constexpr inline T minimum(T a, T b)
 {
diff --git a/src/game/client/components/damageind.cpp b/src/game/client/components/damageind.cpp
index 35001568d..07ddf80a7 100644
--- a/src/game/client/components/damageind.cpp
+++ b/src/game/client/components/damageind.cpp
@@ -41,7 +41,7 @@ void CDamageInd::Create(vec2 Pos, vec2 Dir)
 		pItem->m_Pos = Pos;
 		pItem->m_StartTime = LocalTime();
 		pItem->m_Dir = Dir * -1;
-		pItem->m_StartAngle = (random_float() - 1.0f) * 2.0f * pi;
+		pItem->m_StartAngle = -random_angle();
 	}
 }
 
diff --git a/src/game/client/components/effects.cpp b/src/game/client/components/effects.cpp
index 6cd94a9cd..06f5b125f 100644
--- a/src/game/client/components/effects.cpp
+++ b/src/game/client/components/effects.cpp
@@ -34,7 +34,7 @@ void CEffects::AirJump(vec2 Pos)
 	p.m_LifeSpan = 0.5f;
 	p.m_StartSize = 48.0f;
 	p.m_EndSize = 0;
-	p.m_Rot = random_float() * pi * 2;
+	p.m_Rot = random_angle();
 	p.m_Rotspeed = pi * 2;
 	p.m_Gravity = 500;
 	p.m_Friction = 0.7f;
@@ -71,7 +71,7 @@ void CEffects::PowerupShine(vec2 Pos, vec2 Size)
 	p.m_LifeSpan = 0.5f;
 	p.m_StartSize = 16.0f;
 	p.m_EndSize = 0;
-	p.m_Rot = random_float() * pi * 2;
+	p.m_Rot = random_angle();
 	p.m_Rotspeed = pi * 2;
 	p.m_Gravity = 500;
 	p.m_Friction = 0.9f;
@@ -95,7 +95,7 @@ void CEffects::FreezingFlakes(vec2 Pos, vec2 Size)
 	p.m_UseAlphaFading = true;
 	p.m_StartAlpha = 1.0f;
 	p.m_EndAlpha = 0.0f;
-	p.m_Rot = random_float() * pi * 2;
+	p.m_Rot = random_angle();
 	p.m_Rotspeed = pi;
 	p.m_Gravity = random_float() * 250.0f;
 	p.m_Friction = 0.9f;
@@ -171,7 +171,7 @@ void CEffects::PlayerSpawn(vec2 Pos)
 		p.m_LifeSpan = 0.3f + random_float() * 0.3f;
 		p.m_StartSize = 64.0f + random_float() * 32;
 		p.m_EndSize = 0;
-		p.m_Rot = random_float() * pi * 2;
+		p.m_Rot = random_angle();
 		p.m_Rotspeed = random_float();
 		p.m_Gravity = random_float() * -400.0f;
 		p.m_Friction = 0.7f;
@@ -212,7 +212,7 @@ void CEffects::PlayerDeath(vec2 Pos, int ClientID)
 		p.m_LifeSpan = 0.3f + random_float() * 0.3f;
 		p.m_StartSize = 24.0f + random_float() * 16;
 		p.m_EndSize = 0;
-		p.m_Rot = random_float() * pi * 2;
+		p.m_Rot = random_angle();
 		p.m_Rotspeed = (random_float() - 0.5f) * pi;
 		p.m_Gravity = 800.0f;
 		p.m_Friction = 0.8f;
@@ -243,7 +243,7 @@ void CEffects::Explosion(vec2 Pos)
 	p.m_LifeSpan = 0.4f;
 	p.m_StartSize = 150.0f;
 	p.m_EndSize = 0;
-	p.m_Rot = random_float() * pi * 2;
+	p.m_Rot = random_angle();
 	m_pClient->m_Particles.Add(CParticles::GROUP_EXPLOSIONS, &p);
 
 	// add the smoke
@@ -273,7 +273,7 @@ void CEffects::HammerHit(vec2 Pos)
 	p.m_LifeSpan = 0.3f;
 	p.m_StartSize = 120.0f;
 	p.m_EndSize = 0;
-	p.m_Rot = random_float() * pi * 2;
+	p.m_Rot = random_angle();
 	m_pClient->m_Particles.Add(CParticles::GROUP_EXPLOSIONS, &p);
 	if(g_Config.m_SndGame)
 		m_pClient->m_Sounds.PlayAt(CSounds::CHN_WORLD, SOUND_HAMMER_HIT, 1.0f, Pos);