Add 'ellipse' distribution to ParticleSystem

src/modules/graphics/ParticleSystem.cpp

@@ -242,6 +242,7 @@ void ParticleSystem::initParticle(Particle *p, float t)
 
 	p->position = pos;
 
+	float rand_x, rand_y;
 	switch (areaSpreadDistribution)
 	{
 	case DISTRIBUTION_UNIFORM:
@@ -252,6 +253,12 @@ void ParticleSystem::initParticle(Particle *p, float t)
 		p->position.x += (float) rng.randomNormal(areaSpread.getX());
 		p->position.y += (float) rng.randomNormal(areaSpread.getY());
 		break;
+	case DISTRIBUTION_ELLIPSE:
+		rand_x = (float) rng.random(-1, 1);
+		rand_y = (float) rng.random(-1, 1);
+		p->position.x += areaSpread.getX() * (rand_x * sqrt(1 - 0.5f*pow(rand_y, 2)));
+		p->position.y += areaSpread.getY() * (rand_y * sqrt(1 - 0.5f*pow(rand_x, 2)));
+		break;
 	case DISTRIBUTION_NONE:
 	default:
 		break;
@@ -969,6 +976,7 @@ StringMap<ParticleSystem::AreaSpreadDistribution, ParticleSystem::DISTRIBUTION_M
 	{ "none",    DISTRIBUTION_NONE },
 	{ "uniform", DISTRIBUTION_UNIFORM },
 	{ "normal",  DISTRIBUTION_NORMAL },
+	{ "ellipse",  DISTRIBUTION_ELLIPSE },
 };
 
 StringMap<ParticleSystem::AreaSpreadDistribution, ParticleSystem::DISTRIBUTION_MAX_ENUM> ParticleSystem::distributions(ParticleSystem::distributionsEntries, sizeof(ParticleSystem::distributionsEntries));

src/modules/graphics/ParticleSystem.h

@@ -46,13 +46,14 @@ class ParticleSystem : public Drawable
 {
 public:
 	/**
-	 * Type of distribution new particles are drawn from: None, uniform, normal.
+	 * Type of distribution new particles are drawn from: None, uniform, normal, ellipse.
 	 */
 	enum AreaSpreadDistribution
 	{
 		DISTRIBUTION_NONE,
 		DISTRIBUTION_UNIFORM,
 		DISTRIBUTION_NORMAL,
+		DISTRIBUTION_ELLIPSE,
 		DISTRIBUTION_MAX_ENUM
 	};