Fix culling for particles that have length (#7136)

* fix culling

* further check

* rotate check

* fix error

* bithackery

Author: Kestrellius

code/particle/hosts/EffectHostParticle.cpp

@@ -81,7 +81,7 @@ float EffectHostParticle::getScale() const {
 	const auto& particle = m_particle.lock();
 	//For anything apart from the velocity curve, "Post-Curves Velocity" is well defined. This is needed to facilitate complex but common particle scaling and appearance curves.
 	const auto& curve_input = std::forward_as_tuple(*particle,
-		vm_vec_mag_quick(&particle->velocity) * particle->parent_effect.getParticleEffect().m_lifetime_curves.get_output(particle::ParticleEffect::ParticleLifetimeCurvesOutput::ANIM_STATE, std::forward_as_tuple(*particle, vm_vec_mag_quick(&particle->velocity))));
+		vm_vec_mag_quick(&particle->velocity) * particle->parent_effect.getParticleEffect().m_lifetime_curves.get_output(particle::ParticleEffect::ParticleLifetimeCurvesOutput::VELOCITY_MULT, std::forward_as_tuple(*particle, vm_vec_mag_quick(&particle->velocity))));
 
 	return particle->radius * particle->parent_effect.getParticleEffect().m_lifetime_curves.get_output(particle::ParticleEffect::ParticleLifetimeCurvesOutput::RADIUS_MULT, curve_input);
 }

code/particle/particle.cpp

@@ -422,10 +422,36 @@ namespace particle
 			p_pos = part->pos;
 		}
 
-		if (vm_vec_dot_to_point(&Eye_matrix.vec.fvec, &Eye_position, &p_pos) <= 0.0f)
+		bool part_has_length = part->length != 0.0f;
+
+		if (!part_has_length && vm_vec_dot_to_point(&Eye_matrix.vec.fvec, &Eye_position, &p_pos) <= 0.0f)
 		{
 			return false;
 		}
+		
+		const auto& source_effect = part->parent_effect.getParticleEffect();
+
+		//For anything apart from the velocity curve, "Post-Curves Velocity" is well defined. This is needed to facilitate complex but common particle scaling and appearance curves.
+		const auto& curve_input = std::forward_as_tuple(*part,
+			vm_vec_mag_quick(&part->velocity) * source_effect.m_lifetime_curves.get_output(ParticleEffect::ParticleLifetimeCurvesOutput::VELOCITY_MULT, std::forward_as_tuple(*part, vm_vec_mag_quick(&part->velocity))));
+			
+		vec3d p1 = vmd_x_vector;
+
+		if (part_has_length) {
+			vm_vec_copy_normalize_safe(&p1, &part->velocity);
+			if (part->attached_objnum >= 0) {
+				vm_vec_unrotate(&p1, &p1, &Objects[part->attached_objnum].orient);
+			}
+			p1 *= part->length * source_effect.m_lifetime_curves.get_output(ParticleEffect::ParticleLifetimeCurvesOutput::LENGTH_MULT, curve_input);
+			p1 += p_pos;
+
+			float dot0 = vm_vec_dot_to_point(&Eye_matrix.vec.fvec, &Eye_position, &p_pos);
+			float dot1 = vm_vec_dot_to_point(&Eye_matrix.vec.fvec, &Eye_position, &p1);
+
+			if (dot0 <= 0.0f && dot1 <= 0.0f) {
+				return false;
+			}
+		}
 
 		// calculate the alpha to draw at
 		auto alpha = get_current_alpha(&p_pos, part->radius);
@@ -441,17 +467,19 @@ namespace particle
 
 		if (flags)
 		{
-			return false;
+			if (part_has_length) {
+				vertex pos2;
+				auto flags2 = g3_rotate_vertex(&pos2, &p1);
+				if (flags & flags2) {
+					return false;
+				}
+			} else {
+				return false;
+			}
 		}
 
 		g3_transfer_vertex(&pos, &p_pos);
 
-		const auto& source_effect = part->parent_effect.getParticleEffect();
-
-		//For anything apart from the velocity curve, "Post-Curves Velocity" is well defined. This is needed to facilitate complex but common particle scaling and appearance curves.
-		const auto& curve_input = std::forward_as_tuple(*part,
-			vm_vec_mag_quick(&part->velocity) * source_effect.m_lifetime_curves.get_output(ParticleEffect::ParticleLifetimeCurvesOutput::ANIM_STATE, std::forward_as_tuple(*part, vm_vec_mag_quick(&part->velocity))));
-
 		// figure out which frame we should be using
 		int framenum;
 		int cur_frame;
@@ -475,17 +503,8 @@ namespace particle
 
 		float radius = part->radius * source_effect.m_lifetime_curves.get_output(ParticleEffect::ParticleLifetimeCurvesOutput::RADIUS_MULT, curve_input);
 
-		if (part->length != 0.0f) {
+		if (part_has_length) {
 			vec3d p0 = p_pos;
-
-			vec3d p1;
-			vm_vec_copy_normalize_safe(&p1, &part->velocity);
-			if (part->attached_objnum >= 0) {
-				vm_vec_unrotate(&p1, &p1, &Objects[part->attached_objnum].orient);
-			}
-			p1 *= part->length * source_effect.m_lifetime_curves.get_output(ParticleEffect::ParticleLifetimeCurvesOutput::LENGTH_MULT, curve_input);
-			p1 += p_pos;
-
 			batching_add_laser(framenum + cur_frame, &p0, radius, &p1, radius);
 		}
 		else {