Fix hair random rotation limited to 180 degrees

The issue was caused by phase being limited from 0 to 1, which gave only
0..M_PI distribution which is not good enough for good randomness.

Now the phase is being randomized across full 0..2*M_PI range.

4 files changed, 11 insertions, 3 deletions

diff --git a/source/blender/blenkernel/BKE_blender.h b/source/blender/blenkernel/BKE_blender.h
index 86576f9a11b..f5e7643085a 100644
--- a/source/blender/blenkernel/BKE_blender.h
+++ b/source/blender/blenkernel/BKE_blender.h
@@ -42,7 +42,7 @@ extern "C" {
  * and keep comment above the defines.
  * Use STRINGIFY() rather than defining with quotes */
 #define BLENDER_VERSION         274
-#define BLENDER_SUBVERSION      4
+#define BLENDER_SUBVERSION      5
 /* Several breakages with 270, e.g. constraint deg vs rad */
 #define BLENDER_MINVERSION      270
 #define BLENDER_MINSUBVERSION   5
diff --git a/source/blender/blenkernel/intern/particle.c b/source/blender/blenkernel/intern/particle.c
index 6c354c59d7a..0e200c73918 100644
--- a/source/blender/blenkernel/intern/particle.c
+++ b/source/blender/blenkernel/intern/particle.c
@@ -4100,7 +4100,7 @@ void psys_get_dupli_path_transform(ParticleSimulationData *sim, ParticleData *pa
 			float q_phase[4];
 			float phasefac = psys->part->phasefac;
 			if (psys->part->randphasefac != 0.0f)
-				phasefac += psys->part->randphasefac * psys_frand(psys, (pa - psys->particles) + 20);
+				phasefac += psys->part->randphasefac * psys_frand(psys, (pa - psys->particles) + 20) * 2.0f;
 			axis_angle_to_quat(q_phase, vec, phasefac * (float)M_PI);
 
 			mul_qt_v3(q_phase, side);
diff --git a/source/blender/blenkernel/intern/particle_system.c b/source/blender/blenkernel/intern/particle_system.c
index 5a263e24fc4..0439e56c294 100644
--- a/source/blender/blenkernel/intern/particle_system.c
+++ b/source/blender/blenkernel/intern/particle_system.c
@@ -928,7 +928,7 @@ void psys_get_birth_coords(ParticleSimulationData *sim, ParticleData *pa, Partic
 			/* rotation phase */
 			phasefac = part->phasefac;
 			if (part->randphasefac != 0.0f)
-				phasefac += part->randphasefac * psys_frand(psys, p + 20);
+				phasefac += part->randphasefac * psys_frand(psys, p + 20) * 2.0f;
 			axis_angle_to_quat( q_phase,x_vec, phasefac*(float)M_PI);
 
 			/* combine base rotation & phase */
diff --git a/source/blender/blenloader/intern/versioning_270.c b/source/blender/blenloader/intern/versioning_270.c
index 1b91d3d869e..49e81b1cfff 100644
--- a/source/blender/blenloader/intern/versioning_270.c
+++ b/source/blender/blenloader/intern/versioning_270.c
@@ -799,4 +799,12 @@ void blo_do_versions_270(FileData *fd, Library *UNUSED(lib), Main *main)
 			}
 		}
 	}
+
+	if (!MAIN_VERSION_ATLEAST(main, 274, 5)) {
+		/* Particle random phase range doubled. */
+		ParticleSettings *part;
+		for (part = main->particle.first; part; part = part->id.next) {
+			part->randphasefac *= 0.5f;
+		}
+	}
 }