[Bf-blender-cvs] [f61d166] hair_system: Fix for wrong hair root evaluation: The time value passed to the solver was the end of the time step interval.

[Lukas Tönne]

Commit: f61d166a874772ea948ed00a41ee6d618ef9ddca
Author: Lukas Tönne
Date:   Thu Jul 31 10:31:40 2014 +0200
Branches: hair_system
https://developer.blender.org/rBf61d166a874772ea948ed00a41ee6d618ef9ddca

Fix for wrong hair root evaluation: The time value passed to the solver
was the end of the time step interval.

This causes extrapolation of the hair root location and overshooting
hair.

===================================================================

M       source/blender/hair/intern/HAIR_solver.cpp
M       source/blender/modifiers/intern/MOD_hair.c

===================================================================

diff --git a/source/blender/hair/intern/HAIR_solver.cpp 
b/source/blender/hair/intern/HAIR_solver.cpp
index cb250f2..4a6b147 100644
--- a/source/blender/hair/intern/HAIR_solver.cpp
+++ b/source/blender/hair/intern/HAIR_solver.cpp
@@ -224,7 +224,10 @@ static void step(const HairParams &params, const 
SolverForces &forces, float tim
                k = 0;
                point = curve->points;
                
-               calc_root_animation(t0, t1, time, curve, point->next.co, 
point->next.vel);
+               /* note: roots are evaluated at the end of the timestep: time + 
timestep
+                * so the hair points align perfectly with them
+                */
+               calc_root_animation(t0, t1, time + timestep, curve, 
point->next.co, point->next.vel);
                
                if (k < numpoints-1) {
                        stretch = calc_stretch_force(params, curve, point, 
point+1, time);
diff --git a/source/blender/modifiers/intern/MOD_hair.c 
b/source/blender/modifiers/intern/MOD_hair.c
index ce04401..70af492 100644
--- a/source/blender/modifiers/intern/MOD_hair.c
+++ b/source/blender/modifiers/intern/MOD_hair.c
@@ -97,7 +97,7 @@ static DerivedMesh *applyModifier(ModifierData *md, Object 
*ob,
                int s;
                
                float dt = 1.0f / (float)hmd->steps_per_second;
-               /*float prev_time = floorf(prev_steps) * dt;*/
+               float prev_time = floorf(prev_steps) * dt;
                float time = floorf(steps) * dt;
                
                if (!hmd->solver) {
@@ -116,9 +116,10 @@ static DerivedMesh *applyModifier(ModifierData *md, Object 
*ob,
                
                if (num_steps < 10000) {
                        struct HAIR_Solver *solver = hmd->solver;
+                       float curtime = prev_time;
                        for (s = 0; s < num_steps; ++s) {
-                               HAIR_solver_step(solver, time, dt);
-                               time += dt;
+                               HAIR_solver_step(solver, curtime, dt);
+                               curtime += dt;
                        }
                }

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