improve spring animations

Author: baggepinnen

docs/src/examples/three_springs.md

@@ -24,9 +24,9 @@ systems = @named begin
     bar1 = FixedTranslation(r = [0.3, 0, 0])
     bar2 = FixedTranslation(r = [0, 0, 0.3])
     spring1 = Multibody.Spring(c = 20, m = 0, s_unstretched = 0.1, fixed_rotation_at_frame_b=true,
-                               r_rel_0 = [-0.2, -0.2, 0.2], radius=0.05, num_windings=10)
-    spring2 = Multibody.Spring(c = 40, m = 0, s_unstretched = 0.1, color=[0,0,0.3,1])
-    spring3 = Multibody.Spring(c = 20, m = 0, s_unstretched = 0.1, radius=0.05, num_windings=10)
+                               r_rel_0 = [-0.2, -0.2, 0.2], radius=0.05, num_windings=10, end_ratio=0.1)
+    spring2 = Multibody.Spring(c = 40, m = 0, s_unstretched = 0.1, color=[0,0,0.3,1], end_ratio=0.1)
+    spring3 = Multibody.Spring(c = 20, m = 0, s_unstretched = 0.1, radius=0.05, num_windings=10, end_ratio=0.1)
 end
 eqs = [connect(world.frame_b, bar1.frame_a)
        connect(world.frame_b, bar2.frame_a)

ext/Render.jl

@@ -661,7 +661,7 @@ function render!(scene, ::typeof(BodyShape), sys, sol, t)
                 Makie.transform!(m, translation=r1, rotation=Q)
             end
         else
-            error("Shape $shape not supported")
+            error("""Shape $shape not supported, currently only supports "cylinder" and "box".""")
         end
     else
         T = get_frame_fun(sol, sys.frame_a)
@@ -834,12 +834,13 @@ function render!(scene, ::Union{typeof(Spring), typeof(SpringDamperParallel)}, s
     n_wind = sol(sol.t[1], idxs=sys.num_windings)
     radius = sol(sol.t[1], idxs=sys.radius) |> Float32
     N = round(Int, sol(sol.t[1], idxs=sys.N))
+    end_ratio = sol(sol.t[1], idxs=sys.end_ratio) |> Float32
     thing = @lift begin
         r1 = Point3f(r_0a($t))
         r2 = Point3f(r_0b($t))
-        spring_mesh(r1,r2; n_wind, radius, N)
+        spring_mesh(r1,r2; n_wind, radius, N, end_ratio)
     end
-    plot!(scene, thing; color)
+    plot!(scene, thing; color, transparency=true)
     true
 end
 
@@ -894,16 +895,18 @@ function render!(scene, ::Function, sys, sol, t, args...) # Fallback for systems
     false
 end
 
-function spring_mesh(p1, p2; n_wind=6, radius=0.1f0, N=200)
+function spring_mesh(p1, p2; n_wind=6, radius=0.1f0, N=200, end_ratio = 0.1)
     phis = range(0, n_wind*2π, length=N)
     d = p2 - p1
     z = range(0, norm(d), length=N) # Correct length
     dn = d ./ norm(d)
     R = rot_from_line(dn)
 
     points = map(enumerate(phis)) do (i,phi)
-        x = radius*cos(phi)
-        y = radius*sin(phi)
+        n_ramp = N * end_ratio
+        ri = i <= n_ramp ? i/n_ramp : i > N-n_ramp ? (N-i)/n_ramp : 1
+        x = ri*radius*cos(phi)
+        y = ri*radius*sin(phi)
         pᵢ = Point3f(x, y, z[i])
 
         R * pᵢ + p1
@@ -1041,12 +1044,13 @@ function render!(scene, ::Union{typeof(P.Spring), typeof(P.SpringDamper)}, sys,
     n_wind = sol(sol.t[1], idxs=sys.num_windings)
     radius = sol(sol.t[1], idxs=sys.radius) |> Float32
     N = sol(sol.t[1], idxs=sys.N) |> Int
+    end_ratio = sol(sol.t[1], idxs=sys.end_ratio) |> Float32
     thing = @lift begin
         r1 = Point3f(r_0a($t)..., 0)
         r2 = Point3f(r_0b($t)..., 0)
-        spring_mesh(r1,r2; n_wind, radius, N)
+        spring_mesh(r1,r2; n_wind, radius, N, end_ratio, end_ratio)
     end
-    plot!(scene, thing; color)
+    plot!(scene, thing; color, transparency=true)
     true
 end
 
@@ -1108,8 +1112,8 @@ function render!(scene, ::typeof(Multibody.BoxVisualizer), sys, sol, t)
     height = Float32(sol(sol.t[1], idxs=sys.height))
     length = Float32(sol(sol.t[1], idxs=sys.length))
 
-    length_dir = sol(sol.t[1], idxs=collect(sys.render_length_dir))
-    width_dir = sol(sol.t[1], idxs=collect(sys.render_width_dir))
+    length_dir = sol(sol.t[1], idxs=collect(sys.length_direction))
+    width_dir = sol(sol.t[1], idxs=collect(sys.width_direction))
     height_dir = normalize(cross(normalize(length_dir), normalize(width_dir)))
     width_dir = normalize(cross(height_dir, length_dir))
 

src/PlanarMechanics/components.jl

@@ -215,6 +215,7 @@ Linear 2D translational spring
 - `render = true` Render the spring in animations
 - `radius = 0.1` Radius of spring when rendered
 - `N = 200` Number of points in mesh when rendered
+- `end_ratio = 0.0`: Ratio of the length of the spring [0, 0.5] that is rendered with decreasing radius at the ends. Set this to 0 to have uniform radius along the entire spring.
 
 # Connectors:
 - `frame_a` [Frame](@ref) Coordinate system fixed to the component with one cut-force and cut-torque
@@ -239,6 +240,7 @@ Linear 2D translational spring
         render = true, [description = "Render the spring in animations"]
         radius = 0.1, [description = "Radius of spring when rendered"]
         N = 200, [description = "Number of points in mesh when rendered"]
+        end_ratio = 0.0
     end
 
     @variables begin
@@ -352,6 +354,7 @@ Linear 2D translational spring damper model
 - `render = true` Render the spring in animations
 - `radius = 0.1` Radius of spring when rendered
 - `N = 200` Number of points in mesh when rendered
+- `end_ratio = 0.0`: Ratio of the length of the spring that is rendered with decreasing radius at the ends.
 
 # Connectors:
 - `frame_a` [Frame](@ref) Coordinate system fixed to the component with one cut-force and cut-torque
@@ -379,6 +382,7 @@ Linear 2D translational spring damper model
         render = true, [description = "Render the spring in animations"]
         radius = 0.1, [description = "Radius of spring when rendered"]
         N = 200, [description = "Number of points in mesh when rendered"]
+        end_ratio = 0.0
     end
 
     @variables begin

src/forces.jl

@@ -388,10 +388,11 @@ additional equations to handle the mass are removed.
 - `color = [0,0,1,1]`: Color of the spring when rendered
 - `radius = 0.1`: Radius of spring when rendered
 - `N = 200`: Number of points in mesh when rendered. Rendering time can be reduced somewhat by reducing this number.
+- `end_ratio = 0.0`: Ratio of the length of the spring [0, 0.5] that is rendered with decreasing radius at the ends. Set this to 0 to have uniform radius along the entire spring.
 
 See also [`SpringDamperParallel`](@ref)
 """
-@component function Spring(; c, name, m = 0, lengthfraction = 0.5, s_unstretched = 0, num_windings=6, color=[0,0,1,1], radius=0.1, N=200, kwargs...)
+@component function Spring(; c, name, m = 0, lengthfraction = 0.5, s_unstretched = 0, num_windings=6, color=[0,0,1,1], radius=0.1, N=200, end_ratio = 0.0, kwargs...)
     @named ptf = PartialTwoFrames()
     @unpack frame_a, frame_b = ptf
     pars = @parameters begin
@@ -401,6 +402,7 @@ See also [`SpringDamperParallel`](@ref)
             bounds = (0, Inf),
         ]
         num_windings = num_windings, [description = "Number of windings of the coil when rendered"]
+        end_ratio = 0.0
         color[1:4] = color
         radius = radius, [description = "Radius of spring when rendered"]
         N = N, [description = "Number of points in mesh when rendered"]
@@ -501,7 +503,7 @@ f = c (s - s_{unstretched}) + d \\cdot D(s)
 where `c`, `s_unstretched` and `d` are parameters, `s` is the distance between the origin of `frame_a` and the origin of `frame_b` and `D(s)` is the time derivative of `s`.
 """
 @component function SpringDamperParallel(; name, c, d, s_unstretched=0,
-    color = [0, 0, 1, 1], radius = 0.1, N = 200, num_windings = 6, kwargs...)
+    color = [0, 0, 1, 1], radius = 0.1, N = 200, num_windings = 6, end_ratio = 0.0, kwargs...)
     @named plf = PartialLineForce(; kwargs...)
     @unpack s, f = plf
 
@@ -516,6 +518,7 @@ where `c`, `s_unstretched` and `d` are parameters, `s` is the distance between t
         radius = radius, [description = "Radius of spring when rendered"]
         N = N, [description = "Number of points in mesh when rendered"]
         num_windings = num_windings, [description = "Number of windings of the coil when rendered"]
+        end_ratio = end_ratio
     end
     # pars = collect_all(pars)