make COM cylinder in Body configurable in rendering

Author: baggepinnen

docs/src/examples/swing.md

@@ -102,7 +102,7 @@ Next, we create the full swing assembly
         body_left  = BodyShape(m=0.1, r = [0, 0, w])
         body_right = BodyShape(m=0.1, r = [0, 0, -w])
 
-        body  = Body(m=6, isroot=true, r_cm = [w/2, -w/2, w/2], vel_from_R=true)
+        body  = Body(m=6, isroot=true, r_cm = [w/2, -w/2, w/2], vel_from_R=true, cylinder_radius=0.01)
 
         damper = Damper(d=0.5)
     end

ext/Render.jl

@@ -242,11 +242,8 @@ function render!(scene, ::typeof(Body), sys, sol, t)
     color = get_color(sys, sol, :purple)
     r_cm = get_fun(sol, collect(sys.r_cm))
     framefun = get_frame_fun(sol, sys.frame_a)
-    radius = try
-        sol(sol.t[1], idxs=sys.radius)
-    catch
-        0.05f0
-    end
+    radius = sol(sol.t[1], idxs=sys.radius) |> Float32
+    cylinder_radius = sol(sol.t[1], idxs=sys.cylinder_radius) |> Float32
     thing = @lift begin # Sphere
         Ta = framefun($t)
         coords = (Ta*[r_cm($t); 1])[1:3] # TODO: make use of a proper transformation library instead of rolling own?
@@ -257,7 +254,7 @@ function render!(scene, ::typeof(Body), sys, sol, t)
 
     iszero(r_cm(sol.t[1])) && (return true)
 
-    thing = @lift begin # Cylinder
+    thing2 = @lift begin # Cylinder
         Ta = framefun($t)
 
         r_cmt = r_cm($t) # r_cm is the center of the sphere in frame a
@@ -274,10 +271,9 @@ function render!(scene, ::typeof(Body), sys, sol, t)
         extremity = tip
         origin = point
 
-        radius = 0.05f0
-        Makie.GeometryBasics.Cylinder(origin, extremity, radius)
+        Makie.GeometryBasics.Cylinder(origin, extremity, cylinder_radius)
     end
-    mesh!(scene, thing; color, specular = Vec3f(1.5), shininess=20f0, diffuse=Vec3f(1))
+    mesh!(scene, thing2; color, specular = Vec3f(1.5), shininess=20f0, diffuse=Vec3f(1))
     true
 end
 

src/components.jl

@@ -220,6 +220,7 @@ Representing a body with 3 translational and 3 rotational degrees-of-freedom.
 
 # Rendering options
 - `radius`: Radius of the joint in animations
+- `cylinder_radius`: Radius of the cylinder from frame to COM in animations (only drawn if `r_cm` is non-zero). Defaults to `radius/2`
 - `color`: Color of the joint in animations, a vector of length 4 with values between [0, 1] providing RGBA values
 """
 @component function Body(; name, m = 1, r_cm = [0, 0, 0],
@@ -238,6 +239,7 @@ Representing a body with 3 translational and 3 rotational degrees-of-freedom.
               v_0 = 0,
               w_a = 0,
               radius = 0.05,
+              cylinder_radius = radius/2,
               air_resistance = 0.0,
               color = [1,0,0,1],
               quat=false,)
@@ -269,6 +271,9 @@ Representing a body with 3 translational and 3 rotational degrees-of-freedom.
     @parameters radius=radius [
         description = "Radius of the body in animations",
     ]
+    @parameters cylinder_radius=cylinder_radius [
+        description = "Radius of the cylinder from frame to COM in animations",
+    ]
     @parameters color[1:4] = color [description = "Color of the body in animations (RGBA)"]
     # @parameters I[1:3, 1:3]=I [description="inertia tensor"]
 
@@ -345,7 +350,7 @@ Representing a body with 3 translational and 3 rotational degrees-of-freedom.
     # pars = [m;r_cm;radius;I_11;I_22;I_33;I_21;I_31;I_32;color]
 
     sys = ODESystem(eqs, t; name=:nothing, metadata = Dict(:isroot => isroot), systems = [frame_a])
-    add_params(sys, [radius; color]; name)
+    add_params(sys, [radius; cylinder_radius; color]; name)
 end