add path tracing option to animations

Author: baggepinnen

docs/src/examples/pendulum.md

@@ -225,9 +225,10 @@ sol = solve(prob, Rodas4())
 plot(sol, layout=4)
 ```
 
+In the animation below, we visualize the path that the origin of the pendulum tip traces by providing the tip frame in a vector of frames passed to `traces`
 ```@example pendulum
 import GLMakie
-Multibody.render(model, sol, filename = "furuta.gif")
+Multibody.render(model, sol, filename = "furuta.gif", traces=[model.tip.frame_a])
 nothing # hide
 ```
 ![furuta](furuta.gif)

docs/src/rendering.md

@@ -24,6 +24,10 @@ Many components allows the user to select with which color it is rendered. This
 ## Rendering the world frame
 The display of the world frame can be turned off by setting `world.render => false` in the variable map.
 
+## Tracing the path of a frame in 3D visualizations
+The path that a frame traces out during simulation can be visualized by passing a vector of frames to the `render` function using the `traces` keyword, e.g., `render(..., traces=[frame1, frame2])`.
+See the Furuta-pendulum demonstration [Going 3D](@ref) for an example of this.
+
 
 ## Rendering API
 

ext/Render.jl

@@ -129,6 +129,7 @@ function render(model, sol,
     up = Vec3f(0,1,0),
     show_axis = false,
     timescale = 1.0,
+    traces = nothing,
     kwargs...
     )
     scene, fig = default_scene(x,y,z; lookat,up,show_axis)
@@ -139,27 +140,49 @@ function render(model, sol,
     t = Observable(timevec[1])
 
     recursive_render!(scene, complete(model), sol, t)
+
+    if traces !== nothing
+        tvec = range(sol.t[1], stop=sol.t[end], length=500)
+        for frame in traces
+            (frame.metadata !== nothing && get(frame.metadata, :frame, false)) || error("Only frames can be traced in animations.")
+            points = get_trans(sol, frame, tvec) |> Matrix
+            Makie.lines!(scene, points)
+        end
+    end
+
     fn = record(fig, filename, timevec; framerate) do time
         t[] = time/timescale
     end
     fn, scene, fig
 end
 
 function render(model, sol, time::Real;
+    traces = nothing,
+    x = 2,
+    y = 0.5,
+    z = 2,
     kwargs...,
     )
 
     # fig = Figure()
     # scene = LScene(fig[1, 1]).scene
     # cam3d!(scene)
-    scene, fig = default_scene(0,0,10; kwargs...)
+    scene, fig = default_scene(x,y,z; kwargs...)
     # mesh!(scene, Rect3f(Vec3f(-5, -3.6, -5), Vec3f(10, 0.1, 10)), color=:gray) # Floor
 
     steps = range(sol.t[1], sol.t[end], length=3000)
 
     t = Slider(fig[2, 1], range = steps, startvalue = time).value
-    
     recursive_render!(scene, complete(model), sol, t)
+
+    if traces !== nothing
+        tvec = range(sol.t[1], stop=sol.t[end], length=500)
+        for frame in traces
+            (frame.metadata !== nothing && get(frame.metadata, :frame, false)) || error("Only frames can be traced in animations.")
+            points = get_trans(sol, frame, tvec) |> Matrix
+            Makie.lines!(scene, points)
+        end
+    end
     fig, t
 end
 

src/Multibody.jl

@@ -11,7 +11,7 @@ export Rotational, Translational
 export render, render!
 
 """
-    scene, time = render(model, sol, t::Real; framerate = 30)
+    scene, time = render(model, sol, t::Real; framerate = 30, traces = [])
     path        = render(model, sol, timevec = range(sol.t[1], sol.t[end], step = 1 / framerate); framerate = 30, timescale=1)
 
 Create a 3D animation of a multibody system
@@ -24,6 +24,7 @@ Create a 3D animation of a multibody system
 - `framerate`: Number of frames per second.
 - `timescale`: Scaling of the time vector. This argument can be made to speed up animations (`timescale < 1`) or slow them down (`timescale > 1`). A value of `timescale = 2` will be 2x slower than real time.
 - `filename` controls the name and the file type of the resulting animation
+- `traces`: An optional array of frames to show the trace of.
 
 # Camera control
 The following keyword arguments are available to control the camera pose:

src/orientation.jl

@@ -381,9 +381,8 @@ end
 Extract the translational part of a frame from a solution at time `t`.
 See also [`get_rot`](@ref), [`get_frame`](@ref), [Orientations and directions](@ref) (docs section).
 """
-function get_trans(sol, frame, t)
-    SVector{3}(sol(t, idxs = collect(frame.r_0)))
-end
+get_trans(sol, frame, t::Number) = SVector{3}(sol(t, idxs = collect(frame.r_0)))
+get_trans(sol, frame, t::AbstractArray) = sol(t, idxs = collect(frame.r_0))
 
 """
     T_W_F = get_frame(sol, frame, t)