[NTG-context] animation using \startuseMPgraphic

[Hans Hagen]

On 4/19/2020 9:02 PM, Jeong Dal wrote:
> Dear Wolfgang,
> 
> I’d like to ask you one more.
> 
> To make an animation, almost same graphics are drawn repeatedly.
> In my code, for example,
> The base figure(two circles, line, boundingbox) is fixed and only points 
> are moved.
> But it draws the base figure every time and it is not inefficient.

In what sense? Runtime? Even moving the definitions doesn't really save 
cpu cycles. MP runtime is normally not the bottleneck in a run.

\startMPextensions
vardef findPointD(expr C, Q, r) =
     numeric dist, ang;
     pair X, Y;
     dist := r**2/sqrt((xpart Q - xpart C)**2 + (ypart Q - ypart C)**2);
     ang := angle(Q - C);
     Y := C + dir(ang)*dist;
     Y
enddef;
\stopMPextensions

> Is there a way to draw the base figure once, and draw the points only at 
> each frame?
I guess you could stack them on top of a base background image but I 
wonder if it's worth the trouble.

Hans

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