Stop making window flicker with draw()

[tmiethlinger]

Hi,
I really like the library and I would like to use it for some sort of simple animation.

The following code works, but unfortunately the window "flickers" whenever the window updates / I call draw. I hope it is clear, what I mean. Is it possible to somehow fix that?

#include
#include <matplot/matplot.h>

#include <unistd.h>
inline void mysleep(unsigned millis)
{
usleep(millis * 1000);
}

int main()
{
using namespace matplot;
auto f = figure(true);
auto ax = gca();
std::vector x = linspace(0, 2pi);
axis({0, 2pi, -1, 1});
std::vector y = transform(x, [](auto x) { return sin(x); });

plot(ax, x, y);
f->draw();

double theta = 0;
while(true)
{
    y = transform(x, [theta](auto x) { return sin(x + theta); });
    plot(ax, x, y);
    f->draw();
    mysleep(100);
    theta += 0.01;
}

return 0;
}

Thanks a lot!

Thomas

[alandefreitas]

I don't it's possible to change that with gnuplot + pipes. It's not really meant for high FPS. This will probably only be fixed in matplot++ v2.

[tmiethlinger]

Ok, thank you for your response! The thing is: I originally found the repo https://github.com/dstahlke/gnuplot-iostream where they have an animation example ("demo_animation" in example-misc.cc). There, I can increase the FPS very high (here: 10 milliseconds) without problem. Do you know by any chance the reason for the different behavior? Do they not use pipes (since you wrote you use gnuplot + pipes)?

By the way, I find that gnuplot-iostream is kinda difficult to use. I was able to animate one function, but I didn't understand the syntax for animating two functions... which is why I tried matplot++.
I.e., I tried the following (and different variants thereof)

#include
#include
#include
#include
#include
#include

#include "gnuplot-iostream.h"

#define M_PI 3.14159265358979323846

#include <unistd.h>
inline void mysleep(unsigned millis)
{
::usleep(millis * 1000);
}

void animation()
{
Gnuplot gp;

std::cout << "Press Ctrl-C to quit (closing gnuplot window doesn't quit)." << std::endl;

gp << "set yrange [-1:1]\n";

const int N = 1000;
std::vector<double> f1(N);
std::vector<double> f2(N);

double theta = 0;
while(true)
{
    for(int i=0; i<N; i++)
    {
        double alpha = (static_cast<double>(i)/N - 0.5) * 10;
        f1[i] = sin(alpha*8.0 + theta) * exp(-alpha*alpha/2.0);
        f2[i] = sin(alpha*8.0 + theta) * exp(-alpha*alpha/1.0);
    }

    // 1 function: works
    gp << "plot" << " '-' binary" << gp.binFmt1d(f1, "array") << "with lines title 'f1(x)'\n";
    gp.sendBinary1d(f1);
    gp.flush();

    // 2 functions: doesn't work
    //gp << "plot" << " '-' binary" << gp.binFmt1d(f1, "array") << "with lines notitle";
    //gp.sendBinary1d(f1);
    //gp << "plot" << " '-' binary" << gp.binFmt1d(f2, "array") << "with lines notitle\n";
    //gp.sendBinary1d(f2);
    //gp.flush();

    mysleep(10);
    theta += 0.05;
}

}

int main(int argc, char *argv[])
{
animation();
}

I thought that you might find that interesting :-) I added a video just for reference.
Anyway, thank you for your answer and the great library!

Best regards, Thomas

gnuplot-iostream-1.mp4