gnuplotC

Simple and easy C interface to gnuplot. Allows to draw figures and create video animations (efficient by using parallelism).

Currently, gnuplotC supports the following modes:

	png	pdf	eps	video (mp4)
2D	PNG_2D	PDF_2D	EPS_2D	VIDEO_2D
3D	PNG_3D	PDF_3D		VIDEO_3D

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Creating a plot

1. Start gnuplot interface. Select mode, file name, figure size, ...
2. (Optional) Set gnuplot configurations. Before adding elements!
3. Add elements.
4. End.

int fontsize = 18, figsize[2] = {1080, 1080};

t_gnuplot *ifc = gnuplot_start(PNG_2D, "segment.png", figsize, fontsize);
draw_segment_2d(ifc, 1, 0, 0.4, 0.6, "lw 2"); 
gnuplot_end(ifc);

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Creating a video

Videos are built using ffmpeg, which must be installed and available. Treat each frame as its own independent figure. By default, each frame is piped directly to ffmpeg without the need to store it.

1. Start gnuplot interface. Select framerate, ...
2. (Optional) Set configurations.
3. Add elements.
4. Start a new frame.
5. Repeat from step 2 as needed.
6. End.

Optionally, the default framerate (24 fps) can be changed by modifying the global variable GNUPLOTC_FRAMERATE before starting the interface.

GNUPLOTC_FRAMERATE = 12;

char *video_config[] = {"unset border", "unset tics", "set isosamples 100", 
                        "set view equal xyz", NULL};

ifc = gnuplot_start(VIDEO_3D, "sphere.mp4", figsize, fontsize, 
                    GNUPLOTC_ARRAY(video_config), "set view 70, 0");
draw_sphere_3d(ifc, 0.5, 0.5, 0.5, 0.2, "lines", NULL);
for (int ii=1; ii<GNUPLOTC_FRAMERATE*3+1; ii++) {
    char buff[256]; 
    snprintf(buff, 256, "set view 70, %f", fmod(ii*360.0/(GNUPLOTC_FRAMERATE*3), 360.0));
    next_frame(ifc, GNUPLOTC_ARRAY(video_config), buff);
    draw_sphere_3d(ifc, 0.5, 0.5, 0.5, 0.2, "lines", NULL);
}
gnuplot_end(ifc);

Faster parallel video processing

Parallel processing of the frames is possible, with each thread running gnuplot in parallel resulting in much faster processing times. The downside is that all the frames must be saved to disc beforehand (in a temporal directory), which can take up some space.

To activate this mode, simply call activate_parallel_video_processing(...) before starting the interface.

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Configuring the interface

The gnuplot configuration can be specified:

• When calling gnuplot_start(...), in the form of additional optional parameters.
• Calling gnuplot_config(...), before drawing any element.
• In the case of a video, also when calling new_frame(...).

Once an element in a plot (or frame) is drawn, it is not possible to change the gnuplot configuration.

t_gnuplot *ifc = gnuplot_start(PNG_2D, "circle.png", figsize, fontsize, "set title 'CIRCLE'", "set xlabel 'x'");
gnuplot_config(ifc, "set xrange [0:1]", "set yrange [0:1]");
[...]

Also, we may define a NULL terminated array of configurations, which we can pass at any point as an additional configuration using GNUPLOTC_ARRAY():

char *cmd_array[] = {"set xrange [0:1]", "set yrange [0:1]", NULL};
t_gnuplot *ifc = gnuplot_start(PNG_2D, "test.png", figsize, fontsize, GNUPLOTC_ARRAY(cmd_array));
[...]

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Dependencies and compilation

The user must have available gnuplot and ffmpeg (for video creation) as command line tools.

Optional OMP mode

By default, parallel processing of frames is implemented using fork() to spawn child processes. However, those users who prefer an OMP approach, may activate it one of two ways:

• Defining GNUPLOTC_USE_OMP before including gnuplotc.h.

  #define GNUPLOTC_USE_OMP
  #include "gnuplotc.h"

• Or by passing -DGNUPLOTC_USE_OMP as an argument to the compiler.

  gcc-15 -DGNUPLOTC_USE_OMP example.c plot.c -o example_omp
  

In this case, the compiler should support OMP (in my Macbook the native gcc does not and I have to use a Homebrew version).

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Examples

Basic examples (see /example/example.c)

Other examples I made using the library