When generating 3D animations in Gnuplot—such as rotating a 3x3x3 matrix cube with text labels inside each cell—you might encounter an annoying flickering or blinking effect on text elements across frames. This issue typically arises when creating animated GIFs using a loop and combining splot with replot.

Understanding the Cause of Flickering Labels

The primary reason text labels flicker in Gnuplot animations is the use of the replot command inside an explicit frame rendering loop. In Gnuplot, replot appends previous plot commands to the plot queue. When executed inside a loop targeting an animated GIF terminal, this can cause layering artifacts, frame buffer conflicts, or redrawing sync issues where labels are briefly erased or overwritten before the next frame is committed.

The Solution: Avoid replot Inside Animation Loops

To eliminate blinking and ensure smooth rendering, combine your 3D cube geometry plot and your label plot into a single splot command separated by a comma. Removing replot entirely from the animation loop ensures every frame is rendered cleanly in a single pass.

Refining the Code

Here is how you can restructure your Gnuplot script to combine the polygons and labels into one single plot call during the loop:

reset session
set datafile separator comma

# Create the cube geometry datablock
set table $Cube
    f0(n,i) = !((n-i)%3)*(((n-i)>2-i)*2-1)
    f1(n) = ((n%4)>1)-0.5
    f2(n) = (((n+1)%4)>1)-0.5
    set samples 6
    plot for [n=0:5] '+' u (m=int($0), m>3 ? "" : sprintf("%+g, %+g, %+g", \
                (x=f0(n,0), x ? x*0.5 : f1(m)), \
                (y=f0(n,1), y ? y*0.5 : x ? f1(m) : f2(m)), \
                (z=f0(n,2), z ? z*0.5 : f2(m)))) w table
unset table

# Populate sample data array
N=29
array luis[N]
do for [j=1:28] {
    luis[j] = int(10*rand(0))
}
f(x1,y1,z1) = z1*9 + y1*3 + x1 + 1

# Styling setup
unset border
unset tics
set view equal xyz
set style fill solid 1.0 border
set pm3d depthorder hidden3d
set key noautotitle
color(i) = word("0xff0000 0x00ff00 0x0000ff 0xff00ff 0xffff00 0x00ffff", i+1)

# Terminal setup for GIF animation
set angles degrees
set term gif size 600,400 animate delay 5
set output "Cubo4.gif"

# Single splot animation loop
do for [a=0:360:10] {
    set view 60-60*sin(a), a, 1.2
    
    splot for [z=0:2] for [y=0:2] for [x=0:2] for [i=0:5] \
          $Cube index i u ($1*0.8+x):($2*0.8+y):($3*0.8+z) w polygons fc rgb color(i), \
          for [z1=0:2] for [y1=0:2] for [x1=0:2] \
          '+' using (x1):(y1):(z1):(sprintf("%d", luis[f(x1,y1,z1)])) \
          with labels tc rgb "black" center
}

set output

Key Takeaways for Smooth Gnuplot Animations

  • Never use replot in loops: Combine multiple datasets or layers into a single comma-separated splot or plot statement.
  • Set depth order: Using set pm3d depthorder hidden3d ensures 3D polygons are sorted correctly relative to the camera angle.
  • Flush output properly: Always finish your animation script with set output to close and finalize the GIF file cleanly.