Improve gmt events docs for events without duration

[Esteban82]

The video and the graphs explain the case when the event has a duration. But this is optional. The docs should be improve to describe better when the event has no duration.

I could do it but after the AGU.

[Esteban82]

For example I made this animation with this code

gmt events violet.t -T${MOVIE_COL0} -Sc2c -W1p -Gblueviolet
gmt events blue.t   -T${MOVIE_COL0} -Sc2c -W1p -Gblue   -Ms1.5+c0.25 -Mi1+c-0.5 -Mt+c0 -Es+r0.25
gmt events green.t  -T${MOVIE_COL0} -Sc2c -W1p -Ggreen  -Ms1.5+c0.25 -Mi1+c-0.5 -Mt+c0 -Es+r0.25+d0.25
gmt events yellow.t -T${MOVIE_COL0} -Sc2c -W1p -Gyellow -Ms1.5+c0.25 -Mi1+c-0.5 -Mt+c0 -Es+r0.25+p0.25
gmt events orange.t -T${MOVIE_COL0} -Sc2c -W1p -Gorange -Ms1.5+c0.25 -Mi1+c-0.5 -Mt+c0 -Es+r0.25+p0.25+d0.25
gmt events red.t    -T${MOVIE_COL0} -Sc2c -W1p -Gred    -Ms1.5+c0.25 -Mi1+c-0.5 -Mt+c0 -Es+r0.25+p0.25+d0.25+f0.25

Tutorial_1.mp4

Full script:

#!/usr/bin/env bash
#
# Video 1 in this paper: WED-A_Vid_1.sh
# https://github.com/GenericMappingTools/gmt-2024-animation
#
# Wessel, Esteban & Delaviel-Anger, 2024,
#	The Generic Mapping Tools and Animations for the Masses,
#	Geochem. Geophys. Geosyst.
#
# Purpose: Show short movie of the life of two simple events.
# The movie took 53 seconds to render on an 8-core Intel® Core™ i7-3700 CPU @ 3.60GHz.
#--------------------------------------------------------------------------------
NAME=Tutorial_1
NAME=$(basename $0 .sh)
#
# Create a short MP4 showing the life of two simple events.
# Both events starts at 0 and ends at 1, but we add rise
# and fade and coda to one of them (red) and let the other
# be plain default (green) and only visible from 0-1.

cat <<- EOF > labels.txt
-0.125 2 RISE
0.125 2 PLATEAU
0.375 2 DECAY
1.125 2 FADE
0.75 2 NORMAL
1.375 2 CODA
EOF

# Create an approximate default scaling step function we can interpolate in events
cat <<- EOF > normal.txt
	-0.5	0
	-0.001	0
	0	1
	0.999	1
	1	0
	1.5	0
EOF
# Create the exact default scaling step function
cat <<- EOF > stepfunction.txt
	-0.5	0
	0	0
	0	1
	1	1
	1	0
	1.5	0
EOF

# X Y Time
echo  -15 6.5 0 Default > violet.t
echo  -5 6.5 0  "-Es+r" > blue.t
echo  5 6.5 0   "-Es+r+d" > green.t
echo  15 6.5 0  "-Es+r+p" > yellow.t
echo  25 6.5 0  "-Es+r+p+d" > orange.t
echo 35 6.5 0   "-Es+r+p+d+f" > red.t

# Create file to plot event duration
echo "0 0.5 1 0.5 " > duration.txt
cat <<- EOF > pre.sh
gmt begin
	# Build the more complicated size vs time curve based on knowledge of what events does internally
	echo "-0.5 0" > size_vs_time.txt
	# Rise (t = -0.25 to 0 symbol size goes from 0 to 2x)
	gmt math -T-0.25/0/0.01 1 T 0.25 ADD 0.25 DIV PI MUL COS SUB = >> size_vs_time.txt
	# plateau (t = 0 to 0.25 symbol size stays at 2x)
	# Decay (t = 0.25 to 0.5 symbol size decays from 2x to 1x)
	gmt math -T0.25/0.5/0.01 1.5 T 0.25 SUB 0.25 DIV PI MUL COS 2 DIV ADD = >> size_vs_time.txt
	# active (t = 0.5 to 1 symbol size stays at 1x)
	gmt math -T0.6/1/0.1 1 = >> size_vs_time.txt
	# Fade (t = 1 to 1.25 symbol size linearly drops to 0.25 during fading)
	gmt math -T1.1/1.25/0.05 1 T 1 SUB 0.25 DIV SUB 0.75 MUL 0.25 ADD = >> size_vs_time.txt
	# Code (t = 1.25 to 1.5 symbol size stays at 0.25 during code)
	gmt math -T1.3/1.5/0.1 0.25 = >> size_vs_time.txt
	# Lay down the two curves and labels as background plot. Movie starts each frame with this plot
	gmt plot -R-0.5/1.5/-0.1/2.1 -JX13.2c/3c -X4.4c -Y2.25c stepfunction.txt -W5p,green@50
	gmt plot size_vs_time.txt -W1p,red -BW -Bafg0.25+l"Size scale"
	gmt text -F+f8p+jBC -Dj6p -N labels.txt
	# Plot event width with an arrow
	gmt plot duration.txt -Sv12p+s+bt+et -W1.5p -Gblack
	echo 0.5 0.5 EVENT DURATION | gmt text -F+f8p+jMC -Gwhite -W0.25p
gmt end
EOF

cat << 'EOF' > main.sh
gmt begin
	# Set basemap
	gmt basemap -R-20/40/1/9 -JX20c/10c -B -B+t"No duration" -X1c -Y1c


	gmt events violet.t -T${MOVIE_COL0} -Sc2c -W1p -Gblueviolet
	gmt events blue.t   -T${MOVIE_COL0} -Sc2c -W1p -Gblue   -Ms1.5+c0.25 -Mi1+c-0.5 -Mt+c0 -Es+r0.25
	gmt events green.t  -T${MOVIE_COL0} -Sc2c -W1p -Ggreen  -Ms1.5+c0.25 -Mi1+c-0.5 -Mt+c0 -Es+r0.25+d0.25
	gmt events yellow.t -T${MOVIE_COL0} -Sc2c -W1p -Gyellow -Ms1.5+c0.25 -Mi1+c-0.5 -Mt+c0 -Es+r0.25+p0.25
	gmt events orange.t -T${MOVIE_COL0} -Sc2c -W1p -Gorange -Ms1.5+c0.25 -Mi1+c-0.5 -Mt+c0 -Es+r0.25+p0.25+d0.25
	gmt events red.t    -T${MOVIE_COL0} -Sc2c -W1p -Gred    -Ms1.5+c0.25 -Mi1+c-0.5 -Mt+c0 -Es+r0.25+p0.25+d0.25+f0.25

	# Plot text
	gmt events violet.t -T${MOVIE_COL0} -D0/2.3c -Et+r6+f6
	gmt events blue.t   -T${MOVIE_COL0} -D0/2.3c -Et+r6+f6
	gmt events green.t  -T${MOVIE_COL0} -D0/2.3c -Et+r6+f6
	gmt events yellow.t -T${MOVIE_COL0} -D0/2.3c -Et+r6+f6
	gmt events orange.t -T${MOVIE_COL0} -D0/2.3c -Et+r6+f6
	gmt events red.t    -T${MOVIE_COL0} -D0/2.3c -Et+r6+f6

	# Plot red circle moving along the red size curve as function of time
	gmt sample1d size_vs_time.txt -T${MOVIE_COL0}, -Fl > red_circle.txt
	gmt plot red_circle.txt -Sc4p -Gred -W0.25p -R-0.5/1.5/-0.1/2.1 -JX13.2c/3c -N -X3.4c -Y1.25c

	# Plot smaller green circle moving along the default green curve as function of time
	gmt sample1d normal.txt -T${MOVIE_COL0}, -Fl > green_circle.txt
	gmt plot green_circle.txt -Sc2p -Ggreen -W0.25p -N

gmt end
EOF

# Run the movie and add frame counter and horizontal time-progress bar
gmt movie -C22cx12cx100 main.sh -Sbpre.sh -N${NAME} -T-0.5/1.5/0.01 -D24 -Lc0 -Lf+jTR -Pf+jBC+o0/1.5c+ac -M75,png -Vi -Fmp4 -Zs

# Delete temporary files
rm -f main.sh *.t normal.txt labels.txt stepfunction.txt duration.txt