saveframe() screenshots into file but cannot read image files in processing - processing

Question

I want to use processing to take screenshots and use the screenshot to generate animations. The way I try to do it is save the frames into a directory and reload the image files into an image String. Not sure if it is the right way to do it, but I get error when I load the images:
error message
String[] listFileNames(String dir) {
File file = new File(dir);
if (file.isDirectory()) {
String names[] = file.list();
return names;
} else {
// If it's not a directory
return null;
}
}
void draw(){
if (frameCount % 60 == 0) screen();
if (screen != null) image(screen, 0, 0, width, height);
if(recording){
saveFrame("output//screenshot_####.png");
}
names = listFileNames("/Users/lj/Desktop/JingLang_vis145A_Midterm/screenshot/output/");
print(names);
if(names.length != 0){
for(int i = 0; i < names.length; i = i+1){
img[i] = loadImage(names[i]);
for (int j = 0; j < particles.length; j++) {
particles[j].display();
particles[j].move();
}
}
}
}
I wonder if anyone knows the problem and if there is another way to do the screenshot animations.Thank you!

Answer 1

I think the issue is that listFileNames() simply list the file names, not the absolute paths to the files. Unless those images are in the sketch directory (or within the data directory of the sketch) you will need to use the full path to the images to load them.
One option would be to concatenate the absolute directory path with the filename:
String[] listFileNames(String dir) {
File file = new File(dir);
if (file.isDirectory()) {
String names[] = file.list();
return names;
} else {
// If it's not a directory
return null;
}
}
void draw(){
if (frameCount % 60 == 0) screen();
if (screen != null) image(screen, 0, 0, width, height);
if(recording){
saveFrame("output//screenshot_####.png");
}
String dir = "/Users/lj/Desktop/JingLang_vis145A_Midterm/screenshot/output/"
names = listFileNames(dir);
print(names);
if(names.length != 0){
for(int i = 0; i < names.length; i = i+1){
// concatenate the directory with each fine name
// dir inclues / at the end (otherwise you can use File.separator (e.g. dir/image.png = dir + File.separator + "image.png"))
img[i] = loadImage(dir + names[i]);
for (int j = 0; j < particles.length; j++) {
particles[j].display();
particles[j].move();
}
}
}
}
You could use listFiles() instead which returns File objects that do provide the absolute path.
Here's a snippet illustrating usage of listFiles():
File[] listFiles(String dir) {
File file = new File(dir);
if (file.isDirectory()) {
File[] files = file.listFiles();
return files;
} else {
// If it's not a directory
return null;
}
}
File[] files;
void draw(){
if (frameCount % 60 == 0) screen();
if (screen != null) image(screen, 0, 0, width, height);
if(recording){
saveFrame("output//screenshot_####.png");
}
String dir = "/Users/lj/Desktop/JingLang_vis145A_Midterm/screenshot/output/"
files = listFiles(dir);
if(files == null) {
println(dir + "is not a directory");
return;
}
for(int i = 0; i < files.length; i = i+1){
// concatenate the directory with each fine name
// dir inclues / at the end (otherwise you can use File.separator (e.g. dir/image.png = dir + File.separator + "image.png"))
img[i] = loadImage(files[i].getAbsolutePath());
for (int j = 0; j < particles.length; j++) {
particles[j].display();
particles[j].move();
}
}
}
You can find this function and a few more under Daniel Shiffman's DirectoryList example via Processing > Examples > Topics > File IO
Additionally, listFiles() / listPaths() are present in Processing already, just a bit tucked away. The nice thing about these variants is that you can filter results to be files with png extension only (e.g. excluding folder, hidden files, etc.).
Here's a modified version of the above snippet:
void draw(){
if (frameCount % 60 == 0) screen();
if (screen != null) image(screen, 0, 0, width, height);
if(recording){
saveFrame("output//screenshot_####.png");
}
String dir = "/Users/lj/Desktop/JingLang_vis145A_Midterm/screenshot/output/"
File[] files = listFiles(dir,"files","extension=png")
if(files == null) {
println(dir + "is not a directory");
return;
}
for(int i = 0; i < files.length; i = i+1){
// concatenate the directory with each fine name
// dir inclues / at the end (otherwise you can use File.separator (e.g. dir/image.png = dir + File.separator + "image.png"))
img[i] = loadImage(files[i].getAbsolutePath());
for (int j = 0; j < particles.length; j++) {
particles[j].display();
particles[j].move();
}
}
}
A bit off-topic from your question I am noticing a few confusing things:
you're listing files and loading images multiple times per frame in draw(). You might want to load the images once in setup(), store them in a PImage[], then simply use them in draw()
It appears you're updating particles only while loading images and there doesn't seem to be a connection between the loaded images and the particles from the code you're shared. You might want to separate the particle code from the image loading code
Shameless plug: If you want to easily load and display png sequences in Processing you can use the ImageSequencePlayer Processing library I worked on:
// import library
import com.hirschandmann.image.*;
// create a reference to an image sequence
ISPlayer player;
void setup() {
size(640, 360);
// create instance and load all valid images from the data folder
player = new ISPlayer(this,"/Users/lj/Desktop/JingLang_vis145A_Midterm/screenshot/output/"));
}
void draw() {
// clear background with yellow
background(255, 204, 0);
// render image sequence, ISPlayer extends PImage, use it as such
image(player,mouseX,mouseY);
}
// image sequence events
// all frames loaded
void onSequenceLoaded(ISPlayer player){
println(player+" sequence fully loaded");
player.loop();
}