No loadPixels() for PGraphicsPDF

Processing Beginners
1

i found this code Pointillism | Learning Processing 2nd Edition

but instead of run it on the screen, I wanted to run in 5 times on backend and save it as a pdf file,
and got this error
RuntimeException: No loadPixels() for PGraphicsPDF

here is the code I used:

import processing.pdf.*;


PImage img;
int pointillize = 16;

void setup() {
  //size(600,400);
  size(600,400,PDF,"f:\\process\\acres-01.pdf");
  img = loadImage("f:\\process\\acres-1.jpg");
  
  smooth();
}

void draw() {
  
  for (int loop = 0; loop<5; loop++)
  {
  background(0);
  
  for (int i=0; i<500; i++)
  
  {
      
  
  
  // Pick a random point
  int x = int(random(img.width));
  int y = int(random(img.height));
  int loc = x + y*img.width;

  // Look up the RGB color in the source image
  loadPixels();
  float r = red(img.pixels[loc]);
  float g = green(img.pixels[loc]);
  float b = blue(img.pixels[loc]);
  noStroke();

  // Draw an ellipse at that location with that color
  fill(r,g,b,100);
  ellipse(x,y,pointillize,pointillize);
  }
   PGraphicsPDF pdf = (PGraphicsPDF) g;  // Get the renderer
  
  //saveFrame("f:\\process\\ellipse-a-loop.png");
      pdf.nextPage();  // Tell it to go to the next page 
      
  }
  exit();
  
      
}
2

it won’t work because PDF is a vector file and it does not store pixels.

But in fact, I think the original code is wrong. loadPixels loads what is on the canvas window. Instead, you need to call img.loadPixels to specifically load pixels from the image.

1 Like
3

Thanks for your reply.

As a matter of fact, I don’t need to save the imgae to the pdf.
I only want to save ellipses I create.

After I load all the pixels from the image, I no longer need it

4

I figured it out
I changes the loadPixels() to img.loadPixels as you suggested,
and moved it to the setup,

and it worked

1 Like
5

Hello,

In this example you did not need loadPixels() or img.loadPixels (for the PImage) at all.

Try it!

There is a GitHub issue here that discusses the language in the references and tutorials:

:)