pdf generates black page

Core Library Questions

ofeyrpf

in Core Library Questions • 1 year ago

Hi,

I'm having a little difficulty creating a pdf. All I get is a white background.

One other thing, I've seen people upload code this this forum with lines numbered. How is that done?

Any help would be greatly appreciated.

Thanks,

Copy code

import processing.pdf.*; // Import PDF code

int cols = 5;
int rows = 10;
int xn0 = 1;
int yn0 = 1;
float y = 1, y1;
float h = 0.1;
float[][] myArray = new float[cols][rows]; // declares array

void setup() {
size(400, 400);
// size(400, 400, PDF, "Euler.pdf");
background(255);
fill(0);
populateArray();
readArray();
}

void draw() {
noLoop();
pushMatrix();
translate(width/2 + 52, height/2 + 55);
line(-100, 0, 100, 0);
line(0, 100, 0, -100);
scale(60);
strokeWeight(1/10);
line(-0.05, -1, 0.05, -1);
line(1, -0.05, 1, 0.05);
popMatrix();
text("(0,1)", width/2 + 22, height/2 - 5);
text("(1,0)", width/2 + 102, height/2 + 72
    );
pushMatrix();
translate(width/2 + 52, height/2 + 55);
scale(60);
for (int j = 0; j < rows - 1; j++) {
    stroke(0, 0, 255);
    int i = 1;
    line(myArray[i][j], -myArray[i+1][j], myArray[i][j+1], -myArray[i+1][j+1]);
    ellipse(myArray[i][j], -myArray[i+1][j], 0.05, 0.05);
}

// Graph original function y(x)=(x^4 + 3)/4x
for (float x = 1.0; x < 2.5; x += 0.01) {
    y = (pow(x, 4) + 3)/4*x;
    stroke(255, 0, 0);
    ellipse(x, -y, 0.01, 0.01);
    // point(x, -y);
}
popMatrix();
}

void keyPressed() {
if (key == 'B' || key == 'b') {
    beginRecord(PDF, "Euler.pdf");
}
else if (key == 'E' || key == 'e') {
    endRecord();
    exit();
}
}

void populateArray() {
for (int j = 0; j < rows; j++) {
    for (int i = 0; i < cols; i++) {
      if (j==0);
      {
        myArray[1][0] = xn0;
        myArray[2][0] = yn0;
      }
      if (i==0) // first column
      {
        myArray[i][j] = j+1;
      }
      if ((i==1) && (j!=0)) // xn values, adds h to the previous xn value
      {
        myArray[i][j] = h + myArray[i][j-1];
      }
      if ((i==2) && (j!=0)) // yn values, previous yn value
      {
        myArray[i][j] = myArray[i+2][j-1];
      }
      if (i==3) // fn values, fn = (xn^3 - yn)/xn (this is the derivative dy/dx)
      {
        myArray[i][j] = (pow(myArray[i-2][j], 3) - myArray[i-1][j])/myArray[i-2][j];
      }
      if ((i==4)) // y_{n+1} values, yn+1 = yn + h*fn
      {
        myArray[i][j] = myArray[i-2][j] + h*myArray[i-1][j];
      }
    }
}
}

void readArray() { // reads the myArray and tabulates it
translate(-20, 20);
for (int i = 0; i < cols; i++) {
    for (int j = 0; j < rows; j++) {
      if (j==0);
      {
        text(myArray[i][j], ((i+1)*40), ((j+1)*20)+20);
      }
    }
}
stroke(0, 0, 0);
text("Euler method: dy/dx=(x^3-y)/x)", 40, -3);
text("n", 50, 15);
text("xn", 90, 15);
text("yn", 130, 15);
text("fn", 170, 15);
text("y_{n+1}", 200, 15);
line(40, 23, 247, 23);
line(80, 5, 80, (rows*20)+30);
}

Replies(8)

PhiLho

Re: pdf generates black page

1 year ago

black, blank or white page?

You draw on the PDF when hitting a key, but the noLoop() in draw() makes the drawing to occur only once.
The PDF library doesn't make a copy of what is displayed, it applies the current drawing instructions to the PDF document, so the drawing code must be running to generate a PDF.

ofeyrpf

Re: pdf generates black page

1 year ago

Hi,

Thanks for the reply. I greatly simplified the code below. If I comment out noLoop() the text looks strange. but I can create a pdf. But if I dont' comment out noLoop() the text looks fine but I can't generate a pdf.

Thanks,

Shane

Copy code

import processing.pdf.*; // Import PDF code

void setup() {
size(400, 400);
background(255);
fill(0);
}

void draw() {
// noLoop();
someText();
line(100, 300, 300, 100);
}

void keyPressed() {
if (key == 'B' || key == 'b') {
    beginRecord(PDF, "Euler.pdf");
}
else if (key == 'E' || key == 'e') {
    endRecord();
    exit();
}
}

void someText() {
text("writing", 100, 200);
}

PhiLho

Re: pdf generates black page

1 year ago

If you want only one draw in the PDF, just drop the key handling, put the beginRecord at the start of draw, the endRecord and exit at the end, and let it run.

ofeyrpf

Re: pdf generates black page

1 year ago

I placed the beginRecord at the beginning of draw(). When I run the program and hit 'e' I get an error

Missing a popMatrix() to go with the pushMatrix()

I'm not using a popMatrix here. Also the pdf isn't generating.

When I comment out // noLoop() I can generate the pdf but no text shows. I also get an error

isRecording(), or this particular variation of it, is not available with this renderer.

Thanks,

Shane

Copy code

import processing.pdf.*; // Import PDF code

void setup() {
size(400, 400);
background(255);
fill(0);
}

void draw() {
beginRecord(PDF, "Euler.pdf");
noLoop();
someText();
line(100, 300, 300, 100);
}

void keyPressed() {
if (key == 'E' || key == 'e') {
endRecord();
exit();
}
}

void someText() {
text("writing", 100, 200);
}

PhiLho

Re: pdf generates black page

1 year ago

You made only half of the changes I suggested. So you cumulate the beginRecord calls without the corresponding endRecord.
I suggest to study more closely the examples given in the PDF reference page.

ofeyrpf

Re: pdf generates black page

1 year ago

This is working now. But i am getting the error

isRecording(), or this particular variation of it, is not available with this renderer.

Thanks,

Shane

Copy code

import processing.pdf.*; // Import PDF code

void setup() {
size(400, 400);
beginRecord(PDF, "Euler.pdf");
background(255);
fill(0);
}

void draw() {
noLoop();
text("writing", 100, 200);
line(100, 300, 300, 100);

endRecord();
}

PhiLho

Re: pdf generates black page

1 year ago

If I run your code in Processing 1.5.1, I get the same warning. But the PDF is generated. I suppose it is a bug in Processing, not an important one (as long as you get the wanted result).

milazzi

Re: Re: pdf generates black page

1 year ago

Hi Phi.lho
I really would like you were right but in my case (i make several PDF one after another) the first PDF get "cropped", measuring 100×100 pt instead of 192×192 as it should. I say "as it should" since the size is

Copy code

size(img.width,img.height);

and all the images I process measure exactly the same (192×192). The error message

isRecording(), or this particular variation of it, is not available with this renderer.

appears just while the first image is processed and the first PDF generated get saved with a size of 100×100 pt.
With all the following (15) images everything runs smoothly, and the corresponding PDFs measure 192×192 each.

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