java - 字符串变量的 NullPointEException 错误(初学者)

Question

我正在尝试模仿此处看到的类似代码 http://www.openprocessing.org/sketch/7050但我似乎对代码有点困惑。我试图获得字母的效果，本质上是绘制图片的海报图像。但我得到了一个 NullPointException 并假设这与我初始化字符串变量的方式有关，但我似乎找不到我做错了什么。

错误

Exception in thread "Animation Thread" java.lang.NullPointerException
    at processing.opengl.PGL.getString(PGL.java:1029)
    at processing.opengl.PGraphicsOpenGL.getGLParameters(PGraphicsOpenGL.java:6076)
    at processing.opengl.PGraphicsOpenGL.beginDraw(PGraphicsOpenGL.java:1547)
    at MLKpractice.letterfit(MLKpractice.java:147)
    at MLKpractice.draw(MLKpractice.java:98)
    at processing.core.PApplet.handleDraw(PApplet.java:2120)
    at processing.core.PGraphicsJava2D.requestDraw(PGraphicsJava2D.java:197)
    at processing.core.PApplet.run(PApplet.java:1998)
    at java.lang.Thread.run(Thread.java:680)

程序说错误发生在第 127 行

lettersquare.beginDraw();

但我相信错误是在上面的某个地方

PFont font;
String fontpath = "ArialMT-200.vlw";
int fontstart = 300;
int fontend = 8;
float fontsize = fontstart;
float fontsizedecrease = 0.97;
PImage bg;
PImage australia;
PImage austria;
String country1 = "australia.jpg";
String country2 = "austria.jpg";
String letters = "Australia";
char[] chars = new char[52];
int nchars = 0;
int iterations = 500;
int c = 0;
PGraphics letter,lettersquare,drawing;

void setup(){
  //initialize the sketch
  size(900,600);
  //background(255);
  //initialize the font
  //font = loadFont(fontpath);
  ///*
  for(int i=0;i<letters.length();i++){
    boolean found = false;
    char lc = letters.charAt(i);
    for(int j=0;j<nchars;j++){
      if(chars[j]==lc){
        found = true;
        break;
      }
    }
    if(!found) chars[nchars++] = lc;
  }
  chars = (char[]) subset(chars,0,nchars);
  font = createFont("Arial",200,true,chars);
  //*/
  textAlign(CENTER,CENTER);
  //load the image that will be filled with letters
  australia = loadImage(country1);
   austria = loadImage(country2);

  bg = loadImage("background.jpg");
  //posterize the image
  australia.filter(THRESHOLD,0.4);
  australia.filter(BLUR,3);
  australia.filter(THRESHOLD,0.6);
  //initialize the drawing buffers
  letter = createGraphics((int)fontsize,(int)fontsize,JAVA2D);
  lettersquare = createGraphics((int)fontsize,(int)fontsize,P2D);
  drawing = createGraphics(width,height,JAVA2D);
  drawing.beginDraw();
  drawing.background(255);
  // THIS STUPID THING NEEDS TO GO HERE!!!!
  drawing.image(bg,0,0);
  drawing.endDraw();
}

void draw(){

  if(floor(fontsize)>fontend&&c<letters.length()-1){
    if(!letterfit()){
      fontsize *= fontsizedecrease;
    }else{
      c++;
      if(c==11){
        fontsize *= 0.75;
      }
    }

    tint(255);
    image(drawing,0,0);


  if (keyCode == LEFT) {
    image(austria,0,0);
    }
   // if (keyCode == RIGHT) {
     // frog1.frogx = frog1.frogx + 1;
   // }


    if(mousePressed){
      tint(255,100);
      image(australia,0,0);
    }
  }else{
    tint(255);
    image(drawing,0,0);
    println(c+" "+letters.length());
    /*
    save("mlk-"+hour()+""+minute()+""+second()+".tif");
    exit();
    */
    noLoop();
  }
} 
boolean letterfit(){
  letter.beginDraw();
  letter.background(255,0);
  letter.fill(0);
  letter.textAlign(CENTER,CENTER);
  letter.translate(fontsize/2,fontsize/2);
  letter.rotate(random(TWO_PI));
  letter.scale(fontsize/fontstart);
  letter.textFont(font);
  letter.smooth();
  letter.text(letters.charAt(c),0,0);
  letter.endDraw();
  lettersquare.beginDraw();

Answer 1

您很可能被 issue 1217 击中了，如果主渲染器是 Java2D，这会阻止您使用 OpenGL PGraphics 渲染器。

该链接有一个解决方法，主要涉及将主渲染器更改为 OpenGL。

较新版本的 PGraphics 应该会为您提供更详细的异常。