// Sets the screen to be 640 pixels wide and 360 pixels high 窗口大小
size(640, 360);

// Set the background to black and turn off the fill color背景颜色
background(0);
noFill();

// The two parameters of the point() method each specify coordinates.
// The first parameter is the x-coordinate and the second is the Y 
stroke(255);//画笔颜色
point(width * 0.5, height * 0.5);
point(width * 0.5, height * 0.25); 

// Coordinates are used for drawing all shapes, not just points.
// Parameters for different functions are used for different purposes.
// For example, the first two parameters to line() specify 
// the coordinates of the first endpoint and the second two parameters 
// specify the second endpoint
stroke(0, 153, 255);
line(0, height*0.33, width, height*0.33);

// By default, the first two parameters to rect() are the 
// coordinates of the upper-left corner and the second pair
// is the width and height
stroke(255, 153, 0);
rect(width*0.25, height*0.1, width * 0.5, height * 0.8);//矩形

// The size function is a statement that tells the computer 
// how large to make the window.
// Each function statement has zero or more parameters. 
// Parameters are data passed into the function
// and are used as values for telling the computer what to do.
size(640, 360);

// The background function is a statement that tells the computer
// which color (or gray value) to make the background of the display window 
background(204, 153, 0);

int y = 100;

// The statements in the setup() function 
// execute once when the program begins //只执行一次
void setup() {
  size(640, 360);  // Size must be the first statement
  stroke(255);     // Set line drawing color to white
  frameRate(30); //帧率
}
// The statements in draw() are executed until the 
// program is stopped. Each statement is executed in 
// sequence and after the last line is read, the first 
// line is executed again.//一直执行直到程序停止，每一个变量以队列的方式被读取来执行，直到最后一个，然后又去执行第一个。
void draw() { 
  background(0);   // Clear the screen with a black background
  y = y - 1; 
  if (y < 0) { 
    y = height; 
  } 
  line(0, y, width, y);  
} 

float y;

// The statements in the setup() function 
// execute once when the program begins
void setup() 
{
  size(640, 360);  // Size should be the first statement
  stroke(255);     // Set line drawing color to white
  noLoop();
  
  y = height * 0.5;
}

// The statements in draw() are executed until the 
// program is stopped. Each statement is executed in 
// sequence and after the last line is read, the first 
// line is executed again.
void draw() 
{ 
  background(0);   // Set the background to black
  y = y - 1; 
  if (y < 0) { y = height; } 
  line(0, y, width, y);  
} 

void setup() {
  size(640, 360);
  background(51);
  noStroke();
  noLoop();
}

void draw() {
  drawTarget(width*0.25, height*0.4, 200, 4);
  drawTarget(width*0.5, height*0.5, 300, 10);
  drawTarget(width*0.75, height*0.3, 120, 6);
}

void drawTarget(float xloc, float yloc, int size, int num) {
  float grayvalues = 255/num;
  float steps = size/num;
  for (int i = 0; i < num; i++) {
    fill(i*grayvalues);
    ellipse(xloc, yloc, size - i*steps, size - i*steps);
  }
}

void setup() {
  size(640, 360);
  noStroke();
  noLoop();
}

void draw() {
  drawCircle(width/2, 280, 6);
}

void drawCircle(int x, int radius, int level) {                    
  float tt = 126 * level/4.0;
  fill(tt);
  ellipse(x, height/2, radius*2, radius*2);      
  if(level > 1) {
    level = level - 1;
    drawCircle(x - radius/2, radius/2, level);
    drawCircle(x + radius/2, radius/2, level);
  }
}

PGraphics pg;

void setup() {
  size(640, 360);
  pg = createGraphics(400, 200);
}

void draw() {
  fill(0, 12);
  rect(0, 0, width, height);
  fill(255);
  noStroke();
  ellipse(mouseX, mouseY, 60, 60);
  
  pg.beginDraw();
  pg.background(51);
  pg.noFill();
  pg.stroke(255);
  pg.ellipse(mouseX-120, mouseY-60, 60, 60);
  pg.endDraw();
  
  // Draw the offscreen buffer to the screen with image() 
  image(pg, 120, 60); 
}