我想在一个更大的圆形表面内绘制一个随机中心的圆。 (我实际上是在尝试模拟房间内的人和他的视力!)我需要绘制一条随机线(称为 line1)穿过其中心，该中心将与表面相交。 line1 不一定通过圆面的圆心。我还需要画两条线形成 60 度，面向 line1 的一侧。任何人都可以帮我吗？
我创建了一个我需要绘制的示例。
import java.awt.Color;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Point;
import java.util.Random;
import javax.swing.JFrame;
public class ShapeTest extends JFrame{
int width=500;
int height=500;
public ShapeTest(){
setSize(width,height);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setResizable(false);
setLocationRelativeTo(null);
setVisible(true);
}
public static void main(String a[]){
new ShapeTest();
}
public void paint(Graphics g){
// Circular Surface
drawCircleByCenter(g, width/2, height/2, width/2);
Random r = new Random();
Point center = new Point();
center.x=r.nextInt(width/2);
center.y=r.nextInt(width/2);
drawCircleByCenter(g, center.x, center.y, width/15);
}
void drawCircleByCenter(Graphics g, int x, int y, int radius){
//g.setColor(Color.LIGHT_GRAY);
g.drawOval(x-radius, y-radius, 2*radius, 2*radius);
}
}
最佳答案
首先将根据圆心和半径绘制圆的方法更改为返回表示圆的 Ellipse2D 对象的方法。这将使我们能够对形状进行一些剪裁和其他操作，而不仅仅是绘制它。
将剪辑设置为大圆圈的形状可以防止在您不想要的地方产生杂散标记(想想“线条内的颜色”)。这很重要，因为当我们在大圆圈内绘制圆圈和线时，其中一些会太大，否则会标记在大圆圈的边界之外。
设置剪辑后，我们使用方法 Line2D getVector(Point2D, double, length) 以大圆的中心为原点，随机角度和随机长度(上限为将蓝色小圆圈放在大圆圈内)。想想这是一个随机的 polar coordinate以大圆的圆心为原点。这个 vector 的终点用来标记小圆的圆心。
以小圆的中心为起点，我们可以使用随机方向角生成两个相反方向的 vector (只需取反一个 vector 的长度，使其朝另一个方向移动)。我们使用等于大圆直径的长度来确保线条始终一直延伸到大圆的边缘(但不会超过，这要归功于我们的剪辑)。
我们只需将蓝色虚线的角度分别增加 60 度和 120 度，然后绘制两条绿线，计算 vector 的方式与我们对两条蓝色虚线所做的相同，只是我们不需要创建长度为负值的 vector .我们还可以通过将蓝色虚线的角度加上 90 度来添加一个法 vector ，以达到更好的效果。
最后，我们选择一些随机的极坐标(就像我们对蓝色小圆圈所做的那样)来代表一些人，并使用人与各种线创建的区域的交点，我们可以看到他们在什么地方并用颜色编码值绘制它们。
既然我们有了所有的人，我们就消除剪辑并画出大圆圈，瞧!
查看 Draw a line at a specific angle in Java有关我如何计算线 vector 的详细信息。
废话不多说了，下面是代码:
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.Shape;
import java.awt.Stroke;
import java.awt.geom.Area;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Line2D;
import java.awt.geom.Path2D;
import java.awt.geom.Point2D;
import java.awt.geom.Rectangle2D;
import java.awt.image.BufferedImage;
import java.util.ArrayList;
import java.util.Random;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class ShapeTest extends JFrame {
private static final long serialVersionUID = 1L;
private int width = 500;
private int height = 500;
private int padding = 50;
private BufferedImage graphicsContext;
private JPanel contentPanel = new JPanel();
private JLabel contextRender;
private Stroke dashedStroke = new BasicStroke(3.0f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_ROUND, 2f, new float[] {3f, 3f}, 0f);
private Stroke solidStroke = new BasicStroke(3.0f);
private RenderingHints antialiasing;
private Random random = new Random();
public static void main(String[] args) {
//you should always use the SwingUtilities.invodeLater() method
//to perform actions on swing elements to make certain everything
//is happening on the correct swing thread
Runnable swingStarter = new Runnable()
{
@Override
public void run(){
new ShapeTest();
}
};
SwingUtilities.invokeLater(swingStarter);
}
public ShapeTest(){
antialiasing = new RenderingHints(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
graphicsContext = new BufferedImage(width + (2 * padding), width + (2 * padding), BufferedImage.TYPE_INT_RGB);
contextRender = new JLabel(new ImageIcon(graphicsContext));
contentPanel.add(contextRender);
contentPanel.setSize(width + padding * 2, height + padding * 2);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setResizable(false);
this.setContentPane(contentPanel);
//take advantage of auto-sizing the window based on the size of its contents
this.pack();
this.setLocationRelativeTo(null);
this.paint();
setVisible(true);
}
public void paint() {
Graphics2D g2d = graphicsContext.createGraphics();
g2d.setRenderingHints(antialiasing);
//Set up the font to print on the circles
Font font = g2d.getFont();
font = font.deriveFont(Font.BOLD, 14f);
g2d.setFont(font);
FontMetrics fontMetrics = g2d.getFontMetrics();
//clear the background
g2d.setColor(Color.WHITE);
g2d.fillRect(0, 0, graphicsContext.getWidth(), graphicsContext.getHeight());
//set up the large circle
Point2D largeCircleCenter = new Point2D.Double((double)width / 2 + padding, (double)height / 2 + padding);
double largeCircleRadius = (double)width / 2;
Ellipse2D largeCircle = getCircleByCenter(largeCircleCenter, largeCircleRadius);
//here we build the small circle
Point2D smallCircleCenter = new Point2D.Double();
double smallCircleRadius = 15;
//we need to make certain it is confined inside the larger circle
//so we choose the following values carefully
//we want to go a random direction from the circle, so chose an
//angle randomly in any direction
double smallCenterVectorAngle = random.nextDouble() * 360.0d;
//and we want to be a random distance from the center of the large circle, but
//we limit the distance based on the radius of the small circle to prevent it
//from appearing outside the large circle
double smallCenterVectorLength = random.nextDouble() * (largeCircleRadius - smallCircleRadius);
Line2D vectorToSmallCenter = getVector(largeCircleCenter, smallCenterVectorAngle, smallCenterVectorLength);
//the resulting end point of the vector is a random distance from the center of the large circle
//in a random direction, and guaranteed to not place the small circle outside the large
smallCircleCenter.setLocation(vectorToSmallCenter.getP2());
Ellipse2D smallCircle = getCircleByCenter(smallCircleCenter, smallCircleRadius);
//before we draw any of the circles or lines, set the clip to the large circle
//to prevent drawing outside our boundaries
g2d.setClip(largeCircle);
//chose a random angle for the line through the center of the small circle
double angle = random.nextDouble() * 360.0d;
//we create two lines that start at the center and go out at the angle in
//opposite directions. We use 2*largeCircleRadius to make certain they
//will be large enough to fill the circle, and the clip we set prevent stray
//marks outside the big circle
Line2D centerLine1 = getVector(smallCircleCenter, angle, largeCircleRadius * 2);
Line2D centerLine2 = getVector(smallCircleCenter, angle, -largeCircleRadius * 2);
//now we just add 20 and 120 to our angle for the center-line, start at the center
//and again, use largeCircleRadius*2 to make certain the lines are big enough
Line2D sightVector1 = getVector(smallCircleCenter, angle + 60, largeCircleRadius * 2);
Line2D sightVector2 = getVector(smallCircleCenter, angle + 120, largeCircleRadius * 2);
Path2D visible = new Path2D.Double();
visible.moveTo(sightVector1.getX2(), sightVector1.getY2());
visible.lineTo(smallCircleCenter.getX(), smallCircleCenter.getY());
visible.lineTo(sightVector2.getX2(), sightVector2.getY2());
visible.closePath();
Path2D greenSide = new Path2D.Double();
greenSide.moveTo(centerLine1.getX2(), centerLine1.getY2());
greenSide.lineTo(smallCircleCenter.getX(), smallCircleCenter.getY());
greenSide.lineTo(centerLine2.getX2(), centerLine2.getY2());
greenSide.lineTo(sightVector1.getX2(), sightVector1.getY2());
greenSide.closePath();
int personCount = 5;
Area visibleArea = new Area(visible);
visibleArea.intersect(new Area(largeCircle));
Area greenSideArea = new Area(greenSide);
greenSideArea.intersect(new Area(largeCircle));
//we create a list of the people in the circle to
//prevent overlap
ArrayList<Shape> people = new ArrayList<Shape>();
people.add(smallCircle);
int i = 0;
personLoop: while (i < personCount){
double personCenterVectorAngle = random.nextDouble() * 360.0d;
double personCenterVectorLength = random.nextDouble() * (largeCircleRadius - smallCircleRadius);
Line2D vectorToPersonCenter = getVector(largeCircleCenter, personCenterVectorAngle, personCenterVectorLength);
Point2D personCircleCenter = vectorToPersonCenter.getP2();
Ellipse2D personCircle = getCircleByCenter(personCircleCenter, smallCircleRadius);
//this little loop lets us skip a person if they have overlap
//with another person, since people don't generally overlap
Area personArea = new Area(personCircle);
for (Shape person : people)
{
Area overlapArea = new Area(person);
overlapArea.intersect(personArea);
//this means that we have found a conflicting
//person, so should skip them
if (!overlapArea.isEmpty()){
continue personLoop;
}
}
people.add(personCircle);
personArea.intersect(visibleArea);
Area greenSideAreaTest = new Area(personCircle);
greenSideAreaTest.intersect(greenSideArea);
if (personArea.isEmpty()){
if (greenSideAreaTest.isEmpty()){
g2d.setColor(Color.orange);
System.out.println("Person " + i + " is behind the blue line");
}
else {
System.out.println("Person " + i + " is in front of the blue line");
g2d.setColor(Color.cyan);
}
}
else
{
System.out.println("Person " + i + " is between the green lines");
g2d.setColor(Color.magenta);
}
//alternatively to circles intersecting the area of interest, we can check whether the center
//is in the area of interest which may make more intuitive sense visually
// if (visibleArea.contains(personCircleCenter)){
// System.out.println("Person " + i + " is between the green lines");
// g2d.setColor(Color.magenta);
// }
// else {
// if (greenSideArea.contains(personCircleCenter)) {
// System.out.println("Person " + i + " is in front of the blue line");
// g2d.setColor(Color.cyan);
// }
// else{
// g2d.setColor(Color.orange);
// System.out.println("Person " + i + " is behind the blue line");
// }
// }
g2d.fill(personCircle);
g2d.setColor(Color.black);
String itemString = "" + i;
Rectangle2D itemStringBounds = fontMetrics.getStringBounds(itemString, g2d);
double textX = personCircleCenter.getX() - (itemStringBounds.getWidth() / 2);
double textY = personCircleCenter.getY() + (itemStringBounds.getHeight()/ 2);
g2d.drawString("" + i, (float)textX, (float)textY);
i++;
}
//fill the small circle with blue
g2d.setColor(Color.BLUE);
g2d.fill(smallCircle);
//draw the two center lines lines
g2d.setStroke(dashedStroke);
g2d.draw(centerLine1);
g2d.draw(centerLine2);
//create and draw the black offset vector
Line2D normalVector = getVector(smallCircleCenter, angle + 90, largeCircleRadius * 2);
g2d.setColor(Color.black);
g2d.draw(normalVector);
//draw the offset vectors
g2d.setColor(new Color(0, 200, 0));
g2d.draw(sightVector1);
g2d.draw(sightVector2);
//we save the big circle for last, to cover up any stray marks under the stroke
//of its perimeter. We also set the clip back to null to prevent the large circle
//itselft from accidentally getting clipped
g2d.setClip(null);
g2d.setStroke(solidStroke);
g2d.setColor(Color.BLACK);
g2d.draw(largeCircle);
g2d.dispose();
//force the container for the context to re-paint itself
contextRender.repaint();
}
private static Line2D getVector(Point2D start, double degrees, double length){
//we just multiply the unit vector in the direction we want by the length
//we want to get a vector of correct direction and magnitute
double endX = start.getX() + (length * Math.sin(Math.PI * degrees/ 180.0d));
double endY = start.getY() + (length * Math.cos(Math.PI * degrees/ 180.0d));
Point2D end = new Point2D.Double(endX, endY);
Line2D vector = new Line2D.Double(start, end);
return vector;
}
private static Ellipse2D getCircleByCenter(Point2D center, double radius)
{
Ellipse2D.Double myCircle = new Ellipse2D.Double(center.getX() - radius, center.getY() - radius, 2 * radius, 2 * radius);
return myCircle;
}
}
关于Java在Swing上画圆和线，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22573385/