作为大学项目的一部分，我正在开发一个用于注释图像的Java swing程序。该程序的一个特点是能够在图像的某些区域周围绘制多边形，然后可以用标题标记。
绘制多边形时，每次单击都会在图像上绘制一个新的绿色顶点，并通过绘制一条线将此顶点链接到前一个顶点。当用户移动鼠标时，还会绘制一条预览线，以便他们可以看到下一次点击将添加到多边形的形状。
我遇到的问题是，一旦用户绘制了一个多边形，整体程序性能就会显着下降。预览线的绘制变得异常紧张，难以使用。
负责程序这一部分的代码位于ImagePanel.java文件中：
package hci;
import javax.imageio.ImageIO;
import javax.swing.JPanel;
import javax.swing.JOptionPane;
import java.awt.Color;
import java.awt.BasicStroke;
import java.awt.Stroke;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Polygon;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.image.BufferedImage;
import java.awt.geom.Point2D;
import java.io.File;
import java.util.ArrayList;
import hci.utils.*;
public class ImagePanel extends JPanel implements MouseListener, MouseMotionListener {
private static final long serialVersionUID = 1L;
BufferedImage image = null;
CaptionedPolygon currentPolygon = null;
ArrayList<CaptionedPolygon> polygonsList = null;
Point mousePos;
public static final int FIRST_NODE_SIZE = 15;
public ImagePanel() {
currentPolygon = new CaptionedPolygon();
polygonsList = new ArrayList<CaptionedPolygon>();
mousePos = new Point(0,0);
this.setVisible(true);
Dimension panelSize = new Dimension(800, 600);
this.setSize(panelSize);
this.setMinimumSize(panelSize);
this.setPreferredSize(panelSize);
this.setMaximumSize(panelSize);
addMouseListener(this);
addMouseMotionListener(this);
}
public ImagePanel(String imageName) throws Exception{
this();
image = ImageIO.read(new File(imageName));
if (image.getWidth() > 800 || image.getHeight() > 600) {
int newWidth = image.getWidth() > 800 ? 800 : (image.getWidth() * 600)/image.getHeight();
int newHeight = image.getHeight() > 600 ? 600 : (image.getHeight() * 800)/image.getWidth();
System.out.println("SCALING TO " + newWidth + "x" + newHeight );
Image scaledImage = image.getScaledInstance(newWidth, newHeight, Image.SCALE_FAST);
image = new BufferedImage(newWidth, newHeight, BufferedImage.TYPE_INT_RGB);
image.getGraphics().drawImage(scaledImage, 0, 0, this);
}
}
public void ShowImage(Graphics g) {
if (image != null) {
g.drawImage(
image, 0, 0, null);
}
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
//display image
ShowImage(g);
drawPreviewLine(g);
//display all the completed polygons
for(CaptionedPolygon polygon : polygonsList) {
fillPolygon(polygon, g);
drawPolygon(polygon, g);
finishPolygon(polygon, g);
}
//display current polygon
drawPolygon(currentPolygon, g);
}
public void drawPreviewLine(Graphics g){
if (currentPolygon.points.size() > 0 && mousePos != null){
Point currentPoint = currentPolygon.points.get(currentPolygon.points.size() - 1);
g.setColor(Color.GREEN);
g.drawLine(currentPoint.getX(), currentPoint.getY(), mousePos.getX(), mousePos.getY());
}
}
public void fillPolygon(CaptionedPolygon polygon, Graphics g){
Color fillColor = new Color((float)0.0,(float)1.0,(float)0.0, (float)0.3);
Polygon polyToDraw = new Polygon();
for (Point point : polygon.points){
polyToDraw.addPoint(point.getX(), point.getY());
}
g.setColor(fillColor);
g.fillPolygon(polyToDraw);
}
public void drawPolygon(CaptionedPolygon polygon, Graphics g) {
for(int i = 0; i < polygon.points.size(); i++) {
int sizeModifier = 0;
Graphics2D g2 = (Graphics2D)g;
g2.setColor(Color.GREEN);
g2.setStroke(new BasicStroke(1));
Point currentVertex = polygon.points.get(i);
if(currentPolygon.equals(polygon) && i == 0){ //First point of the current polygon
//Enlarge circle drawn if mouse hovers over point
if(pointWithinCircle(mousePos.getX(), mousePos.getY(), currentVertex.getX(), currentVertex.getY(), (FIRST_NODE_SIZE + 2)/2)){
sizeModifier = 3;
}
int nodeSize = FIRST_NODE_SIZE + sizeModifier;
g2.setColor(Color.WHITE);
g2.fillOval(currentVertex.getX() - nodeSize/2 , currentVertex.getY() - nodeSize/2, nodeSize, nodeSize);
g2.setStroke(new BasicStroke(2));
g2.setColor(Color.GREEN);
g2.drawOval(currentVertex.getX() - nodeSize/2 , currentVertex.getY() - nodeSize/2, nodeSize, nodeSize);
}
else if (i != 0){ //Some arbitary middle point
Point prevVertex = polygon.points.get(i - 1);
g2.drawLine(prevVertex.getX(), prevVertex.getY(), currentVertex.getX(), currentVertex.getY());
g2.fillOval(currentVertex.getX() - 5, currentVertex.getY() - 5, 10, 10);
}
else{ //First point of some non current polygon
g2.fillOval(currentVertex.getX() - 5, currentVertex.getY() - 5, 10, 10);
}
}
}
public void finishPolygon(CaptionedPolygon polygon, Graphics g) {
//if there are less than 3 vertices than nothing to be completed
if (polygon.points.size() >= 3) {
Point firstVertex = polygon.points.get(0);
Point lastVertex = polygon.points.get(polygon.points.size() - 1);
g.setColor(Color.GREEN);
g.drawLine(firstVertex.getX(), firstVertex.getY(), lastVertex.getX(), lastVertex.getY());
}
}
public void addNewPolygon() {
//finish the current polygon if any
if (currentPolygon.points.size() > 0 ) {
currentPolygon.caption = JOptionPane.showInputDialog(this, "Please enter a caption for this area") ;
polygonsList.add(currentPolygon);
}
currentPolygon = new CaptionedPolygon();
repaint();
}
public boolean pointWithinCircle(int targetX, int targetY, int circleCentX, int circleCentY, double circleRadius){
Point2D.Double mousePoint = new Point2D.Double(targetX,targetY);
Point2D.Double firstNodePoint = new Point2D.Double(circleCentX, circleCentY);
return (mousePoint.distance(firstNodePoint) <= circleRadius);
}
@Override
public void mouseClicked(MouseEvent e) {
}
@Override
public void mouseEntered(MouseEvent arg0) {
}
@Override
public void mouseExited(MouseEvent arg0) {
}
@Override
public void mousePressed(MouseEvent e) {
int x = e.getX();
int y = e.getY();
//check if the cursor is within image area
if (x > image.getWidth() || y > image.getHeight()) {
return;
}
//Clicking the left button will either add a new vertex or finish off a polygon
if (e.getButton() == MouseEvent.BUTTON1) {
if (currentPolygon.points.size() > 0 ){
if(pointWithinCircle(x, y, currentPolygon.points.get(0).getX(), currentPolygon.points.get(0).getY(), FIRST_NODE_SIZE + 2)){
addNewPolygon();
}
else{
currentPolygon.points.add(new Point(x,y));
System.out.println(x + " " + y);
repaint();
}
}
else{
currentPolygon.points.add(new Point(x,y));
System.out.println(x + " " + y);
repaint();
}
}
}
@Override
public void mouseReleased(MouseEvent arg0) {
}
public void mouseDragged(MouseEvent e){
}
public void mouseMoved(MouseEvent e){
mousePos.setX(e.getX());
mousePos.setY(e.getY());
repaint();
}
}
我已经尝试过在几种不同的操作系统和笔记本电脑下运行这个程序，并且所有这些都显而易见。这表明我的代码存在问题，而不仅仅是运行它的问题。
我觉得我的问题与我调用repaint()方法的次数过多有关。我没有真正在网上找到很多关于使用Java的swing和图形库来实现绘图功能的最佳方法的好资源，因此我希望对一般实践提出建议，以及直接解决这个问题。< / p>
答案 0 :(得分：4)
看起来您正在直接绘制到帧缓冲区。这是非常慢的，因为每次绘制任何内容时，JVM都必须进行系统调用以更新屏幕上的图像。
如果您在JVM内存中的单个帧上执行所有绘制操作，并且仅在整个图像准备就绪时输出到系统，您将看到更好的渲染速度。 （这是你用背景图像image已经做的事情，事实上你可以重新使用你已经创建的图形对象，但不要使用） < / p>
因此，您需要创建一个要绘制的画布;
BufferedImage canvas = new BufferedImage(width, height, BufferedImage.TYPE_3BYTE_BGR);
然后抓住你将用于绘制到画布的Graphics对象;
Graphics cg = canvas.getGraphics();
在cg上完成所有绘图操作，然后在paintComponent(Graphics g)函数中，只需使用一次调用将canvas绘制到组件中;
g.drawImage(canvas, 0, 0, null);
为了获得更好的效果，您应该使用VolatileImage而不是BufferedImage。但是BufferedImage更容易使用，并且可以很好地满足您的需要。