更容易用Java制作绘画应用程序的方法？

Question

所以基本上，我有几天前在工作的代码，类似于Paint，它可以让您使用鼠标在屏幕上进行绘制。我偶然发现了该属性，但我意识到它的效率很低，我想知道是否有更实用的方法可以做到这一点。确实没有任何理由要提供我的所有代码，但是这里是重要的部分

private static void createAndShowGui() {
    SimpleDraw mainPanel = new SimpleDraw();
    MenuBar.createMenuBar();
    JLabel label = new JLabel();
    label.setText("Drawing prototype 0.0.1");
     // label.setHorizontalTextPosition(JLabel.NORTH);
    label.setFont(new Font("Serif", Font.BOLD, 20));
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().add(mainPanel);
    frame.pack();
    frame.setLocationByPlatform(true);
    frame.getContentPane().setLayout(new BoxLayout(frame.getContentPane(),BoxLayout.PAGE_AXIS));
    frame.setVisible(true);
    frame.setJMenuBar(MenuBar.getMenuBar());
    frame.setBackground(Color.WHITE);
    frame.add(label);

上面的代码块设置了jframe（窗口）

 @Override
    public void mouseDragged(MouseEvent e)
    {
    // These console outputs are just so that I know what is happening
        System.out.println("Event: MOUSE_DRAG");
        System.out.println(e.getX());
        System.out.println(e.getY());
        System.out.println(e.getComponent());
        System.out.println(e.getWhen());
        System.out.println(e.getButton());
         MOUSE_X = e.getX() - 5;  //-5 so that the cursor represents the center of the square, not the top left corner.
         MOUSE_Y = e.getY() - 5;  //^
         rect = new Rectangle(MOUSE_X, MOUSE_Y, 10, 10 ); //This doesn't ever come into action.
         repaint();  

     }

上面的代码几乎只设置了MOUSE_X和MOUSE_Y变量以及repaint（）;方法

@Override
    protected void paintComponent(Graphics g) {

    Graphics2D g2 = (Graphics2D) g;
    if (rect != null) {

        if (!colorChoice.equals("Default"))
        {
            g2.setColor(Color.BLACK);
        }

        switch(colorChoice) {

        case "GRAY":
            g2.setColor(Color.GRAY);
            break;
        case "CYAN":
            g2.setColor(Color.CYAN);
            break;
        case "BLUE":
            g2.setColor(Color.BLUE);
            break;
        case "RED":
            g2.setColor(Color.RED);
            break;
        case "PINK":
            g2.setColor(Color.PINK);
            break;
        case "YELLOW":
            g2.setColor(Color.YELLOW);
            break;
        case "GREEN":
            g2.setColor(Color.GREEN);
            break;
        case "PURPLE":
            g2.setColor(Color.MAGENTA);
            break;
        case "RESET":
            g2.setColor(Color.WHITE);
        case "WHITE":
            g2.setColor(Color.WHITE);

        }





        g2.fillRect(MOUSE_X, MOUSE_Y, 15, 15); 

        if (colorChoice.equals("RESET")) 
        resetColorOnCursor(); 

        }
    }

    public static void clearBoard()
    {
    tempColor = colorChoice;
    setColorChoice("RESET");
    frame.repaint();




    }


    public static void resetColorOnCursor()
    {
    setColorChoice(tempColor);
    }

这是我偶然遇到的东西。当我发现这种情况时，我试图做的基本上是在您移动鼠标时使光标跟随一个正方形。但是我忘了键入代码部分paintComponent(g);，这把程序变成了我最初想要的东西。从本质上讲，这是我如何清理电路板的底部。我100％确信这不是清除/重置这样的框架的正确方法，但是我找不到其他方法。如果有人有任何技巧或更好的方法来正确使用此方法，我将不胜感激。谢谢！ ：D

Answer 1

您当前的方法基本上是通过不调用super.paintComponent来打破绘画链的要求。 paintComponent方法执行一系列操作，这些操作您不接手，可能会导致一些非常怪异的绘画瑕疵，难以一致地复制。

Graphics是共享资源，因此用于绘制其他控件的Graphics上下文将与用于绘制组件的上下文相同，除非您事先“清理”了上下文，否则之前保留到上下文的内容将保留（这就是为什么您当前编码“似乎”起作用的原因）。

相反，应该使用MouseListener定义锚点，该锚点代表按下鼠标的点，然后使用MouseMotionListener定义选择区域的范围，例如...

import java.awt.AlphaComposite;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class SelectExample {

    public static void main(String[] args) {
        new SelectExample();
    }

    public SelectExample() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private Rectangle selection;

        public TestPane() {
            MouseAdapter ma = new MouseAdapter() {

                private Point clickPoint;

                @Override
                public void mousePressed(MouseEvent e) {
                    clickPoint = e.getPoint();
                    selection = null;
                }

                @Override
                public void mouseDragged(MouseEvent e) {
                    Point dragPoint = e.getPoint();
                    int x = Math.min(clickPoint.x, dragPoint.x);
                    int y = Math.min(clickPoint.y, dragPoint.y);

                    int width = Math.max(clickPoint.x, dragPoint.x) - x;
                    int height = Math.max(clickPoint.y, dragPoint.y) - y;

                    if (selection == null) {
                        selection = new Rectangle(x, y, width, height);
                    } else {
                        selection.setBounds(x, y, width, height);
                    }
                    repaint();
                }

                @Override
                public void mouseReleased(MouseEvent e) {
                    selection = null;
                    repaint();
                }

            };

            addMouseListener(ma);
            addMouseMotionListener(ma);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            if (selection != null) {
                g.setColor(UIManager.getColor("List.selectionBackground"));
                Graphics2D g2d = (Graphics2D) g.create();
                g2d.setComposite(AlphaComposite.SrcOver.derive(0.5f));
                g2d.fill(selection);
                g2d.dispose();
                g2d = (Graphics2D) g.create();
                g2d.draw(selection);
                g2d.dispose();
            }
        }

    }

}

只是强调如果您继续违反paintComponent方法的要求，您将面临的问题，这就是当我不致电super.paintComponent时发生的事情>

我只是简单地在JButton上添加了两个JFrame（所以甚至没有直接添加到面板上）。 paintComponent做了一系列重要的工作，而您忽略了这些工作，这会引起更多的问题。

自由格式行示例...

自由形式的线实际上是一种错觉，它是在一系列点之间绘制的一系列（小）线，这是因为MouseListener不会报告鼠标移动的每个位置，具体取决于加快鼠标移动的速度，您可能会收到很多回拨或一些回拨。

因此，我们将点存储在List中并在它们之间绘制线，而不是仅绘制点，例如...

import java.awt.AlphaComposite;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class FreeFormLines {

    public static void main(String[] args) {
        new FreeFormLines();
    }

    public FreeFormLines() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private List<List<Point>> points;

        public TestPane() {
            points = new ArrayList<>(25);
            MouseAdapter ma = new MouseAdapter() {

                private List<Point> currentPath;

                @Override
                public void mousePressed(MouseEvent e) {
                    currentPath = new ArrayList<>(25);
                    currentPath.add(e.getPoint());

                    points.add(currentPath);
                }

                @Override
                public void mouseDragged(MouseEvent e) {
                    Point dragPoint = e.getPoint();
                    currentPath.add(dragPoint);
                    repaint();
                }

                @Override
                public void mouseReleased(MouseEvent e) {
                    currentPath = null;
                }

            };

            addMouseListener(ma);
            addMouseMotionListener(ma);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            for (List<Point> path : points) {
                Point from = null;
                for (Point p : path) {
                    if (from != null) {
                        g2d.drawLine(from.x, from.y, p.x, p.y);
                    }
                    from = p;
                }
            }
            g2d.dispose();
        }

    }

}

Answer 2

这是一个实用的绘画应用程序的简单示例，您可以在其中控制和更改图形的大小和颜色。

Answer 3

或者我们可以尝试仅绘制Java代码，我认为它是如此简单和强大。