java - 无法在java中绘制形状

Question

我非常确定这段代码应该在屏幕上的单词文本旁边绘制一个椭圆形。然而，这个词全部出现，屏幕的其余部分是黑色的。这似乎发生在任何原始形状上。我想我对java相当了解，但图形化的东西对我来说真的很困惑。我对此无能为力，任何帮助将不胜感激。

import javax.swing.*;
import java.awt.*;
import java.awt.image.*;
import java.util.ArrayList;

public class Game extends JPanel implements Runnable {
    int W = 4;
    int H = 3;
    int windowSize = 300;
    boolean running;
    static boolean drawHitBoxes = true;
    int FPSLimit = 30;

    private Thread thread;
    private BufferedImage buffer;
    private Graphics2D g;

    public Game() {
        super();
        setPreferredSize(new Dimension(W * windowSize, H * windowSize));
        setFocusable(true);
        requestFocus();
    }

    public void addNotify() {
        super.addNotify();
        if (thread == null) {
            thread = new Thread(this);
            thread.start();
        }
    }

    public void run() {
        running = true;

        buffer = new BufferedImage(W * windowSize, H * windowSize,
                BufferedImage.TYPE_INT_RGB);
        g = (Graphics2D) buffer.getGraphics();

        // citList.add(new Citizen(200, 200, "Joe"));

        long startTime;
        long waitTime;

        long frameTime = 1000 / FPSLimit; // /How long one frame should take
        long currentFrameTime;

        while (running) {
            startTime = System.nanoTime(); // record when loop starts

            gameUpdate();
            gameRender();
            gameDraw();

            // Calculate how long the current frame took
            currentFrameTime = (System.nanoTime() - startTime) / 1000000;
            waitTime = frameTime - currentFrameTime;

            try {
                Thread.sleep(waitTime);
            } catch (Exception e) {
            } // Sleep for the remaining time
        }
    }

    private void gameUpdate() {
        // for(Citizen i:citList){i.update();} //Update citizens
    }

    private void gameRender() {
        g.setColor(Color.WHITE);
        g.drawOval(100, 100, W - 100, H - 100);
        g.setColor(Color.WHITE);
        g.drawString("Text.", 100, 100);
        System.out.println("Drawing white box.");

        // for(Citizen i:citList){i.draw(g);} //Draw citizens
    }

    private void gameDraw() {
        Graphics gMain = this.getGraphics();
        gMain.drawImage(buffer, 0, 0, null);
    }
}

Answer 1

g.drawOval(100, 100, W-100, H-100);

W 为 4，H 为 3，因此由于 W-100 为 -96，H-100 为 -97，因此第三个和第四个参数为负数，这对于 Graphics#drawOval(...) 方法没有意义，因为椭圆形的宽度和高度怎么可能是负数。解决方案:确保在调用此方法时仅使用有意义的正参数。也许您想要的是:

 // but you'll also want to avoid magic numbers such as 100 & 200 as well
 g.drawOval(100, 100, W * windowSize - 200, H * windowSize - 200);

顺便说一句，我自己更喜欢使用被动图形，在 PaintComponent 中绘图，并且每当我看到具有 Graphics 或 Graphics2D 实例字段的 Swing 代码时我都会感到害怕。此外，您的代码看起来不遵守 Swing 线程规则，因为它似乎从 Swing 事件线程发出 Swing 调用。