JAVA2D学习 绘制可拖拽选择框

    弄了一天，基本实现了一般绘图软件的绘制矩形选择框的功能。

• 拖动鼠标用虚线调整矩形选择区域的大小
• 松开鼠标完成选择，更改矩形选择区域边线样式，绘制8个用来调整大小的手柄
• 用鼠标拖动手柄可重新调整矩形的大小

    一共两个类：
    PointRectangle 扩展了AWT的Rectangle类，按左上角和右下角两个坐标点来定义矩形（AWT默认是按左上角坐标和长宽来定义矩形的）。

    SelectableCanvas 扩展了AWT的Canvas，用来充当画板。

 

    考虑到可能有底图存在，这里没用到Double Buffering，每次画图前先按像素级精确擦除前一祯绘制的矩形的手柄，实际效果很理想，基本看不到闪烁。

 

package com.fancy.picture.test;

import java.awt.Rectangle;

public class PointRectangle extends Rectangle {

	private static final long serialVersionUID = -2465363144347743255L;

	int x1, x2, y1, y2;

	public PointRectangle(int x1, int y1, int x2, int y2) {
		this.x1 = x = x1;
		this.x2 = x2;
		this.y1 = y = y1;
		this.y2 = y2;
		width = x2 - x1;
		height = y2 - y1;
		if (x2 < x1) {
			x = x2;
			width = x1 - x2;
		}
		if (y2 < y1) {
			y = y2;
			height = y1 - y2;
		}
	}

	public PointRectangle(Rectangle rectangle) {
		super(rectangle.x, rectangle.y, rectangle.width, rectangle.height);
		this.x1 = rectangle.x;
		this.y1 = rectangle.y;
		this.x2 = rectangle.x + rectangle.width;
		this.y2 = rectangle.y + rectangle.height;
	}

}

 

 

package com.fancy.picture.test;

import java.awt.AlphaComposite;
import java.awt.BasicStroke;
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Cursor;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.awt.geom.Area;

public class SelectableCanvas extends Canvas {

	private static final long serialVersionUID = -7159915510292362753L;

	boolean selecting;// 是否正在拖拽矩形
	int x, y;// 矩形原点坐标

	PointRectangle selection;// 当前绘制的矩形
	int activeHandle = -1;// 激活的Resize手柄
	Rectangle[] handles = new Rectangle[8];// 8个Resize手柄

	public SelectableCanvas() {

		addMouseListener(new MouseAdapter() {
			@Override
			public void mouseReleased(MouseEvent e) {
				if (selecting || activeHandle >= 0) {
					wipeSelection();
					confirmSelection(selection);
					selecting = false;
					activeHandle = -1;
					setCursor(Cursor.getPredefinedCursor(Cursor.DEFAULT_CURSOR));
				}
			}

			@Override
			public void mousePressed(MouseEvent e) {
				x = e.getX();
				y = e.getY();
			}
		});

		addMouseMotionListener(new MouseMotionAdapter() {
			public void mouseMoved(MouseEvent e) {
				for (int i = 0; i < handles.length; i++) {
					if (handles[i] != null && handles[i].contains(e.getX(), e.getY())) {
						activeHandle = i;
						switch (i) {
						case 0:
						case 4:
							setCursor(Cursor.getPredefinedCursor(Cursor.SE_RESIZE_CURSOR));
							break;
						case 1:
						case 5:
							setCursor(Cursor.getPredefinedCursor(Cursor.S_RESIZE_CURSOR));
							break;
						case 2:
						case 6:
							setCursor(Cursor.getPredefinedCursor(Cursor.SW_RESIZE_CURSOR));
							break;
						case 3:
						case 7:
							setCursor(Cursor.getPredefinedCursor(Cursor.E_RESIZE_CURSOR));
							break;
						}
						return;
					}
				}
				activeHandle = -1;
				setCursor(Cursor.getPredefinedCursor(Cursor.DEFAULT_CURSOR));
			}

			public void mouseDragged(MouseEvent e) {
				if (selection != null)
					wipeSelection();
				if (activeHandle >= 0) {
					switch (activeHandle) {
					case 0:
						selection = new PointRectangle(e.getX(), e.getY(), selection.x2, selection.y2);
						break;
					case 1:
						selection = new PointRectangle(selection.x1, e.getY(), selection.x2, selection.y2);
						break;
					case 2:
						selection = new PointRectangle(selection.x1, e.getY(), e.getX(), selection.y2);
						break;
					case 3:
						selection = new PointRectangle(selection.x1, selection.y1, e.getX(), selection.y2);
						break;
					case 4:
						selection = new PointRectangle(selection.x1, selection.y1, e.getX(), e.getY());
						break;
					case 5:
						selection = new PointRectangle(selection.x1, selection.y1, selection.x2, e.getY());
						break;
					case 6:
						selection = new PointRectangle(e.getX(), selection.y1, selection.x2, e.getY());
						break;
					case 7:
						selection = new PointRectangle(e.getX(), selection.y1, selection.x2, selection.y2);
						break;
					}
					drawSelection(selection);
				}
				else {
					selection = new PointRectangle(x, y, e.getX(), e.getY());
					drawSelection(selection);
					selecting = true;
					setCursor(Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR));
				}
			}
		});
	}

	// 清除选择的矩形
	public void clearSelection() {
		selection = null;
		selecting = false;
		activeHandle = -1;
		for (int i = 0; i < handles.length; i++)
			handles[i] = null;
	}

	// 清除上次的绘制的矩形
	private void wipeSelection() {
		Graphics2D graphics = (Graphics2D) getGraphics().create();// 初始化绘图上下文
		// 定义擦除区域
		Area area = new Area(new Rectangle(selection.x, selection.y, selection.width + 1, selection.height + 1));
		area.subtract(new Area(new Rectangle(selection.x + 1, selection.y + 1, selection.width - 1, selection.height - 1)));
		area.add(new Area(new Rectangle(selection.x - 2, selection.y - 2, 5, 5)));
		area.add(new Area(new Rectangle(selection.x + selection.width / 2 - 2, selection.y - 2, 5, 5)));
		area.add(new Area(new Rectangle(selection.x + selection.width - 2, selection.y - 2, 5, 5)));
		area.add(new Area(new Rectangle(selection.x + selection.width - 2, selection.y + selection.height / 2 - 2, 5, 5)));
		area.add(new Area(new Rectangle(selection.x + selection.width - 2, selection.y + selection.height - 2, 5, 5)));
		area.add(new Area(new Rectangle(selection.x + selection.width / 2 - 2, selection.y + selection.height - 2, 5, 5)));
		area.add(new Area(new Rectangle(selection.x - 2, selection.y + selection.height - 2, 5, 5)));
		area.add(new Area(new Rectangle(selection.x - 2, selection.y + selection.height / 2 - 2, 5, 5)));
		graphics.setClip(area);// 应用擦除区域
		update(graphics);// 用背景擦除
	}

	//画虚线矩形
	private void drawSelection(Rectangle selection) {
		Graphics2D graphics = (Graphics2D) getGraphics().create();// 初始化绘图上下文
		graphics.setPaint(Color.WHITE);// 设置边框颜色
		graphics.setStroke(new BasicStroke(1, BasicStroke.CAP_BUTT, BasicStroke.JOIN_ROUND, 1f, new float[] { 5 }, 0));// 设置边框笔触
		graphics.draw(selection);// 绘制选择边框
	}

	//画带手柄的矩形
	private void confirmSelection(Rectangle selection) {
		this.selection = new PointRectangle(selection);
		Graphics2D graphics = (Graphics2D) getGraphics();// 绘图上下文
		if (selection.isEmpty()) {
			clearSelection();
			return;
		}
		graphics.setStroke(new BasicStroke(1));// 设置选择框底色笔触
		graphics.setPaint(Color.BLUE);// 设置边框底色颜色
		graphics.draw(selection);// 绘制选择边框底色
		graphics.setPaint(Color.WHITE);// 设置边框颜色
		graphics.setStroke(new BasicStroke(1, BasicStroke.CAP_BUTT, BasicStroke.JOIN_ROUND, 1f, new float[] { 5 }, 0));// 设置边框笔触
		graphics.draw(selection);// 绘制选择边框
		// 定义手柄
		handles[0] = new Rectangle(selection.x - 2, selection.y - 2, 4, 4);
		handles[1] = new Rectangle(selection.x + selection.width / 2 - 2, selection.y - 2, 4, 4);
		handles[2] = new Rectangle(selection.x + selection.width - 2, selection.y - 2, 4, 4);
		handles[3] = new Rectangle(selection.x + selection.width - 2, selection.y + selection.height / 2 - 2, 4, 4);
		handles[4] = new Rectangle(selection.x + selection.width - 2, selection.y + selection.height - 2, 4, 4);
		handles[5] = new Rectangle(selection.x + selection.width / 2 - 2, selection.y + selection.height - 2, 4, 4);
		handles[6] = new Rectangle(selection.x - 2, selection.y + selection.height - 2, 4, 4);
		handles[7] = new Rectangle(selection.x - 2, selection.y + selection.height / 2 - 2, 4, 4);
		graphics.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 1f));// 设置填充不透明
		graphics.setPaint(Color.WHITE);// 设置手柄填充颜色
		// 填充手柄
		for (Rectangle handle : handles)
			graphics.fill(handle);
		graphics.setPaint(Color.BLACK);// 设置手柄边框颜色
		graphics.setStroke(new BasicStroke(1f));// 设置实线笔触
		// 绘制手柄边框
		for (Rectangle handle : handles)
			graphics.draw(handle);
	}

	//返回当前有效的矩形
	public Rectangle getSelection() {
		return selection;
	}

}

 

 

随便建个窗口，直接在JPanel上放个SelectableCanvas就可以看效果了。