增加文字颜色与背景颜色色差设置

hutool-swing/src/main/java/org/dromara/hutool/swing/img/GraphicsUtil.java

@@ -83,7 +83,40 @@ public class GraphicsUtil {
 	 * @since 4.5.10
 	 */
 	public static Graphics drawStringColourful(final Graphics g, final String str, final Font font, final int width, final int height) {
-		return drawString(g, str, font, null, width, height);
+		return drawStringColourful(g, str, font, width, height, null, 0);
+	}
+
+	/**
+	 * 绘制字符串，使用随机颜色，默认抗锯齿
+	 *
+	 * @param g                {@link Graphics}画笔
+	 * @param str              字符串
+	 * @param font             字体
+	 * @param width            字符串总宽度
+	 * @param height           字符串背景高度
+	 * @param compareColor     对比颜色，用于计算颜色与对比颜色的色差，色差小于minColorDistance则重新生成颜色
+	 * @param minColorDistance 随机生成的颜色与对比颜色的最小色差，小于此值则重新生成颜色
+	 * @return 画笔对象
+	 * @since 6.0.0
+	 */
+	public static Graphics drawStringColourful(final Graphics g, final String str, final Font font,
+											   final int width, final int height, final Color compareColor, final int minColorDistance) {
+		// 抗锯齿
+		enableAntialias(g);
+		// 创建字体
+		g.setFont(font);
+
+		// 文字高度（必须在设置字体后调用）
+		final int midY = getCenterY(g, height);
+
+		final int len = str.length();
+		final int charWidth = width / len;
+		for (int i = 0; i < len; i++) {
+			// 产生随机的颜色值，让输出的每个字符的颜色值都将不同。
+			g.setColor(ColorUtil.randomColor(compareColor, minColorDistance));
+			g.drawString(String.valueOf(str.charAt(i)), i * charWidth, midY);
+		}
+		return g;
 	}
 
 	/**
@@ -93,12 +126,11 @@ public class GraphicsUtil {
 	 * @param str    字符串
 	 * @param font   字体
 	 * @param color  字体颜色，{@code null} 表示使用随机颜色（每个字符单独随机）
-	 * @param width  字符串背景的宽度
 	 * @param height 字符串背景的高度
 	 * @return 画笔对象
-	 * @since 4.5.10
+	 * @since 6.0.0
 	 */
-	public static Graphics drawString(final Graphics g, final String str, final Font font, final Color color, final int width, final int height) {
+	public static Graphics drawString(final Graphics g, final String str, final Font font, final Color color, final int height) {
 		// 抗锯齿
 		enableAntialias(g);
 		// 创建字体
@@ -109,16 +141,7 @@ public class GraphicsUtil {
 		if (null != color) {
 			g.setColor(color);
 		}
-
+		g.drawString(str, 0, midY);
-		final int len = str.length();
-		final int charWidth = width / len;
-		for (int i = 0; i < len; i++) {
-			if (null == color) {
-				// 产生随机的颜色值，让输出的每个字符的颜色值都将不同。
-				g.setColor(ColorUtil.randomColor());
-			}
-			g.drawString(String.valueOf(str.charAt(i)), i * charWidth, midY);
-		}
 		return g;
 	}
 

hutool-swing/src/main/java/org/dromara/hutool/swing/img/color/ColorUtil.java

@@ -233,6 +233,8 @@ public class ColorUtil {
 		return new Color(r, g, b);
 	}
 
+	// region randomColor
+
 	/**
 	 * 生成随机颜色
 	 *
@@ -257,6 +259,42 @@ public class ColorUtil {
 		return new Color(random.nextInt(RGB_COLOR_BOUND), random.nextInt(RGB_COLOR_BOUND), random.nextInt(RGB_COLOR_BOUND));
 	}
 
+	/**
+	 * 生成随机颜色，与指定颜色有一定的区分度
+	 *
+	 * @param compareColor 比较颜色，{@code null}表示无区分要求
+	 * @param minDistance  最小色差，按三维坐标计算的距离值。小于等于0表示无区分要求
+	 * @return 随机颜色
+	 * @since 5.8.30
+	 */
+	public static Color randomColor(final Color compareColor, final int minDistance) {
+		Color color = randomColor();
+		if(null == compareColor || minDistance <= 0){
+			while (computeColorDistance(compareColor, color) < minDistance) {
+				color = randomColor();
+			}
+		}
+		return color;
+	}
+	// endregion
+
+	/**
+	 * 计算两个颜色之间的色差，按三维坐标距离计算
+	 *
+	 * @param color1 颜色1
+	 * @param color2 颜色2
+	 * @return 色差，按三维坐标距离值
+	 * @since 5.8.30
+	 */
+	public static int computeColorDistance(final Color color1, final Color color2) {
+		if (null == color1 || null == color2) {
+			return 0;
+		}
+		return (int) Math.sqrt(Math.pow(color1.getRed() - color2.getRed(), 2)
+			+ Math.pow(color1.getGreen() - color2.getGreen(), 2)
+			+ Math.pow(color1.getBlue() - color2.getBlue(), 2));
+	}
+
 	/**
 	 * AWT的{@link Color}颜色转换为ANSI颜色，由于取最接近颜色，故可能有色差
 	 *

hutool-swing/src/test/java/org/dromara/hutool/swing/captcha/CaptchaUtilTest.java

@@ -12,9 +12,20 @@
 
 package org.dromara.hutool.swing.captcha;
 
+import org.dromara.hutool.core.util.ObjUtil;
+import org.dromara.hutool.core.util.RandomUtil;
+import org.dromara.hutool.swing.img.GraphicsUtil;
+import org.dromara.hutool.swing.img.color.ColorUtil;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
+import java.awt.Color;
+import java.awt.Graphics;
+import java.awt.Graphics2D;
+import java.awt.Image;
+import java.awt.image.BufferedImage;
+import java.util.concurrent.ThreadLocalRandom;
+
 public class CaptchaUtilTest {
 
 	@Test
@@ -24,4 +35,70 @@ public class CaptchaUtilTest {
 			CaptchaUtil.ofShearCaptcha(320, 240);
 		}
 	}
+
+	@Test
+	@Disabled
+	public void drawStringColourfulTest() {
+		for(int i = 0; i < 10; i++) {
+			final AbstractCaptcha lineCaptcha = new TestLineCaptcha(200, 100, 5, 10);
+			lineCaptcha.write("d:/captcha/line"+i+".png");
+		}
+	}
+
+	static class TestLineCaptcha extends AbstractCaptcha{
+		private static final long serialVersionUID = -558846929114465692L;
+
+		public TestLineCaptcha(final int width, final int height, final int codeCount, final int interfereCount) {
+			super(width, height, codeCount, interfereCount);
+		}
+
+		@Override
+		protected Image createImage(final String code) {
+			// 图像buffer
+			final BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
+			final Graphics2D g = GraphicsUtil.createGraphics(image, ObjUtil.defaultIfNull(this.background, Color.WHITE));
+
+			// 干扰线
+			drawInterfere(g);
+
+			// 字符串
+			drawString(g, code);
+
+			return image;
+		}
+
+		// ----------------------------------------------------------------------------------------------------- Private method start
+		/**
+		 * 绘制字符串
+		 *
+		 * @param g {@link Graphics}画笔
+		 * @param code 验证码
+		 */
+		private void drawString(final Graphics2D g, final String code) {
+			// 指定透明度
+			if (null != this.textAlpha) {
+				g.setComposite(this.textAlpha);
+			}
+			GraphicsUtil.drawStringColourful(g, code, this.font, this.width, this.height,Color.WHITE,200);
+		}
+
+		/**
+		 * 绘制干扰线
+		 *
+		 * @param g {@link Graphics2D}画笔
+		 */
+		private void drawInterfere(final Graphics2D g) {
+			final ThreadLocalRandom random = RandomUtil.getRandom();
+			// 干扰线
+			for (int i = 0; i < this.interfereCount; i++) {
+				final int xs = random.nextInt(width);
+				final int ys = random.nextInt(height);
+				final int xe = xs + random.nextInt(width / 3);
+				final int ye = ys + random.nextInt(height / 3);
+				g.setColor(ColorUtil.randomColor(random));
+				g.drawLine(xs, ys, xe, ye);
+			}
+		}
+		// ----------------------------------------------------------------------------------------------------- Private method start
+	}
 }