Java2D Alpha映射图像

Question

使用Graphics2D，我如何拍摄黑白图像，并用来定义
在另一幅图像上应该渲染和不应该渲染的图像？

例如，如果我有一个图像，例如一个字段，并且在该字段上是一头 母牛，那么在用Java渲染时
，
在相同尺寸的另一幅图像上，我会在黑色背景上以与母牛相同的坐标绘制一个白框图像会是
全黑的，除了我有白盒子的那头牛？

Answer 1

编辑：基于聊天中的长时间讨论，很明显有人
对意图有误解，而最初的问题
是XY问题：如何用遮罩
图像合成图像的问题仅是一个解决方案尝试的实际问题-
即画瓦片地图上的某些阴影/高光效果。该
帖子的原始版本可以在修订历史记录中看到。

显然，实际目标是在图像上添加“灯光效果”。这是
如何实现此目的的示例：

原始图像绘制在背景中
在图像上绘制“阴影图像”。
“阴影图像”最初是几乎不透明，几乎黑色的图像。灯光
用绘制成该图像RadialGradientPaint。
选择该涂料的颜色，以使它们
在应有灯光的地方使阴影图像不透明，并减少黑色。这会使这些区域看起来变
亮，而其他部分则保持黑暗。

import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.MultipleGradientPaint.CycleMethod;
import java.awt.Point;
import java.awt.RadialGradientPaint;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.geom.Point2D;
import java.awt.image.BufferedImage;
import java.util.Random;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class LightEffectTest2
{
    public static void main(String args[])
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new LightEffectTest2();
            }
        });
    }


    public LightEffectTest2()
    {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(new LightEffectPanel2());
        f.setSize(600,600);
        f.setVisible(true);
    }
}


class LightEffectPanel2 extends JPanel implements MouseMotionListener
{
    private Point point = new Point(0,0);
    private BufferedImage image;
    private BufferedImage shadow;

    public LightEffectPanel2()
    {
        image = createExampleImage(600,600);
        shadow = new BufferedImage(image.getWidth(), image.getHeight(),
            BufferedImage.TYPE_INT_ARGB);

        addMouseMotionListener(this);
    }

    private static BufferedImage createExampleImage(int w, int h)
    {
        BufferedImage image = new BufferedImage(w, h, 
            BufferedImage.TYPE_INT_ARGB);
        Graphics g = image.getGraphics();
        Random random = new Random(0);
        for (int i=0; i<200; i++)
        {
            int x = random.nextInt(w);
            int y = random.nextInt(h);
            Color c = new Color(
                random.nextInt(255),
                random.nextInt(255),
                random.nextInt(255));
            g.setColor(c);
            g.fillOval(x-20, y-20, 40, 40);
        }
        g.dispose();
        return image;
    }


    @Override
    protected void paintComponent(Graphics gr)
    {
        super.paintComponent(gr);
        Graphics2D g = (Graphics2D)gr;
        g.drawImage(image, 0,0,null);

        drawLights();

        g.drawImage(shadow, 0,0, null);
    }

    private void drawLights()
    {
        Graphics2D g = shadow.createGraphics();
        g.setComposite(AlphaComposite.Src);
        g.setColor(new Color(0,0,16,240));
        g.fillRect(0,0,getWidth(),getHeight());

        drawLight(g, new Point(100,100));
        drawLight(g, point);

        g.dispose();
    }

    private void drawLight(Graphics2D g, Point pt)
    {
        float radius = 100;
        g.setComposite(AlphaComposite.DstOut);
        Point2D center = new Point2D.Float(pt.x, pt.y);
        float[] dist = {0.0f, 1.0f};
        Color[] colors = {new Color(255,255,255,255), new Color(0,0,0,0) };
        RadialGradientPaint p =
            new RadialGradientPaint(
                center, radius, dist, colors, CycleMethod.NO_CYCLE);
        g.setPaint(p);
        g.fillOval(pt.x-(int)radius,pt.y-(int)radius,(int)radius*2,(int)radius*2);
    }



    @Override
    public void mouseDragged(MouseEvent e) {
    }

    @Override
    public void mouseMoved(MouseEvent e) {
        point = e.getPoint();
        repaint();
    }
}

（后）编辑对于注释中的请求：

要添加另一个阴影（与现有的灯光无关），可以创建一种
drawShadow在
绘制灯光之后重新应用阴影的方法。它基本上使用了另一个RadialGradientPaint部分
“还原”原始不透明暗影图像的图像。

（此处阴影被赋予了较清晰的边框，以使效果更
明显）

import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.MultipleGradientPaint.CycleMethod;
import java.awt.Point;
import java.awt.RadialGradientPaint;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.geom.Point2D;
import java.awt.image.BufferedImage;
import java.util.Random;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class LightEffectTest3
{
    public static void main(String args[])
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new LightEffectTest3();
            }
        });
    }


    public LightEffectTest3()
    {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(new LightEffectPanel3());
        f.setSize(600,600);
        f.setVisible(true);
    }
}


class LightEffectPanel3 extends JPanel implements MouseMotionListener
{
    private Point point = new Point(0,0);
    private BufferedImage image;
    private BufferedImage shadow;

    public LightEffectPanel3()
    {
        image = createExampleImage(600,600);
        shadow = new BufferedImage(image.getWidth(), image.getHeight(),
            BufferedImage.TYPE_INT_ARGB);

        addMouseMotionListener(this);
    }

    private static BufferedImage createExampleImage(int w, int h)
    {
        BufferedImage image = new BufferedImage(w, h, 
            BufferedImage.TYPE_INT_ARGB);
        Graphics g = image.getGraphics();
        Random random = new Random(0);
        for (int i=0; i<200; i++)
        {
            int x = random.nextInt(w);
            int y = random.nextInt(h);
            Color c = new Color(
                random.nextInt(255),
                random.nextInt(255),
                random.nextInt(255));
            g.setColor(c);
            g.fillOval(x-20, y-20, 40, 40);
        }
        g.dispose();
        return image;
    }


    @Override
    protected void paintComponent(Graphics gr)
    {
        super.paintComponent(gr);
        Graphics2D g = (Graphics2D)gr;
        g.drawImage(image, 0,0,null);

        drawLights();

        g.drawImage(shadow, 0,0, null);
    }

    private void drawLights()
    {
        Graphics2D g = shadow.createGraphics();
        g.setComposite(AlphaComposite.Src);
        g.setColor(new Color(0,0,16,240));
        g.fillRect(0,0,getWidth(),getHeight());

        drawLight(g, new Point(200,200));
        drawLight(g, point);
        drawShadow(g, new Point(250,250));

        g.dispose();
    }

    private void drawLight(Graphics2D g, Point pt)
    {
        float radius = 150;
        g.setComposite(AlphaComposite.DstOut);
        Point2D center = new Point2D.Float(pt.x, pt.y);
        float[] dist = {0.0f, 1.0f};
        Color[] colors = {new Color(255,255,255,255), new Color(0,0,0,0) };
        RadialGradientPaint p =
            new RadialGradientPaint(
                center, radius, dist, colors, CycleMethod.NO_CYCLE);
        g.setPaint(p);
        g.fillOval(pt.x-(int)radius,pt.y-(int)radius,
            (int)radius*2,(int)radius*2);
    }

    private void drawShadow(Graphics2D g, Point pt)
    {
        float radius = 75;
        g.setComposite(AlphaComposite.DstOver);
        Point2D center = new Point2D.Float(pt.x, pt.y);
        float[] dist = {0.0f, 0.7f, 1.0f};
        Color[] colors = { 
            new Color(0,0,0,200),
            new Color(0,0,0,150),
            new Color(255,255,255,0) };
        RadialGradientPaint p =
            new RadialGradientPaint(
                center, radius, dist, colors, CycleMethod.NO_CYCLE);
        g.setPaint(p);
        g.fillOval(pt.x-(int)radius,pt.y-(int)radius,
            (int)radius*2,(int)radius*2);
    }



    @Override
    public void mouseDragged(MouseEvent e) {
    }

    @Override
    public void mouseMoved(MouseEvent e) {
        point = e.getPoint();
        repaint();
    }
}