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问鼠标拖动时绘制线条时出现的问题
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Stack Overflow用户

提问于 2012-12-29 13:12:02

回答 2查看 7K关注 0票数 4

我正在开发一个绘制不同形状的画图小程序。我想在拖动鼠标的同时绘制线条。问题是，当线条出现时，它们如下图所示。

我有一个用一个点(起始点)构造的类线，它有一个名为setDragPoint的方法，它使用鼠标拖动点来绘制线条，同时drawingImage在拖动模式下绘制时会产生太多的闪烁。为什么会发生这种情况？

import java.applet.*;
import java.awt.event.*;
import java.awt.*;
import java.util.*;

public class PaintBrush extends Applet implements MouseListener, MouseMotionListener {

Shape shape;
Point startPoint;
Point dragPoint;
ArrayList<Shape> shapes;
Choice shapeChoice;
Choice colorChoice;
Choice fillChoice;
Image drawingImage;
Graphics drawGraphics;
String shapeString, colorString, fillString;
boolean isDragMode;

public void init() {
    shapes = new ArrayList<Shape>();
    shapeChoice = new Choice();
    shapeChoice.addItem("Line");
    shapeChoice.addItem("Rectangle");
    shapeChoice.addItem("RoundRect");
    shapeChoice.addItem("Oval");
    shapeChoice.addItem("FreeHand");

    add(shapeChoice);

    colorChoice = new Choice();
    colorChoice.addItem("Red");
    colorChoice.addItem("Green");
    colorChoice.addItem("Blue");

    add(colorChoice);

    fillChoice = new Choice();
    fillChoice.addItem("Filled");
    fillChoice.addItem("Hollow");
    add(fillChoice);

    shapeString = shapeChoice.getSelectedItem();
    colorString = colorChoice.getSelectedItem();
    fillString = fillChoice.getSelectedItem();

    drawingImage = createImage(getSize().width, getSize().height);
    drawGraphics = drawingImage.getGraphics();
    System.out.println("set up image");
    drawGraphics.setColor(Color.black);
    drawGraphics.fillRect(0, 0, getSize().width, getSize().height);
    drawGraphics.setColor(Color.orange);
    drawGraphics.drawRect(0, 0, getSize().width - 1, getSize().height - 1);
    drawGraphics.drawRect(1, 1, getSize().width - 3, getSize().height - 3);
    startPoint = new Point(0, 0);
    dragPoint = new Point(0, 0);
    addMouseListener(this);
    addMouseMotionListener(this);
}

public void mouseEntered(MouseEvent e) {
}

public void mouseExited(MouseEvent e) {
}

public void mouseClicked(MouseEvent e) {
}

public void mousePressed(MouseEvent e) {

    System.out.println("Pressed");

    startPoint.x = e.getX();
    startPoint.y = e.getY();
    repaint();

    switch (shapeString) {
        case "Line":
            shape = new Line(startPoint.x, startPoint.y);  //step 1 here i construct a new line using the start point (the point at which the mouse is pressed)

            break;
        case "FreeHand":
            shape = new FreeShape();
            break;
    }


    }

public void mouseReleased(MouseEvent e) {
    if (isDragMode) {
        shapes.add(shape);
        isDragMode = false;
     }
    repaint();

}

public void mouseMoved(MouseEvent e) {
}

public void mouseDragged(MouseEvent e) {
    System.out.println("Dragged");
    isDragMode = true;
    dragPoint.x = e.getX();
    dragPoint.y = e.getY();

    switch (shapeString) {
        case "Line":
            shape.setDragPoint(dragPoint.x, dragPoint.y);  //here i set the drag points to the already created line at step 1 
              break;
        case "FreeHand":
            shape = new FreeShape();
            break;
    }

    shape.drawWhileDragging(drawGraphics); // i call this method to draw while mouse is dragging

    repaint();


}

public void paint(Graphics g) {

  update(g);
}
 public void update(Graphics g) {

  // create an off-screen graphics drawing environment if none
  //existed
  // or if the user resized the applet drawing area to a different
 // size
   if (drawingImage == null)
{

System.out.println("Image is Null");
    drawingImage = createImage(getSize().width,getSize().height);
drawGraphics = drawingImage.getGraphics();
}



  // erase the previous image
  drawGraphics.setColor(Color.black);
  drawGraphics.fillRect(0,0,getSize().width,getSize().height);
  drawGraphics.setColor(Color.orange);
  drawGraphics.drawRect(0,0,getSize().width-1,getSize().height-1);
  drawGraphics.drawRect(1,1,getSize().width-3,getSize().height-3);  

   for(Shape s:shapes)
         s.draw(drawGraphics);

  // paint the offscreen image to the applet viewing window
  g.drawImage(drawingImage,0,0,this);

   }
 }


abstract class Shape {

Color shapeColor;
boolean filled;

abstract void draw(Graphics g);

void drawWhileDragging(Graphics g) {
}

void setDragPoint(int x, int y) {
}
}

 class Line extends Shape {

private Point startPoint;
private Point currentPoint;

public Point getStartPoint() {
    return startPoint;
}

public Point getCurrentPoint() {
    return currentPoint;
}

public void setStartPoint(Point point) {
    this.startPoint = point;
}

public void setCurrentPoint(Point point) {
    this.currentPoint = point;
}

void drawWhileDragging(Graphics g) {
    g.drawLine(startPoint.x, startPoint.y, currentPoint.x, currentPoint.y); 
}

public void draw(Graphics g) {
    g.drawLine(startPoint.x, startPoint.y, currentPoint.x, currentPoint.y);
}

Line() {
    startPoint = new Point(0, 0);
    currentPoint = new Point(0, 0);
}

Line(int x1, int y1) {
    this();
    this.startPoint.x = x1; 
    this.startPoint.y = y1;
}

void setDragPoint(int x, int y) {
    this.currentPoint.x = x;
    this.currentPoint.y = y;
    System.out.println("Current-X:" + currentPoint.x + " currentPoint-Y" + currentPoint.y);
    System.out.println("start-X:" + startPoint.x + " startPoint-Y" + startPoint.y);
  }

 }

class FreeShape extends Shape {

private ArrayList<Point> dragPoints = new ArrayList<Point>();

public ArrayList<Point> getDragPoints() {
    return dragPoints;
}

public void setDragPoints(Point point) {
    dragPoints.add(point);
}

public void draw(Graphics g) {
}

public FreeShape() {
  }
}


class Rectangle extends Shape {

public void draw(Graphics g) {
   }
 }


class Oval extends Shape {

public void draw(Graphics g) {
   }
 }

awt

java-2d

java

graphics

applet

回答 2

Stack Overflow用户

回答已采纳

发布于 2012-12-29 14:01:32

我最近写了一个类似类型的应用程序。这是屏幕截图。正如您所看到的，它还没有完全发展起来。

现在，我也面临着和你现在面临的类似的问题。你要做的是。

Double Buffer所有绘制操作
不会通过调用repaint来清除屏幕。实际上，Repaint首先用背景颜色填充屏幕&这就是您所看到的闪烁。

您可以在Image中制作当前屏幕画布的副本。Image将在每次绘图操作后更新。因此，您要做的不是通过调用repaint来清除屏幕，而是在画布上绘制Image。这就像是双缓冲。

每次拖动鼠标时，您都会在代码中调用 repaint 。这就是闪烁的原因。

更新

我在新更新的代码中发现了三个主要问题

在drawWhileDragging方法中，您不会更改线条图形上下文绘制颜色。所以这条线实际上是用黑色绘制的，你的背景也是黑色的。结果你看不到任何东西。
在同样的方法中，你正在传递一个drawingImage的图形上下文(即引用)。因此，这条线实际上是在屏幕外的图像上绘制的，而不是在屏幕上绘制的。在mouseDragged方法中，每次拖动后都会调用
。结果，实际上没有任何东西被绘制为

。

我已经在我的机器上运行了你的代码，并做了必要的更改。我只发布更改后的方法，以保持简短。

下面是更新后的mouseDragged方法

    public void mouseDragged(MouseEvent e) {
        System.out.println("Dragged");
        isDragMode = true;
        dragPoint.x = e.getX();
        dragPoint.y = e.getY();

        switch (shapeString) {
            case "Line":
                shape.setDragPoint(dragPoint.x, dragPoint.y);  //here i set the drag points to the already created line at step 1
                break;
            case "FreeHand":
                shape = new FreeShape();
                break;
        }

        getGraphics().drawImage(drawingImage, 0,0,null); //Added this line
        shape.drawWhileDragging(getGraphics()); // i call this method to draw while mouse is dragging
    }

下面是更新后的drawWhileDragging方法

    void drawWhileDragging(Graphics g) {
        g.setColor(Color.ORANGE);
        g.drawLine(startPoint.x, startPoint.y, currentPoint.x, currentPoint.y);
        g.setColor(Color.BLACK);
    }

嗯，我已经把颜色设为橙色了。你要做的就是根据Choice菜单设置颜色。

您也可以实现一个类似的类比来绘制其他形状。

票数 1

Stack Overflow用户

发布于 2012-12-29 15:16:28

你遇到的问题归结为你是如何“尝试”执行双缓冲的。与其在更新线位置时清除后台缓冲区，不如简单地连续绘制到它-有点像在黑板上绘制。

相反，您需要清除图形内容并重新应用更新-令人惊讶的是，这是paint实际工作的一部分，但您从不调用super.paint

很少需要覆盖顶级容器，也不应该很少需要覆盖顶级容器的paint方法。抛开其他所有东西不谈，没有双重缓冲。

取而代之的是，使用像JPanel这样的东西。

我已经更新了您的示例，不包括颜色。颜色实际上应该由形状保持，并在绘制时应用。

public class BadPaint06 extends JApplet {

    public void init() {
        setLayout(new BorderLayout());
    }

    @Override
    public void start() {
        add(new PaintPane());
    }

    public class PaintPane extends JPanel implements MouseListener, MouseMotionListener {

        Shape shape;
        Point startPoint;
        Point dragPoint;
        ArrayList<Shape> shapes;
        Choice shapeChoice;
        Choice colorChoice;
        Choice fillChoice;
        Image drawingImage;
        Graphics drawGraphics;
        String shapeString, colorString, fillString;
        boolean isDragMode;

        public PaintPane() {
            shapes = new ArrayList<Shape>();
            shapeChoice = new Choice();
            shapeChoice.addItem("Line");
            shapeChoice.addItem("Rectangle");
            shapeChoice.addItem("RoundRect");
            shapeChoice.addItem("Oval");
            shapeChoice.addItem("FreeHand");

            add(shapeChoice);

            colorChoice = new Choice();
            colorChoice.addItem("Red");
            colorChoice.addItem("Green");
            colorChoice.addItem("Blue");

            add(colorChoice);

            fillChoice = new Choice();
            fillChoice.addItem("Filled");
            fillChoice.addItem("Hollow");
            add(fillChoice);

            shapeString = shapeChoice.getSelectedItem();
            colorString = colorChoice.getSelectedItem();
            fillString = fillChoice.getSelectedItem();

            startPoint = new Point(0, 0);
            dragPoint = new Point(0, 0);
            addMouseListener(this);
            addMouseMotionListener(this);
        }

        @Override
        public void invalidate() {

            drawingImage = null;

            super.invalidate(); 

        }

        public void mouseEntered(MouseEvent e) {
        }

        public void mouseExited(MouseEvent e) {
        }

        public void mouseClicked(MouseEvent e) {
        }

        public void mousePressed(MouseEvent e) {

            startPoint.x = e.getX();
            startPoint.y = e.getY();
            repaint();

            switch (shapeString) {
                case "Line":
                    shape = new Line(startPoint.x, startPoint.y);  //step 1 here i construct a new line using the start point (the point at which the mouse is pressed)

                    break;
                case "FreeHand":
                    shape = new FreeShape();
                    break;
            }


        }

        public void mouseReleased(MouseEvent e) {
            if (isDragMode) {
                shapes.add(shape);
                isDragMode = false;
            }
            repaint();

        }

        public void mouseMoved(MouseEvent e) {
        }

        public void mouseDragged(MouseEvent e) {
            System.out.println("Dragged");
            isDragMode = true;
            dragPoint.x = e.getX();
            dragPoint.y = e.getY();

            switch (shapeString) {
                case "Line":
                    shape.setDragPoint(dragPoint.x, dragPoint.y);  //here i set the drag points to the already created line at step 1 
                    break;
                case "FreeHand":
                    shape = new FreeShape();
                    break;
            }

            repaint();


        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);

            System.out.println("In Paint");
            if (drawingImage == null) {
                drawingImage = createImage(getSize().width, getSize().height);
                drawGraphics = drawingImage.getGraphics();
                System.out.println("set up image");
                drawGraphics.setColor(Color.black);
                drawGraphics.fillRect(0, 0, getSize().width, getSize().height);
                drawGraphics.setColor(Color.orange);
                drawGraphics.drawRect(0, 0, getSize().width - 1, getSize().height - 1);
                drawGraphics.drawRect(1, 1, getSize().width - 3, getSize().height - 3);
                drawGraphics.dispose();
            }

            g.drawImage(drawingImage, 0, 0, this);

            for (Shape shape : shapes) {
                shape.draw(g);
            }


            if (shape != null) {
                shape.drawWhileDragging(g); // i call this method to draw while mouse is dragging
            }

        }
    }

    abstract class Shape {

        Color shapeColor;
        boolean filled;

        abstract void draw(Graphics g);

        void drawWhileDragging(Graphics g) {
        }

        void setDragPoint(int x, int y) {
        }
    }

    class Line extends Shape {

        private Point startPoint;
        private Point currentPoint;

        public Point getStartPoint() {
            return startPoint;
        }

        public Point getCurrentPoint() {
            return currentPoint;
        }

        public void setStartPoint(Point point) {
            this.startPoint = point;
        }

        public void setCurrentPoint(Point point) {
            this.currentPoint = point;
        }

        void drawWhileDragging(Graphics g) {
            if (currentPoint != null) {
                g.drawLine(startPoint.x, startPoint.y, currentPoint.x, currentPoint.y);
            }
        }

        public void draw(Graphics g) {
            if (currentPoint != null) {
                g.drawLine(startPoint.x, startPoint.y, currentPoint.x, currentPoint.y);
            }
        }

        Line() {
            startPoint = new Point(0, 0);
//            currentPoint = new Point(0, 0);
        }

        Line(int x1, int y1) {
            this();
            this.startPoint.x = x1;
            this.startPoint.y = y1;
        }

        void setDragPoint(int x, int y) {
            currentPoint = new Point(x, y);
//            this.currentPoint.x = x;
//            this.currentPoint.y = y;
            System.out.println("Current-X:" + currentPoint.x + " currentPoint-Y" + currentPoint.y);
            System.out.println("start-X:" + startPoint.x + " startPoint-Y" + startPoint.y);
        }
    }

    class FreeShape extends Shape {

        private ArrayList<Point> dragPoints = new ArrayList<Point>();

        public ArrayList<Point> getDragPoints() {
            return dragPoints;
        }

        public void setDragPoints(Point point) {
            dragPoints.add(point);
        }

        public void draw(Graphics g) {
        }

        public FreeShape() {
        }
    }

    class Rectangle extends Shape {

        public void draw(Graphics g) {
        }
    }

    class Oval extends Shape {

        public void draw(Graphics g) {
        }
    }
}

票数 0

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/14078882

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