鼠标拖动时绘制线条的问题

时间：2012-12-29 05:12:02

标签： java graphics applet awt java-2d

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

enter image description here

我有使用一个点构建的类行（起始点） 并且它有一个名为setDragPoint的方法，它采用鼠标拖动点来绘制线条，同时拖动drawingImage在拖动模式下绘制时会产生太多的闪烁。为什么会这样？ 

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) {
   }
 }

2 个答案:

答案 0 :(得分：1)

我最近写了一个类似的应用程序。这是截图。如您所见，它尚未完全开发。enter image description here

现在，我也面临着与你现在面临的类似问题。你要做的是。

  • Double Buffer所有绘画操作
  • 请勿通过调用重绘来清除屏幕。 Repaint实际上首先使用背景颜色填充屏幕＆amp;那就是你看到的闪烁。

您可以在Image中制作当前屏幕画布的副本。每次绘图操作后都会更新Image。因此，不要通过调用repaint来清除屏幕，而是在画布上绘制Image。这就像双重缓冲。

在您的代码中，每次拖动鼠标时都会调用repaint。这是闪烁的原因。

<强>更新

我在新更新的代码中找到了三个主要问题

  • 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。
  • 在同一方法中，您传递drawingImage的图形上下文（即引用）。因此，该线实际上是在屏幕外图像上绘制的，而不是在屏幕上绘制的。
  • 在mouseDragged方法中，您在每次拖动后调用重绘。因此，实际上没有画任何东西

我已在我的机器上运行您的代码并进行了必要的更改。我只发布更改的方法以保持简短。

以下是更新的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
    }

以下是更新的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);
    }

好吧，我把颜色设置为橙色。您需要做的是根据Choice菜单设置颜色。

您也可以实现类似的类比来绘制其他形状。

答案 1 :(得分：0)

您遇到的问题归结为您“尝试”执行双缓冲的方式。而不是在更新线位置时清除后备缓冲区，您可以简单地连续绘制它 - 有点像在黑板上绘图....

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实际执行的操作的一部分，但您从不致电super.paint

很少需要覆盖顶级容器，也很少需要覆盖顶级容器的paint方法。除了其他一切，没有双重缓冲。

相反，请使用类似JPanel的内容。

我已更新您的示例，不包括颜色。颜色实际上应该由形状保持并在涂漆时应用。

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) {
        }
    }
}
相关问题
最新问题