JavaFX 不呈现数组中较早的项目，无法找到问题，相信线程可能是问题所在

Question

我写了一个画线算法，在计算每个点时都能正常运行，但是当它被渲染时，程序跳过了将近 20 个点，无法找到问题所在。

我试图弄乱算法，特别是将点添加到位置列表的 for 循环，因为我在其他版本的代码中遇到过问题。我一辈子都找不到代码的问题，我是 Java 的新手，您可能会从下面的混乱代码中看出这一点。它说不要 post 整个文件，但我无法查明哪里出错了。我对下面的代码混乱感到非常抱歉，我只是在那个时候我不知道哪里出了问题。

package sample;

import com.sun.jdi.ArrayReference;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.Group;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.paint.Color;
import javafx.scene.Scene;
import javafx.stage.Stage;

import java.util.ArrayList;

class PositionCounter {
    public int position;

    public void setPosition(int newPos){
        position = newPos;
    }
}

public class Main extends Application {

//    public void drawRectangle(int x1, int y1, int x2, int y2, Stage primStage, GraphicsContext gc){
//        drawLine(x1, y2, x2, y2 , primStage, gc);
//        drawLine(x1, y1, x2, y2, primStage, gc);
//        drawLine(x1, y1, x1 , y2, primStage, gc);
//        drawLine(x2, y1, x2 , y2, primStage, gc);
//        drawLine(x1, y1, x2, y1 , primStage, gc);
//
//    }
//

    public void fillPosition(ArrayList<Integer[]> points, GraphicsContext gc, int positionInArray ){
        gc.fillRect(points.get(positionInArray)[0], points.get(positionInArray)[1], squareWidth / 2, squareWidth / 2);
        //System.out.println("(" + points.get(positionInArray)[0] + ", " + points.get(positionInArray)[1]);
    }

    public void drawLine(int x1, int y1, int x2, int y2, Stage primStage, GraphicsContext gc){

        ArrayList<Integer[]> points = calculateLine(x1, y1, x2, y2, gc);
        PositionCounter position = new PositionCounter();

        Thread thread = new Thread(new Runnable() {

            @Override
            public void run() {

                    Runnable updater = new Runnable() {

                        @Override
                        public void run() {

                            fillPosition(points, gc, position.position);

                        }
                    };

                    int dy = Math.abs(y2 - y1);
                    int dx = Math.abs(x2 - x1);
                    int m = (dy >= dx) ? dy : dx;

                    for (int i = 0; i <= points.size(); i++) {

                        position.setPosition(i);

                        try {
                            Thread.sleep(20);
                        } catch (InterruptedException ex) {
                        }

                        Platform.runLater(updater);

                    }


            }
        });

        thread.setDaemon(true);
        thread.start();

    }

    @Override
    public void start(Stage primaryStage) throws Exception{

        //STUFF
        Group root = new Group();
        Scene scene = new Scene(root, 400, 400);
        scene.setFill(Color.GOLD);

        Canvas canvas = new Canvas(400, 400);
        GraphicsContext gc = canvas.getGraphicsContext2D();

        root.getChildren().add(canvas);
        //////////

        gc.fillRect(0, 200, 400, 1);
        gc.fillRect(0, 100, 400, 1);
        gc.fillRect(0, 300, 400, 1);
        gc.fillRect(200, 0, 1, 400);
        gc.fillRect(100, 0, 1, 400);
        gc.fillRect(300, 0, 1, 400);


       // drawRectangle(50, 50, 350, 250, primaryStage, gc);


        //drawLine(50, 250, 350, 250 , primaryStage, gc);
        //drawLine(50, 50, 350, 250, primaryStage, gc);
        //drawLine(50, 50, 50 , 250, primaryStage, gc);
        //drawLine(350, 50, 350 , 250, primaryStage, gc);
        drawLine(50, 50, 350, 50 , primaryStage, gc);



        //////////
        primaryStage.setScene(scene);
        primaryStage.show();
        /////////
    }

    int squareWidth = 2;

    public ArrayList<Integer[]> calculateLine(int x1, int y1, int x2, int y2, GraphicsContext gc){

        ArrayList<Integer[]> points = new ArrayList<Integer[]>();

        int dy = Math.abs(y2 - y1);
        int dx = Math.abs(x2 - x1);

        int sx = (x1 < x2) ? 1 : -1;
        int sy = (y1 < y2) ? 1 : -1;

        int err = dx-dy;
        int x = x1;
        int y = y1;
        int e2 = 0;

        Integer[] pos = new Integer[2];
        pos[0] = x;
        pos[1] = y;
        points.add(pos);

        int m = (dy >= dx) ? dy  : dx ;

        for (int i = 0; i <= m; i++) {

                e2 = 2 * err;
                if (e2 > -dy) {
                    err = err - dy;
                    x = x + sx;
                    Integer[] position = new Integer[2];
                    position[0] = x;
                    position[1] = y;
                    points.add(position);
                }

                if (e2 < dx) {
                    err = err + dx;
                    y = y + sy;
                    Integer[] position = new Integer[2];
                    position[0] = x;
                    position[1] = y;
                    points.add(position);
                }

        }

        return points;
    }


    public static void main(String[] args) {
        launch(args);
    }
}

问题是计算线函数 returns 正确的点，只是没有正确渲染它们。

Answer 1

我建议您使用 Timeline instead of Thread。可以使用 Thread 来完成，但是 Timeline 是为这种情况设计的。

Draw Line Method:

public void drawLine(int x1, int y1, int x2, int y2, Stage primStage, GraphicsContext gc)
{

    ArrayList<Integer[]> points = calculateLine(x1, y1, x2, y2, gc);
    PositionCounter position = new PositionCounter();

    int dy = Math.abs(y2 - y1);
    int dx = Math.abs(x2 - x1);
    int m = (dy >= dx) ? dy : dx;

    AtomicInteger counter = new AtomicInteger();
    Timeline animationTimeline = new Timeline(new KeyFrame(Duration.millis(20), (ActionEvent t) -> {
        position.setPosition(counter.getAndIncrement());
        fillPosition(points, gc, position.position);
    }));
    animationTimeline.setCycleCount(points.size());
    animationTimeline.play();

}

Full Code:

import com.sun.jdi.ArrayReference;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.Group;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.paint.Color;
import javafx.scene.Scene;
import javafx.stage.Stage;

import java.util.ArrayList;
import java.util.concurrent.atomic.AtomicInteger;
import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.util.Duration;

class PositionCounter
{

    public int position;

    public void setPosition(int newPos)
    {
        position = newPos;
    }
}

public class JavaFXTestingGround extends Application
{

//    public void drawRectangle(int x1, int y1, int x2, int y2, Stage primStage, GraphicsContext gc){
//        drawLine(x1, y2, x2, y2 , primStage, gc);
//        drawLine(x1, y1, x2, y2, primStage, gc);
//        drawLine(x1, y1, x1 , y2, primStage, gc);
//        drawLine(x2, y1, x2 , y2, primStage, gc);
//        drawLine(x1, y1, x2, y1 , primStage, gc);
//
//    }
//
    public void fillPosition(ArrayList<Integer[]> points, GraphicsContext gc, int positionInArray)
    {
        gc.fillRect(points.get(positionInArray)[0], points.get(positionInArray)[1], squareWidth / 2, squareWidth / 2);
        //System.out.println("(" + points.get(positionInArray)[0] + ", " + points.get(positionInArray)[1]);
    }

    public void drawLine(int x1, int y1, int x2, int y2, Stage primStage, GraphicsContext gc)
    {

        ArrayList<Integer[]> points = calculateLine(x1, y1, x2, y2, gc);
        PositionCounter position = new PositionCounter();

        int dy = Math.abs(y2 - y1);
        int dx = Math.abs(x2 - x1);
        int m = (dy >= dx) ? dy : dx;

        AtomicInteger counter = new AtomicInteger();
        Timeline animationTimeline = new Timeline(new KeyFrame(Duration.millis(20), (ActionEvent t) -> {
            position.setPosition(counter.getAndIncrement());
            fillPosition(points, gc, position.position);
        }));
        animationTimeline.setCycleCount(points.size());
        animationTimeline.play();

    }

    @Override
    public void start(Stage primaryStage) throws Exception
    {

        //STUFF
        Group root = new Group();
        Scene scene = new Scene(root, 400, 400);
        scene.setFill(Color.GOLD);

        Canvas canvas = new Canvas(400, 400);
        GraphicsContext gc = canvas.getGraphicsContext2D();

        root.getChildren().add(canvas);
        //////////

        gc.fillRect(0, 200, 400, 1);
        gc.fillRect(0, 100, 400, 1);
        gc.fillRect(0, 300, 400, 1);
        gc.fillRect(200, 0, 1, 400);
        gc.fillRect(100, 0, 1, 400);
        gc.fillRect(300, 0, 1, 400);

        // drawRectangle(50, 50, 350, 250, primaryStage, gc);
        //drawLine(50, 250, 350, 250 , primaryStage, gc);
        //drawLine(50, 50, 350, 250, primaryStage, gc);
        //drawLine(50, 50, 50 , 250, primaryStage, gc);
        //drawLine(350, 50, 350 , 250, primaryStage, gc);
        drawLine(50, 50, 350, 50, primaryStage, gc);

        //////////
        primaryStage.setScene(scene);
        primaryStage.show();
        /////////
    }

    int squareWidth = 2;

    public ArrayList<Integer[]> calculateLine(int x1, int y1, int x2, int y2, GraphicsContext gc)
    {

        ArrayList<Integer[]> points = new ArrayList<Integer[]>();

        int dy = Math.abs(y2 - y1);
        int dx = Math.abs(x2 - x1);

        int sx = (x1 < x2) ? 1 : -1;
        int sy = (y1 < y2) ? 1 : -1;

        int err = dx - dy;
        int x = x1;
        int y = y1;
        int e2 = 0;

        Integer[] pos = new Integer[2];
        pos[0] = x;
        pos[1] = y;
        points.add(pos);

        int m = (dy >= dx) ? dy : dx;

        for (int i = 0; i <= m; i++) {

            e2 = 2 * err;
            if (e2 > -dy) {
                err = err - dy;
                x = x + sx;
                Integer[] position = new Integer[2];
                position[0] = x;
                position[1] = y;
                points.add(position);
            }

            if (e2 < dx) {
                err = err + dx;
                y = y + sy;
                Integer[] position = new Integer[2];
                position[0] = x;
                position[1] = y;
                points.add(position);
            }

        }

        return points;
    }

    public static void main(String[] args)
    {
        launch(args);
    }
}

JavaFX 不呈现数组中较早的项目，无法找到问题，相信线程可能是问题所在

JavaFX not rendering earlier items in an array, unable to find issue, believe threading might be the issue

java

javafx

graphics

bresenham