JavaFX 未呈现数组中较早的项目，无法找到问题，认为线程可能是问题所在

Question

我编写了一个线条绘制算法，该算法在计算每个点时可以正常工作，但是当它被渲染时，程序跳过了近 20 个点，无法找到问题。

我试图弄乱算法，特别是将点添加到计算行的位置列表的 for 循环，因为我在其他版本的代码中遇到了问题。我只是一辈子都找不到代码的问题，我对 Java 很陌生，你可能会从下面的代码中看出。它说不要发布整个文件，但我无法确定哪里出了问题。对于下面的代码混乱，我感到非常抱歉，我只是在这一点上我不知道出了什么问题。

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);
}
}

问题是计算线函数返回正确的点，只是没有正确呈现它们。

Answer 1

我建议你使用Timeline而不是Thread。可以使用Thread，但Timeline是为这种情况而设计的。

画线法：

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();
}

完整代码：

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);
}
}