定时JavaFX Canvas应用程序
c0d*_*der 3 graphics performance swing javafx
为了练习JavaFX,我构建了一个绘制Sierpinski Triangles的简单应用程序.
import javafx.application.Application;
import javafx.application.Platform;
import javafx.concurrent.Task;
import javafx.geometry.Insets;
import javafx.geometry.Point2D;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
public class SierpinskiTriangles extends Application {
private final int PADDING = 5;
private static int numberOfLevels;
public static void launch(String... args){
numberOfLevels = 8;
if((args != null) && (args.length > 0)) {
int num = -1;
try {
num = Integer.parseInt(args[0]);
} catch (NumberFormatException ex) {
ex.printStackTrace();
return;
}
numberOfLevels = (num > 0) ? num : numberOfLevels;
}
Application.launch(args);
}
@Override
public void start(Stage stage) {
stage.setOnCloseRequest((ae) -> {
Platform.exit();
System.exit(0);
});
stage.setTitle("Sierpinski Triangles (fx)");
BorderPane mainPane = new BorderPane();
mainPane.setPadding(new Insets(PADDING));
Pane triPanel = new Triangles();
BorderPane.setAlignment(triPanel, Pos.CENTER);
mainPane.setCenter(triPanel);
Scene scene = new Scene(mainPane);
stage.setScene(scene);
stage.centerOnScreen();
stage.setResizable(false);
stage.show();
}
class Triangles extends AnchorPane{
private static final int PANEL_WIDTH =600, PANEL_HEIGHT = 600;
private static final int TRI_WIDTH= 500, TRI_HEIGHT= 500;
private static final int SIDE_GAP = (PANEL_WIDTH - TRI_WIDTH)/2;
private static final int TOP_GAP = (PANEL_HEIGHT - TRI_HEIGHT)/2;
private int countTriangles;
private long startTime;
private Point2D top, left, right;
private Canvas canvas;
private GraphicsContext gc;
Triangles(){
setPrefSize(PANEL_WIDTH, PANEL_HEIGHT);
canvas = getCanvas();
gc = canvas.getGraphicsContext2D();
getChildren().add(canvas);
draw(numberOfLevels);
}
void draw(int numberLevels) {
Platform.runLater(new Runnable() {
@Override
public void run() {
clearCanvas();
setStartPoints();
startTime = System.currentTimeMillis();
countTriangles = 0;
RunTask task = new RunTask(numberLevels, top, left, right);
Thread thread = new Thread(task);
thread.setDaemon(true);
thread.start();
}
});
}
private void drawTriangle( int levels, Point2D top, Point2D left, Point2D right) {
if(levels < 0) {//add stop criteria
return ;
}
gc.strokePolygon( //implementing with strokeLine did not make much difference
new double[]{
top.getX(),left.getX(),right.getX()
},
new double[]{
top.getY(),left.getY(), right.getY()
},3
);
countTriangles++;
//Get the midpoint on each edge in the triangle
Point2D p12 = midpoint(top, left);
Point2D p23 = midpoint(left, right);
Point2D p31 = midpoint(right, top);
// recurse on 3 triangular areas
drawTriangle(levels - 1, top, p12, p31);
drawTriangle(levels - 1, p12, left, p23);
drawTriangle(levels - 1, p31, p23, right);
}
private void setStartPoints() {
top = new Point2D(getPrefWidth()/2, TOP_GAP);
left = new Point2D(SIDE_GAP, TOP_GAP + TRI_HEIGHT);
right = new Point2D(SIDE_GAP + TRI_WIDTH, TOP_GAP + TRI_WIDTH);
}
private Point2D midpoint(Point2D p1, Point2D p2) {
return new Point2D((p1.getX() + p2.getX()) /
2, (p1.getY() + p2.getY()) / 2);
}
private void updateGraphics(boolean success){
if(success) {
gc.fillText("Number of triangles: "+ countTriangles,5,15);
gc.fillText("Time : "+ (System.currentTimeMillis()- startTime)+ " mili seconds", 5,35);
gc.fillText("Levels: "+ numberOfLevels,5,55);
}
System.out.println("Completed after: "+
(System.currentTimeMillis()- startTime)+ " mili seconds"
+" Triangles: " + countTriangles +" Failed: "+ !success );
}
private Canvas getCanvas() {
Canvas canvas = new Canvas();
canvas.widthProperty().bind(widthProperty());
canvas.heightProperty().bind(heightProperty());
canvas.getGraphicsContext2D().setStroke(Color.RED);
canvas.getGraphicsContext2D().setLineWidth(0.3f);
return canvas;
}
private void clearCanvas() {
gc.clearRect(0, 0, canvas.getWidth(), canvas.getHeight());
}
class RunTask extends Task<Void>{
private int levels;
private Point2D top, left;
private Point2D right;
RunTask(int levels, Point2D top, Point2D left, Point2D right){
this.levels = levels;
this.top = top;
this.left = left;
this.right = right;
startTime = System.currentTimeMillis();
countTriangles = 0;
}
@Override public Void call() {
drawTriangle(levels,top, left, right);
return null;
}
@Override
protected void succeeded() {
updateGraphics(true);
super.succeeded();
}
@Override
protected void failed() {
updateGraphics(false);
}
}
}
public static void main(String[] args) {
launch("13");
}
}
输出如预期:
我遇到的问题:
一个.在很久之前(在我的机器上为8秒)updateGraphics()显示的时间打印输出完成了三角形的绘制,因此它不会测量完整的过程.我该如何改进？
湾 在我的机器上,需要30-35秒才能完全拉出面板.类似的挥杆应用需要4秒钟.这可能表明我的javafx实现存在根本性的错误.
您在后台Task调用drawTriangle()以更新a Canvas.关联GraphicsContext要求"一旦Canvas节点附加到场景,就必须在JavaFX应用程序线程上修改它".您的深度递归调用会阻止JavaFX应用程序线程,从而阻止及时更新屏幕.相比之下,您平台的实施System.out.println()可能会使其及时报告.甚至根本没有看到时间差异Task.
令人高兴的是Canvas,"如果它没有附加到任何场景,那么它可以被任何线程修改,只要它一次只能从一个线程使用." 可以在返回部分结果的任务中建议一种方法.创建一个在后台Task<Image>更新分离的名义Canvas.每隔一段时间,或许在递归的每一层,复制的Canvas,并通过发布的快照updateValue().封闭Pane可以监听任务的value属性并更新封闭的Canvasvia drawImage()而不阻塞JavaFX Application Thread.
遗憾的是,快照" IllegalStateException如果在JavaFX应用程序线程以外的线程上调用此方法,则抛出".
在下面显示的替代方案中,在循环的每次迭代中CanvasTask扩展Task<Canvas>并发布一个新Canvas的.封闭CanvasTaskTest侦听value属性并在Canvas每次新的到达时替换先前的属性.下面的示例显示了一系列深度增加的分形树和组成每个分形树所需的时间.请注意,在a中GraphicsContext,"每次调用都会将必要的参数推送到缓冲区,然后Canvas在脉冲结束时通过渲染线程将它们渲染到节点的图像上." 这允许JavaFX利用平台的渲染管道,但是它可能会为大量笔划施加额外的开销.在实践中,成千上万的笔画在不知不觉中缓慢渲染,而数百万个重叠笔画可能是多余的.
import javafx.application.Application;
import javafx.beans.value.ObservableValue;
import javafx.concurrent.Task;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
/**
* @see https://stackoverflow.com/a/44056730/230513
*/
public class CanvasTaskTest extends Application {
private static final int W = 800;
private static final int H = 600;
@Override
public void start(Stage stage) {
stage.setTitle("CanvasTaskTest");
StackPane root = new StackPane();
Canvas canvas = new Canvas(W, H);
root.getChildren().add(canvas);
Scene scene = new Scene(root);
stage.setScene(scene);
stage.show();
CanvasTask task = new CanvasTask();
task.valueProperty().addListener((ObservableValue<? extends Canvas> observable, Canvas oldValue, Canvas newValue) -> {
root.getChildren().remove(oldValue);
root.getChildren().add(newValue);
});
Thread thread = new Thread(task);
thread.setDaemon(true);
thread.start();
}
private static class CanvasTask extends Task<Canvas> {
private int strokeCount;
@Override
protected Canvas call() throws Exception {
Canvas canvas = null;
for (int i = 1; i < 15; i++) {
canvas = new Canvas(W, H);
GraphicsContext gc = canvas.getGraphicsContext2D();
strokeCount = 0;
long start = System.nanoTime();
drawTree(gc, W / 2, H - 50, -Math.PI / 2, i);
double dt = (System.nanoTime() - start) / 1_000d;
gc.fillText("Depth: " + i
+ "; Strokes: " + strokeCount
+ "; Time : " + String.format("%1$07.1f", dt) + " µs", 8, H - 8);
Thread.sleep(200); // simulate rendering latency
updateValue(canvas);
}
return canvas;
}
private void drawTree(GraphicsContext gc, int x1, int y1, double angle, int depth) {
if (depth == 0) {
return;
}
int x2 = x1 + (int) (Math.cos(angle) * depth * 5);
int y2 = y1 + (int) (Math.sin(angle) * depth * 5);
gc.strokeLine(x1, y1, x2, y2);
strokeCount++;
drawTree(gc, x2, y2, angle - Math.PI / 8, depth - 1);
drawTree(gc, x2, y2, angle + Math.PI / 8, depth - 1);
}
}
public static void main(String[] args) {
launch(args);
}
}