Question

下面的代码会生成一个JavaFX Canvas，可以使用鼠标指针绘制但跳过某些点，即如果尝试绘制一条连续线，则留下间隙。随着指针速度的增加，间隙加剧。

导致此行为的原因是什么以及如何实现良好连接的线？ （注意，我正在寻找一个明确切换指针经过的每个像素的答案黑色，而不是平滑或连接点等操作。）

public class DrawingSample extends Application {
    public void start(Stage stage) {
        FlowPane flowPane = new FlowPane();
        Canvas canvas = new Canvas(300, 300);
        flowPane.getChildren().add(canvas);
        GraphicsContext graphicsContext = canvas.getGraphicsContext2D();

        graphicsContext.setFill(Color.WHITE);
        graphicsContext.fillRect(0, 0, 300, 300);

        canvas.setOnMouseDragged((event) -> {
            graphicsContext.setFill(Color.BLACK);
            graphicsContext.fillRect(event.getX(), event.getY(), 1, 1);
        });

        stage.setScene(new Scene(flowPane));
        stage.show();
    }

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

下图显示了在我们下降时以增加的速度从左到右绘制的三条线。

Answer 1

此代码来自here。

import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

/**
 * @web http://java-buddy.blogspot.com/
 */
public class JavaFX_DrawOnCanvas extends Application {

    @Override
    public void start(Stage primaryStage) {

        Canvas canvas = new Canvas(400, 400);
        final GraphicsContext graphicsContext = canvas.getGraphicsContext2D();
        initDraw(graphicsContext);

        canvas.addEventHandler(MouseEvent.MOUSE_PRESSED, 
                new EventHandler<MouseEvent>(){

            @Override
            public void handle(MouseEvent event) {
                graphicsContext.beginPath();
                graphicsContext.moveTo(event.getX(), event.getY());
                graphicsContext.stroke();
            }
        });

        canvas.addEventHandler(MouseEvent.MOUSE_DRAGGED, 
                new EventHandler<MouseEvent>(){

            @Override
            public void handle(MouseEvent event) {
                graphicsContext.lineTo(event.getX(), event.getY());
                graphicsContext.stroke();
            }
        });

        canvas.addEventHandler(MouseEvent.MOUSE_RELEASED, 
                new EventHandler<MouseEvent>(){

            @Override
            public void handle(MouseEvent event) {

            }
        });

        StackPane root = new StackPane();
        root.getChildren().add(canvas);
        Scene scene = new Scene(root, 400, 400);
        primaryStage.setTitle("java-buddy.blogspot.com");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

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

    private void initDraw(GraphicsContext gc){
        double canvasWidth = gc.getCanvas().getWidth();
        double canvasHeight = gc.getCanvas().getHeight();

        gc.setFill(Color.LIGHTGRAY);
        gc.setStroke(Color.BLACK);
        gc.setLineWidth(5);

        gc.fill();
        gc.strokeRect(
                0,              //x of the upper left corner
                0,              //y of the upper left corner
                canvasWidth,    //width of the rectangle
                canvasHeight);  //height of the rectangle

        gc.setFill(Color.RED);
        gc.setStroke(Color.BLUE);
        gc.setLineWidth(1);

    }

}

Answer 2

对于上一条消息感到抱歉，应该在新帖子中提出问题，对吗？

这是一个更好的解决方案，而不是像上面的涂鸦一样创造奇怪的线条。

canvas.addEventHandler(MouseEvent.MOUSE_PRESSED, 
        new EventHandler<MouseEvent>(){
    @Override
    public void handle(MouseEvent event) {
        graphicsContext.beginPath();
        graphicsContext.moveTo(event.getX(), event.getY());
        graphicsContext.stroke();

    }
});

canvas.addEventHandler(MouseEvent.MOUSE_DRAGGED, 
        new EventHandler<MouseEvent>(){
    @Override
    public void handle(MouseEvent event) {
        graphicsContext.lineTo(event.getX(), event.getY());
        graphicsContext.stroke();
        graphicsContext.closePath();
        graphicsContext.beginPath();
        graphicsContext.moveTo(event.getX(), event.getY());
    }
});

canvas.addEventHandler(MouseEvent.MOUSE_RELEASED, 
        new EventHandler<MouseEvent>(){
    @Override
    public void handle(MouseEvent event) {
        graphicsContext.lineTo(event.getX(), event.getY());
        graphicsContext.stroke();
        graphicsContext.closePath();
    }
});

如何在JavaFX画布上用鼠标绘制连续线？

2 个答案: