所以，我知道如何做自由手线，但我想要一条直线，所以当用户点击一个点到用户释放鼠标的点时，当用户拖动鼠标时，终点应该用鼠标移动即类似于在绘画应用程序中绘制直线。
目前正在使用此代码：
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);
}
}
如何修改鼠标拖动事件以绘制直线而不是自由手？
答案 0 :(得分：2)
一般来说，我同意评论 - 使用Line更容易做到这一点。 但是使用canvas可以达到同样的目的：
public class JavaFX_DrawOnCanvas extends Application {
private Pair<Double, Double> initialTouch;
private Canvas layer = new Canvas();
@Override
public void start(Stage primaryStage) {
StackPane root = new StackPane();
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) {
Canvas newLayer = new Canvas(400, 400);
GraphicsContext context = newLayer.getGraphicsContext2D();
initDraw(context);
layer = newLayer;
root.getChildren().add(0, newLayer);
initialTouch = new Pair<>(event.getSceneX(), event.getSceneY());
}
});
canvas.addEventHandler(MouseEvent.MOUSE_DRAGGED,
new EventHandler<MouseEvent>(){
@Override
public void handle(MouseEvent event) {
GraphicsContext context = layer.getGraphicsContext2D();
context.clearRect(0, 0, layer.getWidth(), layer.getHeight());
context.strokeLine(initialTouch.getKey(), initialTouch.getValue(), event.getSceneX(), event.getSceneY());
}
});
root.getChildren().add(canvas);
Scene scene = new Scene(root, 400, 400);
primaryStage.setScene(scene);
primaryStage.show();
}
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);
}
public static void main(String[] args) {
launch(args);
}
}
因此，基本上您需要为每个新行创建单独的图层并使用strokeLine method。请注意，必须在0索引处将新添加的层添加到根子项，因为否则主画布的事件处理程序将停止进程事件。
答案 1 :(得分：0)
每次拖动鼠标时都必须添加新行。你可以尝试这个演示，
public class JavaFX_DrawOnCanvas extends Application {
private double from_x = 0;
private double from_y = 0;
private double to_x = 0;
private double to_y = 0;
private int line_no = 1;
@Override
public void start(Stage primaryStage) {
StackPane root = new StackPane();
Canvas canvas = new Canvas(400, 400);
final GraphicsContext graphicsContext = canvas.getGraphicsContext2D();
this.initDraw(graphicsContext);
canvas.setOnMousePressed((event) -> this.setFromPos(event));
canvas.setOnMouseDragged((event) -> {
root.getChildren().remove(0);
final Canvas temp_canvas = new Canvas(400, 400);
final GraphicsContext gc = temp_canvas.getGraphicsContext2D();
this.setToPos(event);
this.drawLine(gc);
root.getChildren().add(0,temp_canvas);
});
canvas.setOnMouseReleased((event) -> {
final Canvas new_line = new Canvas(400, 400);
final GraphicsContext gc = new_line.getGraphicsContext2D();
this.setToPos(event);
this.drawLine(gc);
//final new stright line
root.getChildren().add(line_no++,new_line);
});
root.getChildren().addAll( new Canvas(), 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 drawLine(GraphicsContext gc) {
gc.setFill(Color.RED);
gc.setStroke(Color.BLUE);
gc.setLineWidth(1);
gc.strokeLine(from_x, from_y, to_x, to_y);
}
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
}
private void setFromPos(MouseEvent event) {
this.from_x = event.getSceneX();
this.from_y = event.getSceneY();
}
private void setToPos(MouseEvent event) {
this.to_x = event.getSceneX();
this.to_y = event.getSceneY();
}
}