JavaFX - 旋转后绘制箭头中的额外水平空间

Question

我有这部分代码:

Group g = new Group();

double xMid = (end.getCenterX() - start.getCenterX())/2;
double yMid = (end.getCenterY() - start.getCenterY())/2;
Line a = new Line(xMid, yMid-4, xMid, yMid+4);
Line b = new Line(xMid, yMid-4, xMid-10, yMid);
Line c = new Line(xMid, yMid+4, xMid-10, yMid);

g.getChildren().add(a);
g.getChildren().add(b);
g.getChildren().add(c);

g.setRotate(getAngle(start, end));
g.setTranslateX(start.getCenterX());
g.setTranslateY(start.getCenterY());

上面的代码负责在一条线的中间绘制一个箭头，从start到end(这些是Circle s 作为起点和终点)。箭头必须朝正确的方向旋转。以下是带有此类箭头的多行的输出:

如您所见，如果角度接近 ±90°，则会向左移动。

我read那:

[...] if transforms and effects are set directly on children of this Group, those will be included in this Group's layout bounds.

但这并没有真正帮助我解决这个问题。您有任何解决此问题的想法吗？

Answer 1

首先，构成三角形的 3 条线最容易使用多边形。

要修复根据布局边界选择的枢轴点，您可以使用 Rotate 转换和 Translate 转换作为 transform或者简单地自行计算两个矩阵的串联并使用仿射:

private static final double[] POLYGON_POINTS = {
    -5, -4,
    -5, 4,
    5, 0
};

private static void makeArrow(Pane parent, Circle start, Circle end, double t) {
    Polygon arrow = new Polygon(POLYGON_POINTS);
    arrow.setFill(null);
    arrow.setStroke(Color.BLACK);
    double dx = end.getCenterX() - start.getCenterX();
    double dy = end.getCenterY() - start.getCenterY();

    double d = Math.hypot(dx, dy);

    double sin = dy / d;
    double cos = dx / d;

    // matrix:
    //  [  cos     -sin     0    t * dx + start.getCenterX() ]        
    //  [  sin      cos     0    t * dy + start.getCenterY() ]        
    //  [   0        0      1                   0            ]        
    //  [   0        0      0                   1            ]
    Affine affine = new Affine(cos, -sin, t * dx + start.getCenterX(), sin, cos, t * dy + start.getCenterY());

    arrow.getTransforms().add(affine);
    parent.getChildren().add(arrow);
}

@Override
public void start(Stage primaryStage) {
    Circle end = new Circle(200, 20, 5);
    Circle start = new Circle(20, 200, 5);
    Line line = new Line(start.getCenterX(), start.getCenterY(), end.getCenterX(), end.getCenterY());

    Pane root = new Pane(line, start, end);

    makeArrow(root, start, end, 0.5);

    Scene scene = new Scene(root, 400, 400);

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