Java Graphics 2D UI箭头方向

Question

我想使用Graphic fillpolygon绘制箭头。但是我的箭头处于反面。任何的想法？

int xpoints[] = { 20, 30, 30, 35, 25, 15, 20 };
int ypoints[] = { 10, 10, 30, 30, 45, 30, 30 };
int npoints = 7;
g2D.fillPolygon(xpoints, ypoints, npoints);

Answer 1

Java 2D坐标在用户空间中给出，其中左上角是（0,0）。见Coordinates：

  

当使用从用户空间到设备空间的默认转换时，用户空间的原点是组件绘图区域的左上角。 x坐标向右增加，y坐标向下增加，如下图所示。窗口的左上角是0,0。所有坐标都使用整数指定，这通常就足够了。但是，某些情况需要浮点或甚至双精度，这也是支持的。

我找到Java 2D - Affine Transform to invert y-axis，所以我修改了它以将原点转换为左下角，并将其与箭头结合：

protected  void paintComponent(Graphics g) {
    super.paintComponent(g);

    Graphics2D g2 = (Graphics2D) g;

    Insets insets = getInsets();
    // int w = getWidth() - insets.left - insets.right;
    int h = getHeight() - insets.top - insets.bottom;

    AffineTransform oldAT = g2.getTransform();
    try {
        //Move the origin to bottom-left, flip y axis
        g2.scale(1.0, -1.0);
        g2.translate(0, -h - insets.top);

        int xpoints[] = { 20, 30, 30, 35, 25, 15, 20 };
        int ypoints[] = { 10, 10, 30, 30, 45, 30, 30 };
        int npoints = 7;
        g2.fillPolygon(xpoints, ypoints, npoints);
    }
    finally {
      //restore
      g2.setTransform(oldAT);
    }
}

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