[英]Why do i get differing line lengths when rotating points with matrices in Android and how do i fix it?
我正在为L-Systems创建一个android应用程序,并使用旋转矩阵旋转点后得到了不同的线长,这导致了不规则的分形。
例:
如您所见,旋转线的长度变化,旋转120°的线比旋转240°的线短。
。
为了旋转点,我在这里根据此答案使用这些Android Matrix Operations 。 我正在围绕线的起点旋转线的终点。
码:
Matrix transform;
public Point rotate(Point angleP, Point p, float degrees) {
// This rotates around the previous Point by degrees
transform.setRotate(degrees, angleP.x, angleP.y);
// Create new float[] to hold the rotated coordinates
float[] pts = new float[2];
// Initialize the array with our Coordinate
pts[0] = p.x;
pts[1] = p.y;
// Use the Matrix to map the points
transform.mapPoints(pts);
// NOTE: pts will be changed by transform.mapPoints call
// after the call, pts will hold the new cooridnates
// Now, create a new Point from our new coordinates
Point newPoint = new Point((int)pts[0], (int)pts[1]);
// Return the new point
return newPoint;
}
根据上面的代码,前五个点对应的点+旋转:
- forward by 30pt, angle is: 0.0°, rotate/translate Point(384, 433) -> Point(384, 433)
- changed rotation by120.0 from 0.0->120.0
- forward by 30pt, angle is: 120.0°, rotate/translate Point(384, 403) -> Point(409, 447)
- changed rotation by-120.0 from 120.0->0.0
- forward by 30pt, angle is: 0.0°, rotate/translate Point(409, 417) -> Point(409, 417)
- changed rotation by-120.0 from 0.0->-120.0
- forward by 30pt, angle is: -120.0°, rotate/translate Point(409, 387) -> Point(383, 431)
- changed rotation by120.0 from -120.0->0.0
- forward by 30pt, angle is: 0.0°, rotate/translate Point(383, 401) -> Point(383, 401)
前五行的调试日志(上->右->上->左->上,与图片相同):
line# line-start line-end line-length
line0 from 384/463 to 384/433, length: 30.0
line1 from 384/433 to 409/447, length: 28.653097563788805
line2 from 409/447 to 409/417, length: 30.0
line3 from 409/417 to 383/431, length: 29.5296461204668
line4 from 383/431 to 383/401, length: 30.0
我遇到的问题是我希望/需要生成的线长度相等,但是由于某些原因,旋转120°的线小于旋转-120°的线。
我的猜测是,不同的行长是舍入错误的结果,但是我不知道如何开始解决这个问题。
任何帮助或指针,将不胜感激。
我不确定我是否能完全解决它,但是看来Android中有两个不同的坐标点类:
整数坐标点和浮点坐标点。 猜猜我用了哪一个? 是的,整数1。对我的点使用浮点坐标消除了舍入误差的不准确性。
。
解决方案 :使用float PointF代替int Point。
https://developer.android.com/reference/android/graphics/Point.html
https://developer.android.com/reference/android/graphics/PointF.html
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