diff options
Diffstat (limited to 'src/com/android/gallery3d/filtershow/filters/SplineMath.java')
| -rw-r--r-- | src/com/android/gallery3d/filtershow/filters/SplineMath.java | 166 |
1 files changed, 166 insertions, 0 deletions
diff --git a/src/com/android/gallery3d/filtershow/filters/SplineMath.java b/src/com/android/gallery3d/filtershow/filters/SplineMath.java new file mode 100644 index 000000000..5b12d0a61 --- /dev/null +++ b/src/com/android/gallery3d/filtershow/filters/SplineMath.java @@ -0,0 +1,166 @@ +package com.android.gallery3d.filtershow.filters; + + +public class SplineMath { + double[][] mPoints = new double[6][2]; + double[] mDerivatives; + SplineMath(int n) { + mPoints = new double[n][2]; + } + + public void setPoint(int index, double x, double y) { + mPoints[index][0] = x; + mPoints[index][1] = y; + mDerivatives = null; + } + + public float[][] calculatetCurve(int n) { + float[][] curve = new float[n][2]; + double[][] points = new double[mPoints.length][2]; + for (int i = 0; i < mPoints.length; i++) { + + points[i][0] = mPoints[i][0]; + points[i][1] = mPoints[i][1]; + + } + double[] derivatives = solveSystem(points); + float start = (float) points[0][0]; + float end = (float) (points[points.length - 1][0]); + + curve[0][0] = (float) (points[0][0]); + curve[0][1] = (float) (points[0][1]); + int last = curve.length - 1; + curve[last][0] = (float) (points[points.length - 1][0]); + curve[last][1] = (float) (points[points.length - 1][1]); + + for (int i = 0; i < curve.length; i++) { + + double[] cur = null; + double[] next = null; + double x = start + i * (end - start) / (curve.length - 1); + int pivot = 0; + for (int j = 0; j < points.length - 1; j++) { + if (x >= points[j][0] && x <= points[j + 1][0]) { + pivot = j; + } + } + cur = points[pivot]; + next = points[pivot + 1]; + if (x <= next[0]) { + double x1 = cur[0]; + double x2 = next[0]; + double y1 = cur[1]; + double y2 = next[1]; + + // Use the second derivatives to apply the cubic spline + // equation: + double delta = (x2 - x1); + double delta2 = delta * delta; + double b = (x - x1) / delta; + double a = 1 - b; + double ta = a * y1; + double tb = b * y2; + double tc = (a * a * a - a) * derivatives[pivot]; + double td = (b * b * b - b) * derivatives[pivot + 1]; + double y = ta + tb + (delta2 / 6) * (tc + td); + + curve[i][0] = (float) (x); + curve[i][1] = (float) (y); + } else { + curve[i][0] = (float) (next[0]); + curve[i][1] = (float) (next[1]); + } + } + return curve; + } + + public double getValue(double x) { + double[] cur = null; + double[] next = null; + if (mDerivatives == null) + mDerivatives = solveSystem(mPoints); + int pivot = 0; + for (int j = 0; j < mPoints.length - 1; j++) { + pivot = j; + if (x <= mPoints[j][0]) { + break; + } + } + cur = mPoints[pivot]; + next = mPoints[pivot + 1]; + double x1 = cur[0]; + double x2 = next[0]; + double y1 = cur[1]; + double y2 = next[1]; + + // Use the second derivatives to apply the cubic spline + // equation: + double delta = (x2 - x1); + double delta2 = delta * delta; + double b = (x - x1) / delta; + double a = 1 - b; + double ta = a * y1; + double tb = b * y2; + double tc = (a * a * a - a) * mDerivatives[pivot]; + double td = (b * b * b - b) * mDerivatives[pivot + 1]; + double y = ta + tb + (delta2 / 6) * (tc + td); + + return y; + + } + + double[] solveSystem(double[][] points) { + int n = points.length; + double[][] system = new double[n][3]; + double[] result = new double[n]; // d + double[] solution = new double[n]; // returned coefficients + system[0][1] = 1; + system[n - 1][1] = 1; + double d6 = 1.0 / 6.0; + double d3 = 1.0 / 3.0; + + // let's create a tridiagonal matrix representing the + // system, and apply the TDMA algorithm to solve it + // (see http://en.wikipedia.org/wiki/Tridiagonal_matrix_algorithm) + for (int i = 1; i < n - 1; i++) { + double deltaPrevX = points[i][0] - points[i - 1][0]; + double deltaX = points[i + 1][0] - points[i - 1][0]; + double deltaNextX = points[i + 1][0] - points[i][0]; + double deltaNextY = points[i + 1][1] - points[i][1]; + double deltaPrevY = points[i][1] - points[i - 1][1]; + system[i][0] = d6 * deltaPrevX; // a_i + system[i][1] = d3 * deltaX; // b_i + system[i][2] = d6 * deltaNextX; // c_i + result[i] = (deltaNextY / deltaNextX) - (deltaPrevY / deltaPrevX); // d_i + } + + // Forward sweep + for (int i = 1; i < n; i++) { + // m = a_i/b_i-1 + double m = system[i][0] / system[i - 1][1]; + // b_i = b_i - m(c_i-1) + system[i][1] = system[i][1] - m * system[i - 1][2]; + // d_i = d_i - m(d_i-1) + result[i] = result[i] - m * result[i - 1]; + } + + // Back substitution + solution[n - 1] = result[n - 1] / system[n - 1][1]; + for (int i = n - 2; i >= 0; --i) { + solution[i] = (result[i] - system[i][2] * solution[i + 1]) / system[i][1]; + } + return solution; + } + + public static void main(String[] args) { + SplineMath s = new SplineMath(10); + for (int i = 0; i < 10; i++) { + s.setPoint(i, i, i); + } + float[][] curve = s.calculatetCurve(40); + + for (int j = 0; j < curve.length; j++) { + System.out.println(curve[j][0] + "," + curve[j][1]); + } + } +} |