1 /*
2  * Copyright (C) 2013 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package com.android.inputmethod.keyboard.internal;
18 
19 import com.android.inputmethod.annotations.UsedForTesting;
20 import com.android.inputmethod.keyboard.internal.MatrixUtils.MatrixOperationFailedException;
21 
22 import android.util.Log;
23 
24 import java.util.Arrays;
25 
26 /**
27  * Utilities to smooth coordinates. Currently, we calculate 3d least squares formula by using
28  * Lagrangian smoothing
29  */
30 @UsedForTesting
31 public class SmoothingUtils {
32     private static final String TAG = SmoothingUtils.class.getSimpleName();
33     private static final boolean DEBUG = false;
34 
SmoothingUtils()35     private SmoothingUtils() {
36         // not allowed to instantiate publicly
37     }
38 
39     /**
40      * Find a most likely 3d least squares formula for specified coordinates.
41      * "retval" should be a 1x4 size matrix.
42      */
43     @UsedForTesting
get3DParameters(final float[] xs, final float[] ys, final float[][] retval)44     public static void get3DParameters(final float[] xs, final float[] ys,
45             final float[][] retval) throws MatrixOperationFailedException {
46         final int COEFF_COUNT = 4; // Coefficient count for 3d smoothing
47         if (retval.length != COEFF_COUNT || retval[0].length != 1) {
48             Log.d(TAG, "--- invalid length of 3d retval " + retval.length + ", "
49                     + retval[0].length);
50             return;
51         }
52         final int N = xs.length;
53         // TODO: Never isntantiate the matrix
54         final float[][] m0 = new float[COEFF_COUNT][COEFF_COUNT];
55         final float[][] m0Inv = new float[COEFF_COUNT][COEFF_COUNT];
56         final float[][] m1 = new float[COEFF_COUNT][N];
57         final float[][] m2 = new float[N][1];
58 
59         // m0
60         for (int i = 0; i < COEFF_COUNT; ++i) {
61             Arrays.fill(m0[i], 0);
62             for (int j = 0; j < COEFF_COUNT; ++j) {
63                 final int pow = i + j;
64                 for (int k = 0; k < N; ++k) {
65                     m0[i][j] += (float) Math.pow(xs[k], pow);
66                 }
67             }
68         }
69         // m0Inv
70         MatrixUtils.inverse(m0, m0Inv);
71         if (DEBUG) {
72             MatrixUtils.dump("m0-1", m0Inv);
73         }
74 
75         // m1
76         for (int i = 0; i < COEFF_COUNT; ++i) {
77             for (int j = 0; j < N; ++j) {
78                 m1[i][j] = (i == 0) ? 1.0f : m1[i - 1][j] * xs[j];
79             }
80         }
81 
82         // m2
83         for (int i = 0; i < N; ++i) {
84             m2[i][0] = ys[i];
85         }
86 
87         final float[][] m0Invxm1 = new float[COEFF_COUNT][N];
88         if (DEBUG) {
89             MatrixUtils.dump("a0", m0Inv);
90             MatrixUtils.dump("a1", m1);
91         }
92         MatrixUtils.multiply(m0Inv, m1, m0Invxm1);
93         if (DEBUG) {
94             MatrixUtils.dump("a2", m0Invxm1);
95             MatrixUtils.dump("a3", m2);
96         }
97         MatrixUtils.multiply(m0Invxm1, m2, retval);
98         if (DEBUG) {
99             MatrixUtils.dump("result", retval);
100         }
101     }
102 }
103