1 /*
2  * Copyright (C) 2017 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.example.android.support.animation;
18 
19 import android.content.Context;
20 import android.graphics.Canvas;
21 import android.graphics.Paint;
22 import android.util.AttributeSet;
23 import android.view.View;
24 
25 import org.jspecify.annotations.NonNull;
26 
27 /**
28  * The view that draws the spring as it reacts (i.e. expands/compresses) to the user touch.
29  */
30 public class SpringView extends View {
31     final Paint mPaint = new Paint();
32     private float mLastHeight = 175;
33 
SpringView(Context context, AttributeSet attrs)34     public SpringView(Context context, AttributeSet attrs) {
35         super(context, attrs);
36         setWillNotDraw(false);
37         mPaint.setColor(context.getResources().getColor(R.color.springColor));
38         mPaint.setStrokeWidth(10);
39     }
40 
41     /**
42      * Sets the other end of the spring.
43      *
44      * @param height height of the mass, which is used to derive how to draw the spring
45      */
setMassHeight(float height)46     public void setMassHeight(float height) {
47         mLastHeight = height;
48         invalidate();
49     }
50 
51     @Override
onDraw(@onNull Canvas canvas)52     public void onDraw(@NonNull Canvas canvas) {
53         // Draws the spring
54         // 30px long, 15 sections
55         int num = 20;
56         float sectionLen = 150; // px
57         final float x = canvas.getWidth() / 2;
58         float sectionHeight = mLastHeight / num;
59         float sectionWidth = (float) Math.sqrt(sectionLen * sectionLen
60                 - sectionHeight * sectionHeight);
61         canvas.drawLine(x, 0, x + sectionWidth / 2, sectionHeight / 2, mPaint);
62         float lastX = x + sectionWidth / 2;
63         float lastY = sectionHeight / 2;
64         for (int i = 1; i < num; i++) {
65             canvas.drawLine(lastX, lastY, 2 * x - lastX, lastY + sectionHeight, mPaint);
66             lastX = 2 * x - lastX;
67             lastY = lastY + sectionHeight;
68         }
69         canvas.drawLine(lastX, lastY, x, mLastHeight, mPaint);
70     }
71 }
72