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
17package com.example.android.support.animation;
18
19import android.content.Context;
20import android.graphics.Canvas;
21import android.graphics.Paint;
22import android.util.AttributeSet;
23import android.view.View;
24
25/**
26 * The view that draws the spring as it reacts (i.e. expands/compresses) to the user touch.
27 */
28public class SpringView extends View {
29    final Paint mPaint = new Paint();
30    private float mLastHeight = 175;
31
32    public SpringView(Context context, AttributeSet attrs) {
33        super(context, attrs);
34        setWillNotDraw(false);
35        mPaint.setColor(context.getResources().getColor(R.color.springColor));
36        mPaint.setStrokeWidth(10);
37    }
38
39    /**
40     * Sets the other end of the spring.
41     *
42     * @param height height of the mass, which is used to derive how to draw the spring
43     */
44    public void setMassHeight(float height) {
45        mLastHeight = height;
46        invalidate();
47    }
48
49    @Override
50    public void onDraw(Canvas canvas) {
51        // Draws the spring
52        // 30px long, 15 sections
53        int num = 20;
54        float sectionLen = 150; // px
55        final float x = canvas.getWidth() / 2;
56        float y = 0;
57        float sectionHeight = mLastHeight / num;
58        float sectionWidth = (float) Math.sqrt(sectionLen * sectionLen
59                - sectionHeight * sectionHeight);
60        canvas.drawLine(x, 0, x + sectionWidth / 2, sectionHeight / 2, mPaint);
61        float lastX = x + sectionWidth / 2;
62        float lastY = sectionHeight / 2;
63        for (int i = 1; i < num; i++) {
64            canvas.drawLine(lastX, lastY, 2 * x - lastX, lastY + sectionHeight, mPaint);
65            lastX = 2 * x - lastX;
66            lastY = lastY + sectionHeight;
67        }
68        canvas.drawLine(lastX, lastY, x, mLastHeight, mPaint);
69    }
70}
71