圣诞节即将来临，PM给了一个需求：在A首页添加一个下雪的特效。事实上，有很多中方法可以实现。
1、用Lottie实现：让UI在AE上画一个动效，然后输出Json文件，前端直接在布局里设置就可以了。
这就又产生了和UI小姐姐的交配问题（哦不，说错了，交流问题）。UI小姐姐心里肯定是拒绝的，心里暗暗的说不定都把我按在她腿上摩擦了一千遍。不过，嘿嘿嘿~来啊，Who 怕 Who？
2、自定义View
国际惯例，先放效果图，如下：
雨雪
(gif图看起来可能有点卡顿的感觉，但是实际在真机上非常流畅，并无卡顿。)
代码依然很简单，来吧，老弟。
下雪：
SnowFlake.java
package com.ctrip.kotlin.view.snow;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Point;
/**
* 雪花的类, 移动, 移出屏幕会重新设置位置.
* <p/>
* Created by w_yong on 18/12/4.
*/
public class SnowFlake {
// 雪花的角度
private static final float ANGE_RANGE = 0.1f; // 角度范围
private static final float HALF_ANGLE_RANGE = ANGE_RANGE / 2f; // 一般的角度
private static final float HALF_PI = (float) Math.PI / 2f; // 半PI
private static final float ANGLE_SEED = 25f; // 角度随机种子
private static final float ANGLE_DIVISOR = 10000f; // 角度的分母
// 雪花的移动速度
private static final float INCREMENT_LOWER = 10f;
private static final float INCREMENT_UPPER = 20f;
// 雪花的大小
private static final float FLAKE_SIZE_LOWER = 5f;
private static final float FLAKE_SIZE_UPPER = 15f;
private final SnowRandomGenerator mRandom; // 随机控制器
private final Point mPosition; // 雪花位置
private float mAngle; // 角度
private final float mIncrement; // 雪花的速度
private final float mFlakeSize; // 雪花的大小
private final Paint mPaint; // 画笔
private SnowFlake(SnowRandomGenerator random, Point position, float angle, float increment, float flakeSize, Paint paint) {
mRandom = random;
mPosition = position;
mIncrement = increment;
mFlakeSize = flakeSize;
mPaint = paint;
mAngle = angle;
}
public static SnowFlake create(int width, int height, Paint paint) {
SnowRandomGenerator random = new SnowRandomGenerator();
int x = random.getRandom(width);
int y = random.getRandom(height);
Point position = new Point(x, y);
float angle = random.getRandom(ANGLE_SEED) / ANGLE_SEED * ANGE_RANGE + HALF_PI - HALF_ANGLE_RANGE;
float increment = random.getRandom(INCREMENT_LOWER, INCREMENT_UPPER);
float flakeSize = random.getRandom(FLAKE_SIZE_LOWER, FLAKE_SIZE_UPPER);
return new SnowFlake(random, position, angle, increment, flakeSize, paint);
}
// 绘制雪花
public void draw(Canvas canvas) {
int width = canvas.getWidth();
int height = canvas.getHeight();
move(width, height);
canvas.drawCircle(mPosition.x, mPosition.y, mFlakeSize, mPaint);
}
// 移动雪花
private void move(int width, int height) {
double x = mPosition.x + (mIncrement * Math.cos(mAngle));
double y = mPosition.y + (mIncrement * Math.sin(mAngle));
mAngle += mRandom.getRandom(-ANGLE_SEED, ANGLE_SEED) / ANGLE_DIVISOR; // 随机晃动
mPosition.set((int) x, (int) y);
// 移除屏幕, 重新开始
if (!isInside(width, height)) {
reset(width);
}
}
// 判断是否在其中
private boolean isInside(int width, int height) {
int x = mPosition.x;
int y = mPosition.y;
return x >= -mFlakeSize - 1 && x + mFlakeSize <= width && y >= -mFlakeSize - 1 && y - mFlakeSize < height;
}
// 重置雪花
private void reset(int width) {
mPosition.x = mRandom.getRandom(width);
mPosition.y = (int) (-mFlakeSize - 1); // 最上面
mAngle = mRandom.getRandom(ANGLE_SEED) / ANGLE_SEED * ANGE_RANGE + HALF_PI - HALF_ANGLE_RANGE;
}
}
SnowRandomGenerator.java
package com.ctrip.kotlin.view.snow;
import java.util.Random;
/**
* 随机生成器
* <p/>
* Created by w_yong on 18/12/4.
*/
public class SnowRandomGenerator {
private static final Random RANDOM = new Random();
// 区间随机
public float getRandom(float lower, float upper) {
float min = Math.min(lower, upper);
float max = Math.max(lower, upper);
return getRandom(max - min) + min;
}
// 上界随机
public float getRandom(float upper) {
return RANDOM.nextFloat() * upper;
}
// 上界随机
public int getRandom(int upper) {
return RANDOM.nextInt(upper);
}
}
SnowView.java
package com.ctrip.kotlin.view.snow;
import android.annotation.TargetApi;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;
/**
* 雪花视图, DELAY时间重绘, 绘制NUM_SNOWFLAKES个雪花
* <p/>
* Created by w_yong on 18/12/4.
*/
public class SnowView extends View {
private static final int NUM_SNOWFLAKES = 120; // 雪花数量
private static final int DELAY = 5; // 延迟
private SnowFlake[] mSnowFlakes; // 雪花
public SnowView(Context context) {
super(context);
}
public SnowView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public SnowView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
if (w != oldw || h != oldh) {
initSnow(w, h);
}
}
private void initSnow(int width, int height) {
Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG); // 抗锯齿
paint.setColor(Color.WHITE); // 白色雪花
paint.setStyle(Paint.Style.FILL); // 填充;
mSnowFlakes = new SnowFlake[NUM_SNOWFLAKES];
for (int i = 0; i < NUM_SNOWFLAKES; ++i) {
mSnowFlakes[i] = SnowFlake.create(width, height, paint);
}
}
@Override protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
for (SnowFlake s : mSnowFlakes) {
s.draw(canvas);
}
// 隔一段时间重绘一次, 动画效果
getHandler().postDelayed(runnable, DELAY);
}
// 重绘线程
private Runnable runnable = new Runnable() {
@Override
public void run() {
invalidate();
}
};
}
下雨：
RainFlake.java
package com.ctrip.kotlin.view.rian;
import android.graphics.Canvas;
import android.graphics.Paint;
/**
* 雨滴的类, 移动, 移出屏幕会重新设置位置.
*/
public class RainFlake {
// 雨滴的移动速度
private static final float INCREMENT_LOWER = 20f;
private static final float INCREMENT_UPPER = 40f;
// 雨滴的大小
private static final float FLAKE_SIZE_LOWER = 2f;
private static final float FLAKE_SIZE_UPPER = 4f;
private final float mIncrement; // 雨滴的速度
private final float mFlakeSize; // 雨滴的大小
private final Paint mPaint; // 画笔
private Line mLine; // 雨滴
private RainRandomGenerator mRandom;
private RainFlake(RainRandomGenerator random, Line line, float increment, float flakeSize, Paint paint) {
mRandom = random;
mLine = line;
mIncrement = increment;
mFlakeSize = flakeSize;
mPaint = paint;
}
//生成雨滴
public static RainFlake create(int width, int height, Paint paint) {
RainRandomGenerator random = new RainRandomGenerator();
int [] nline;
nline = random.getLine(width, height);
Line line = new Line(nline[0], nline[1], nline[2], nline[3]);
float increment = random.getRandom(INCREMENT_LOWER, INCREMENT_UPPER);
float flakeSize = random.getRandom(FLAKE_SIZE_LOWER, FLAKE_SIZE_UPPER);
return new RainFlake(random,line, increment, flakeSize, paint);
}
// 绘制雨滴
public void draw(Canvas canvas) {
int width = canvas.getWidth();
int height = canvas.getHeight();
drawLine(canvas, width, height);
}
/**
* 改成线条，类似于雨滴效果
* @param canvas
* @param width
* @param height
*/
private void drawLine(Canvas canvas, int width, int height) {
//设置线宽
mPaint.setStrokeWidth(mFlakeSize);
//y是竖直方向，就是下落
double y1 = mLine.y1 + (mIncrement * Math.sin(1.5));
double y2 = mLine.y2 + (mIncrement * Math.sin(1.5));
//这个是设置雨滴位置，如果在很短时间内刷新一次，就是连起来的动画效果
mLine.set(mLine.x1,(int) y1,mLine.x2 ,(int) y2);
if (!isInsideLine(height)) {
resetLine(width,height);
}
canvas.drawLine(mLine.x1, mLine.y1, mLine.x2, mLine.y2, mPaint);
}
// 判断是否在其中
private boolean isInsideLine(int height) {
return mLine.y1 < height && mLine.y2 < height;
}
// 重置雨滴
private void resetLine(int width, int height) {
int [] nline;
nline = mRandom.getLine(width, height);
mLine.x1 = nline[0];
mLine.y1 = nline[1];
mLine.x2 = nline[2];
mLine.y2 = nline[3];
}
}
RainRandomGenerator .java
package com.ctrip.kotlin.view.rian;
import java.util.Random;
/**
* 随机生成器
*/
public class RainRandomGenerator {
private final Random RANDOM = new Random();
// 区间随机
public float getRandom(float lower, float upper) {
float min = Math.min(lower, upper);
float max = Math.max(lower, upper);
return getRandom(max - min) + min;
}
// 上界随机
public float getRandom(float upper) {
return RANDOM.nextFloat() * upper;
}
// 上界随机
public int getRandom(int upper) {
return RANDOM.nextInt(upper);
}
/**
* 获得一个给定范围的随机整数
* 可以负数到正数
* @param smallistNum
* @param BiggestNum
* @return
*/
public int getRandomNum(int smallistNum, int BiggestNum) {
Random random = new Random();
return (Math.abs(random.nextInt()) % (BiggestNum - smallistNum + 1))+ smallistNum;
}
//随机产生划线的起始点坐标和结束点坐标
public int[] getLine(int height, int width) {
int[] tempCheckNum = { 0, 0, 0, 0 };
int temp = getRandomWidth(width);
for (int i = 0; i < 4; i += 4) {
tempCheckNum[i] = temp;
tempCheckNum[i + 1] = (int) (Math.random() * height/4);
tempCheckNum[i + 2] = temp;
tempCheckNum[i + 3] = (int) (Math.random() * height/2);
}
return tempCheckNum;
}
public int getRandomWidth(int width){
return (int) (Math.random() * width);
}
}
Line.java
package com.ctrip.kotlin.view.rian;
public class Line {
public int x1;
public int y1;
public int x2;
public int y2;
public Line() {
}
public Line(int x1, int y1,int x2, int y2) {
this.x1 = x1;
this.y1 = y1;
this.x2 = x2;
this.y2 = y2;
}
public Line(Line src) {
this.x1 = src.x1;
this.y1 = src.y1;
this.x2 = src.x2;
this.y2 = src.y2;
}
public void set(int x1, int y1,int x2, int y2) {
this.x1 = x1;
this.y1 = y1;
this.x2 = x2;
this.y2 = y2;
}
public final void negate() {
x1 = -x1;
y1 = -y1;
x2 = -x2;
y2 = -y2;
}
public final void offset(int dx, int dy) {
x1 += dx;
y1 += dy;
x2 += dx;
y2 += dy;
}
public final boolean equals(int x1, int y1,int x2, int y2) {
return this.x1 == x1 && this.y1 == y1 && this.x2 == x2 && this.y2 == y2;
}
@Override
public boolean equals(Object o) {
if (o instanceof Line) {
Line p = (Line) o;
return this.x1 == p.x1 && this.y1 == p.y1 && this.x2 == p.x2 && this.y2 == p.y2;
}
return false;
}
@Override
public String toString() {
return "Line(" + x1 + ", " + y1 + x2 + ", " + y2 +")";
}
}
RainView.java
package com.ctrip.kotlin.view.rian;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;
import com.ctrip.kotlin.R;
/**
* 雨滴视图, DELAY时间重绘, 绘制 NUM_SNOWFLAKES个雨滴
*/
public class RainView extends View {
private static final int NUM_SNOWFLAKES = 100; // 雨滴数量
private static final int DELAY = 5; // 延迟
private RainFlake[] mSnowFlakes; // 雨滴
public RainView(Context context) {
super(context);
}
public RainView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public RainView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
if (w != oldw || h != oldh) {
initSnow(w, h);
}
}
private void initSnow(int width, int height) {
Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG); // 抗锯齿
paint.setColor(Color.WHITE); // 雨滴的颜色
paint.setStyle(Paint.Style.FILL); // 填充;
mSnowFlakes = new RainFlake[NUM_SNOWFLAKES];
//mSnowFlakes所有的雨滴都生成放到这里面
for (int i = 0; i < NUM_SNOWFLAKES; ++i) {
mSnowFlakes[i] = RainFlake.create(width, height, paint);
}
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
//for返回SnowFlake
for (RainFlake s : mSnowFlakes) {
//然后进行绘制
s.draw(canvas);
}
// 隔一段时间重绘一次, 动画效果
getHandler().postDelayed(runnable, DELAY);
}
// 重绘线程
private Runnable runnable = new Runnable() {
@Override
public void run() {
//自动刷新
invalidate();
}
};
}
最后，在XML中直接使用即可
<com.ctrip.kotlin.view.snow.SnowView
android:id="@+id/snowView"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<com.ctrip.kotlin.view.rian.RainView
android:id="@+id/rainView"
android:layout_width="match_parent"
android:layout_height="match_parent" />
