Lottie主要类图：
Lottie对外通过控件LottieAnimationView暴露接口，控制动画。
LottieAnimationView继承自ImageView，通过当前时间绘制canvas显示到界面上。这里有两个关键类：LottieComposition 负责解析json描述文件，把json内容转成Java数据对象；LottieDrawable负责绘制，把LottieComposition转成的数据对象绘制成drawable显示到View上。顺序如下：
LottieComposition负责解析json文件，建立数据到java对象的映射关系。
解析json外部结
LottieComposition封装整个动画的信息，包括动画大小，动画时长，帧率，用到的图片，字体，图层等等。
json外部结构
{
"v": "5.1.13", // bodymovin 版本
"fr": 30, // 帧率
"ip": 0, // 起始关键帧
"op": 20, // 结束关键帧
"w": 150, // 视图宽
"h": 130, // 视图高
"nm": "鹅头收起动画", // 名称
"ddd": 0, // 3d
"assets": [], // 资源集合
"layers": [], // 图层集合
"masker": [] // 蒙层集合
}上图为一个动画json文件，上面给出了各个参数的含义。其中ip表示其实关键帧，一般为0，op表示动画的结束关键帧，fr表示帧率，所以动画时间等于：(op-ip)/fr 。w和h分别表示视图的宽和高。
由于assets、layers、masker里面的数据可能很大，所以上面用空数组代替。其中layers是一个图层集合，它里面数据一般很大，里面包含了当前动画的所有图层数据，assets是一个资源集合，它里面包含了当前动画使用的资源图层数据。masks则表示蒙层集合，里面包含了所有的蒙层数据。
在lottie-android中，处理以上这些数据的代码如下所示（删除了一些相关性不强的代码，完整的代码请看lottie-android源码）：
public static LottieComposition parse(JsonReader reader) throws IOException {
float scale = Utils.dpScale();
float startFrame = 0f;
float endFrame = 0f;
float frameRate = 0f;
final LongSparseArray<Layer> layerMap = new LongSparseArray<>();
final List<Layer> layers = new ArrayList<>();
int width = 0;
int height = 0;
Map<String, List<Layer>> precomps = new HashMap<>();
Map<String, LottieImageAsset> images = new HashMap<>();
Map<String, Font> fonts = new HashMap<>();
List<Marker> markers = new ArrayList<>();
SparseArrayCompat<FontCharacter> characters = new SparseArrayCompat<>();
LottieComposition composition = new LottieComposition();
reader.beginObject();
while (reader.hasNext()) {
switch (reader.nextName()) {
case "w":
width = reader.nextInt();
break;
case "h":
height = reader.nextInt();
break;
case "ip":
startFrame = (float) reader.nextDouble();
break;
case "op":
endFrame = (float) reader.nextDouble() - 0.01f;
break;
case "fr":
frameRate = (float) reader.nextDouble();
break;
case "v":
String version = reader.nextString();
String[] versions = version.split("\\.");
int majorVersion = Integer.parseInt(versions[0]);
int minorVersion = Integer.parseInt(versions[1]);
int patchVersion = Integer.parseInt(versions[2]);
if (!Utils.isAtLeastVersion(majorVersion, minorVersion, patchVersion,
4, 4, 0)) {
composition.addWarning("Lottie only supports bodymovin >= 4.4.0");
}
break;
case "layers":
parseLayers(reader, composition, layers, layerMap);
break;
case "assets":
parseAssets(reader, composition, precomps, images);
break;
case "fonts":
parseFonts(reader, fonts); //解析字体
break;
case "chars":
parseChars(reader, composition, characters); //解析字符
break;
case "markers": //解析蒙层
parseMarkers(reader, composition, markers);
break;
default:
reader.skipValue();
}
}
reader.endObject();
int scaledWidth = (int) (width * scale);
int scaledHeight = (int) (height * scale);
Rect bounds = new Rect(0, 0, scaledWidth, scaledHeight);
composition.init(bounds, startFrame, endFrame, frameRate, layers, layerMap, precomps,
images, characters, fonts, markers);
return composition;
}
图层元素 layer
动画是由一个一个的图层组合起来，并在图层上进行偏移、缩放等操作来实现动画的。图层的解析是lottie的主要功能模块。 一个layer图层的数据格式一般如下：
{
"ddd": 0, // 是否为3d
"ind": 1, // layer的ID，唯一
"ty": 0, // 图层类型
"nm": "鹅头收起", // 图层名称
"refId": "comp_0", // 引用的资源，图片/预合成层
"sr": 1,
"ks": {}, // 变换。对应AE中的变换设置
layer: [], // 该图层包含的子图层
shaps: [], // 形状图层
"ao": 0,
"w": 1334,
"h": 750,
"ip": 0, // 该图层开始关键帧
"op": 60, // 该图层结束关键帧
"st": 0, // 该图层
"bm": 0
}上面是一个layer图层的object的格式。
其中说明一下nm属性，该属性是在AE中对该图层的命名，通过在SVG中修改该命名，可以设置对应的svg的class和id。如果命名为'#svgId'，生成的对应的svg元素的id则为'svgId'；如果命名为'.svg-class'，则生成的对应的svg元素的class为'svg-class'。
ty表示类型，例如：
lottie-android中对layers图层数据相应的处理有：
public static Layer parse(JsonReader reader, LottieComposition composition) throws IOException {
// This should always be set by After Effects. However, if somebody wants to minify
// and optimize their json, the name isn't critical for most cases so it can be removed.
String layerName = "UNSET";
Layer.LayerType layerType = null;
String refId = null;
long layerId = 0;
int solidWidth = 0;
int solidHeight = 0;
int solidColor = 0;
int preCompWidth = 0;
int preCompHeight = 0;
long parentId = -1;
float timeStretch = 1f;
float startFrame = 0f;
float inFrame = 0f;
float outFrame = 0f;
String cl = null;
boolean hidden = false;
Layer.MatteType matteType = Layer.MatteType.NONE;
AnimatableTransform transform = null;
AnimatableTextFrame text = null;
AnimatableTextProperties textProperties = null;
AnimatableFloatValue timeRemapping = null;
List<Mask> masks = new ArrayList<>();
List<ContentModel> shapes = new ArrayList<>();
reader.beginObject();
while (reader.hasNext()) {
switch (reader.nextName()) {
case "nm":
layerName = reader.nextString();
break;
case "ind":
layerId = reader.nextInt();
break;
case "refId":
refId = reader.nextString();
break;
case "ty":
int layerTypeInt = reader.nextInt();
if (layerTypeInt < Layer.LayerType.UNKNOWN.ordinal()) {
layerType = Layer.LayerType.values()[layerTypeInt];
} else {
layerType = Layer.LayerType.UNKNOWN;
}
break;
case "parent":
parentId = reader.nextInt();
break;
case "sw":
solidWidth = (int) (reader.nextInt() * Utils.dpScale());
break;
case "sh":
solidHeight = (int) (reader.nextInt() * Utils.dpScale());
break;
case "sc":
solidColor = Color.parseColor(reader.nextString());
break;
case "ks": //ks变换
transform = AnimatableTransformParser.parse(reader, composition);
break;
case "tt":
matteType = Layer.MatteType.values()[reader.nextInt()];
composition.incrementMatteOrMaskCount(1);
break;
case "masksProperties":
reader.beginArray();
while (reader.hasNext()) {
masks.add(MaskParser.parse(reader, composition));
}
composition.incrementMatteOrMaskCount(masks.size());
reader.endArray();
break;
case "shapes":
reader.beginArray();
while (reader.hasNext()) {
ContentModel shape = ContentModelParser.parse(reader, composition);
if (shape != null) {
shapes.add(shape);
}
}
reader.endArray();
break;
case "t":
reader.beginObject();
while (reader.hasNext()) {
switch (reader.nextName()) {
case "d":
text = AnimatableValueParser.parseDocumentData(reader, composition);
break;
case "a":
reader.beginArray();
if (reader.hasNext()) {
textProperties = AnimatableTextPropertiesParser.parse(reader, composition);
}
while (reader.hasNext()) {
reader.skipValue();
}
reader.endArray();
break;
default:
reader.skipValue();
}
}
reader.endObject();
break;
case "ef":
reader.beginArray();
List<String> effectNames = new ArrayList<>();
while (reader.hasNext()) {
reader.beginObject();
while (reader.hasNext()) {
switch (reader.nextName()) {
case "nm":
effectNames.add(reader.nextString());
break;
default:
reader.skipValue();
}
}
reader.endObject();
}
reader.endArray();
composition.addWarning("Lottie doesn't support layer effects. If you are using them for " +
" fills, strokes, trim paths etc. then try adding them directly as contents " +
" in your shape. Found: " + effectNames);
break;
case "sr":
timeStretch = (float) reader.nextDouble();
break;
case "st":
startFrame = (float) reader.nextDouble();
break;
case "w":
preCompWidth = (int) (reader.nextInt() * Utils.dpScale());
break;
case "h":
preCompHeight = (int) (reader.nextInt() * Utils.dpScale());
break;
case "ip":
inFrame = (float) reader.nextDouble();
break;
case "op":
outFrame = (float) reader.nextDouble();
break;
case "tm":
timeRemapping = AnimatableValueParser.parseFloat(reader, composition, false);
break;
case "cl":
cl = reader.nextString();
break;
case "hd":
hidden = reader.nextBoolean();
break;
default:
reader.skipValue();
}
}
reader.endObject();
// Bodymovin pre-scales the in frame and out frame by the time stretch. However, that will
// cause the stretch to be double counted since the in out animation gets treated the same
// as all other animations and will have stretch applied to it again.
inFrame /= timeStretch;
outFrame /= timeStretch;
List<Keyframe<Float>> inOutKeyframes = new ArrayList<>();
// Before the in frame
if (inFrame > 0) {
Keyframe<Float> preKeyframe = new Keyframe<>(composition, 0f, 0f, null, 0f, inFrame);
inOutKeyframes.add(preKeyframe);
}
// The + 1 is because the animation should be visible on the out frame itself.
outFrame = (outFrame > 0 ? outFrame : composition.getEndFrame());
Keyframe<Float> visibleKeyframe =
new Keyframe<>(composition, 1f, 1f, null, inFrame, outFrame);
inOutKeyframes.add(visibleKeyframe);
Keyframe<Float> outKeyframe = new Keyframe<>(
composition, 0f, 0f, null, outFrame, Float.MAX_VALUE);
inOutKeyframes.add(outKeyframe);
if (layerName.endsWith(".ai") || "ai".equals(cl)) {
composition.addWarning("Convert your Illustrator layers to shape layers.");
}
return new Layer(shapes, composition, layerName, layerId, layerType, parentId, refId,
masks, transform, solidWidth, solidHeight, solidColor, timeStretch, startFrame,
preCompWidth, preCompHeight, text, textProperties, inOutKeyframes, matteType,
timeRemapping, hidden);
}
}ks变换
ks对应AE中图层的变换属性，可以通过设置锚点、位置、旋转、缩放、透明度等来控制图层，并设置这些属性的变换曲线，来实现动画。下面是一个ks属性值：
"ks": { // 变换。对应AE中的变换设置
"o": { // 透明度
"a": 0,
"k": 100,
"ix": 11
},
"r": { // 旋转
"a": 0,
"k": 0,
"ix": 10
},
"p": { // 位置
"a": 0,
"k": [-167, 358.125, 0],
"ix": 2
},
"a": { // 锚点
"a": 0,
"k": [667, 375, 0],
"ix": 1
},
"s": { // 缩放
"a": 0,
"k": [100, 100, 100],
"ix": 6
}
}lottie-android会把ks处理成transform的属性，用于对元素进行变换操作。transform包含了translate（平移）、scale（缩放）、rotate（旋转）、skew（倾斜）等几种。lottie-android中处理ks（变换）的相关代码为：
public static AnimatableTransform parse(
JsonReader reader, LottieComposition composition) throws IOException {
AnimatablePathValue anchorPoint = null;
AnimatableValue<PointF, PointF> position = null;
AnimatableScaleValue scale = null;
AnimatableFloatValue rotation = null;
AnimatableIntegerValue opacity = null;
AnimatableFloatValue startOpacity = null;
AnimatableFloatValue endOpacity = null;
AnimatableFloatValue skew = null;
AnimatableFloatValue skewAngle = null;
boolean isObject = reader.peek() == JsonToken.BEGIN_OBJECT;
if (isObject) {
reader.beginObject();
}
while (reader.hasNext()) {
switch (reader.nextName()) {
case "a":
reader.beginObject();
while (reader.hasNext()) {
if (reader.nextName().equals("k")) {
anchorPoint = AnimatablePathValueParser.parse(reader, composition);
} else {
reader.skipValue();
}
}
reader.endObject();
break;
case "p":
position =
AnimatablePathValueParser.parseSplitPath(reader, composition);
break;
case "s":
scale = AnimatableValueParser.parseScale(reader, composition);
break;
case "rz":
composition.addWarning("Lottie doesn't support 3D layers.");
case "r":
/**
* Sometimes split path rotation gets exported like:
* "rz": {
* "a": 1,
* "k": [
* {}
* ]
* },
* which doesn't parse to a real keyframe.
*/
rotation = AnimatableValueParser.parseFloat(reader, composition, false);
if (rotation.getKeyframes().isEmpty()) {
rotation.getKeyframes().add(new Keyframe(composition, 0f, 0f, null, 0f, composition.getEndFrame()));
} else if (rotation.getKeyframes().get(0).startValue == null) {
rotation.getKeyframes().set(0, new Keyframe(composition, 0f, 0f, null, 0f, composition.getEndFrame()));
}
break;
case "o":
opacity = AnimatableValueParser.parseInteger(reader, composition);
break;
case "so":
startOpacity = AnimatableValueParser.parseFloat(reader, composition, false);
break;
case "eo":
endOpacity = AnimatableValueParser.parseFloat(reader, composition, false);
break;
case "sk":
skew = AnimatableValueParser.parseFloat(reader, composition, false);
break;
case "sa":
skewAngle = AnimatableValueParser.parseFloat(reader, composition, false);
break;
default:
reader.skipValue();
}
}
if (isObject) {
reader.endObject();
}
if (isAnchorPointIdentity(anchorPoint)) {
anchorPoint = null;
}
if (isPositionIdentity(position)) {
position = null;
}
if (isRotationIdentity(rotation)) {
rotation = null;
}
if (isScaleIdentity(scale)) {
scale = null;
}
if (isSkewIdentity(skew)) {
skew = null;
}
if (isSkewAngleIdentity(skewAngle)) {
skewAngle = null;
}
return new AnimatableTransform(anchorPoint, position, scale, rotation, opacity, startOpacity, endOpacity, skew, skewAngle);
}
shape
shape参数的值，对应AE中图层的内容中的形状设置的内容，其主要用于绘制图形。下面一个shape的json为例：
"shapes": [{
"ty": "gr", // 类型。混合图层
"it": [{ // 各图层json
"ind": 0,
"ty": "sh", // 类型，sh表示图形路径
"ix": 1,
"ks": {
"a": 0,
"k": {
"i": [ // 内切线点集合
[0, 0],
[0, 0]
],
"o": [ // 外切线点集合
[0, 0],
[0, 0]
],
"v": [ // 顶点坐标集合
[182, -321.75],
[206.25, -321.75]
],
"c": false // 贝塞尔路径闭合
},
"ix": 2
},
"nm": "路径 1",
"mn": "ADBE Vector Shape - Group",
"hd": false
},{
"ty": "st", // 类型。图形描边
"c": { // 线的颜色
"a": 0,
"k": [0, 0, 0, 1],
"ix": 3
},
"o": { // 线的不透明度
"a": 0,
"k": 100,
"ix": 4
},
"w": { // 线的宽度
"a": 0,
"k": 3,
"ix": 5
},
"lc": 2, // 线段的头尾样式
"lj": 1, // 线段的连接样式
"ml": 4, // 尖角限制
"nm": "描边 1",
"mn": "ADBE Vector Graphic - Stroke",
"hd": false
}]
}]上面是一个shape形状的json示例，可以看出不同的shape类型，参数也不同。shape对应的是AE中的图层的内容的设置。shape中的ty字段表示shape的类型，ty有以下几种：
lottie-android中处理shape的相关代码为：
static ContentModel parse(JsonReader reader, LottieComposition composition)
throws IOException {
String type = null;
reader.beginObject();
// Unfortunately, for an ellipse, d is before "ty" which means that it will get parsed
// before we are in the ellipse parser.
// "d" is 2 for normal and 3 for reversed.
int d = 2;
typeLoop:
while (reader.hasNext()) {
switch (reader.nextName()) {
case "ty":
type = reader.nextString();
break typeLoop;
case "d":
d = reader.nextInt();
break;
default:
reader.skipValue();
}
}
if (type == null) {
return null;
}
ContentModel model = null;
switch (type) {
case "gr":
model = ShapeGroupParser.parse(reader, composition);
break;
case "st":
model = ShapeStrokeParser.parse(reader, composition);
break;
case "gs":
model = GradientStrokeParser.parse(reader, composition);
break;
case "fl":
model = ShapeFillParser.parse(reader, composition);
break;
case "gf":
model = GradientFillParser.parse(reader, composition);
break;
case "tr":
model = AnimatableTransformParser.parse(reader, composition);
break;
case "sh":
model = ShapePathParser.parse(reader, composition);
break;
case "el":
model = CircleShapeParser.parse(reader, composition, d);
break;
case "rc":
model = RectangleShapeParser.parse(reader, composition);
break;
case "tm":
model = ShapeTrimPathParser.parse(reader, composition);
break;
case "sr":
model = PolystarShapeParser.parse(reader, composition);
break;
case "mm":
model = MergePathsParser.parse(reader);
composition.addWarning("Animation contains merge paths. Merge paths are only " +
"supported on KitKat+ and must be manually enabled by calling " +
"enableMergePathsForKitKatAndAbove().");
break;
case "rp":
model = RepeaterParser.parse(reader, composition);
break;
default:
Log.w(L.TAG, "Unknown shape type " + type);
}
while (reader.hasNext()) {
reader.skipValue();
}
reader.endObject();
return model;
}