音视频开发（五十二）Lottie 源码分析之json解析
1 年前
· 来自专栏
音视频开发技术知识点
目录
- Lottie能做什么
- Lottie 动画使用调用流程
- Json字段介绍
- 解析为LottieComposition
一、Lottie能做什么
在实现动画方面，原生的方式开发成本比较高，airbnb开源的lottie有Android、iOS、RN等多个版本的支持，设计师通过AE设计好动画后，通过AE插件Bodymovin导出json和素材文件。
客户端通过加载解析渲染播放 即可实现对应的动画效果，这个思路和设计非常值得学习借鉴。接下来两篇我们对其进行学习分析，欢迎讨论交流。
二、Lottie 动画使用调用流程
Lottie 的动画调用流程
1. 创建LottieAnimationView
2. 创建LottieDrawable
3. 解析json文件为LottieComposition对象
4. lottieDrawable.setComposition(lottieComposition)
lottieAnimationView.setImageDrawable(lottieDrawable)
5. 播放动画playAnimation()
在onValueChanged时，各个创建好的Drawable会根据需求进行重绘，达到动画的效果。对于开发者使用非常简单, 可以参考lottie源码中sample的使用。
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三、Json字段介绍
我们以Lottie-android提供的demo中的AndroidWave.json和anima.json 为例来学习
object
下面我们看下assets中的字段
object->assets：资源
可以看到object中有layers ,assets中也可能有layers，那边layers这个图层字段包含了什么信息呐。
object->layers：图层
object->layers->ty：图层类型
object->layers->ks：图层变换
“o 、r、 p、 a、 s”中字段相同，都是
a、k、x、ix
下面对a、k做说明。x、ix也不知道什么用处。
object->layers->ks-> o 、r、 p、 a、 s
Lottie json的字段基本解释完，下面我们结合Lottie-android的源码看下解析为LottieComposition的过程
四、 解析为LottieComposition
json的解析器，解析为LottieComposition对象
4.1 LottieComposition解析的过程
LottieComposition对象
json的解析器，解析为LottieComposition对象
//lottie json的解析器，解析为LottieComposition对象
public class LottieCompositionMoshiParser {
private static final JsonReader.Options NAMES = JsonReader.Options.of(
"w", // 0
"h", // 1
"ip", // 2
"op", // 3
"fr", // 4
"v", // 5
"layers", // 6
"assets", // 7
"fonts", // 8
"chars", // 9
"markers" // 10
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.selectName(NAMES)) {
case 0:
width = reader.nextInt();
break;
case 1:
height = reader.nextInt();
break;
case 2:
startFrame = (float) reader.nextDouble();
break;
case 3:
endFrame = (float) reader.nextDouble() - 0.01f;
break;
case 4:
frameRate = (float) reader.nextDouble();
break;
case 5:
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 6://重点看下parseLayers的实现
parseLayers(reader, composition, layers, layerMap);
break;
case 7:
parseAssets(reader, composition, precomps, images);
break;
case 8:
parseFonts(reader, fonts);
break;
case 9:
parseChars(reader, composition, characters);
break;
case 10:
parseMarkers(reader, markers);
break;
default:
reader.skipName();
reader.skipValue();
// w、h会根据像素密度自动适配
int scaledWidth = (int) (width * scale);
int scaledHeight = (int) (height * scale);
Rect bounds = new Rect(0, 0, scaledWidth, scaledHeight);
//json内容解析完之后，调用composition的init进行LottieComposition字段的赋值，完成json对LottieComposition的工作
composition.init(bounds, startFrame, endFrame, frameRate, layers, layerMap, precomps,
images, characters, fonts, markers);
return composition;
private static void parseLayers(JsonReader reader, LottieComposition composition,
List<Layer> layers, LongSparseArray<Layer> layerMap) throws IOException {
int imageCount = 0;
reader.beginArray();
//遍历解析每个layer图层，
while (reader.hasNext()) {
//图层解析
Layer layer = LayerParser.parse(reader, composition);
if (layer.getLayerType() == Layer.LayerType.IMAGE) {
imageCount++;
//加入到layers和map提高效率
layers.add(layer);
layerMap.put(layer.getId(), layer);
reader.endArray();
}4.2 layers图层的解析过程
被解析为Layer对象
通过LayerParser把json中layers解析为Layer对象
//通过LayerParser把json中layers解析为Layer对象
public class LayerParser {
//对应 json中layers的字段
private static final JsonReader.Options NAMES = JsonReader.Options.of(
"nm", // 0
"ind", // 1
"refId", // 2
"ty", // 3
"parent", // 4
"sw", // 5
"sh", // 6
"sc", // 7
"ks", // 8
"tt", // 9
"masksProperties", // 10
"shapes", // 11
"t", // 12
"ef", // 13
"sr", // 14
"st", // 15
"w", // 16
"h", // 17
"ip", // 18
"op", // 19
"tm", // 20
"cl", // 21
"hd" // 22
private static final JsonReader.Options TEXT_NAMES = JsonReader.Options.of(
private static final JsonReader.Options EFFECTS_NAMES = JsonReader.Options.of(
"ty",
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;
BlurEffect blurEffect = null;
DropShadowEffect dropShadowEffect = null;
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.selectName(NAMES)) {
case 0:
layerName = reader.nextString();
break;
case 1:
layerId = reader.nextInt();
break;
case 2:
refId = reader.nextString();
break;
case 3:
int layerTypeInt = reader.nextInt();
//看下Layer.LayerType的值 对应json中ty
if (layerTypeInt < Layer.LayerType.UNKNOWN.ordinal()) {
layerType = Layer.LayerType.values()[layerTypeInt];
} else {
layerType = Layer.LayerType.UNKNOWN;
break;
case 4:
parentId = reader.nextInt();
break;
case 5:
solidWidth = (int) (reader.nextInt() * Utils.dpScale());
break;
case 6:
solidHeight = (int) (reader.nextInt() * Utils.dpScale());
break;
case 7:
solidColor = Color.parseColor(reader.nextString());
break;
case 8:
//图层变换，动画的 这个重点看下
transform = AnimatableTransformParser.parse(reader, composition);
break;
case 9:
int matteTypeIndex = reader.nextInt();
if (matteTypeIndex >= Layer.MatteType.values().length) {
composition.addWarning("Unsupported matte type: " + matteTypeIndex);
break;
matteType = Layer.MatteType.values()[matteTypeIndex];
switch (matteType) {
case LUMA:
composition.addWarning("Unsupported matte type: Luma");
break;
case LUMA_INVERTED:
composition.addWarning("Unsupported matte type: Luma Inverted");
break;
composition.incrementMatteOrMaskCount(1);
break;
case 10:
//蒙层解析
reader.beginArray();
while (reader.hasNext()) {
masks.add(MaskParser.parse(reader, composition));
composition.incrementMatteOrMaskCount(masks.size());
reader.endArray();
break;
case 11:
reader.beginArray();
while (reader.hasNext()) {
ContentModel shape = ContentModelParser.parse(reader, composition);
if (shape != null) {
shapes.add(shape);
reader.endArray();
break;
case 12:
reader.beginObject();
while (reader.hasNext()) {
switch (reader.selectName(TEXT_NAMES)) {
case 0:
text = AnimatableValueParser.parseDocumentData(reader, composition);
break;
case 1:
reader.beginArray();
if (reader.hasNext()) {
textProperties = AnimatableTextPropertiesParser.parse(reader, composition);
while (reader.hasNext()) {
reader.skipValue();
reader.endArray();
break;
default:
reader.skipName();
reader.skipValue();
reader.endObject();
break;
case 13:
reader.beginArray();
List<String> effectNames = new ArrayList<>();
while (reader.hasNext()) {
reader.beginObject();
while (reader.hasNext()) {
switch (reader.selectName(EFFECTS_NAMES)) {
case 0:
int type = reader.nextInt();
if (type == 29) {
blurEffect = BlurEffectParser.parse(reader, composition);
} else if (type == 25) {
dropShadowEffect = new DropShadowEffectParser().parse(reader, composition);
break;
case 1:
String effectName = reader.nextString();
effectNames.add(effectName);
break;
default:
reader.skipName();
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 14:
timeStretch = (float) reader.nextDouble();
break;
case 15:
startFrame = (float) reader.nextDouble();
break;
case 16:
preCompWidth = (int) (reader.nextInt() * Utils.dpScale());
break;
case 17:
preCompHeight = (int) (reader.nextInt() * Utils.dpScale());
break;
case 18:
inFrame = (float) reader.nextDouble();
break;
case 19:
outFrame = (float) reader.nextDouble();
break;
case 20:
timeRemapping = AnimatableValueParser.parseFloat(reader, composition, false);
break;
case 21:
cl = reader.nextString();
break;
case 22:
hidden = reader.nextBoolean();
break;
default:
reader.skipName();
reader.skipValue();
reader.endObject();
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.");
//根据上面解析的值，生成对应的Layer对象。这个对象是进行绘制
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, blurEffect, dropShadowEffect);
}4.3 ks图层变换的解析过程
被解析为对象AnimatableTransform
音视频开发技能知识点大纲：
通过AnimatableTransformParser把json中ks解析为AnimatableTransform对象
//通过AnimatableTransformParser把json中ks解析为AnimatableTransform对象
public class AnimatableTransformParser {
private static final JsonReader.Options NAMES = JsonReader.Options.of(
"a", // 1
"p", // 2
"s", // 3
"rz", // 4
"r", // 5
"o", // 6
"so", // 7
"eo", // 8
"sk", // 9
"sa" // 10
private static final JsonReader.Options ANIMATABLE_NAMES = JsonReader.Options.of("k");
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() == JsonReader.Token.BEGIN_OBJECT;
if (isObject) {
reader.beginObject();
while (reader.hasNext()) {
switch (reader.selectName(NAMES)) {
case 0: // a
reader.beginObject();
while (reader.hasNext()) {
switch (reader.selectName(ANIMATABLE_NAMES)) {
case 0:
anchorPoint = AnimatablePathValueParser.parse(reader, composition);
break;
default:
reader.skipName();
reader.skipValue();
reader.endObject();
break;
case 1: // p
position =
AnimatablePathValueParser.parseSplitPath(reader, composition);
break;
case 2: // s
scale = AnimatableValueParser.parseScale(reader, composition);
break;
case 3: // rz
composition.addWarning("Lottie doesn't support 3D layers.");
case 4: // r
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 5: // o
opacity = AnimatableValueParser.parseInteger(reader, composition);
break;
case 6: // so
startOpacity = AnimatableValueParser.parseFloat(reader, composition, false);
break;
case 7: // eo
endOpacity = AnimatableValueParser.parseFloat(reader, composition, false);
break;
case 8: // sk
skew = AnimatableValueParser.parseFloat(reader, composition, false);
break;
case 9: // sa
skewAngle = AnimatableValueParser.parseFloat(reader, composition, false);
break;
default:
reader.skipName();
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;