是否可以手动获取新的 ImageDecoder class 到 return 位图，一帧又一帧？
Is it possible to get the new ImageDecoder class to return Bitmaps, one frame after another, manually?
背景
我正在尝试手动（逐帧）查看动画 GIF 和 WEBP 文件的位图，这样它不仅适用于视图，也适用于其他情况（例如动态壁纸）。
问题
仅 Android P 支持动画 GIF/WEBP 文件，使用 ImageDecoder API（示例 here）。
对于 GIF，我想尝试 Glide 来完成任务，但我失败了，所以我尝试通过使用允许加载它们的库 (here, solution ) 来克服这个问题。我觉得还行。
对于 WebP，我想我找到了另一个可以在旧 Android 版本 (here, made fork here), but it seems that it can't handle WebP files well in some cases (reported here) 上工作的库。我试图弄清楚问题是什么以及如何解决它，但我没有成功。
所以，假设有一天 Google 将通过支持库（他们写的 here）支持旧 Android 版本的 GIF 和 WEBP 动画，我决定尝试使用 ImageDecoder 完成任务。
事实是，纵观 ImageDecoder 的整个 API，我们应该如何使用它非常受限。我不知道如何克服它的局限性。
我发现了什么
这就是如何使用 ImageDecoder 在 ImageView 上显示动画 WebP（当然，只是一个示例，可用 here）：
class MainActivity : AppCompatActivity() {
@SuppressLint("StaticFieldLeak")
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val source = ImageDecoder.createSource(resources, R.raw.test)
object : AsyncTask<Void, Void, Drawable?>() {
override fun doInBackground(vararg params: Void?): Drawable? {
return try {
ImageDecoder.decodeDrawable(source)
} catch (e: Exception) {
null
}
}
override fun onPostExecute(result: Drawable?) {
super.onPostExecute(result)
imageView.setImageDrawable(result)
if (result is AnimatedImageDrawable) {
result.start()
}
}
}.execute()
}
}
我试图阅读 ImageDecoder and AnimatedImageDrawable 的所有文档，也查看了它的代码，但我不知道如何手动遍历每一帧，并且有时间中间需要等待
问题
有没有办法使用 ImageDecoder API 手动遍历每一帧，获取要绘制的位图并知道帧之间需要等待多长时间？有什么解决方法吗？甚至可以使用 AnimatedImageDrawable ?
我想在旧的 Android 版本上做同样的事情。可能吗？如果是这样怎么办？也许在不同的 API/library 上？ Google 写道它可以在旧的 Android 版本上使用 ImageDecoder，但我没有看到它在任何地方被提及（除了我提供的 link）。可能还没有准备好... Android P 甚至还没有达到 0.1% 的用户... 也许 Fresco 可以做到？我也试过在那里检查它，但我也没有看到它有能力做这样的事情，而且它是一个巨大的库，只用于这个任务，所以我宁愿使用不同的库。 . 我也知道 libwebp 可用，但它在 C/C++ 中，不确定它是否适合 Android，以及 Java/Kotlin 上是否有用于 [=69] 的端口=].
编辑：
因为我认为我得到了我想要的东西，对于第三方库和 ImageDecoder，能够从动画 WebP 中获取位图，我仍然想知道如何获取帧数和当前如果可能的话，使用 ImageDecoder 框架。我尝试使用 ImageDecoder.decodeDrawable(source, object : ImageDecoder.OnHeaderDecodedListener... ，但它不提供帧计数信息，并且在 API 中我无法看到我可以转到特定的帧索引并从那里开始，或者了解特定帧需要多长时间才能进入下一帧。所以我对那些 here.
提出了要求
遗憾的是我也找不到 Google 有适用于旧 Android 版本的 ImageDecoder。
如果有某种方法可以像我对相对较新的 HEIC 动画文件那样做同样的事情，那也很有趣。目前仅 Android P.
支持
好的，我找到了一个可能的解决方案，使用 Glide library, together with GlideWebpDecoder library .
我不确定这是否是最好的方法，但我认为它应该可以正常工作。下一个代码显示了如何为动画需要显示的每一帧将可绘制对象绘制到我创建的 Bitmap 实例中。这不是我问的，但它可能对其他人有帮助。
这是代码（项目可用here）：
CallbackEx.kt
abstract class CallbackEx : Drawable.Callback {
override fun unscheduleDrawable(who: Drawable, what: Runnable) {}
override fun invalidateDrawable(who: Drawable) {}
override fun scheduleDrawable(who: Drawable, what: Runnable, `when`: Long) {}
}
MyAppGlideModule.kt
@GlideModule
class MyAppGlideModule : AppGlideModule()
MainActivity.kt
class MainActivity : AppCompatActivity() {
var webpDrawable: WebpDrawable? = null
var gifDrawable: GifDrawable? = null
var callback: Drawable.Callback? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
useFrameByFrameDecoding()
// useNormalDecoding()
}
fun useNormalDecoding() {
//webp url : https://res.cloudinary.com/demo/image/upload/fl_awebp/bored_animation.webp
Glide.with(this)
// .load(R.raw.test)
// .load(R.raw.fast)
.load(R.raw.example2)
// .load("https://res.cloudinary.com/demo/image/upload/fl_awebp/bored_animation.webp")
.into(object : SimpleTarget<Drawable>() {
override fun onResourceReady(drawable: Drawable, transition: Transition<in Drawable>?) {
imageView.setImageDrawable(drawable)
when (drawable) {
is GifDrawable -> {
drawable.start()
}
is WebpDrawable -> {
drawable.start()
}
}
}
})
}
fun useFrameByFrameDecoding() {
//webp url : https://res.cloudinary.com/demo/image/upload/fl_awebp/bored_animation.webp
Glide.with(this)
.load(R.raw.test)
// .load(R.raw.fast)
// .load(R.raw.example2)
// .load("https://res.cloudinary.com/demo/image/upload/fl_awebp/bored_animation.webp")
.into(object : SimpleTarget<Drawable>() {
override fun onResourceReady(drawable: Drawable, transition: Transition<in Drawable>?) {
// val callback
when (drawable) {
is GifDrawable -> {
gifDrawable = drawable
val bitmap = Bitmap.createBitmap(drawable.intrinsicWidth, drawable.intrinsicHeight, Bitmap.Config.ARGB_8888)
val canvas = Canvas(bitmap)
drawable.setBounds(0, 0, bitmap.width, bitmap.height)
drawable.setLoopCount(GifDrawable.LOOP_FOREVER)
callback = object : CallbackEx() {
override fun invalidateDrawable(who: Drawable) {
who.draw(canvas)
imageView.setImageBitmap(bitmap)
Log.d("AppLog", "invalidateDrawable ${drawable.toString().substringAfter('@')} ${drawable.frameIndex}/${drawable.frameCount}")
}
}
drawable.callback = callback
drawable.start()
}
is WebpDrawable -> {
webpDrawable = drawable
val bitmap = Bitmap.createBitmap(drawable.intrinsicWidth, drawable.intrinsicHeight, Bitmap.Config.ARGB_8888)
val canvas = Canvas(bitmap)
drawable.setBounds(0, 0, bitmap.width, bitmap.height)
drawable.setLoopCount(WebpDrawable.LOOP_FOREVER)
callback = object : CallbackEx() {
override fun invalidateDrawable(who: Drawable) {
who.draw(canvas)
imageView.setImageBitmap(bitmap)
Log.d("AppLog", "invalidateDrawable ${drawable.toString().substringAfter('@')} ${drawable.frameIndex}/${drawable.frameCount}")
}
}
drawable.callback = callback
drawable.start()
}
}
}
})
}
override fun onStart() {
super.onStart()
gifDrawable?.start()
gifDrawable?.start()
}
override fun onStop() {
super.onStop()
Log.d("AppLog", "onStop")
webpDrawable?.stop()
gifDrawable?.stop()
}
}
不确定为什么 SimpleTarget 被标记为已弃用，但我应该使用什么来代替。
使用类似的技术，我还发现了如何使用 ImageDecoder 来实现它，但由于某种原因没有使用相同的功能。示例项目可用 here.
代码如下：
MainActivity.kt
class MainActivity : AppCompatActivity() {
var webpDrawable: AnimatedImageDrawable? = null
@SuppressLint("StaticFieldLeak")
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val source = ImageDecoder.createSource(resources, R.raw.test)
object : AsyncTask<Void, Void, Drawable?>() {
override fun doInBackground(vararg params: Void?): Drawable? {
return try {
ImageDecoder.decodeDrawable(source)
} catch (e: Exception) {
null
}
}
override fun onPostExecute(drawable: Drawable?) {
super.onPostExecute(drawable)
// imageView.setImageDrawable(result)
if (drawable is AnimatedImageDrawable) {
webpDrawable = drawable
val bitmap =
Bitmap.createBitmap(drawable.intrinsicWidth, drawable.intrinsicHeight, Bitmap.Config.ARGB_8888)
val canvas = Canvas(bitmap)
drawable.setBounds(0, 0, bitmap.width, bitmap.height)
drawable.repeatCount = AnimatedImageDrawable.REPEAT_INFINITE
drawable.callback = object : Drawable.Callback {
val handler = Handler()
override fun unscheduleDrawable(who: Drawable, what: Runnable) {
Log.d("AppLog", "unscheduleDrawable")
}
override fun invalidateDrawable(who: Drawable) {
who.draw(canvas)
imageView.setImageBitmap(bitmap)
Log.d("AppLog", "invalidateDrawable")
}
override fun scheduleDrawable(who: Drawable, what: Runnable, `when`: Long) {
Log.d("AppLog", "scheduleDrawable next frame in ${`when` - SystemClock.uptimeMillis()} ms")
handler.postAtTime(what, `when`)
}
}
drawable.start()
}
}
}.execute()
}
override fun onStart() {
super.onStart()
webpDrawable?.start()
}
override fun onStop() {
super.onStop()
webpDrawable?.stop()
}
}
参见ImageDecoder.Source ...
首先需要创建一个源，使用：
// source from file
val source = ImageDecoder.createSource(file)
// source from byte buffer
val source = ImageDecoder.createSource(byteBuffer)
// source from resource
val source = ImageDecoder.createSource(resources, resId)
// source from URI
val source = ImageDecoder.createSource(contentResolver, uri)
// source from asset file
val source = ImageDecoder.createSource(assetManager, assetFileName)
然后解码，使用：
// create bitmap
val bitmap = ImageDecoder.decodeBitmap(source)
// create drawable
val drawable = ImageDecoder.decodeDrawable(source)
更新：问题是，结果AnimatedImageDrawable doesn't have the two methods: getNumberOfFrames() and getFrame(int) as an AnimationDrawable has. as @androiddeveloper pointed out ...I've messed up two different classes. I've double-checked the documentation and there seems to be no way. with the GIFImageReader it still can be extracted (source):
ArrayList<BufferedImage> getFrames(File gif) throws IOException {
ArrayList<BufferedImage> frames = new ArrayList<BufferedImage>();
ImageReader ir = new GIFImageReader(new GIFImageReaderSpi());
ir.setInput(ImageIO.createImageInputStream(gif));
for(int i = 0; i < ir.getNumImages(true); i++) {
frames.add(ir.read(i));
}
return frames;
}
刚刚尝试将其转换为 Kotlin，但 javax.imageio.ImageIO 在 Android 上不可用。
几年前我玩过 GIF 图片。我的想法是将 GIF 图像解码为帧，将帧转换为位图，添加从位图创建动画可绘制对象并在帧之间延迟。这是解码 class:
public class GifDecoder extends Thread {
public static final int STATUS_PARSING = 0;
public static final int STATUS_FORMAT_ERROR = 1;
public static final int STATUS_OPEN_ERROR = 2;
public static final int STATUS_FINISH = -1;
private static final int MaxStackSize = 4096;
public int width; // full image width
public int height; // full image height
int[] lastPixels;
int[] dest;
private InputStream in;
private int status;
private boolean gctFlag; // global color table used
private int gctSize; // size of global color table
private int loopCount = 1; // iterations; 0 = repeat forever
private int[] gct; // global color table
private int[] lct; // local color table
private int[] act; // active color table
private int bgIndex; // background color index
private int bgColor; // background color
private int lastBgColor; // previous bg color
private int pixelAspect; // pixel aspect ratio
private boolean lctFlag; // local color table flag
private boolean interlace; // interlace flag
private int lctSize; // local color table size
private int ix, iy, iw, ih; // current image rectangle
private int lrx, lry, lrw, lrh;
private GifFrame currentFrame = null;
private boolean isShow = false;
private byte[] block = new byte[256]; // current data block
private int blockSize = 0; // block size
private int dispose = 0;
private int lastDispose = 0;
private boolean transparency = false; // use transparent color
// max decoder pixel stack size
private int delay = 0; // delay in milliseconds
private int transIndex; // transparent color index
// LZW decoder working arrays
private short[] prefix;
private byte[] suffix;
private byte[] pixelStack;
private byte[] pixels;
private GifFrame gifFrame; // frames read from current file
private int frameCount;
private GifAction action = null;
private byte[] gifData = null;
private int gifDataOffset;
private int gifDataLength;
private GifDecoder() {
}
public GifDecoder(byte[] data, GifAction act) {
this(data, 0, data.length, act);
}
public GifDecoder(byte[] data, int offset, int length, GifAction act) {
gifData = data;
action = act;
gifDataOffset = offset;
gifDataLength = length;
}
public GifDecoder(InputStream is, GifAction act) {
in = is;
action = act;
}
public void run() {
if (in != null) {
readStream();
} else if (gifData != null) {
readByte();
}
}
public void free() {
GifFrame fg = gifFrame;
while (fg != null) {
if (fg.image != null) {
fg.image.recycle();
}
fg.image = null;
fg = null;
gifFrame = gifFrame.nextFrame;
fg = gifFrame;
}
if (in != null) {
try {
in.close();
} catch (Exception ex) {
}
in = null;
}
gifData = null;
}
public int getStatus() {
return status;
}
public boolean parseOk() {
return status == STATUS_FINISH;
}
public int getDelay(int n) {
delay = -1;
if ((n >= 0) && (n < frameCount)) {
GifFrame f = getFrame(n);
if (f != null) delay = f.delay;
}
return delay;
}
public GifFrame getFrame(int n) {
GifFrame frame = gifFrame;
int i = 0;
while (frame != null) {
if (i == n) {
return frame;
} else {
frame = frame.nextFrame;
}
i++;
}
return null;
}
public int[] getDelays() {
GifFrame f = gifFrame;
int[] d = new int[frameCount];
int i = 0;
while (f != null && i < frameCount) {
d[i] = f.delay;
f = f.nextFrame;
i++;
}
return d;
}
public int getFrameCount() {
return frameCount;
}
public Bitmap getImage() {
return getFrameImage(0);
}
public Bitmap getFrameImage(int n) {
GifFrame frame = getFrame(n);
if (frame == null) {
return null;
} else {
return frame.image;
}
}
public int getLoopCount() {
return loopCount;
}
public GifFrame getCurrentFrame() {
return currentFrame;
}
public void reset() {
currentFrame = gifFrame;
}
public GifFrame next() {
if (isShow == false) {
isShow = true;
return gifFrame;
} else {
if (status == STATUS_PARSING) {
if (currentFrame.nextFrame != null) currentFrame = currentFrame.nextFrame;
//currentFrame = gifFrame;
} else {
currentFrame = currentFrame.nextFrame;
if (currentFrame == null) {
currentFrame = gifFrame;
}
}
return currentFrame;
}
}
private Bitmap setPixels() {
if (dest == null) dest = new int[width * height];
// fill in starting image contents based on last image's dispose code
if (lastDispose > 0) {
if (lastDispose == 3) {
// use image before last
int n = frameCount - 2;
if (n > 0) {
Bitmap lastImage = getFrameImage(n - 1);
if (lastPixels == null) lastPixels = new int[width * height];
lastImage.getPixels(lastPixels, 0, width, 0, 0, width, height);
} else {
lastPixels = null;
}
}
if (lastPixels != null) {
dest = Arrays.copyOf(lastPixels, lastPixels.length);
// copy pixels
if (lastDispose == 2) {
// fill last image rect area with background color
int c = 0;
if (!transparency) {
c = lastBgColor;
}
for (int i = 0; i < lrh; i++) {
int n1 = (lry + i) * width + lrx;
int n2 = n1 + lrw;
for (int k = n1; k < n2; k++) {
dest[k] = c;
}
}
}
}
}
// copy each source line to the appropriate place in the destination
int pass = 1;
int inc = 8;
int iline = 0;
for (int i = 0; i < ih; i++) {
int line = i;
if (interlace) {
if (iline >= ih) {
pass++;
switch (pass) {
case 2:
iline = 4;
break;
case 3:
iline = 2;
inc = 4;
break;
case 4:
iline = 1;
inc = 2;
}
}
line = iline;
iline += inc;
}
line += iy;
if (line < height) {
int k = line * width;
int dx = k + ix; // start of line in dest
int dlim = dx + iw; // end of dest line
if ((k + width) < dlim) {
dlim = k + width; // past dest edge
}
int sx = i * iw; // start of line in source
while (dx < dlim) {
// map color and insert in destination
int index = ((int) pixels[sx++]) & 0xff;
int c = act[index];
if (c != 0) {
dest[dx] = c;
}
dx++;
}
}
}
return Bitmap.createBitmap(dest, width, height, Config.ARGB_4444);
}
private int readByte() {
in = new ByteArrayInputStream(gifData, gifDataOffset, gifDataLength);
gifData = null;
return readStream();
}
private int readStream() {
init();
if (in != null) {
readHeader();
if (!err()) {
readContents();
if (frameCount < 0) {
status = STATUS_FORMAT_ERROR;
action.parseOk(false, -1);
} else {
status = STATUS_FINISH;
action.parseOk(true, -1);
}
}
try {
in.close();
} catch (Exception e) {
e.printStackTrace();
}
} else {
status = STATUS_OPEN_ERROR;
action.parseOk(false, -1);
}
return status;
}
private void decodeImageData() {
int NullCode = -1;
int npix = iw * ih;
int available, clear, code_mask, code_size, end_of_information, in_code, old_code, bits,
code,
count, i, datum, data_size, first, top, bi, pi;
if ((pixels == null) || (pixels.length < npix)) {
pixels = new byte[npix]; // allocate new pixel array
}
if (prefix == null) {
prefix = new short[MaxStackSize];
}
if (suffix == null) {
suffix = new byte[MaxStackSize];
}
if (pixelStack == null) {
pixelStack = new byte[MaxStackSize + 1];
}
// Initialize GIF data stream decoder.
data_size = read();
clear = 1 << data_size;
end_of_information = clear + 1;
available = clear + 2;
old_code = NullCode;
code_size = data_size + 1;
code_mask = (1 << code_size) - 1;
for (code = 0; code < clear; code++) {
prefix[code] = 0;
suffix[code] = (byte) code;
}
// Decode GIF pixel stream.
datum = bits = count = first = top = pi = bi = 0;
for (i = 0; i < npix; ) {
if (top == 0) {
if (bits < code_size) {
// Load bytes until there are enough bits for a code.
if (count == 0) {
// Read a new data block.
count = readBlock();
if (count <= 0) {
break;
}
bi = 0;
}
datum += (((int) block[bi]) & 0xff) << bits;
bits += 8;
bi++;
count--;
continue;
}
// Get the next code.
code = datum & code_mask;
datum >>= code_size;
bits -= code_size;
// Interpret the code
if ((code > available) || (code == end_of_information)) {
break;
}
if (code == clear) {
// Reset decoder.
code_size = data_size + 1;
code_mask = (1 << code_size) - 1;
available = clear + 2;
old_code = NullCode;
continue;
}
if (old_code == NullCode) {
pixelStack[top++] = suffix[code];
old_code = code;
first = code;
continue;
}
in_code = code;
if (code == available) {
pixelStack[top++] = (byte) first;
code = old_code;
}
while (code > clear) {
pixelStack[top++] = suffix[code];
code = prefix[code];
}
first = ((int) suffix[code]) & 0xff;
// Add a new string to the string table,
if (available >= MaxStackSize) {
break;
}
pixelStack[top++] = (byte) first;
prefix[available] = (short) old_code;
suffix[available] = (byte) first;
available++;
if (((available & code_mask) == 0) && (available < MaxStackSize)) {
code_size++;
code_mask += available;
}
old_code = in_code;
}
// Pop a pixel off the pixel stack.
top--;
pixels[pi++] = pixelStack[top];
i++;
}
for (i = pi; i < npix; i++) {
pixels[i] = 0; // clear missing pixels
}
}
private boolean err() {
return status != STATUS_PARSING;
}
private void init() {
status = STATUS_PARSING;
frameCount = 0;
gifFrame = null;
gct = null;
lct = null;
}
private int read() {
int curByte = 0;
try {
curByte = in.read();
} catch (Exception e) {
status = STATUS_FORMAT_ERROR;
}
return curByte;
}
private int readBlock() {
blockSize = read();
int n = 0;
if (blockSize > 0) {
try {
int count = 0;
while (n < blockSize) {
count = in.read(block, n, blockSize - n);
if (count == -1) {
break;
}
n += count;
}
} catch (Exception e) {
e.printStackTrace();
}
if (n < blockSize) {
status = STATUS_FORMAT_ERROR;
}
}
return n;
}
private int[] readColorTable(int ncolors) {
int nbytes = 3 * ncolors;
int[] tab = null;
byte[] c = new byte[nbytes];
int n = 0;
try {
n = in.read(c);
} catch (Exception e) {
e.printStackTrace();
}
if (n < nbytes) {
status = STATUS_FORMAT_ERROR;
} else {
tab = new int[256]; // max size to avoid bounds checks
int i = 0;
int j = 0;
while (i < ncolors) {
int r = ((int) c[j++]) & 0xff;
int g = ((int) c[j++]) & 0xff;
int b = ((int) c[j++]) & 0xff;
tab[i++] = 0xff000000 | (r << 16) | (g << 8) | b;
}
}
return tab;
}
private void readContents() {
// read GIF file content blocks
boolean done = false;
while (!(done || err())) {
int code = read();
switch (code) {
case 0x2C: // image separator
readImage();
break;
case 0x21: // extension
code = read();
switch (code) {
case 0xf9: // graphics control extension
readGraphicControlExt();
break;
case 0xff: // application extension
readBlock();
String app = "";
for (int i = 0; i < 11; i++) {
app += (char) block[i];
}
if (app.equals("NETSCAPE2.0")) {
readNetscapeExt();
} else {
skip(); // don't care
}
break;
default: // uninteresting extension
skip();
}
break;
case 0x3b: // terminator
done = true;
break;
case 0x00: // bad byte, but keep going and see what happens
break;
default:
status = STATUS_FORMAT_ERROR;
}
}
}
private void readGraphicControlExt() {
read(); // block size
int packed = read(); // packed fields
dispose = (packed & 0x1c) >> 2; // disposal method
if (dispose == 0) {
dispose = 1; // elect to keep old image if discretionary
}
transparency = (packed & 1) != 0;
delay = readShort() * 10; // delay in milliseconds
transIndex = read(); // transparent color index
read(); // block terminator
}
private void readHeader() {
String id = "";
for (int i = 0; i < 6; i++) {
id += (char) read();
}
if (!id.startsWith("GIF")) {
status = STATUS_FORMAT_ERROR;
return;
}
readLSD();
if (gctFlag && !err()) {
gct = readColorTable(gctSize);
bgColor = gct[bgIndex];
}
}
private void readImage() {
ix = readShort(); // (sub)image position & size
iy = readShort();
iw = readShort();
ih = readShort();
int packed = read();
lctFlag = (packed & 0x80) != 0; // 1 - local color table flag
interlace = (packed & 0x40) != 0; // 2 - interlace flag
// 3 - sort flag
// 4-5 - reserved
lctSize = 2 << (packed & 7); // 6-8 - local color table size
if (lctFlag) {
lct = readColorTable(lctSize); // read table
act = lct; // make local table active
} else {
act = gct; // make global table active
if (bgIndex == transIndex) {
bgColor = 0;
}
}
int save = 0;
if (transparency) {
save = act[transIndex];
act[transIndex] = 0; // set transparent color if specified
}
if (act == null) {
status = STATUS_FORMAT_ERROR; // no color table defined
}
if (err()) {
return;
}
try {
decodeImageData(); // decode pixel data
skip();
if (err()) {
return;
}
frameCount++;
// create new image to receive frame data
// createImage(width, height);
Bitmap image = setPixels(); // transfer pixel data to image
if (gifFrame == null) {
gifFrame = new GifFrame(image, delay);
currentFrame = gifFrame;
} else {
GifFrame f = gifFrame;
while (f.nextFrame != null) {
f = f.nextFrame;
}
f.nextFrame = new GifFrame(image, delay);
}
// frames.addElement(new GifFrame(image, delay)); // add image to frame
// list
if (transparency) {
act[transIndex] = save;
}
resetFrame();
if (!action.parseOk(true, frameCount)) {
status = STATUS_FINISH;
return;
}
} catch (OutOfMemoryError e) {
Log.e("GifDecoder", ">>> log : " + e.toString());
e.printStackTrace();
}
}
private void readLSD() {
// logical screen size
width = readShort();
height = readShort();
// packed fields
int packed = read();
gctFlag = (packed & 0x80) != 0; // 1 : global color table flag
// 2-4 : color resolution
// 5 : gct sort flag
gctSize = 2 << (packed & 7); // 6-8 : gct size
bgIndex = read(); // background color index
pixelAspect = read(); // pixel aspect ratio
}
private void readNetscapeExt() {
do {
readBlock();
if (block[0] == 1) {
// loop count sub-block
int b1 = ((int) block[1]) & 0xff;
int b2 = ((int) block[2]) & 0xff;
loopCount = (b2 << 8) | b1;
}
} while ((blockSize > 0) && !err());
}
private int readShort() {
// read 16-bit value, LSB first
return read() | (read() << 8);
}
private void resetFrame() {
lastDispose = dispose;
lrx = ix;
lry = iy;
lrw = iw;
lrh = ih;
lastPixels = dest;
lastBgColor = bgColor;
dispose = 0;
transparency = false;
delay = 0;
lct = null;
}
/**
* Skips variable length blocks up to and including next zero length block.
*/
private void skip() {
do {
readBlock();
} while ((blockSize > 0) && !err());
}
}
我上传了完整的演示源 here。希望对你有帮助。
编辑：在实际实现中，我遇到了一些意想不到的问题，但没有什么是无法克服的：
AnimatedImageDrawable 似乎忽略了其配置的边界。我改为缩放 canvas。- 由于我不明白的原因，
AnimatedImageDrawable.draw()偶尔会忘记安排下一帧。我决定调用该函数两次。第二次，我翻译 canvas 以便所有绘图都超出范围，这应该可以优化大部分工作。
这是示例代码。
import android.annotation.*;
import android.graphics.*;
import android.graphics.drawable.*;
import android.os.*;
import android.service.wallpaper.*;
import android.support.annotation.*;
import android.view.*;
@TargetApi(28)
public class TestWallpaper extends WallpaperService
{
@Override public Engine onCreateEngine()
{
return new Engine();
}
private class Engine extends WallpaperService.Engine implements Drawable.Callback
{
private final Drawable d;
private final Handler h = new Handler();
private float scaleX, scaleY;
private Engine()
{
this.setOffsetNotificationsEnabled(false);
Drawable d = null;
try
{
d = ImageDecoder
.decodeDrawable(ImageDecoder.createSource(getResources(), R.drawable.test));
d.setCallback(this);
// AnimatedImageDrawable seems to ignore its configured bounds and use its
// intrinsic bounds instead.
// In case they fix this bug, we'll go ahead and request the current
// behavior, and then before drawing we'll transform the canvas to compensate
d.setBounds(0, 0, d.getIntrinsicWidth(), d.getIntrinsicHeight());
if (d instanceof AnimatedImageDrawable)
{
final AnimatedImageDrawable anim = (AnimatedImageDrawable) d;
anim.setRepeatCount(AnimatedImageDrawable.REPEAT_INFINITE);
anim.start();
}
}
catch (Throwable t) // should never happen
{
t.printStackTrace();
}
this.d = d;
}
@Override public void invalidateDrawable(@NonNull Drawable _d)
{
if(isVisible())
draw(getSurfaceHolder().getSurface());
}
@Override public void scheduleDrawable(@NonNull Drawable _d, @NonNull Runnable _r, long _at)
{
if(isVisible())
h.postAtTime(_r, _d, _at);
}
@Override public void unscheduleDrawable(@NonNull Drawable _d, @NonNull Runnable _r)
{
h.removeCallbacks(_r, _d);
}
@Override public void onSurfaceChanged(SurfaceHolder _sh, int _format, int _w, int _h)
{
scaleX = (float) _w / d.getIntrinsicWidth();
scaleY = (float) _h / d.getIntrinsicHeight();
draw(_sh.getSurface());
}
@Override public void onSurfaceRedrawNeeded(SurfaceHolder _sh)
{
draw(_sh.getSurface());
}
private void draw(Surface _s)
{
try
{
final Canvas c = _s.lockCanvas(null);
c.scale(scaleX, scaleY);
d.draw(c);
// Sometimes AnimatedImageDrawable neglects to schedule the next frame
// after only one draw() of the current frame, so we'll draw() it again,
// but outside the canvas this time
c.translate(Float.MAX_VALUE, Float.MAX_VALUE);
d.draw(c);
//
_s.unlockCanvasAndPost(c);
}
catch (Throwable t)
{
t.printStackTrace();
// Most likely, the surface was destroyed while we were using it
// The new one will be delivered to onSurfaceChanged and we'll be fine
}
}
@Override public void onVisibilityChanged(boolean _visible)
{
super.onVisibilityChanged(_visible);
if(_visible)
draw(getSurfaceHolder().getSurface());
else
h.removeCallbacksAndMessages(null);
}
}
}
背景
我正在尝试手动（逐帧）查看动画 GIF 和 WEBP 文件的位图，这样它不仅适用于视图，也适用于其他情况（例如动态壁纸）。
问题
仅 Android P 支持动画 GIF/WEBP 文件，使用 ImageDecoder API（示例 here）。
对于 GIF，我想尝试 Glide 来完成任务，但我失败了，所以我尝试通过使用允许加载它们的库 (here, solution
对于 WebP，我想我找到了另一个可以在旧 Android 版本 (here, made fork here), but it seems that it can't handle WebP files well in some cases (reported here) 上工作的库。我试图弄清楚问题是什么以及如何解决它，但我没有成功。
所以，假设有一天 Google 将通过支持库（他们写的 here）支持旧 Android 版本的 GIF 和 WEBP 动画，我决定尝试使用 ImageDecoder 完成任务。
事实是，纵观 ImageDecoder 的整个 API，我们应该如何使用它非常受限。我不知道如何克服它的局限性。
我发现了什么
这就是如何使用 ImageDecoder 在 ImageView 上显示动画 WebP（当然，只是一个示例，可用 here）：
class MainActivity : AppCompatActivity() {
@SuppressLint("StaticFieldLeak")
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val source = ImageDecoder.createSource(resources, R.raw.test)
object : AsyncTask<Void, Void, Drawable?>() {
override fun doInBackground(vararg params: Void?): Drawable? {
return try {
ImageDecoder.decodeDrawable(source)
} catch (e: Exception) {
null
}
}
override fun onPostExecute(result: Drawable?) {
super.onPostExecute(result)
imageView.setImageDrawable(result)
if (result is AnimatedImageDrawable) {
result.start()
}
}
}.execute()
}
}
我试图阅读 ImageDecoder and AnimatedImageDrawable 的所有文档，也查看了它的代码，但我不知道如何手动遍历每一帧，并且有时间中间需要等待
问题
有没有办法使用 ImageDecoder API 手动遍历每一帧，获取要绘制的位图并知道帧之间需要等待多长时间？有什么解决方法吗？甚至可以使用 AnimatedImageDrawable ?
我想在旧的 Android 版本上做同样的事情。可能吗？如果是这样怎么办？也许在不同的 API/library 上？ Google 写道它可以在旧的 Android 版本上使用 ImageDecoder，但我没有看到它在任何地方被提及（除了我提供的 link）。可能还没有准备好... Android P 甚至还没有达到 0.1% 的用户... 也许 Fresco 可以做到？我也试过在那里检查它，但我也没有看到它有能力做这样的事情，而且它是一个巨大的库，只用于这个任务，所以我宁愿使用不同的库。 . 我也知道 libwebp 可用，但它在 C/C++ 中，不确定它是否适合 Android，以及 Java/Kotlin 上是否有用于 [=69] 的端口=].
编辑：
因为我认为我得到了我想要的东西，对于第三方库和 ImageDecoder，能够从动画 WebP 中获取位图，我仍然想知道如何获取帧数和当前如果可能的话，使用 ImageDecoder 框架。我尝试使用 ImageDecoder.decodeDrawable(source, object : ImageDecoder.OnHeaderDecodedListener... ，但它不提供帧计数信息，并且在 API 中我无法看到我可以转到特定的帧索引并从那里开始，或者了解特定帧需要多长时间才能进入下一帧。所以我对那些 here.
遗憾的是我也找不到 Google 有适用于旧 Android 版本的 ImageDecoder。
如果有某种方法可以像我对相对较新的 HEIC 动画文件那样做同样的事情，那也很有趣。目前仅 Android P.
支持好的，我找到了一个可能的解决方案，使用 Glide library, together with GlideWebpDecoder library .
我不确定这是否是最好的方法，但我认为它应该可以正常工作。下一个代码显示了如何为动画需要显示的每一帧将可绘制对象绘制到我创建的 Bitmap 实例中。这不是我问的，但它可能对其他人有帮助。
这是代码（项目可用here）：
CallbackEx.kt
abstract class CallbackEx : Drawable.Callback {
override fun unscheduleDrawable(who: Drawable, what: Runnable) {}
override fun invalidateDrawable(who: Drawable) {}
override fun scheduleDrawable(who: Drawable, what: Runnable, `when`: Long) {}
}
MyAppGlideModule.kt
@GlideModule
class MyAppGlideModule : AppGlideModule()
MainActivity.kt
class MainActivity : AppCompatActivity() {
var webpDrawable: WebpDrawable? = null
var gifDrawable: GifDrawable? = null
var callback: Drawable.Callback? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
useFrameByFrameDecoding()
// useNormalDecoding()
}
fun useNormalDecoding() {
//webp url : https://res.cloudinary.com/demo/image/upload/fl_awebp/bored_animation.webp
Glide.with(this)
// .load(R.raw.test)
// .load(R.raw.fast)
.load(R.raw.example2)
// .load("https://res.cloudinary.com/demo/image/upload/fl_awebp/bored_animation.webp")
.into(object : SimpleTarget<Drawable>() {
override fun onResourceReady(drawable: Drawable, transition: Transition<in Drawable>?) {
imageView.setImageDrawable(drawable)
when (drawable) {
is GifDrawable -> {
drawable.start()
}
is WebpDrawable -> {
drawable.start()
}
}
}
})
}
fun useFrameByFrameDecoding() {
//webp url : https://res.cloudinary.com/demo/image/upload/fl_awebp/bored_animation.webp
Glide.with(this)
.load(R.raw.test)
// .load(R.raw.fast)
// .load(R.raw.example2)
// .load("https://res.cloudinary.com/demo/image/upload/fl_awebp/bored_animation.webp")
.into(object : SimpleTarget<Drawable>() {
override fun onResourceReady(drawable: Drawable, transition: Transition<in Drawable>?) {
// val callback
when (drawable) {
is GifDrawable -> {
gifDrawable = drawable
val bitmap = Bitmap.createBitmap(drawable.intrinsicWidth, drawable.intrinsicHeight, Bitmap.Config.ARGB_8888)
val canvas = Canvas(bitmap)
drawable.setBounds(0, 0, bitmap.width, bitmap.height)
drawable.setLoopCount(GifDrawable.LOOP_FOREVER)
callback = object : CallbackEx() {
override fun invalidateDrawable(who: Drawable) {
who.draw(canvas)
imageView.setImageBitmap(bitmap)
Log.d("AppLog", "invalidateDrawable ${drawable.toString().substringAfter('@')} ${drawable.frameIndex}/${drawable.frameCount}")
}
}
drawable.callback = callback
drawable.start()
}
is WebpDrawable -> {
webpDrawable = drawable
val bitmap = Bitmap.createBitmap(drawable.intrinsicWidth, drawable.intrinsicHeight, Bitmap.Config.ARGB_8888)
val canvas = Canvas(bitmap)
drawable.setBounds(0, 0, bitmap.width, bitmap.height)
drawable.setLoopCount(WebpDrawable.LOOP_FOREVER)
callback = object : CallbackEx() {
override fun invalidateDrawable(who: Drawable) {
who.draw(canvas)
imageView.setImageBitmap(bitmap)
Log.d("AppLog", "invalidateDrawable ${drawable.toString().substringAfter('@')} ${drawable.frameIndex}/${drawable.frameCount}")
}
}
drawable.callback = callback
drawable.start()
}
}
}
})
}
override fun onStart() {
super.onStart()
gifDrawable?.start()
gifDrawable?.start()
}
override fun onStop() {
super.onStop()
Log.d("AppLog", "onStop")
webpDrawable?.stop()
gifDrawable?.stop()
}
}
不确定为什么 SimpleTarget 被标记为已弃用，但我应该使用什么来代替。
使用类似的技术，我还发现了如何使用 ImageDecoder 来实现它，但由于某种原因没有使用相同的功能。示例项目可用 here.
代码如下：
MainActivity.kt
class MainActivity : AppCompatActivity() {
var webpDrawable: AnimatedImageDrawable? = null
@SuppressLint("StaticFieldLeak")
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val source = ImageDecoder.createSource(resources, R.raw.test)
object : AsyncTask<Void, Void, Drawable?>() {
override fun doInBackground(vararg params: Void?): Drawable? {
return try {
ImageDecoder.decodeDrawable(source)
} catch (e: Exception) {
null
}
}
override fun onPostExecute(drawable: Drawable?) {
super.onPostExecute(drawable)
// imageView.setImageDrawable(result)
if (drawable is AnimatedImageDrawable) {
webpDrawable = drawable
val bitmap =
Bitmap.createBitmap(drawable.intrinsicWidth, drawable.intrinsicHeight, Bitmap.Config.ARGB_8888)
val canvas = Canvas(bitmap)
drawable.setBounds(0, 0, bitmap.width, bitmap.height)
drawable.repeatCount = AnimatedImageDrawable.REPEAT_INFINITE
drawable.callback = object : Drawable.Callback {
val handler = Handler()
override fun unscheduleDrawable(who: Drawable, what: Runnable) {
Log.d("AppLog", "unscheduleDrawable")
}
override fun invalidateDrawable(who: Drawable) {
who.draw(canvas)
imageView.setImageBitmap(bitmap)
Log.d("AppLog", "invalidateDrawable")
}
override fun scheduleDrawable(who: Drawable, what: Runnable, `when`: Long) {
Log.d("AppLog", "scheduleDrawable next frame in ${`when` - SystemClock.uptimeMillis()} ms")
handler.postAtTime(what, `when`)
}
}
drawable.start()
}
}
}.execute()
}
override fun onStart() {
super.onStart()
webpDrawable?.start()
}
override fun onStop() {
super.onStop()
webpDrawable?.stop()
}
}
参见ImageDecoder.Source ...
首先需要创建一个源，使用：
// source from file
val source = ImageDecoder.createSource(file)
// source from byte buffer
val source = ImageDecoder.createSource(byteBuffer)
// source from resource
val source = ImageDecoder.createSource(resources, resId)
// source from URI
val source = ImageDecoder.createSource(contentResolver, uri)
// source from asset file
val source = ImageDecoder.createSource(assetManager, assetFileName)
然后解码，使用：
// create bitmap
val bitmap = ImageDecoder.decodeBitmap(source)
// create drawable
val drawable = ImageDecoder.decodeDrawable(source)
更新：问题是，结果AnimatedImageDrawable doesn't have the two methods: getNumberOfFrames() and getFrame(int) as an AnimationDrawable has. as @androiddeveloper pointed out ...I've messed up two different classes. I've double-checked the documentation and there seems to be no way. with the GIFImageReader it still can be extracted (source):
ArrayList<BufferedImage> getFrames(File gif) throws IOException {
ArrayList<BufferedImage> frames = new ArrayList<BufferedImage>();
ImageReader ir = new GIFImageReader(new GIFImageReaderSpi());
ir.setInput(ImageIO.createImageInputStream(gif));
for(int i = 0; i < ir.getNumImages(true); i++) {
frames.add(ir.read(i));
}
return frames;
}
刚刚尝试将其转换为 Kotlin，但 javax.imageio.ImageIO 在 Android 上不可用。
几年前我玩过 GIF 图片。我的想法是将 GIF 图像解码为帧，将帧转换为位图，添加从位图创建动画可绘制对象并在帧之间延迟。这是解码 class:
public class GifDecoder extends Thread {
public static final int STATUS_PARSING = 0;
public static final int STATUS_FORMAT_ERROR = 1;
public static final int STATUS_OPEN_ERROR = 2;
public static final int STATUS_FINISH = -1;
private static final int MaxStackSize = 4096;
public int width; // full image width
public int height; // full image height
int[] lastPixels;
int[] dest;
private InputStream in;
private int status;
private boolean gctFlag; // global color table used
private int gctSize; // size of global color table
private int loopCount = 1; // iterations; 0 = repeat forever
private int[] gct; // global color table
private int[] lct; // local color table
private int[] act; // active color table
private int bgIndex; // background color index
private int bgColor; // background color
private int lastBgColor; // previous bg color
private int pixelAspect; // pixel aspect ratio
private boolean lctFlag; // local color table flag
private boolean interlace; // interlace flag
private int lctSize; // local color table size
private int ix, iy, iw, ih; // current image rectangle
private int lrx, lry, lrw, lrh;
private GifFrame currentFrame = null;
private boolean isShow = false;
private byte[] block = new byte[256]; // current data block
private int blockSize = 0; // block size
private int dispose = 0;
private int lastDispose = 0;
private boolean transparency = false; // use transparent color
// max decoder pixel stack size
private int delay = 0; // delay in milliseconds
private int transIndex; // transparent color index
// LZW decoder working arrays
private short[] prefix;
private byte[] suffix;
private byte[] pixelStack;
private byte[] pixels;
private GifFrame gifFrame; // frames read from current file
private int frameCount;
private GifAction action = null;
private byte[] gifData = null;
private int gifDataOffset;
private int gifDataLength;
private GifDecoder() {
}
public GifDecoder(byte[] data, GifAction act) {
this(data, 0, data.length, act);
}
public GifDecoder(byte[] data, int offset, int length, GifAction act) {
gifData = data;
action = act;
gifDataOffset = offset;
gifDataLength = length;
}
public GifDecoder(InputStream is, GifAction act) {
in = is;
action = act;
}
public void run() {
if (in != null) {
readStream();
} else if (gifData != null) {
readByte();
}
}
public void free() {
GifFrame fg = gifFrame;
while (fg != null) {
if (fg.image != null) {
fg.image.recycle();
}
fg.image = null;
fg = null;
gifFrame = gifFrame.nextFrame;
fg = gifFrame;
}
if (in != null) {
try {
in.close();
} catch (Exception ex) {
}
in = null;
}
gifData = null;
}
public int getStatus() {
return status;
}
public boolean parseOk() {
return status == STATUS_FINISH;
}
public int getDelay(int n) {
delay = -1;
if ((n >= 0) && (n < frameCount)) {
GifFrame f = getFrame(n);
if (f != null) delay = f.delay;
}
return delay;
}
public GifFrame getFrame(int n) {
GifFrame frame = gifFrame;
int i = 0;
while (frame != null) {
if (i == n) {
return frame;
} else {
frame = frame.nextFrame;
}
i++;
}
return null;
}
public int[] getDelays() {
GifFrame f = gifFrame;
int[] d = new int[frameCount];
int i = 0;
while (f != null && i < frameCount) {
d[i] = f.delay;
f = f.nextFrame;
i++;
}
return d;
}
public int getFrameCount() {
return frameCount;
}
public Bitmap getImage() {
return getFrameImage(0);
}
public Bitmap getFrameImage(int n) {
GifFrame frame = getFrame(n);
if (frame == null) {
return null;
} else {
return frame.image;
}
}
public int getLoopCount() {
return loopCount;
}
public GifFrame getCurrentFrame() {
return currentFrame;
}
public void reset() {
currentFrame = gifFrame;
}
public GifFrame next() {
if (isShow == false) {
isShow = true;
return gifFrame;
} else {
if (status == STATUS_PARSING) {
if (currentFrame.nextFrame != null) currentFrame = currentFrame.nextFrame;
//currentFrame = gifFrame;
} else {
currentFrame = currentFrame.nextFrame;
if (currentFrame == null) {
currentFrame = gifFrame;
}
}
return currentFrame;
}
}
private Bitmap setPixels() {
if (dest == null) dest = new int[width * height];
// fill in starting image contents based on last image's dispose code
if (lastDispose > 0) {
if (lastDispose == 3) {
// use image before last
int n = frameCount - 2;
if (n > 0) {
Bitmap lastImage = getFrameImage(n - 1);
if (lastPixels == null) lastPixels = new int[width * height];
lastImage.getPixels(lastPixels, 0, width, 0, 0, width, height);
} else {
lastPixels = null;
}
}
if (lastPixels != null) {
dest = Arrays.copyOf(lastPixels, lastPixels.length);
// copy pixels
if (lastDispose == 2) {
// fill last image rect area with background color
int c = 0;
if (!transparency) {
c = lastBgColor;
}
for (int i = 0; i < lrh; i++) {
int n1 = (lry + i) * width + lrx;
int n2 = n1 + lrw;
for (int k = n1; k < n2; k++) {
dest[k] = c;
}
}
}
}
}
// copy each source line to the appropriate place in the destination
int pass = 1;
int inc = 8;
int iline = 0;
for (int i = 0; i < ih; i++) {
int line = i;
if (interlace) {
if (iline >= ih) {
pass++;
switch (pass) {
case 2:
iline = 4;
break;
case 3:
iline = 2;
inc = 4;
break;
case 4:
iline = 1;
inc = 2;
}
}
line = iline;
iline += inc;
}
line += iy;
if (line < height) {
int k = line * width;
int dx = k + ix; // start of line in dest
int dlim = dx + iw; // end of dest line
if ((k + width) < dlim) {
dlim = k + width; // past dest edge
}
int sx = i * iw; // start of line in source
while (dx < dlim) {
// map color and insert in destination
int index = ((int) pixels[sx++]) & 0xff;
int c = act[index];
if (c != 0) {
dest[dx] = c;
}
dx++;
}
}
}
return Bitmap.createBitmap(dest, width, height, Config.ARGB_4444);
}
private int readByte() {
in = new ByteArrayInputStream(gifData, gifDataOffset, gifDataLength);
gifData = null;
return readStream();
}
private int readStream() {
init();
if (in != null) {
readHeader();
if (!err()) {
readContents();
if (frameCount < 0) {
status = STATUS_FORMAT_ERROR;
action.parseOk(false, -1);
} else {
status = STATUS_FINISH;
action.parseOk(true, -1);
}
}
try {
in.close();
} catch (Exception e) {
e.printStackTrace();
}
} else {
status = STATUS_OPEN_ERROR;
action.parseOk(false, -1);
}
return status;
}
private void decodeImageData() {
int NullCode = -1;
int npix = iw * ih;
int available, clear, code_mask, code_size, end_of_information, in_code, old_code, bits,
code,
count, i, datum, data_size, first, top, bi, pi;
if ((pixels == null) || (pixels.length < npix)) {
pixels = new byte[npix]; // allocate new pixel array
}
if (prefix == null) {
prefix = new short[MaxStackSize];
}
if (suffix == null) {
suffix = new byte[MaxStackSize];
}
if (pixelStack == null) {
pixelStack = new byte[MaxStackSize + 1];
}
// Initialize GIF data stream decoder.
data_size = read();
clear = 1 << data_size;
end_of_information = clear + 1;
available = clear + 2;
old_code = NullCode;
code_size = data_size + 1;
code_mask = (1 << code_size) - 1;
for (code = 0; code < clear; code++) {
prefix[code] = 0;
suffix[code] = (byte) code;
}
// Decode GIF pixel stream.
datum = bits = count = first = top = pi = bi = 0;
for (i = 0; i < npix; ) {
if (top == 0) {
if (bits < code_size) {
// Load bytes until there are enough bits for a code.
if (count == 0) {
// Read a new data block.
count = readBlock();
if (count <= 0) {
break;
}
bi = 0;
}
datum += (((int) block[bi]) & 0xff) << bits;
bits += 8;
bi++;
count--;
continue;
}
// Get the next code.
code = datum & code_mask;
datum >>= code_size;
bits -= code_size;
// Interpret the code
if ((code > available) || (code == end_of_information)) {
break;
}
if (code == clear) {
// Reset decoder.
code_size = data_size + 1;
code_mask = (1 << code_size) - 1;
available = clear + 2;
old_code = NullCode;
continue;
}
if (old_code == NullCode) {
pixelStack[top++] = suffix[code];
old_code = code;
first = code;
continue;
}
in_code = code;
if (code == available) {
pixelStack[top++] = (byte) first;
code = old_code;
}
while (code > clear) {
pixelStack[top++] = suffix[code];
code = prefix[code];
}
first = ((int) suffix[code]) & 0xff;
// Add a new string to the string table,
if (available >= MaxStackSize) {
break;
}
pixelStack[top++] = (byte) first;
prefix[available] = (short) old_code;
suffix[available] = (byte) first;
available++;
if (((available & code_mask) == 0) && (available < MaxStackSize)) {
code_size++;
code_mask += available;
}
old_code = in_code;
}
// Pop a pixel off the pixel stack.
top--;
pixels[pi++] = pixelStack[top];
i++;
}
for (i = pi; i < npix; i++) {
pixels[i] = 0; // clear missing pixels
}
}
private boolean err() {
return status != STATUS_PARSING;
}
private void init() {
status = STATUS_PARSING;
frameCount = 0;
gifFrame = null;
gct = null;
lct = null;
}
private int read() {
int curByte = 0;
try {
curByte = in.read();
} catch (Exception e) {
status = STATUS_FORMAT_ERROR;
}
return curByte;
}
private int readBlock() {
blockSize = read();
int n = 0;
if (blockSize > 0) {
try {
int count = 0;
while (n < blockSize) {
count = in.read(block, n, blockSize - n);
if (count == -1) {
break;
}
n += count;
}
} catch (Exception e) {
e.printStackTrace();
}
if (n < blockSize) {
status = STATUS_FORMAT_ERROR;
}
}
return n;
}
private int[] readColorTable(int ncolors) {
int nbytes = 3 * ncolors;
int[] tab = null;
byte[] c = new byte[nbytes];
int n = 0;
try {
n = in.read(c);
} catch (Exception e) {
e.printStackTrace();
}
if (n < nbytes) {
status = STATUS_FORMAT_ERROR;
} else {
tab = new int[256]; // max size to avoid bounds checks
int i = 0;
int j = 0;
while (i < ncolors) {
int r = ((int) c[j++]) & 0xff;
int g = ((int) c[j++]) & 0xff;
int b = ((int) c[j++]) & 0xff;
tab[i++] = 0xff000000 | (r << 16) | (g << 8) | b;
}
}
return tab;
}
private void readContents() {
// read GIF file content blocks
boolean done = false;
while (!(done || err())) {
int code = read();
switch (code) {
case 0x2C: // image separator
readImage();
break;
case 0x21: // extension
code = read();
switch (code) {
case 0xf9: // graphics control extension
readGraphicControlExt();
break;
case 0xff: // application extension
readBlock();
String app = "";
for (int i = 0; i < 11; i++) {
app += (char) block[i];
}
if (app.equals("NETSCAPE2.0")) {
readNetscapeExt();
} else {
skip(); // don't care
}
break;
default: // uninteresting extension
skip();
}
break;
case 0x3b: // terminator
done = true;
break;
case 0x00: // bad byte, but keep going and see what happens
break;
default:
status = STATUS_FORMAT_ERROR;
}
}
}
private void readGraphicControlExt() {
read(); // block size
int packed = read(); // packed fields
dispose = (packed & 0x1c) >> 2; // disposal method
if (dispose == 0) {
dispose = 1; // elect to keep old image if discretionary
}
transparency = (packed & 1) != 0;
delay = readShort() * 10; // delay in milliseconds
transIndex = read(); // transparent color index
read(); // block terminator
}
private void readHeader() {
String id = "";
for (int i = 0; i < 6; i++) {
id += (char) read();
}
if (!id.startsWith("GIF")) {
status = STATUS_FORMAT_ERROR;
return;
}
readLSD();
if (gctFlag && !err()) {
gct = readColorTable(gctSize);
bgColor = gct[bgIndex];
}
}
private void readImage() {
ix = readShort(); // (sub)image position & size
iy = readShort();
iw = readShort();
ih = readShort();
int packed = read();
lctFlag = (packed & 0x80) != 0; // 1 - local color table flag
interlace = (packed & 0x40) != 0; // 2 - interlace flag
// 3 - sort flag
// 4-5 - reserved
lctSize = 2 << (packed & 7); // 6-8 - local color table size
if (lctFlag) {
lct = readColorTable(lctSize); // read table
act = lct; // make local table active
} else {
act = gct; // make global table active
if (bgIndex == transIndex) {
bgColor = 0;
}
}
int save = 0;
if (transparency) {
save = act[transIndex];
act[transIndex] = 0; // set transparent color if specified
}
if (act == null) {
status = STATUS_FORMAT_ERROR; // no color table defined
}
if (err()) {
return;
}
try {
decodeImageData(); // decode pixel data
skip();
if (err()) {
return;
}
frameCount++;
// create new image to receive frame data
// createImage(width, height);
Bitmap image = setPixels(); // transfer pixel data to image
if (gifFrame == null) {
gifFrame = new GifFrame(image, delay);
currentFrame = gifFrame;
} else {
GifFrame f = gifFrame;
while (f.nextFrame != null) {
f = f.nextFrame;
}
f.nextFrame = new GifFrame(image, delay);
}
// frames.addElement(new GifFrame(image, delay)); // add image to frame
// list
if (transparency) {
act[transIndex] = save;
}
resetFrame();
if (!action.parseOk(true, frameCount)) {
status = STATUS_FINISH;
return;
}
} catch (OutOfMemoryError e) {
Log.e("GifDecoder", ">>> log : " + e.toString());
e.printStackTrace();
}
}
private void readLSD() {
// logical screen size
width = readShort();
height = readShort();
// packed fields
int packed = read();
gctFlag = (packed & 0x80) != 0; // 1 : global color table flag
// 2-4 : color resolution
// 5 : gct sort flag
gctSize = 2 << (packed & 7); // 6-8 : gct size
bgIndex = read(); // background color index
pixelAspect = read(); // pixel aspect ratio
}
private void readNetscapeExt() {
do {
readBlock();
if (block[0] == 1) {
// loop count sub-block
int b1 = ((int) block[1]) & 0xff;
int b2 = ((int) block[2]) & 0xff;
loopCount = (b2 << 8) | b1;
}
} while ((blockSize > 0) && !err());
}
private int readShort() {
// read 16-bit value, LSB first
return read() | (read() << 8);
}
private void resetFrame() {
lastDispose = dispose;
lrx = ix;
lry = iy;
lrw = iw;
lrh = ih;
lastPixels = dest;
lastBgColor = bgColor;
dispose = 0;
transparency = false;
delay = 0;
lct = null;
}
/**
* Skips variable length blocks up to and including next zero length block.
*/
private void skip() {
do {
readBlock();
} while ((blockSize > 0) && !err());
}
}
我上传了完整的演示源 here。希望对你有帮助。
编辑：在实际实现中，我遇到了一些意想不到的问题，但没有什么是无法克服的：
AnimatedImageDrawable似乎忽略了其配置的边界。我改为缩放 canvas。- 由于我不明白的原因，
AnimatedImageDrawable.draw()偶尔会忘记安排下一帧。我决定调用该函数两次。第二次，我翻译 canvas 以便所有绘图都超出范围，这应该可以优化大部分工作。
这是示例代码。
import android.annotation.*;
import android.graphics.*;
import android.graphics.drawable.*;
import android.os.*;
import android.service.wallpaper.*;
import android.support.annotation.*;
import android.view.*;
@TargetApi(28)
public class TestWallpaper extends WallpaperService
{
@Override public Engine onCreateEngine()
{
return new Engine();
}
private class Engine extends WallpaperService.Engine implements Drawable.Callback
{
private final Drawable d;
private final Handler h = new Handler();
private float scaleX, scaleY;
private Engine()
{
this.setOffsetNotificationsEnabled(false);
Drawable d = null;
try
{
d = ImageDecoder
.decodeDrawable(ImageDecoder.createSource(getResources(), R.drawable.test));
d.setCallback(this);
// AnimatedImageDrawable seems to ignore its configured bounds and use its
// intrinsic bounds instead.
// In case they fix this bug, we'll go ahead and request the current
// behavior, and then before drawing we'll transform the canvas to compensate
d.setBounds(0, 0, d.getIntrinsicWidth(), d.getIntrinsicHeight());
if (d instanceof AnimatedImageDrawable)
{
final AnimatedImageDrawable anim = (AnimatedImageDrawable) d;
anim.setRepeatCount(AnimatedImageDrawable.REPEAT_INFINITE);
anim.start();
}
}
catch (Throwable t) // should never happen
{
t.printStackTrace();
}
this.d = d;
}
@Override public void invalidateDrawable(@NonNull Drawable _d)
{
if(isVisible())
draw(getSurfaceHolder().getSurface());
}
@Override public void scheduleDrawable(@NonNull Drawable _d, @NonNull Runnable _r, long _at)
{
if(isVisible())
h.postAtTime(_r, _d, _at);
}
@Override public void unscheduleDrawable(@NonNull Drawable _d, @NonNull Runnable _r)
{
h.removeCallbacks(_r, _d);
}
@Override public void onSurfaceChanged(SurfaceHolder _sh, int _format, int _w, int _h)
{
scaleX = (float) _w / d.getIntrinsicWidth();
scaleY = (float) _h / d.getIntrinsicHeight();
draw(_sh.getSurface());
}
@Override public void onSurfaceRedrawNeeded(SurfaceHolder _sh)
{
draw(_sh.getSurface());
}
private void draw(Surface _s)
{
try
{
final Canvas c = _s.lockCanvas(null);
c.scale(scaleX, scaleY);
d.draw(c);
// Sometimes AnimatedImageDrawable neglects to schedule the next frame
// after only one draw() of the current frame, so we'll draw() it again,
// but outside the canvas this time
c.translate(Float.MAX_VALUE, Float.MAX_VALUE);
d.draw(c);
//
_s.unlockCanvasAndPost(c);
}
catch (Throwable t)
{
t.printStackTrace();
// Most likely, the surface was destroyed while we were using it
// The new one will be delivered to onSurfaceChanged and we'll be fine
}
}
@Override public void onVisibilityChanged(boolean _visible)
{
super.onVisibilityChanged(_visible);
if(_visible)
draw(getSurfaceHolder().getSurface());
else
h.removeCallbacksAndMessages(null);
}
}
}