Add constant to parse Gif Loop Count and apply to repeatCount

coil-gif/src/main/java/coil3/gif/AnimatedImageDecoder.kt

@@ -16,6 +16,8 @@ import coil3.decode.Decoder
 import coil3.decode.ImageSource
 import coil3.decode.toImageDecoderSourceOrNull
 import coil3.fetch.SourceFetchResult
+import coil3.gif.MovieDrawable.Companion.GIF_LOOP_COUNT
+import coil3.gif.MovieDrawable.Companion.REPEAT_INFINITE
 import coil3.gif.internal.animatable2CallbackOf
 import coil3.gif.internal.asPostProcessor
 import coil3.gif.internal.maybeWrapImageSourceToRewriteFrameDelay
@@ -54,10 +56,22 @@ class AnimatedImageDecoder(
 
     override suspend fun decode(): DecodeResult {
         var isSampled = false
+
+        val loopCount = if (options.repeatCount == GIF_LOOP_COUNT) {
+            extractLoopCountFromGif(source.source().peek()) ?: REPEAT_INFINITE
+        } else {
+            options.repeatCount
+        }
+
         val drawable = runInterruptible {
-            maybeWrapImageSourceToRewriteFrameDelay(source, enforceMinimumFrameDelay).use { source ->
+            maybeWrapImageSourceToRewriteFrameDelay(
+                source,
+                enforceMinimumFrameDelay,
+            ).use { source ->
                 val imageSource = source.toImageDecoderSourceOrNull(options, animated = true)
-                    ?: ImageDecoder.createSource(source.source().use { it.squashToDirectByteBuffer() })
+                    ?: ImageDecoder.createSource(
+                        source.source().use { it.squashToDirectByteBuffer() },
+                    )
                 imageSource.decodeDrawable { info, _ ->
                     // Configure the output image's size.
                     val (srcWidth, srcHeight) = info.size
@@ -88,14 +102,13 @@ class AnimatedImageDecoder(
                             setTargetSize(targetWidth, targetHeight)
                         }
                     }
-
                     // Configure any other attributes.
                     configureImageDecoderProperties()
                 }
             }
         }
         return DecodeResult(
-            image = wrapDrawable(drawable).asImage(),
+            image = wrapDrawable(drawable, loopCount).asImage(),
             isSampled = isSampled,
         )
     }
@@ -117,12 +130,12 @@ class AnimatedImageDecoder(
         postProcessor = options.animatedTransformation?.asPostProcessor()
     }
 
-    private suspend fun wrapDrawable(baseDrawable: Drawable): Drawable {
+    private suspend fun wrapDrawable(baseDrawable: Drawable, loopCount: Int): Drawable {
         if (baseDrawable !is AnimatedImageDrawable) {
             return baseDrawable
         }
 
-        baseDrawable.repeatCount = options.repeatCount
+        baseDrawable.repeatCount = loopCount
 
         // Set the start and end animation callbacks if any one is supplied through the request.
         val onStart = options.animationStartCallback

coil-gif/src/main/java/coil3/gif/GifDecoder.kt

@@ -34,6 +34,13 @@ class GifDecoder(
 ) : Decoder {
 
     override suspend fun decode() = runInterruptible {
+        val loopCount = if (options.repeatCount == MovieDrawable.GIF_LOOP_COUNT) {
+            source.source().peek().let { extractLoopCountFromGif(it) }
+                ?: MovieDrawable.REPEAT_INFINITE
+        } else {
+            options.repeatCount
+        }
+
         val source = maybeWrapImageSourceToRewriteFrameDelay(source, enforceMinimumFrameDelay)
         val movie: Movie? = source.use { Movie.decodeStream(it.source().inputStream()) }
 
@@ -49,9 +56,8 @@ class GifDecoder(
             scale = options.scale,
         )
 
-        drawable.setRepeatCount(options.repeatCount)
+        drawable.setRepeatCount(loopCount)
 
-        // Set the start and end animation callbacks if any one is supplied through the request.
         val onStart = options.animationStartCallback
         val onEnd = options.animationEndCallback
         if (onStart != null || onEnd != null) {

coil-gif/src/main/java/coil3/gif/MovieDrawable.kt

@@ -151,7 +151,7 @@ class MovieDrawable @JvmOverloads constructor(
      * Default: [REPEAT_INFINITE]
      */
     fun setRepeatCount(repeatCount: Int) {
-        require(repeatCount >= REPEAT_INFINITE) { "Invalid repeatCount: $repeatCount" }
+        require(repeatCount >= GIF_LOOP_COUNT) { "Invalid repeatCount: $repeatCount" }
         this.repeatCount = repeatCount
     }
 
@@ -193,7 +193,8 @@ class MovieDrawable @JvmOverloads constructor(
     @Suppress("DEPRECATION")
     override fun getOpacity(): Int {
         return if (paint.alpha == 255 &&
-            (pixelOpacity == OPAQUE || (pixelOpacity == UNCHANGED && movie.isOpaque))) {
+            (pixelOpacity == OPAQUE || (pixelOpacity == UNCHANGED && movie.isOpaque))
+        ) {
             PixelFormat.OPAQUE
         } else {
             PixelFormat.TRANSLUCENT
@@ -284,5 +285,12 @@ class MovieDrawable @JvmOverloads constructor(
     companion object {
         /** Pass this to [setRepeatCount] to repeat infinitely. */
         const val REPEAT_INFINITE = -1
+
+        /**
+         * Pass this to [setRepeatCount] to repeat according to GIF's LoopCount metadata.
+         *
+         * If the metadata is not available, it will default to infinite repetition.
+         */
+        const val GIF_LOOP_COUNT = -2
     }
 }

coil-gif/src/main/java/coil3/gif/decodeUtils.kt

@@ -63,3 +63,63 @@ fun DecodeUtils.isAnimatedHeif(source: BufferedSource): Boolean {
             source.rangeEquals(8, HEIF_HEADER_HEVC) ||
             source.rangeEquals(8, HEIF_HEADER_HEVX))
 }
+
+internal fun extractLoopCountFromGif(source: BufferedSource): Int? {
+    return try {
+        parseLoopCount(source)
+    } catch (e: Exception) {
+        null
+    }
+}
+
+private fun parseLoopCount(source: BufferedSource): Int? {
+    val headerBytes = ByteArray(6)
+    if (source.read(headerBytes) != 6) return null
+
+    val screenDescriptorBytes = ByteArray(7)
+    if (source.read(screenDescriptorBytes) != 7) return null
+
+    if ((screenDescriptorBytes[4] and 0b10000000.toByte()) != 0.toByte()) {
+        val colorTableSize = 3 * (1 shl ((screenDescriptorBytes[4].toInt() and 0b00000111) + 1))
+        source.skip(colorTableSize.toLong())
+    }
+
+    // Handle Application Extension Block
+    while (!source.exhausted()) {
+        val blockType = source.readByte().toInt() and 0xFF
+        if (blockType == 0x21) { // Extension Introducer
+            val label = source.readByte().toInt() and 0xFF
+            if (label == 0xFF) { // Application Extension
+                val blockSize = source.readByte().toInt() and 0xFF
+                val appIdentifier = source.readUtf8(8)
+                val appAuthCode = source.readUtf8(3)
+
+                if (appIdentifier == "NETSCAPE" && appAuthCode == "2.0") {
+                    val dataBlockSize = source.readByte().toInt() and 0xFF
+                    val loopCountIndicator = source.readByte().toInt() and 0xFF
+
+                    // Read low and high bytes for loop count
+                    val loopCountLow = source.readByte().toInt() and 0xFF
+                    val loopCountHigh = source.readByte().toInt() and 0xFF
+                    val loopCount = (loopCountHigh shl 8) or loopCountLow
+                    val blockTerminator = source.readByte().toInt() and 0xFF
+                    return if (loopCount == 0) null else loopCount
+                } else {
+                    skipExtensionBlock(source) // Skip if not NETSCAPE
+                }
+            } else {
+                skipExtensionBlock(source) // Skip other extension blocks
+            }
+        }
+    }
+    return null
+}
+
+// Extension Blocks always terminate with a zero
+private fun skipExtensionBlock(source: BufferedSource) {
+    while (true) {
+        val size = source.readByte().toInt() and 0xFF
+        if (size == 0) break
+        source.skip(size.toLong())
+    }
+}

coil-gif/src/main/java/coil3/gif/imageRequests.kt

@@ -6,6 +6,7 @@ import android.graphics.drawable.Drawable
 import coil3.Extras
 import coil3.annotation.ExperimentalCoilApi
 import coil3.getExtra
+import coil3.gif.MovieDrawable.Companion.GIF_LOOP_COUNT
 import coil3.gif.MovieDrawable.Companion.REPEAT_INFINITE
 import coil3.request.ImageRequest
 import coil3.request.Options
@@ -17,7 +18,7 @@ import coil3.request.Options
  * @see AnimatedImageDrawable.setRepeatCount
  */
 fun ImageRequest.Builder.repeatCount(repeatCount: Int) = apply {
-    require(repeatCount >= REPEAT_INFINITE) { "Invalid repeatCount: $repeatCount" }
+    require(repeatCount >= GIF_LOOP_COUNT) { "Invalid repeatCount: $repeatCount" }
     extras[repeatCountKey] = repeatCount
 }