From 2ca642e02a2f38dd64ac0204f3b8cc8d01944e74 Mon Sep 17 00:00:00 2001
From: Urvang Joshi <urvang@google.com>
Date: Fri, 9 Nov 2012 14:37:20 -0800
Subject: [PATCH] Rectify WebPMuxGetFeatures:

It should return ALPHA_FLAG for lossless bit-stream

Change-Id: I900bd5b58bf75bc25fca1abf4ecc12aea26eac1c
---
 src/mux/muxinternal.c | 12 +++++++-----
 src/mux/muxread.c     | 29 +++++++++++++++++------------
 2 files changed, 24 insertions(+), 17 deletions(-)

diff --git a/src/mux/muxinternal.c b/src/mux/muxinternal.c
index 06882bbf..ebeb651e 100644
--- a/src/mux/muxinternal.c
+++ b/src/mux/muxinternal.c
@@ -578,12 +578,14 @@ WebPMuxError MuxValidate(const WebPMux* const mux) {
   if (num_vp8x == 0 && num_images != 1) return WEBP_MUX_INVALID_ARGUMENT;
 
   // ALPHA_FLAG & alpha chunk(s) are consistent.
-  if (num_vp8x > 0 && MuxHasLosslessImages(mux->images_)) {
-    // Special case: we have a VP8X chunk as well as some lossless images.
-    if (!(flags & ALPHA_FLAG)) return WEBP_MUX_INVALID_ARGUMENT;
+  if (MuxHasLosslessImages(mux->images_)) {
+    if (num_vp8x > 0) {
+      // Special case: we have a VP8X chunk as well as some lossless images.
+      if (!(flags & ALPHA_FLAG)) return WEBP_MUX_INVALID_ARGUMENT;
+    }
   } else {
-    err = ValidateChunk(mux, IDX_ALPHA, ALPHA_FLAG, flags, -1, &num_alpha);
-    if (err != WEBP_MUX_OK) return err;
+      err = ValidateChunk(mux, IDX_ALPHA, ALPHA_FLAG, flags, -1, &num_alpha);
+      if (err != WEBP_MUX_OK) return err;
   }
 
   // num_fragments & num_images are consistent.
diff --git a/src/mux/muxread.c b/src/mux/muxread.c
index 239a36e0..e1862e4e 100644
--- a/src/mux/muxread.c
+++ b/src/mux/muxread.c
@@ -254,27 +254,32 @@ WebPMux* WebPMuxCreateInternal(const WebPData* bitstream, int copy_data,
 //------------------------------------------------------------------------------
 // Get API(s).
 
-// TODO(urvang): Change the behavior of this to return ALPHA_FLAG when the mux
-// doesn't contain a VP8X chunk, but does contain a VP8L chunk with real alpha.
 WebPMuxError WebPMuxGetFeatures(const WebPMux* mux, uint32_t* flags) {
   WebPData data;
-  WebPMuxError err;
 
   if (mux == NULL || flags == NULL) return WEBP_MUX_INVALID_ARGUMENT;
   *flags = 0;
 
   // Check if VP8X chunk is present.
-  err = MuxGet(mux, IDX_VP8X, 1, &data);
-  if (err == WEBP_MUX_NOT_FOUND) {
-    return MuxValidateForImage(mux);  // Check if a single image is present.
-  } else if (err != WEBP_MUX_OK) {
-    return err;
+  if (MuxGet(mux, IDX_VP8X, 1, &data) == WEBP_MUX_OK) {
+    if (data.size < CHUNK_SIZE_BYTES) return WEBP_MUX_BAD_DATA;
+    *flags = GetLE32(data.bytes);  // All OK. Fill up flags.
+  } else {
+    WebPMuxError err = MuxValidateForImage(mux);  // Check for single image.
+    if (err != WEBP_MUX_OK) return err;
+    if (MuxHasLosslessImages(mux->images_)) {
+      const WebPData* const vp8l_data = &mux->images_->img_->data_;
+      int has_alpha = 0;
+      if (!VP8LGetInfo(vp8l_data->bytes, vp8l_data->size, NULL, NULL,
+                       &has_alpha)) {
+        return WEBP_MUX_BAD_DATA;
+      }
+      if (has_alpha) {
+        *flags = ALPHA_FLAG;
+      }
+    }
   }
 
-  if (data.size < CHUNK_SIZE_BYTES) return WEBP_MUX_BAD_DATA;
-
-  // All OK. Fill up flags.
-  *flags = GetLE32(data.bytes);
   return WEBP_MUX_OK;
 }