From 06a38c7b1cffeeb8216efb465fafc1c40d1150d7 Mon Sep 17 00:00:00 2001
From: Pascal Massimino <pascal.massimino@gmail.com>
Date: Fri, 24 Jun 2016 17:15:31 +0200
Subject: [PATCH] fix rescaling bug: alpha plane wasn't filled with 0xff

(in case no alpha was present in the source .webp,
but user requested some)

Change-Id: I9011d38237907c60d6796a86bd2c72166aa80f27
---
 src/dec/io.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/src/dec/io.c b/src/dec/io.c
index 13e469ab..8d5c43f3 100644
--- a/src/dec/io.c
+++ b/src/dec/io.c
@@ -119,6 +119,14 @@ static int EmitFancyRGB(const VP8Io* const io, WebPDecParams* const p) {
 
 //------------------------------------------------------------------------------
 
+static void FillAlphaPlane(uint8_t* dst, int w, int h, int stride) {
+  int j;
+  for (j = 0; j < h; ++j) {
+    memset(dst, 0xff, w * sizeof(*dst));
+    dst += stride;
+  }
+}
+
 static int EmitAlphaYUV(const VP8Io* const io, WebPDecParams* const p,
                         int expected_num_lines_out) {
   const uint8_t* alpha = io->a;
@@ -137,10 +145,7 @@ static int EmitAlphaYUV(const VP8Io* const io, WebPDecParams* const p,
     }
   } else if (buf->a != NULL) {
     // the user requested alpha, but there is none, set it to opaque.
-    for (j = 0; j < mb_h; ++j) {
-      memset(dst, 0xff, mb_w * sizeof(*dst));
-      dst += buf->a_stride;
-    }
+    FillAlphaPlane(dst, mb_w, mb_h, buf->a_stride);
   }
   return 0;
 }
@@ -269,8 +274,8 @@ static int EmitRescaledYUV(const VP8Io* const io, WebPDecParams* const p) {
 
 static int EmitRescaledAlphaYUV(const VP8Io* const io, WebPDecParams* const p,
                                 int expected_num_lines_out) {
+  const WebPYUVABuffer* const buf = &p->output->u.YUVA;
   if (io->a != NULL) {
-    const WebPYUVABuffer* const buf = &p->output->u.YUVA;
     uint8_t* dst_y = buf->y + p->last_y * buf->y_stride;
     const uint8_t* src_a = buf->a + p->last_y * buf->a_stride;
     const int num_lines_out = Rescale(io->a, io->width, io->mb_h, &p->scaler_a);
@@ -280,6 +285,11 @@ static int EmitRescaledAlphaYUV(const VP8Io* const io, WebPDecParams* const p,
       WebPMultRows(dst_y, buf->y_stride, src_a, buf->a_stride,
                    p->scaler_a.dst_width, num_lines_out, 1);
     }
+  } else if (buf->a != NULL) {
+    // the user requested alpha, but there is none, set it to opaque.
+    assert(p->last_y + expected_num_lines_out <= io->scaled_height);
+    FillAlphaPlane(buf->a + p->last_y * buf->a_stride,
+                   io->scaled_width, expected_num_lines_out, buf->a_stride);
   }
   return 0;
 }