Make JXELIB bug workaround a pref.

There's still a risk for crashes with this enabled, so preffed off by default for now.
Live pref, so can be toggled on-the-fly if needed.

Tag #1659.

3 files changed, 34 insertions, 18 deletions

diff --git a/gfx/thebes/gfxPrefs.h b/gfx/thebes/gfxPrefs.h
index 750cb2b5d..638e929b9 100644
--- a/gfx/thebes/gfxPrefs.h
+++ b/gfx/thebes/gfxPrefs.h
@@ -250,7 +250,7 @@ private:
   DECL_GFX_PREF(Live, "image.mozsamplesize.enabled",           ImageMozSampleSizeEnabled, bool, false);
   DECL_GFX_PREF(Once, "image.multithreaded_decoding.limit",    ImageMTDecodingLimit, int32_t, -1);
   DECL_GFX_PREF(Live, "image.single-color-optimization.enabled", ImageSingleColorOptimizationEnabled, bool, true);
-
+  
   DECL_GFX_PREF(Once, "layers.acceleration.disabled",          LayersAccelerationDisabled, bool, false);
   DECL_GFX_PREF(Live, "layers.acceleration.draw-fps",          LayersDrawFPS, bool, false);
   DECL_GFX_PREF(Live, "layers.acceleration.draw-fps.print-histogram",  FPSPrintHistogram, bool, false);
@@ -330,6 +330,7 @@ private:
   DECL_GFX_PREF(Once, "layout.paint_rects_separately",         LayoutPaintRectsSeparately, bool, true);
 #ifdef MOZ_JXR
   DECL_GFX_PREF(Live, "media.jxr.enabled",                     MediaJXREnabled, bool, false);
+  DECL_GFX_PREF(Live, "media.jxr.workaround_alphaplane_bug",   MediaJXRWorkaroundAlphaplaneBug, bool, false);
 #endif
 
   DECL_GFX_PREF(Live, "nglayout.debug.widget_update_flashing", WidgetUpdateFlashing, bool, false);
diff --git a/image/decoders/nsJXRDecoder.cpp b/image/decoders/nsJXRDecoder.cpp
index 16a6f78c7..0ab12aa63 100644
--- a/image/decoders/nsJXRDecoder.cpp
+++ b/image/decoders/nsJXRDecoder.cpp
@@ -88,6 +88,7 @@
 #include "gfxColor.h"
 #include "gfxPlatform.h"
 #include "qcms.h" // icSigRgbData, icSigGrayData
+#include "gfxPrefs.h" // to control workarounds
 
 //////////////////// Mozilla JPEG-XR decoder ///////////////////////////
 
@@ -2673,17 +2674,23 @@ void nsJXRDecoder::FinishInternal()
                 // Circumvent the bug in JXELIB's JPEG-XR encoder that writes wrong alpha plane byte count.
                 if (m_pDecoder->WMP.wmiDEMisc.uAlphaOffset + m_pDecoder->WMP.wmiI_Alpha.uImageByteCount > GetTotalNumBytesReceived())
                 {
-                    // Make sure we're not having incomplete data and avoid Bad Things(tm) [Moonchild]
-                    if (GetTotalNumBytesReceived() <= m_pDecoder->WMP.wmiDEMisc.uAlphaOffset) {
+                    if (gfxPrefs::MediaJXRWorkaroundAlphaplaneBug()) {
+                        // Make sure we're not having incomplete data and avoid Bad Things(tm) [Moonchild]
+                        if (GetTotalNumBytesReceived() <= m_pDecoder->WMP.wmiDEMisc.uAlphaOffset) {
+                            PostDataError();
+                            return;
+                        }
+                    
+                        // Adjust the alpha plane byte count if the value is wrong.
+                        // If received data is still incomplete but cut off in the alpha plane data,
+                        // the alpha plane size will be wrong but should still be an acceptable value
+                        // for the decoder. [Moonchild]
+                        m_pDecoder->WMP.wmiI_Alpha.uImageByteCount = GetTotalNumBytesReceived() - m_pDecoder->WMP.wmiDEMisc.uAlphaOffset;
+                    } else {
+                        // Don't hack around this encoder bug, report an encoding error instead.
                         PostDataError();
                         return;
                     }
-                    
-                    // Adjust the alpha plane byte count if the value is wrong.
-                    // If received data is still incomplete but cut off in the alpha plane data,
-                    // the alpha plane size will be wrong but will should be an acceptable value
-                    // for the decoder. [Moonchild]
-                    m_pDecoder->WMP.wmiI_Alpha.uImageByteCount = GetTotalNumBytesReceived() - m_pDecoder->WMP.wmiDEMisc.uAlphaOffset;
                 }
 
                 StartDecodingMBRows_Alpha();
@@ -2727,20 +2734,25 @@ void nsJXRDecoder::FinishInternal()
                 m_pStream->DiscardHead(m_pStream, m_pDecoder->WMP.wmiDEMisc.uAlphaOffset, &discarded);
 
                 // Circumvent the bug in JXELIB's JPEG-XR encoder that writes wrong alpha plane byte count.
-                // Adjust the alpha plane byte count if the value is wrong.
                 if (m_pDecoder->WMP.wmiDEMisc.uAlphaOffset + m_pDecoder->WMP.wmiI_Alpha.uImageByteCount > GetTotalNumBytesReceived())
                 {
-                    // Make sure we're not having incomplete data and avoid Bad Things(tm) [Moonchild]
-                    if (GetTotalNumBytesReceived() <= m_pDecoder->WMP.wmiDEMisc.uAlphaOffset) {
+                    if (gfxPrefs::MediaJXRWorkaroundAlphaplaneBug()) {
+                        // Make sure we're not having incomplete data and avoid Bad Things(tm) [Moonchild]
+                        if (GetTotalNumBytesReceived() <= m_pDecoder->WMP.wmiDEMisc.uAlphaOffset) {
+                            PostDataError();
+                            return;
+                        }
+
+                        // Adjust the alpha plane byte count if the value is wrong.
+                        // If received data is still incomplete but cut off in the alpha plane data,
+                        // the alpha plane size will be wrong but should still be an acceptable value
+                        // for the decoder. [Moonchild]
+                        m_pDecoder->WMP.wmiI_Alpha.uImageByteCount = GetTotalNumBytesReceived() - m_pDecoder->WMP.wmiDEMisc.uAlphaOffset;
+                    } else {
+                        // Don't hack around this encoder bug, report an encoding error instead.
                         PostDataError();
                         return;
                     }
-                    
-                    // Adjust the alpha plane byte count if the value is wrong.
-                    // If received data is still incomplete but cut off in the alpha plane data,
-                    // the alpha plane size will be wrong but should still be an acceptable value
-                    // for the decoder. [Moonchild]
-                    m_pDecoder->WMP.wmiI_Alpha.uImageByteCount = GetTotalNumBytesReceived() - m_pDecoder->WMP.wmiDEMisc.uAlphaOffset;
                 }
 
                 StartDecodingMBRows_Alpha();
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index df91f87c7..554179fe6 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -316,6 +316,9 @@ pref("media.jxr.autoaccept", true);
 // updated with the new type. This pref is mainly for testing and should be
 // removed once the preferred type (most likely "image/jxr") has been chosen.
 pref("media.jxr.advertised_mime_type", "image/jxr");
+// Work around the JXELIB encoding bug for incorrect bytecounts.
+// Enabling this -may- lead to crashes in rare circumstances.
+pref("media.jxr.workaround_alphaplane_bug", false);
 #endif
 #ifdef MOZ_DIRECTSHOW
 pref("media.directshow.enabled", true);