Code to fastpath Alpha PNGs in LCMS - part of bug 445552. r=vlad

modules/lcms/src/cmsxform.c

@@ -615,8 +615,13 @@ void MatrixShaperXFORMFloat(_LPcmsTRANSFORM p,
        register LPBYTE In, Out;
        register unsigned int i;
        LPMATSHAPER MatShaper;
+       unsigned Increment;
 
+       // We support a very limited number of configurations for the floatpath
+       CMSASSERT(p->InputFormat == p->OutputFormat);
+       CMSASSERT((p->InputFormat == TYPE_RGB_8) || (p->InputFormat == TYPE_RGBA_8));
 
+       Increment = (p->InputFormat == TYPE_RGB_8) ? 3 : 4;
        In  = (LPBYTE) in;
        Out = (LPBYTE) out;
        MatShaper = p -> SmeltMatShaper;
@@ -758,8 +763,8 @@ void MatrixShaperXFORMFloat(_LPcmsTRANSFORM p,
               Out[2] = RGB_16_TO_8((WORD)tmp[2]);
               }
 
-              In += 3;
-              Out += 3;
+              In += Increment;
+              Out += Increment;
        }
 }
 #endif

modules/libpr0n/decoders/png/nsPNGDecoder.cpp

@@ -542,20 +542,24 @@ info_callback(png_structp png_ptr, png_infop info_ptr)
   }
   if (decoder->mInProfile && gfxPlatform::GetCMSOutputProfile()) {
     PRUint32 outType;
+    PRUint32 dwFlags = 0;
 
     if (color_type & PNG_COLOR_MASK_ALPHA || num_trans)
       outType = TYPE_RGBA_8;
     else
       outType = TYPE_RGB_8;
 
+    /* Determine if we can use the optimized floating point path. */
+    if ((inType == outType) && 
+        ((inType == TYPE_RGB_8) || (inType == TYPE_RGBA_8)))
+      dwFlags |= cmsFLAGS_FLOATSHAPER;
+
     decoder->mTransform = cmsCreateTransform(decoder->mInProfile,
                                              inType,
                                              gfxPlatform::GetCMSOutputProfile(),
                                              outType,
                                              intent,
-                                             ((inType == TYPE_RGB_8) && 
-                                              (outType == TYPE_RGB_8))
-                                             ? cmsFLAGS_FLOATSHAPER : 0);
+                                             dwFlags);
   } else {
     png_set_gray_to_rgb(png_ptr);
     if (gfxPlatform::GetCMSMode() == eCMSMode_All) {