Commented Issue: Bug in Blit function for WPF [21788]

Hello,
there is bug in Blit function, when using BlendMode.Alpha.

instead of code

```
if (blendMode == BlendMode.Alpha)
{
var isa = 255 - sa;
#if NETFX_CORE
// Special case for WinRT since it does not use pARGB (pre-multiplied alpha)
destPixel = ((da & 0xff) << 24) |
((((sr * sa + isa * dr) >> 8) & 0xff) << 16) |
((((sg * sa + isa * dg) >> 8) & 0xff) << 8) |
(((sb * sa + isa * db) >> 8) & 0xff);
#else
destPixel =
((((sa << 8) + isa * da) >> 8) << 24) |
(((((sr << 8) + isa * dr) >> 8) & 0xff) << 16) |
(((((sg << 8) + isa * dg) >> 8) & 0xff) << 8) |
((((sb << 8) + isa * db) >> 8) & 0xff);
#endif
```

should be

```
if (BlendMode == BlendMode.Alpha)
{
var isa = 255 - sa;
#if NETFX_CORE
// Special case for WinRT since it does not use pARGB (pre-multiplied alpha)
destPixel = ((da & 0xff) << 24) |
((((sr * sa + isa * dr) >> 8) & 0xff) << 16) |
((((sg * sa + isa * dg) >> 8) & 0xff) << 8) |
(((sb * sa + isa * db) >> 8) & 0xff);
#else
destPixel = ((da & 0xff) << 24) |
(((((sr * sa) + isa * dr) >> 8) & 0xff) << 16) |
(((((sg * sa) + isa * dg) >> 8) & 0xff) << 8) |
((((sb * sa) + isa * db) >> 8) & 0xff);
#endif
}
```

(instead of (((sr << 8) + isa * dr) >> 8) should be (((sr * sa + isa * dr) >> 8), difference in A component is not subject of this issue
Tested with some icons, fixed version renders nice blended icons
Comments: ** Comment from web user: dbshell **

Sorry for typing error is mean:
FillRectangle function draws rectangles one pixel smaller than previous __version__