Why blending with Color white?

On Thu, Jan 9, 2014 at 6:54 PM,  <commits at source.squeak.org> wrote:
> Nicolas Cellier uploaded a new version of Graphics to project The Trunk:
> http://source.squeak.org/trunk/Graphics-nice.287.mcz
>
> ==================== Summary ====================
>
> Name: Graphics-nice.287
> Author: nice
> Time: 10 January 2014, 1:54:29.094 am
> UUID: e853e088-f3a2-47b0-b991-98b23543c4e2
> Ancestors: Graphics-nice.284
>
> Fix display of embedded Form in Text.
> CombinationRule Form over apparently does not correctly handle transparency, Form blend does a better job.
> The mistake is that DisplayScanner and MultiDisplayScanner did have two different versions of placeEmbeddedObject:, and I picked the wrong one when unifying. Since I only tested with embedded Morph and opaque Form, I failed to see it...
> Thanks to Sean DeNigris for report and solution.
>
> =============== Diff against Graphics-nice.284 ===============
>
> Item was changed:
>   ----- Method: BitBltDisplayScanner>>displayEmbeddedForm: (in category 'displaying') -----
>   displayEmbeddedForm: aForm
>         aForm
>                 displayOn: bitBlt destForm
>                 at: destX @ (lineY + line baseline - aForm height)
> +               clippingBox: bitBlt clipRect
> +               rule: Form blend
> +               fillColor: Color white !
> -               clippingBox: bitBlt clipRect!
>
>