Pixel Bender custom multiply blend and other questions

Question

I am creating photo editing application on iPad and i am using Pixel Bender to calculate effects. But ive got a problem with multiply blend mode.When i run it in CPU/GPU mode, it runs fine(result looks absolutly 1:1 as from photoshop). But when i switch to Flash Player mode, it dont want to render properly. I dont get any compilation errors. Ive got also some other questions:
1.How does PB performs on iOS ?
2.If my problem is becouse of  incapability of FP, is there any other solution to this ? I cant afford AS3.0 computing, becouse it is really slow even on PC.
3. Can be Pixel Bender 3D sollution to this ? If yes, when will it come out to iOS ?
4. How are filters computed in FP ? CPU or GPU ?
here, you can see the difference : http://ponozka.php5.cz/gpuMode.jpg  http://ponozka.php5.cz/flashMode.jpg
Thanks
source code :
<languageVersion : 1.0;>
kernel MultiplyLayer
<   namespace : "Your Namespace";
    vendor : "Richard Molnar";
    version : 1;
>
    input image4 src;
    input image4 layer;
    output pixel4 dst;
    parameter float4 param <
        minValue:float4(0.0,0.0,0.0,0.0);
        maxValue:float4(1.0,1.0,1.0,1.0);
        defaultValue:float4(1.0,1.0,1.0,1.0);
    >;
    void
    evaluatePixel()
        pixel4 pix;
        pixel4 pix2;
        pix = sampleNearest(src,outCoord());
        pix2 = sampleNearest(layer,outCoord());
        dst.r = pix.r - pix.r * (1.0-(pix2.r))*param.r*pix2.a*param.a;
        dst.g = pix.g- pix.g * (1.0-(pix2.g))*param.g*pix2.a*param.a;
        dst.b = pix.b -pix.b * (1.0-(pix2.b))*param.b*pix2.a*param.a;
        dst.a = 1.0;

Answer 1

Ok, so i already know, that CPU/GPU and flash are giving different results. So lets have a situation, where you need to display transparent image without transparency. On GPU/CPU, you will need only this :
dst.r = src.r;
dst.g = src.g;
dst.b = src.b;
dst.a = 1.0;
but for flash, you will need this :
dst.r = (1.0/src.a)*src.r;
dst.g = (1.0/src.a)*src.g;
dst.b = (1.0/src.a)*src.b;
dst.a = 1.0;
First kernel on GPU will show the exact same result as second kernel on flash. But the question remains : is it bug ?