Channel number agnostic pixel fill

        Uint32 mask = 0;
        switch ( numChannels )
        {
        case 1:
            mask = 0xFF000000;
            break;
        case 2:
            mask = 0xFFFF0000;
            break;
        case 3:
            mask = 0xFFFFFF00;
            break;
        case 4:
            mask = 0xFFFFFFFF;
            break;
        default:
            Assert(0);
        }
        const Uint32 WRITEVAL = inVal & mask;

        // sample inner loop random access pixel wmrite
        Uint32 *px = (Uint32*)(channels + (j * numChannels) + (pt.y * pitch));
        *px |= WRITEVAL;