I need to write an external for LiveCode in C++, but I doubt my ability to do it.

[Phil Davis]

Jonathan,

I see I am out of my league here. I'm sure others can give good advice 
however - this list is read by a lot of very smart people.

Phil


On 3/6/16 3:36 PM, Jonathan Lynch wrote:
> A green-screen extraction on a large image requires millions of
> calculations. I am not using a flood-fill based extraction, so that helps a
> bit, but it still requires looking at every single pixel and checking to
> see if the colors are within a certain range. I want to improve the
> algorithm, so that it uses both a color-range comparison and a hue
> comparison. Colors that are outside of the color-range comparison but
> within the hue comparison probably have splashback from the green screen,
> and I could remove some of the green from those pixels - maybe cut the
> green component of the pixel in half or something like that.
>
> So, well, that is a whole ton of calculations right there. I really worked
> to optimize it in LC, but those optimizations only made a small difference.
> An interpreted language would be very unlikely to come close in speed on
> raw numerical comparisons like that. From what I understand, even LCB is
> more like Java than like C++, so it might be a bit faster than LC, but not
> in the range I need. Don't quote me on that.
>
> In general, LC is supposed to be able to to be extended with externals. In
> practical terms, this means it should work with the current version of
> Visual Studio. I don't have much C++ experience. I was hoping to just
> trudge through setting up the external so that I could focus on the
> algorithm. Instead, I could not even use the tutorial.
>
> I will try to find a way, though. I am just hoping for advice so that I can
> avoid any more blind alleys.
>
> Thanks,
>
> J
>
>
>
> On Sun, Mar 6, 2016 at 5:49 PM, Roland Huettmann <roland.huettmann at gmail.com
>> wrote:
>> But I would also appreciate a reply, maybe from Peter, which is of general
>> interest to all of us.
>>
>> Optimizing is one possibility, then the question about what would LC
>> Builder accomplish, and then C++, if nothing else does the job fast enough?
>>
>> I am thinking about some optimisation algorithms which are already
>> available in C++ and would probably execute not well enough in LCS.
>>
>> Roland
>>
>> On Sun, Mar 6, 2016, 23:10 Phil Davis <revdev at pdslabs.net> wrote:
>>
>>> Hi Jonathan,
>>>
>>> I would start by seeing if your LC code can be optimized so the time it
>>> takes per screen is acceptable. There are many small changes a person
>>> can sometimes make to code that causes dramatic speed increases.
>>>
>>> Or is the bulk of the time spent in areas LC can't address natively?
>>> Maybe that's why you want to go toward an external.
>>>
>>> Thanks -
>>> Phil Davis
>>>
>>>
>>> On 3/6/16 1:55 PM, Jonathan Lynch wrote:
>>>> Hello fellow LiveCoders,
>>>>
>>>> I need to write an external and it needs to be fast. It is for
>> extracting
>>>> images from a green screen. I wrote a good algorithm for this in
>>> LiveCode,
>>>> but it takes 20-30 seconds to handle all of the data processing. I want
>>> to
>>>> use C++ for speed advantages.
>>>>
>>>> I tried following the desktop externals tutorial that LiveCode uses,
>> but
>>> it
>>>> seems that the external generator that LiveCode offers does not work
>>>> properly with Visual Studio 2015.
>>>>
>>>> Should I try to find a free version of VS 2010? Should I try to fix the
>>> C++
>>>> library files so that they work with VS 2015? Is there some other very
>>> fast
>>>> compiled language, like Fortran, that I should try?
>>>>
>>>> I welcome any advice on how to do this.
>>>>
>>>> Thanks,
>>>>
>>>> Jonathan
>>>>
>>>>
>>>>
>>> --
>>> Phil Davis
>>>
>>>
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>
>

-- 
Phil Davis