Re: [ggt-devel] Getting gmtl Matrix data from a PositionalInterface

[Doug M. <mc...@ia...>]

On Jun 25, 2007, at 8:21 PM, Patrick Hartling wrote:

> Doug McCorkle wrote:
>> On Jun 12, 2007, at 10:57 PM, Doug McCorkle wrote:
>>
>>> On Jun 12, 2007, at 10:02 PM, Patrick Hartling wrote:
>>>
>>>> Doug McCorkle wrote:
>>>>> On Jun 12, 2007, at 9:13 PM, Patrick Hartling wrote:
>>>>>
>>>>>> Doug McCorkle wrote:
>>>>>>> On Jun 12, 2007, at 8:45 AM, Patrick Hartling wrote:
>>>>>>>
>>>>>>>> Patrick Hartling wrote:
>>>>>>>>> Doug McCorkle wrote:
>>>>>>>>>> On Jun 7, 2007, at 7:51 AM, Patrick Hartling wrote:
>>>>>>>>>>
>>>>>>>>>>> Doug McCorkle wrote:
>>>>>>>>>>>> Hello,
>>>>>>>>>>>>
>>>>>>>>>>>>       When getting the matrix information from a
>>>>>>>>>>>> PositionalInterface
>>>>>>>>>>>> such as head position the matrix returned is a Matrix44f.
>>>>>>>>>>>> Is it
>>>>>>>>>>>> possible to get a Matrix44d?
>>>>>>>>>>> Not from gadget::PositionProxy::getData(). The chain of data
>>>>>>>>>>> from
>>>>>>>>>>> the input
>>>>>>>>>>> device to your application object is all in single-precision
>>>>>>>>>>> floating-point
>>>>>>>>>>> data.
>>>>>>>>>>>
>>>>>>>>>> OK.
>>>>>>>>>>
>>>>>>>>>>>> Is there any easy way to convert from a
>>>>>>>>>>>> float matrix to a double matrix? Thanks for the help.
>>>>>>>>>>> Given the nature of C/C++, the simplest way that I know of
>>>>>>>>>>> to do it
>>>>>>>>>>> would be
>>>>>>>>>>> the following:
>>>>>>>>>>>
>>>>>>>>>>>    gmtl::Matrix44d double_mat;
>>>>>>>>>>>    gmtl::Matrix44f float_mat = mDev->getData();
>>>>>>>>>>>
>>>>>>>>>>>    for ( unsigned int i = 0; i < 16; ++i )
>>>>>>>>>>>    {
>>>>>>>>>>>       double_mat.mData[i] = float_mat.mData[i];
>>>>>>>>>>>    }
>>>>>>>>>>>
>>>>>>>>>> This is what we are doing now.
>>>>>>>>>>
>>>>>>>>>>> You could easily make a function with a signature such as
>>>>>>>>>>> this to
>>>>>>>>>>> hide the
>>>>>>>>>>> details:
>>>>>>>>>>>
>>>>>>>>>>>    gmtl::Matrix44d convert(const gmtl::Matrix44f& m);
>>>>>>>>>>>
>>>>>>>>>>> You could even take it a step further and make a generic
>>>>>>>>>>> GMTL-style
>>>>>>>>>>> generator function. There might be some template-based
>>>>>>>>>>> approach
>>>>>>>>>>> that would
>>>>>>>>>>> allow for the loop to be unrolled, but I don't know what
>>>>>>>>>>> that would
>>>>>>>>>>> be off
>>>>>>>>>>> the top of my head.
>>>>>>>>>>>
>>>>>>>>>> I was hoping for something like this. I will look into it.
>>>>>>>>>> Thanks.
>>>>>>>>> I was thinking about this some more last night, and I just put
>>>>>>>>> together the
>>>>>>>>> attached code. The loop gets unrolled, and it will work for  
>>>>>>>>> any
>>>>>>>>> pairing of
>>>>>>>>> gmtl::Matrix<S,R,C>/gmtl::Matrix<T,R,C> where S is
>>>>>>>>> convertible to
>>>>>>>>> T. If
>>>>>>>>> Boost.Lambda could be used, the code would be simpler because
>>>>>>>>> the
>>>>>>>>> separate
>>>>>>>>> set<...>() helper function and the usage of boost::bind()
>>>>>>>>> wouldn't be
>>>>>>>>> needed, but in my experience, when data members are involved,
>>>>>>>>> boost::bind()
>>>>>>>>> always has to be used.
>>>>>>>> I thought of a way to use Boost.Lambda. See the attachment.
>>>>>>>>
>>>>>>>>> Nevertheless, the loop unrolling and inlining should
>>>>>>>>> result in better performance than a regular for loop.
>>>>>>>> I may have overstated this. I haven't done any performance
>>>>>>>> tests on
>>>>>>>> this,
>>>>>>>> and boost::bind() carries with it a fair amount of overhead.
>>>>>>>> There is
>>>>>>>> plenty
>>>>>>>> of inlining that can be taken advantage of, but the number of
>>>>>>>> instructions
>>>>>>>> executed is probably more than when using a loop. The question,
>>>>>>>> then, is
>>>>>>>> whether the cost of those extra instructions is different than
>>>>>>>> the
>>>>>>>> cost of
>>>>>>>> the branch instructions needed for looping.
>>>>>>>>
>>>>>>> Thanks! I will give this a try. After thinking about this more
>>>>>>> over the
>>>>>>> past few days I wondered if it would be possible to generalize
>>>>>>> this to
>>>>>>> the datatype within gmtl? I thought that most underlying
>>>>>>> datatypes in
>>>>>>> gmtl are raw arrays so did not know if this could even be
>>>>>>> extended to
>>>>>>> quats and all the other gmtl datatypes.
>>>>>> That would require rather more sophisticated type traits than
>>>>>> current
>>>>>> exist
>>>>>> in GMTL, and I think that the conversion functions would still
>>>>>> have to be
>>>>>> specialized on a per-type basis. For example, you wouldn't  
>>>>>> want to
>>>>>> copy the
>>>>>> internal array from a gmtl::Quatf to a gmtl::Vec4i just because
>>>>>> they both
>>>>>> have four values.
>>>>> Right. I was more thinking same type to same type restrictions.
>>>> I am not sure if this could be generalized fully. I tried some
>>>> stuff with a
>>>> template template parameter so that the input and output types
>>>> could be
>>>> matched without being identified explicitly, but I haven't been
>>>> able to get
>>>> anything to compile yet. The basic idea I have is shown in the
>>>> attached
>>>> file. My current suspicion is that the variation in number of
>>>> template
>>>> parameters among GMTL types (gmtl::Matrix<T,R,C>, gmtl::Vec<T,S>,
>>>> gmtl::Quat<T>, etc.) will make things tough. Beyond that, the mData
>>>> member
>>>> is not always an array, so specialization would be needed anyway.
>>>> There may
>>>> yet be a way to do it, but I am reaching the (current) limits of my
>>>> understanding of C++ templates. Overloading the function that I
>>>> sent out
>>>> earlier is the simplest approach.
>>>>
>>> What you sent out earlier is very helpful. I am not trying to imply
>>> that I need anything more, it was more just a thought of something
>>> interesting to add to GMTL. Thanks for the effort in figuring
>>> something out.
>>>
>>
>> The template functions worked great! Thanks for the help. Will these
>> be included in future releases of GMTL?
>
> I went ahead and checked in a documented version of the function in  
> the new
> file gmtl/Misc/MatrixConvert.h. It will be included with the 0.5.1  
> release
> that will happen tonight.
>
>
Great! This release will also have the build fix in for the pc files  
which I am after. We have been using the matrix conversion in our  
code for a week with no issues.

Doug