[CMake] Best Practise for Multiple Platforms of External Project

[Bo Zhou]

Hi Craig

I got a workaround for that, using FILE command to create an empty file
inside that folder, then it works. I also tried your script, because of too
many dependencies, so it takes such a long time in Configuration phase, I
will use that later in small project.

Thank you for your help.

On Wed, Dec 14, 2016 at 4:51 AM, Craig Scott <craig.scott at crascit.com>
wrote:

> You could try using file(MAKE_DIRECTORY ...) between the two
> ExternalProject_Add() calls to actually ensure the directory exists, but
> I'm not 100% sure whether this would not interfere with the download step
> when it goes to do that at build time. I'm pretty sure it works, but you
> should confirm it.
>
> Another choice is to do the download at configure time rather than build
> time. This would mean the source would already be there by the time you
> reached the second ExternalProject_Add() call in your example. There are
> pros and cons to this, with the main objection being that ideally the
> configure step should be quick and making the download part of configure
> can increase the time that stage takes. For a general implementation
> supporting this functionality, have a look here:
>
> https://github.com/Crascit/DownloadProject
>
>
>
> On Wed, Dec 14, 2016 at 12:29 AM, Bo Zhou <bo.schwarzstein at gmail.com>
> wrote:
>
>> Hi
>>
>> In my project I have to compile the same external projects by the
>> different generators, is that possible to handle this cases
>> by ExternalProject_Add ?
>>
>> I tried this way, firstly, just download the repository
>>
>> ExternalProject_Add(OPENEXR_DOWNLOAD
>>     PREFIX ${OPENEXR_PREFIX}
>>     GIT_REPOSITORY https://github.com/openexr/openexr.git
>>     GIT_TAG v2.2.0
>>     CONFIGURE_COMMAND ""
>>     BUILD_COMMAND ""
>>     INSTALL_COMMAND "")
>>
>>
>> ExternalProject_Get_Property(OPENEXR_DOWNLOAD SOURCE_DIR)
>> SET(OPENEXR_SOURCE_DIR ${SOURCE_DIR})
>>
>> Then I tried to create a specific new target to use specific generator
>>
>> ExternalProject_Add(OPENEXR_VC11
>>   DEPENDS OPENEXR_DOWNLOAD
>>   SOURCE_DIR ${OPENEXR_SOURCE_DIR}/IlmBase)
>>
>>
>> Seems can't work, it requires an non-empty SOURCE_DIR, but before
>> downloading, it's empty :(
>>
>> So is there any better way to do this ? Thanks very much !
>>
>>
>> --
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>
>
> --
> Craig Scott
> Melbourne, Australia
> https://crascit.com
>
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