Fix FindAssimp on Windows

[traversaro]

The logic of FindAssimp is broken on Windows, as on VS2019 it looks only for assimp libraries compiled under VS2019 (i.e. with the -vc150 suffix) but VS2019 is perfectly compatible with assimp libraries compiled with VS2015 or VS2017. This was causing the problem reported in robotology/idyntree#832 (comment) .

The fix is to first look for an assimp CMake config file in the system, and only do the manual search if this is not found.

[traversaro]

Actually, looking a bit at the history of this file, it seems that it was added by @claudiofantacci in #229 with the explicit goal of not using the CMake config file of assimp, as that was frequently broken.

Indeed, unfortunately the assimp cmake config is still broken in Ubuntu 20.04, see https://bugs.launchpad.net/ubuntu/+source/assimp/+bug/1882427 . In iDynTree I have a workaround for that in https://github.com/robotology/idyntree/blob/v3.0.0/cmake/iDynTreeDependencies.cmake#L93 . Furthermore, in the long term all this issue should be solved by assimp/assimp#3455 .

However, I am not sure how we should proceed with this PR. I opened it to avoid forgetting about it, but I don't know the best way to proceed. Possible options:

• Only call find_package(assimp NO_CONFIG) on Windows
• Add the iDynTree workaround for the imported target also here, but I am not sure if that will work on Ubuntu 18.04
• Don't do anything, and fix everything in downstream projects.

Launchpad

Bug #1882427 “Assimp's CMake config files are malformed” : Bugs : assimp package : Ubuntu

The CMake config files shipped with the libassimp-dev package in Ubuntu 20.04 are malformed, and export the wrong include directories.

I prepare a minimal reproducible example in https://gist.github.com/traversaro/1046013d018ff998fac1cea6987be7e0 .

To reproduce it, just compile it as:
git clone https://gist.github.com/traversaro/1046013d018ff998fac1cea6987be7e0
cd 1046013d018ff998fac1cea6987be7e0
chmod +x build.sh
./build.sh

This will fail with the message:

-- Detecting CXX compile fea...</div></blockquote>
<blockquote><img src="https://avatars.githubusercontent.com/u/1587191?s=400&v=4" width="48" align="right"><div><img src="https://assets.fantasygmm.top/favicons/favicon.svg" height="14"> GitHub</div><div><strong><a href="https://github.com/robotology/idyntree">robotology/idyntree</a></strong></div><div>Multibody Dynamics Library designed for Free Floating Robots  - robotology/idyntree</div></blockquote>

[traversaro]

fyi @xEnVrE

[traversaro]

In iDynTree to avoid the problem I just added a NO_CONFIG option to the call find_package(assimp), so Findassimp.cmake of YCM is always ignored, so I am not in an hurry for this. However, I opened the PR as this problem could affect other repos such as:

• https://github.com/robotology/superimpose-mesh-lib
• https://github.com/robotology/visual-tactile-localization

GitHub

robotology/superimpose-mesh-lib

A modern C++ augmented-reality library to superimpose 3D objects on images. - robotology/superimpose-mesh-lib

GitHub

robotology/visual-tactile-localization

In-hand object tracking for the iCub humanoid robot. - robotology/visual-tactile-localization

[drdanz]

LGTM