FreeType: improve library dependency handling, add example

[igrr]

• Updated Zlib library to be compatible with CMake FindPackage module. Now, third party libraries which callfind_package(ZLIB) will find espressif/zlib component automatically, provided that it has been added as a dependency into the project.

  • We should do the same in other common components, as well.
  • Updated freetype component to have a dependency on zlib
  • Will do the above in another PR

• Configured freetype to not look for Brotli, Harfbuzz, BZ2, libpng, zlib libraries in the system (espressif__freetype component doesn't build (IEC-101) #317)

• Added a simple example to freetype component to validate its operation, added pytest script

[igrr]

@fhrbata May I ask you to take a look at this MR, especially the part in e90d4a7? If you think this is a good idea, I'll add find_package support for other common-enough libraries, like libpng.

[fhrbata]

Hello @igrr ,

with my limited understanding it looks ok to me. Maybe few questions if you don't mind.

1. Do we need to keep this in cache or is this intentional to prevent possible future override?
2. The idf prefix seems hardcoded in esp-idf, so it should be fine. But I'm wondering if this can change. Meaning is it possible that the target/alias will have different prefix than idf?
3. I guess that using e.g. ZLIBConfig.cmake and CMAKE_FIND_PACKAGE_REDIRECTS_DIR or other cmake's ways how to find a package(config/module mode) is not suitable for this use case and IIUC it would be probably unnecessary complicated.

Thank you

[igrr]

@fhrbata Sorry for missing your comment.

Do we need to keep this in cache or is this intentional to prevent possible future override?

I will check this again, I guess it didn't work for me without defining the variables as CACHE due to the (otherwise limited) variable scope.

The idf prefix seems hardcoded in esp-idf, so it should be fine. But I'm wondering if this can change. Meaning is it possible that the target/alias will have different prefix than idf?

This is a good point! I guess it would be unreasonable to change this prefix now, as many components were already written under the assumption that alias targets such as idf::component_name exist...

CMAKE_FIND_PACKAGE_REDIRECTS_DIR

I didn't try this. I will need more time to check if this works.

For now I have removed Zlib changes from this PR, leaving just the fix to FreeType dependencies configuration, and the addition of the new example.

I will open another PR for FindPackage support once I check the two points mentioned above.

[igrr]

@espressif2022 PTAL as well

[igrr]

cc @espzav

[igrr]

@espressif2022 @suda-morris Could you please help review?

[espzav]

@igrr Nice example! Thank you (I am thinking that it can be used for example for BSP NOGLIB - for testing)
LGTM

[igrr]

Thanks for the review @espzav!