/cc @diablodale

👍

This pull request has a bug that severely limits the number of kernel arguments. The intent of the code seems to be limiting the number of image arguments to MAX_ARRS, but it actually limits the number of all kinds of kernel arguments to MAX_ARRS.

registerImageArgument(int arg, const Image2D& image) treats int arg as image index and limits it to MAX_ARRS. However, Kernel::set(int i, const Image2D& image2D) calls registerImageArgument() treating int arg as kernel argument index. This means a kernel can not have Image2D arguments after MAX_ARRS arguments have been set.

As a result of this pull request, previously working code now fails at CV_CheckLT(arg, (int)MAX_ARRS, "");.

Would you write a test case that demonstrates that fail?
Such would both help us all understand the issue + add a good test case into the project for now and future regressions. :-)

Here is the test that triggers the exception: https://github.com/rasmus25/opencv/commit/0365be4877d5f9428b72b58d5b32bdc8abaff9e1
The exception prints this in the terminal:

unknown file: Failure
C++ exception with description "OpenCV(4.5.2-dev) /home/rasmus/Allalaadimised/opencvbug/opencv/modules/core/src/ocl.cpp:3485: error: (-2:Unspecified error) in function 'void cv::ocl::Kernel::Impl::registerImageArgument(int, const cv::ocl::Image2D&)'
>  (expected: 'arg < (int)MAX_ARRS'), where
>     'arg' is 16
> must be less than
>     '(int)MAX_ARRS' is 16
" thrown in the test body.

MAX_ARRS is 16, but the test reaches that limit already with 4 arrays.

@rasmus25 Thank you for the report and the test!
This buggy check is removed here #20172 (not really necessary, because it is called iff clSetKernelArg() passes).
Please take a look.