in my opinion, the patch is perfectly fine. drawing functions in OpenCV are not speed champions, they could be done more efficient, of course, but the proposed change should not affect speed. It's just a few more clocks spent in coordinates handling. As for checks for the input - the problem is that the use case may be real. If we use 16 bits for fractional part and if the image is huge satellite image with more than 32K pixels in width/height, it can indeed overflow 32 bits. This is where 64-bit arithmetics may come handy.

Please take a look on build warnings from MSVS compiler: https://pullrequest.opencv.org/buildbot/builders/3_4-win64-vc14/builds/100002

C:\build\3_4-win64-vc14\opencv\modules\imgproc\src\drawing.cpp(1491): warning C4244: 'argument': conversion from 'int64_t' to 'int', possible loss of data [C:\build\3_4-win64-vc14\build\modules\imgproc\opencv_imgproc.vcxproj]
C:\build\3_4-win64-vc14\opencv\modules\imgproc\src\drawing.cpp(1492): warning C4244: 'argument': conversion from 'int64_t' to 'int', possible loss of data [C:\build\3_4-win64-vc14\build\modules\imgproc\opencv_imgproc.vcxproj]
C:\build\3_4-win64-vc14\opencv\modules\imgproc\src\drawing.cpp(1507): warning C4244: 'argument': conversion from 'int64_t' to 'int', possible loss of data [C:\build\3_4-win64-vc14\build\modules\imgproc\opencv_imgproc.vcxproj]
C:\build\3_4-win64-vc14\opencv\modules\imgproc\src\drawing.cpp(1508): warning C4244: 'argument': conversion from 'int64_t' to 'int', possible loss of data [C:\build\3_4-win64-vc14\build\modules\imgproc\opencv_imgproc.vcxproj]
C:\build\3_4-win64-vc14\opencv\modules\imgproc\src\drawing.cpp(1531): warning C4244: 'argument': conversion from 'int64_t' to 'int', possible loss of data [C:\build\3_4-win64-vc14\build\modules\imgproc\opencv_imgproc.vcxproj]
C:\build\3_4-win64-vc14\opencv\modules\imgproc\src\drawing.cpp(1546): warning C4244: 'argument': conversion from 'int64_t' to 'int', possible loss of data [C:\build\3_4-win64-vc14\build\modules\imgproc\opencv_imgproc.vcxproj]
C:\build\3_4-win64-vc14\opencv\modules\imgproc\src\drawing.cpp(1569): warning C4244: 'argument': conversion from 'int64_t' to 'int', possible loss of data [C:\build\3_4-win64-vc14\build\modules\imgproc\opencv_imgproc.vcxproj]
C:\build\3_4-win64-vc14\opencv\modules\imgproc\src\drawing.cpp(1584): warning C4244: 'argument': conversion from 'int64_t' to 'int', possible loss of data [C:\build\3_4-win64-vc14\build\modules\imgproc\opencv_imgproc.vcxproj]