meson: fix build with opencv=enabled and opencv4. Fixes #964

Having the opencv feature enabled would lead to the opencv3 dependency
being required which failed with only opencv4 being available.

Instead don't require anything and error out at the end if the feature was enabled
but no dependency was found.

diff --git a/gst-libs/gst/opencv/meson.build b/gst-libs/gst/opencv/meson.build
index 3fd472f..8dc2ad9 100644 (file)
--- a/gst-libs/gst/opencv/meson.build
+++ b/gst-libs/gst/opencv/meson.build
@@ -9,9 +9,9 @@ opencv_headers = [
   'gstopencvvideofilter.h',
 ]
 
-opencv_dep = dependency('opencv', version : '>= 3.0.0', required : get_option('opencv'))
+opencv_dep = dependency('opencv', version : '>= 3.0.0', required : false)
 if not opencv_dep.found()
-  opencv_dep = dependency('opencv4', version : '>= 4.0.0', required : get_option('opencv'))
+  opencv_dep = dependency('opencv4', version : '>= 4.0.0', required : false)
 endif
 if opencv_dep.found()
   gstopencv = library('gstopencv-' + api_version,
@@ -30,4 +30,6 @@ if opencv_dep.found()
     dependencies : [gstvideo_dep, opencv_dep])
 
   install_headers(opencv_headers, subdir : 'gstreamer-1.0/gst/opencv')
+elif get_option('opencv').enabled()
+  error('OpenCV support enabled but required dependencies were not found.')
 endif