Remove OpenCL warper

- Even when OpenCL was detected at build time, this has been disabled
  at runtime by default due to multiple issues
- Performance improvements weren't that big compared to multithreaded
  CPU
- Wasn't functionaly on par with CPU version
- Nobody cared enough about it to maintain it
- Big users of GDAL (remote sensing companies) don't care that much
  about GPU uage of GDAL.

Author: rouault

.github/workflows/cmake_builds.yml

@@ -55,7 +55,7 @@ jobs:
            libpoppler-dev libpoppler-private-dev gpsbabel libhdf4-alt-dev libhdf5-serial-dev libpodofo-dev poppler-utils \
            libfreexl-dev unixodbc-dev libwebp-dev liblcms2-2 libcrypto++-dev libkml-dev \
            libmysqlclient-dev libarmadillo-dev wget libfyba-dev libjsoncpp-dev libexpat1-dev \
-           libclc-dev ocl-icd-opencl-dev libsqlite3-dev sqlite3-pcre libpcre3-dev libspatialite-dev libsfcgal-dev fossil libcairo2-dev libjson-c-dev libdeflate-dev liblz4-dev libblosc-dev libarchive-dev \
+           libsqlite3-dev sqlite3-pcre libpcre3-dev libspatialite-dev libsfcgal-dev fossil libcairo2-dev libjson-c-dev libdeflate-dev liblz4-dev libblosc-dev libarchive-dev \
            libqhull-dev libcfitsio-dev libopenjp2-7-dev libheif-dev \
            python3-dev libpython3-dev libpython3.10-dev python3.10-dev python3-numpy python3-lxml python3-pyflakes python3-setuptools python3-pip python3-venv \
            python3-pytest swig doxygen texlive-latex-base make cppcheck ccache g++ \

.github/workflows/ubuntu_20.04/Dockerfile.ci

@@ -74,8 +74,6 @@ RUN apt-get update -y \
     make \
     mono-mcs \
     numactl \
-    ocl-icd-opencl-dev \
-    opencl-c-headers \
     openjdk-8-jdk-headless \
     pkg-config \
     python3-dev \

alg/CMakeLists.txt

@@ -82,12 +82,6 @@ if (GDAL_USE_ARMADILLO)
   gdal_target_link_libraries(alg PRIVATE ${ARMADILLO_LIBRARIES})
 endif ()
 
-if (GDAL_USE_OPENCL)
-  gdal_target_link_libraries(alg PRIVATE OpenCL::OpenCL)
-  target_compile_definitions(alg PRIVATE -DHAVE_OPENCL)
-  target_sources(alg PRIVATE gdalwarpkernel_opencl.h gdalwarpkernel_opencl.cpp)
-endif ()
-
 gdal_target_link_libraries(alg PRIVATE PROJ::proj)
 
 if (GDAL_USE_QHULL_INTERNAL)

alg/gdalwarpkernel.cpp

@@ -409,7 +409,6 @@ gdal_check_package(NetCDF "Enable netCDF driver" CAN_DISABLE
   NAMES netCDF
   TARGETS netCDF::netcdf NETCDF::netCDF
   VERSION "4.7")
-gdal_check_package(OpenCL "Enable OpenCL (may be used for warping)" CAN_DISABLE)
 
 set(PostgreSQL_ADDITIONAL_VERSIONS "14" CACHE STRING "Additional PostgreSQL versions to check")
 gdal_check_package(PostgreSQL "" CAN_DISABLE)

alg/gdalwarpkernel_opencl.cpp

@@ -21,9 +21,6 @@
 /* Define if gdal use geos*/
 #cmakedefine GDAL_USE_GEOS
 
-/* Define if gdal use opencl*/
-#cmakedefine GDAL_USE_OPENCL
-
 /* Define if gdal use armadillo*/
 #cmakedefine GDAL_USE_ARMADILLO
 

alg/gdalwarpkernel_opencl.h

@@ -1516,32 +1516,6 @@ driver. If not found, an internal copy can be used.
     to ON, has precedence over GDAL_USE_OPENCAD=ON
 
 
-
-OpenCL
-******
-
-The OpenCL library may be used to accelerate warping computations, typically
-with a GPU.
-
-.. note:: (GDAL 3.5 and 3.6) It is disabled by default even when detected, since the current OpenCL
-          warping implementation lags behind the generic implementation.
-          Starting with GDAL 3.7, build support is enabled by default when OpenCL is detected,
-          but it is disabled by default at runtime. The warping option USE_OPENCL
-          or the configuration option GDAL_USE_OPENCL must be set to YES to enable it.
-
-.. option:: OpenCL_INCLUDE_DIR
-
-    Path to an include directory with the ``CL/cl.h`` header file.
-
-.. option:: OpenCL_LIBRARY
-
-    Path to a shared or static library file.
-
-.. option:: GDAL_USE_OPENCL=ON/OFF
-
-    Control whether to use OPENCL. Defaults to *OFF* when OPENCL is found.
-
-
 OpenEXR
 *******
 

cmake/helpers/CheckDependentLibraries.cmake

@@ -56,7 +56,6 @@ constexpr static const char* const apszKnownConfigOptions[] =
    "BAG_GEOREF_MD_BLOCKYSIZE", // from bagdataset.cpp
    "BASISU_MAX_FILE_SIZE", // from basisudataset.cpp
    "BIGTIFF_OVERVIEW", // from gt_overview.cpp
-   "BLACKLISTED_OPENCL_VENDOR", // from gdalwarpkernel_opencl.cpp
    "BLOCKXSIZE", // from netcdfdataset.cpp
    "BLOCKYSIZE", // from netcdfdataset.cpp
    "BSB_DISABLE_INDEX", // from bsb_read.c
@@ -390,7 +389,6 @@ constexpr static const char* const apszKnownConfigOptions[] =
    "GDAL_USE_AVX", // from gdalgrid.cpp
    "GDAL_USE_GEOJP2", // from gdaljp2metadata.cpp
    "GDAL_USE_GMLJP2", // from gdaljp2metadata.cpp
-   "GDAL_USE_OPENCL", // from gdalwarpkernel.cpp
    "GDAL_USE_SSE", // from gdalgrid.cpp
    "GDAL_USE_SSSE3", // from cpl_cpu_features.cpp
    "GDAL_VALIDATE_CREATION_OPTIONS", // from gdaldataset.cpp, gdaldriver.cpp
@@ -831,7 +829,6 @@ constexpr static const char* const apszKnownConfigOptions[] =
    "OGR_XLS_HEADERS", // from ogrxlslayer.cpp
    "OGR_XLSX_FIELD_TYPES", // from ogrxlsxdatasource.cpp
    "OGR_XLSX_HEADERS", // from ogrxlsxdatasource.cpp
-   "OPENCL_USE_CPU", // from gdalwarpkernel_opencl.cpp
    "OPENFILEGDB_CREATE_FIELD_BEFORE_GEOMETRY", // from ogropenfilegdblayer_write.cpp
    "OPENFILEGDB_CREATOR", // from filegdbtable_write.cpp
    "OPENFILEGDB_DEFAULT_STRING_WIDTH", // from ogropenfilegdblayer_write.cpp
@@ -946,7 +943,6 @@ constexpr static const char* const apszKnownConfigOptions[] =
    "PR_RESOLUTION_STRATEGY", // from postgisrasterdataset.cpp
    "PR_WE_RES", // from postgisrasterdataset.cpp
    "PREDICTOR_OVERVIEW", // from gt_overview.cpp
-   "PREFERRED_OPENCL_VENDOR", // from gdalwarpkernel_opencl.cpp
    "PROJ_DATA", // from ogr_proj_p.cpp
    "PROJ_LIB", // from ogr_proj_p.cpp
    "PST_INSTANCE", // from jpipkakdataset.cpp