cmake: add option HELLOIMGUI_DOWNLOAD_THIRD (OFF under Linux)

.github/workflows/ci_automation_test.yml

@@ -24,9 +24,9 @@ jobs:
         with:
           submodules: true
 
-      - name: install xorg-dev (ubuntu only)
+      - name: apt install libglfw3-dev xorg-dev (ubuntu only)
         if: ${{ matrix.platform == 'ubuntu-latest' }}
-        run: sudo apt-get update && sudo apt-get install -y xorg-dev
+        run: sudo apt-get update && sudo apt-get install -y xorg-dev libglfw3-dev
 
       - name: Install & Start Xvfb (ubuntu only)
         if: ${{ matrix.platform == 'ubuntu-latest' }}

.github/workflows/easy_integration.yml

@@ -22,9 +22,9 @@ jobs:
 #    - name: Setup interactive tmate session
 #      uses: mxschmitt/action-tmate@v3
 
-    - name: install xorg-dev (ubuntu only)
+    - name: apt install xorg-dev  libglfw3-dev (ubuntu only)
       if: ${{ matrix.platform == 'ubuntu-latest' }}
-      run: sudo apt-get update && sudo apt-get install -y xorg-dev
+      run: sudo apt-get update && sudo apt-get install -y xorg-dev  libglfw3-dev
 
     - name: Build _example_integration
       run: |

.github/workflows/multiplatform_default.yml

@@ -23,9 +23,9 @@ jobs:
         with:
           submodules: true
 
-      - name: install xorg-dev (ubuntu only)
+      - name: apt install xorg-dev  libglfw3-dev (ubuntu only)
         if: ${{ matrix.platform == 'ubuntu-latest' }}
-        run: sudo apt-get update && sudo apt-get install -y xorg-dev
+        run: sudo apt-get update && sudo apt-get install -y xorg-dev  libglfw3-dev
 
       - name: Build and install
         shell: bash

CMakeLists.txt

@@ -52,38 +52,40 @@ if(MACOSX)
 endif()
 
 #------------------------------------------------------------------------------
-# Options / Backend selection
+# Options / backend selection
 #------------------------------------------------------------------------------
-# If no backend option is selected, automatically download glfw and build it
-if (NOT HELLOIMGUI_WITH_GLFW
-    AND NOT HELLOIMGUI_WITH_SDL
-    AND NOT HELLOIMGUI_USE_SDL_OPENGL3
-    AND NOT HELLOIMGUI_USE_GLFW_OPENGL3
-    AND NOT HELLOIMGUI_USE_QT
-    AND NOT EMSCRIPTEN
-    )
-    set(HELLOIMGUI_WITH_GLFW ON CACHE BOOL "")
-    message(WARNING "
-            HelloImGui: using Glfw as default default backend (it will be downloaded and built inside {CMAKE_CURRENT_BINARY_DIR}/_deps/glfw-*)
-            In order to select your own backend, use one of the cmake options below:
-                -DHELLOIMGUI_WITH_GLFW=ON            # To download and build glfw automatically
-                -DHELLOIMGUI_WITH_SDL=ON             # To download and build SDL automatically
-                -DHELLOIMGUI_USE_GLFW_OPENGL3=ON      # To use your own version of GLFW (it should be findable via find_package(glfw3))
-                -DHELLOIMGUI_USE_SDL_OPENGL3=ON       # To use your own version of SDL (it should be findable via find_package(SDL2))
-            ")
-endif()
-
-# Backend selection with automatic backend compilation
+# Backend selection with automatic backend download
 # (if you set any of those options, the corresponding backend will be automatically downloaded at build time)
+# Note: if HELLOIMGUI_DOWNLOAD_THIRD is OFF, these options will not work (this is the default under Linux)
 option(HELLOIMGUI_WITH_GLFW "Add GLFW+OpenGl3 support (glfw will be automatically compiled via ExternalProject_Add)" OFF)
 option(HELLOIMGUI_WITH_SDL "Add SDL+OpenGl3 support (SDL will be automatically compiled via ExternalProject_Add)" OFF)
 
-# Backend selection with manual backend compilation
+# Backend selection without automatic download (you need to provide them system-wide, or via a package manager)
 # (setting those options without setting HELLOIMGUI_WITH_XXX will require that the backend can be found by find_package())
 option(HELLOIMGUI_USE_SDL_OPENGL3 "Build HelloImGui for SDL+OpenGL3" OFF)
 option(HELLOIMGUI_USE_GLFW_OPENGL3 "Build HelloImGui for GLFW+OpenGL3" OFF)
 option(HELLOIMGUI_USE_QT "Build HelloImGui for Qt" OFF)
 
+
+#------------------------------------------------------------------------------
+# HELLOIMGUI_DOWNLOAD_THIRD: download third party libraries as part of the build
+#     This is the default, except under Linux, where it is expected that the libraries are installed system-wide.
+#
+#     When ON, the libraries that can be downloaded are SDL and Glfw. This is governed by the options
+#     HELLOIMGUI_WITH_GLFW and HELLOIMGUI_WITH_SDL, where HELLOIMGUI_WITH_GLFW is set to ON if no backend
+#     is selected manually.
+#------------------------------------------------------------------------------
+if (CMAKE_SYSTEM_NAME MATCHES "Linux")
+    option(HELLOIMGUI_DOWNLOAD_THIRD "Automatically download third party libraries during the build" OFF)
+else()
+    option(HELLOIMGUI_DOWNLOAD_THIRD "Automatically download third party libraries during the build" ON)
+endif()
+if (NOT HELLOIMGUI_DOWNLOAD_THIRD)
+    set(HELLOIMGUI_WITH_GLFW OFF)
+    set(HELLOIMGUI_WITH_SDL OFF)
+endif()
+
+
 #------------------------------------------------------------------------------
 # Build options / ImGui
 #------------------------------------------------------------------------------
@@ -167,6 +169,61 @@ option(HELLOIMGUI_USE_GLAD "Use Glad OpenGl loader" ${need_opengl_loader})
 ###############################################################################
 
 
+#------------------------------------------------------------------------------
+# Backend check: If no backend option is selected, 
+# either select Glfw automatically if possible, or fail
+#------------------------------------------------------------------------------
+# 
+if (NOT HELLOIMGUI_WITH_GLFW
+    AND NOT HELLOIMGUI_WITH_SDL
+    AND NOT HELLOIMGUI_USE_SDL_OPENGL3
+    AND NOT HELLOIMGUI_USE_GLFW_OPENGL3
+    AND NOT HELLOIMGUI_USE_QT
+    AND NOT EMSCRIPTEN
+    )
+    set(backend_message "
+                    In order to select your own backend, use one of the cmake options below:
+                    -DHELLOIMGUI_WITH_GLFW=ON             # To download and build glfw automatically
+                    -DHELLOIMGUI_WITH_SDL=ON              # To download and build SDL automatically
+                    -DHELLOIMGUI_USE_GLFW_OPENGL3=ON      # To use your own version of GLFW (it should be findable via find_package(glfw3))
+                    -DHELLOIMGUI_USE_SDL_OPENGL3=ON       # To use your own version of SDL (it should be findable via find_package(SDL2))
+
+                    (Note: under Linux, it is advised to use system-wide libraries, and not to use
+                    -DHELLOIMGUI_WITH_GLFW=ON or -DHELLOIMGUI_WITH_SDL=ON)
+    ")
+    if (HELLOIMGUI_DOWNLOAD_THIRD)
+        set(HELLOIMGUI_WITH_GLFW ON)
+        message(STATUS "
+                HelloImGui: using Glfw as default default backend (it will be downloaded and built inside {CMAKE_CURRENT_BINARY_DIR}/_deps/glfw-*)
+                ${backend_message}
+                ")
+    else()
+        # Check if Glfw can be found
+        find_package(glfw3 QUIET)
+        if (glfw3_FOUND)
+            set(HELLOIMGUI_USE_GLFW_OPENGL3 ON)
+            message(STATUS
+                    "HelloImGui: using Glfw as default default backend (it was found via find_package(glfw3))
+                    ${backend_message}
+                    ")
+        else()
+            set(glfw_help_msg "")
+            if (CMAKE_SYSTEM_NAME MATCHES "Linux")
+                set(glfw_help_msg "
+                    you can install glfw via your package manager (apt, pacman, etc).
+                    For example, on Ubuntu, you can run:
+                        sudo apt install libglfw3-dev
+                ")
+            endif()
+            message(FATAL_ERROR "
+                        HelloImGui: no backend selected, and could not find Glfw via find_package(glfw3).                    
+                        ${backend_message} ${glfw_help_msg}
+                        ")
+        endif()
+    endif()
+endif()
+
+
 ###############################################################################
 # HelloImGui Build Actions
 ###############################################################################
@@ -182,7 +239,7 @@ endif()
 # Download backend glfw or sdl if required
 #------------------------------------------------------------------------------
 if (HELLOIMGUI_WITH_GLFW)
-    set(HELLOIMGUI_USE_GLFW_OPENGL3 ON CACHE BOOL "" FORCE)
+    set(HELLOIMGUI_USE_GLFW_OPENGL3 ON)
     if (NOT TARGET glfw AND NOT EMSCRIPTEN)
         include(FetchContent)
         Set(FETCHCONTENT_QUIET FALSE)
@@ -196,7 +253,7 @@ if (HELLOIMGUI_WITH_GLFW)
 endif()
 
 if (HELLOIMGUI_WITH_SDL)
-    set(HELLOIMGUI_USE_SDL_OPENGL3 ON CACHE BOOL "" FORCE)
+    set(HELLOIMGUI_USE_SDL_OPENGL3 ON)
     if (NOT TARGET sdl AND NOT EMSCRIPTEN)
         include(FetchContent)
         Set(FETCHCONTENT_QUIET FALSE)