Clarify the dependency to OpenGL

Dear ImGui itself does not have a dependency on OpenGL::GL because
it has its own customm OpenGL loader.
However, our application has that dependency, because we de not use a
loader (such as glad or gl3w) despite a few OpenGL calls: glClear()
to clear the framebuffer, glGetString() to read GL_VERSION, etc.

README.md

@@ -163,7 +163,7 @@ Command line interface:
 Graphical UI:
 
 * OpenGL
-* [GLFW3](http://glfw.sf.net)
+* [GLFW](https://www.glfw.org/)
 * [Dear ImGui](https://github.com/ocornut/imgui)
 * [Portable File Dialogs](https://github.com/samhocevar/portable-file-dialogs)
 

src/gui/CMakeLists.txt

@@ -5,6 +5,7 @@
 option(PICROSS_GUI_IMGUI_DEMO "Show ImGUI demo window" OFF)
 
 # Dependencies
+find_package(OpenGL REQUIRED)       # Necessary because we do not use a loader (such as gl3w or glad)
 include(pfd)
 
 set(GUI_SOURCES
@@ -53,7 +54,9 @@ target_link_libraries(picross_solver
     stdutils
     picross::picross
     picross::utils
+    glfw
     imgui
+    OpenGL::GL
     pfd
 )
 

src/gui/imgui/CMakeLists.txt

@@ -1,5 +1,4 @@
 # Dependencies
-find_package(OpenGL REQUIRED)
 include(glfw)
 include(imgui)
 
@@ -40,9 +39,8 @@ target_compile_definitions(imgui
 )
 
 target_link_libraries(imgui
-    PUBLIC
+    PRIVATE
     glfw
-    OpenGL::GL
 )
 
 set_property(TARGET imgui PROPERTY FOLDER "third_parties")

src/gui/src/imgui_helpers.cpp

@@ -75,11 +75,21 @@ void DearImGuiContext::render() const
 
 void DearImGuiContext::backend_info(std::ostream& out) const
 {
+    // Dear ImGui
     const ImGuiIO& io = ImGui::GetIO();
     out << "Dear ImGui " << IMGUI_VERSION
         << " (Backend platform: " << (io.BackendPlatformName ? io.BackendPlatformName : "NULL")
         << ", renderer: " << (io.BackendRendererName ? io.BackendRendererName : "NULL") << ")" << std::endl;
+
+    // GLFW
     out << "GLFW " << GLFW_VERSION_MAJOR << "." << GLFW_VERSION_MINOR << "." << GLFW_VERSION_REVISION << std::endl;
-    out << "OpenGL Version " << glGetString(GL_VERSION) << std::endl;
-    out << "OpenGL Renderer " << glGetString(GL_RENDERER) << std::endl;
+
+    // OpenGL
+    const auto* open_gl_version_str = glGetString(GL_VERSION);      // Will return NULL if there is no current OpenGL context!
+    if (open_gl_version_str)
+        out << "OpenGL Version: " << open_gl_version_str << std::endl;
+    const auto* open_gl_vendor_str = glGetString(GL_VENDOR);
+    const auto* open_gl_renderer_str = glGetString(GL_RENDERER);
+    if (open_gl_vendor_str && open_gl_renderer_str)
+        out << "OpenGL Vendor: " << open_gl_vendor_str << "; Renderer: " << open_gl_renderer_str << std::endl;
 }

src/gui/src/main.cpp

@@ -22,7 +22,7 @@
 #include <pfd_wrap.h>
 #include <GLFW/glfw3.h>
 #include "glfw_context.h"
-// NB: No OpenGL loader here: This project only relies on the drawing features provided by Dear ImGui.
+// NB: No OpenGL loader here: This project mainly relies on the drawing features provided by Dear ImGui.
 // Dear ImGui embeds its own minimal loader for the OpenGL 3.x functions it needs.
 // See: https://github.com/ocornut/imgui/issues/4445 "OpenGL backend now embeds its own GL loader"