Work / possible multiple renderer backends

hello_imgui_cmake/hello_imgui_build_lib.cmake

@@ -711,39 +711,6 @@ function(him_has_directx12 target)
 endfunction()
 
 
-###################################################################################################
-# Check only one rendering backend is selected: API = him_check_only_one_backend_selected
-###################################################################################################
-function(him_check_only_one_rendering_backend_selected)
-    # Only one of HELLOIMGUI_HAS_OPENGL, HELLOIMGUI_HAS_METAL, HELLOIMGUI_HAS_VULKAN can be ON
-    # count selected rendering backends
-    set(selected_backends 0)
-    if (HELLOIMGUI_HAS_OPENGL)
-        math(EXPR selected_backends "${selected_backends} + 1")
-    endif()
-    if (HELLOIMGUI_HAS_METAL)
-        math(EXPR selected_backends "${selected_backends} + 1")
-    endif()
-    if (HELLOIMGUI_HAS_VULKAN)
-        math(EXPR selected_backends "${selected_backends} + 1")
-    endif()
-    if (HELLOIMGUI_HAS_DIRECTX11)
-        math(EXPR selected_backends "${selected_backends} + 1")
-    endif()
-    if (HELLOIMGUI_HAS_DIRECTX12)
-        math(EXPR selected_backends "${selected_backends} + 1")
-    endif()
-    # selected_backends should be 1
-    if (selected_backends EQUAL 0)
-        message(FATAL_ERROR "HelloImGui: no rendering backend selected")
-    endif()
-    if (NOT selected_backends EQUAL 1)
-        message(FATAL_ERROR "HelloImGui: only one of HELLOIMGUI_HAS_OPENGL, HELLOIMGUI_HAS_METAL, HELLOIMGUI_HAS_VULKAN, HELLOIMGUI_HAS_DIRECTX12 can be ON")
-    endif()
-endfunction()
-
-
-
 ###################################################################################################
 # SDL platform backend: API = him_use_sdl2_backend
 ###################################################################################################
@@ -1095,7 +1062,6 @@ function(him_main_add_hello_imgui_library)
         target_compile_definitions(${HELLOIMGUI_TARGET} PUBLIC HELLOIMGUI_USE_SDL_DIRECTX12)
     endif ()
 
-    him_check_only_one_rendering_backend_selected()
     him_add_apple_options()
     him_add_linux_options()
     him_add_windows_options()

src/hello_imgui/doc_params.md

@@ -110,10 +110,17 @@ struct RunnerParams
     // These pointers will be filled when the application starts
     BackendPointers backendPointers;
 
-    // `backendType`: _enum BackendType, default=BackendType::FirstAvailable_
+    // `backendType`: _enum BackendType, default=PlatformBackendType::FirstAvailable_
     // Select the wanted platform backend type between `Sdl`, `Glfw`.
+    // if `FirstAvailable`, Glfw will be preferred over Sdl when both are available.
     // Only useful when multiple backend are compiled and available.
-    BackendType backendType = BackendType::FirstAvailable;
+    PlatformBackendType backendType = PlatformBackendType::FirstAvailable;
+
+    // `rendererBackendType`: _enum RendererBackendType, default=RendererBackendType::FirstAvailable_
+    // Select the wanted rendering backend type between `OpenGL3`, `Metal`, `Vulkan`, `DirectX11`, `DirectX12`.
+    // if `FirstAvailable`, it will be selected in the order of preference mentioned above.
+    // Only useful when multiple rendering backend are compiled and available.
+    RendererBackendType rendererBackendType = RendererBackendType::FirstAvailable;
 
     // `rendererBackendOptions`: _see renderer_backend_options.h_
     // Options for the renderer backend
@@ -181,6 +188,39 @@ struct RunnerParams
 };
 ```
 
+### Backend selection
+
+
+```cpp
+
+// You can select the platform backend type (SDL, GLFW) and the rendering backend type
+// via RunnerParams.backendType and RunnerParams.rendererBackendType.
+
+// Platform backend type (SDL, GLFW)
+// They are listed in the order of preference when FirstAvailable is selected.
+enum class PlatformBackendType
+{
+    FirstAvailable,
+    Glfw,
+    Sdl,
+};
+
+using BackendType = PlatformBackendType; // for backward compatibility
+
+// Rendering backend type (OpenGL3, Metal, Vulkan, DirectX11, DirectX12)
+// They are listed in the order of preference when FirstAvailable is selected.
+enum class RendererBackendType
+{
+    FirstAvailable,
+    OpenGL3,
+    Metal,
+    Vulkan,
+    DirectX11,
+    DirectX12,
+};
+
+```
+
 
 # Fps Idling
 
@@ -203,7 +243,7 @@ struct FpsIdling
     float fpsIdle = 9.f;
 
     // `enableIdling`: _bool, default=true_.
-    //  Set this to false to disable idling 
+    //  Disable idling by setting this to false.
     //  (this can be changed dynamically during execution)
     bool  enableIdling = true;
 

src/hello_imgui/doc_params.src.md

@@ -22,6 +22,13 @@ See [runner_params.h](https://github.com/pthom/hello_imgui/blob/master/src/hello
 @import "runner_params.h" {md_id=RunnerParams}
 ```
 
+### Backend selection
+
+
+```cpp
+@import "runner_params.h" {md_id=BackendType}
+```
+
 
 # Fps Idling
 

src/hello_imgui/hello_imgui.h

@@ -107,6 +107,14 @@ float FrameRate(float durationForMean = 0.5f);
 //  of ImGuiTestEngine that was initialized by HelloImGui
 //  (iif ImGui Test Engine is active).
 ImGuiTestEngine* GetImGuiTestEngine();
+
+// `GetBackendDescription()`: returns a string with the backend info
+// Could be for example:
+//     "Glfw - OpenGL3"
+//     "Glfw - Metal"
+//     "Sdl - Vulkan"
+std::string GetBackendDescription();
+
 // @@md
 
 

src/hello_imgui/impl/hello_imgui.cpp

@@ -152,6 +152,41 @@ float FrameRate(float durationForMean)
     return fps;
 }
 
+std::string PlatformBackendTypeToString(PlatformBackendType platformBackendType)
+{
+    if (platformBackendType == PlatformBackendType::Glfw)
+        return "Glfw";
+    else if (platformBackendType == PlatformBackendType::Sdl)
+        return "Sdl";
+    else
+        return "Unknown platform backend";
+}
+
+std::string RendererBackendTypeToString(RendererBackendType rendererBackendType)
+{
+    if (rendererBackendType == RendererBackendType::OpenGL3)
+        return "OpenGL3";
+    else if (rendererBackendType == RendererBackendType::Vulkan)
+        return "Vulkan";
+    else if (rendererBackendType == RendererBackendType::Metal)
+        return "Metal";
+    else if (rendererBackendType == RendererBackendType::DirectX11)
+        return "DirectX11";
+    else if (rendererBackendType == RendererBackendType::DirectX12)
+        return "DirectX12";
+    else
+        return "Unknown renderer backend";
+}
+
+std::string GetBackendDescription()
+{
+    const auto& params = GetRunnerParams();
+    std::string platformBackend = PlatformBackendTypeToString(params->platformBackendType);
+    std::string rendererBackend = RendererBackendTypeToString(params->rendererBackendType);
+    return platformBackend + " - " + rendererBackend;
+}
+
+
 #ifdef HELLOIMGUI_WITH_TEST_ENGINE
 extern ImGuiTestEngine *GHImGuiTestEngine;
 ImGuiTestEngine* GetImGuiTestEngine() { return GHImGuiTestEngine; }