Examples: GLFW: User previously installed GLFW callbacks are now saved and chain-called by the default callbacks. (#1759)

docs/CHANGELOG.txt

@@ -78,6 +78,7 @@ Other Changes:
   in particular, points_count==0 could lead to a memory stomp if the draw list was previously empty.
 - Examples: DirectX10, DirectX11: Removed seemingly unnecessary calls to invalidate and recreate device objects
   in the WM_SIZE handler. (#2088) [@ice1000]
+- Examples: GLFW: User previously installed GLFW callbacks are now saved and chain-called by the default callbacks. (#1759)
 - Examples: OpenGL3+GLFW: Fixed error condition when using the GLAD loader. (#2157) [@blackball]
 - Examples: OpenGL3+GLFW/SDL: Made main.cpp compile with IMGUI_IMPL_OPENGL_LOADER_CUSTOM (may be missing init). (#2178) [@doug-moen]
 

examples/example_glfw_opengl2/main.cpp

@@ -44,7 +44,6 @@ int main(int, char**)
     //io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad;   // Enable Gamepad Controls
 
     // Setup Platform/Renderer bindings
-    // If you have already installed GLFW callbacks in your app, call ImGui_ImplGlfw_InitForOpenGL() with install_callbacks=false and call them yourself.
     ImGui_ImplGlfw_InitForOpenGL(window, true);
     ImGui_ImplOpenGL2_Init();
 

examples/example_glfw_opengl3/main.cpp

@@ -90,7 +90,6 @@ int main(int, char**)
     //io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad;   // Enable Gamepad Controls
 
     // Setup Platform/Renderer bindings
-    // If you have already installed GLFW callbacks in your app, call ImGui_ImplGlfw_InitForOpenGL() with install_callbacks=false and call them yourself.
     ImGui_ImplGlfw_InitForOpenGL(window, true);
     ImGui_ImplOpenGL3_Init(glsl_version);
 

examples/example_glfw_vulkan/main.cpp

@@ -358,7 +358,6 @@ int main(int, char**)
     //io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad;   // Enable Gamepad Controls
 
     // Setup Platform/Renderer bindings
-    // If you have already installed GLFW callbacks in your app, call ImGui_ImplGlfw_InitForVulkan() with install_callbacks=false and call the functions yourself.
     ImGui_ImplGlfw_InitForVulkan(window, true);
     ImGui_ImplVulkan_InitInfo init_info = {};
     init_info.Instance = g_Instance;

examples/imgui_impl_glfw.cpp

@@ -14,6 +14,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2018-11-07: Inputs: When installing our GLFW callbacks, we save user's previously installed ones - if any - and chain call them.
 //  2018-08-01: Inputs: Workaround for Emscripten which doesn't seem to handle focus related calls.
 //  2018-06-29: Inputs: Added support for the ImGuiMouseCursor_Hand cursor.
 //  2018-06-08: Misc: Extracted imgui_impl_glfw.cpp/.h away from the old combined GLFW+OpenGL/Vulkan examples.
@@ -51,11 +52,17 @@ enum GlfwClientApi
     GlfwClientApi_OpenGL,
     GlfwClientApi_Vulkan
 };
-static GLFWwindow*      g_Window = NULL;
-static GlfwClientApi    g_ClientApi = GlfwClientApi_Unknown;
-static double           g_Time = 0.0;
-static bool             g_MouseJustPressed[5] = { false, false, false, false, false };
-static GLFWcursor*      g_MouseCursors[ImGuiMouseCursor_COUNT] = { 0 };
+static GLFWwindow*          g_Window = NULL;
+static GlfwClientApi        g_ClientApi = GlfwClientApi_Unknown;
+static double               g_Time = 0.0;
+static bool                 g_MouseJustPressed[5] = { false, false, false, false, false };
+static GLFWcursor*          g_MouseCursors[ImGuiMouseCursor_COUNT] = { 0 };
+
+// Chain GLFW callbacks: our callbacks will call the user's previously installed callbacks, if any.
+static GLFWmousebuttonfun   g_PrevUserCallbackMousebutton = NULL;
+static GLFWscrollfun        g_PrevUserCallbackScroll = NULL;
+static GLFWkeyfun           g_PrevUserCallbackKey = NULL;
+static GLFWcharfun          g_PrevUserCallbackChar = NULL;
 
 static const char* ImGui_ImplGlfw_GetClipboardText(void* user_data)
 {
@@ -67,36 +74,48 @@ static void ImGui_ImplGlfw_SetClipboardText(void* user_data, const char* text)
     glfwSetClipboardString((GLFWwindow*)user_data, text);
 }
 
-void ImGui_ImplGlfw_MouseButtonCallback(GLFWwindow*, int button, int action, int /*mods*/)
+void ImGui_ImplGlfw_MouseButtonCallback(GLFWwindow* window, int button, int action, int mods)
 {
+    if (g_PrevUserCallbackMousebutton != NULL)
+        g_PrevUserCallbackMousebutton(window, button, action, mods);
+
     if (action == GLFW_PRESS && button >= 0 && button < IM_ARRAYSIZE(g_MouseJustPressed))
         g_MouseJustPressed[button] = true;
 }
 
-void ImGui_ImplGlfw_ScrollCallback(GLFWwindow*, double xoffset, double yoffset)
+void ImGui_ImplGlfw_ScrollCallback(GLFWwindow* window, double xoffset, double yoffset)
 {
+    if (g_PrevUserCallbackScroll != NULL)
+        g_PrevUserCallbackScroll(window, xoffset, yoffset);
+
     ImGuiIO& io = ImGui::GetIO();
     io.MouseWheelH += (float)xoffset;
     io.MouseWheel += (float)yoffset;
 }
 
-void ImGui_ImplGlfw_KeyCallback(GLFWwindow*, int key, int, int action, int mods)
+void ImGui_ImplGlfw_KeyCallback(GLFWwindow* window, int key, int scancode, int action, int mods)
 {
+    if (g_PrevUserCallbackKey != NULL) 
+        g_PrevUserCallbackKey(window, key, scancode, action, mods);
+
     ImGuiIO& io = ImGui::GetIO();
     if (action == GLFW_PRESS)
         io.KeysDown[key] = true;
     if (action == GLFW_RELEASE)
         io.KeysDown[key] = false;
 
-    (void)mods; // Modifiers are not reliable across systems
+    // Modifiers are not reliable across systems
     io.KeyCtrl = io.KeysDown[GLFW_KEY_LEFT_CONTROL] || io.KeysDown[GLFW_KEY_RIGHT_CONTROL];
     io.KeyShift = io.KeysDown[GLFW_KEY_LEFT_SHIFT] || io.KeysDown[GLFW_KEY_RIGHT_SHIFT];
     io.KeyAlt = io.KeysDown[GLFW_KEY_LEFT_ALT] || io.KeysDown[GLFW_KEY_RIGHT_ALT];
     io.KeySuper = io.KeysDown[GLFW_KEY_LEFT_SUPER] || io.KeysDown[GLFW_KEY_RIGHT_SUPER];
 }
 
-void ImGui_ImplGlfw_CharCallback(GLFWwindow*, unsigned int c)
+void ImGui_ImplGlfw_CharCallback(GLFWwindow* window, unsigned int c)
 {
+    if (g_PrevUserCallbackChar != NULL)
+        g_PrevUserCallbackChar(window, c);
+
     ImGuiIO& io = ImGui::GetIO();
     if (c > 0 && c < 0x10000)
         io.AddInputCharacter((unsigned short)c);
@@ -151,12 +170,17 @@ static bool ImGui_ImplGlfw_Init(GLFWwindow* window, bool install_callbacks, Glfw
     g_MouseCursors[ImGuiMouseCursor_ResizeNWSE] = glfwCreateStandardCursor(GLFW_ARROW_CURSOR);  // FIXME: GLFW doesn't have this.
     g_MouseCursors[ImGuiMouseCursor_Hand] = glfwCreateStandardCursor(GLFW_HAND_CURSOR);
     
+    // Chain GLFW callbacks: our callbacks will call the user's previously installed callbacks, if any.
+    g_PrevUserCallbackMousebutton = NULL;
+    g_PrevUserCallbackScroll = NULL;
+    g_PrevUserCallbackKey = NULL;
+    g_PrevUserCallbackChar = NULL;
     if (install_callbacks)
     {
-        glfwSetMouseButtonCallback(window, ImGui_ImplGlfw_MouseButtonCallback);
-        glfwSetScrollCallback(window, ImGui_ImplGlfw_ScrollCallback);
-        glfwSetKeyCallback(window, ImGui_ImplGlfw_KeyCallback);
-        glfwSetCharCallback(window, ImGui_ImplGlfw_CharCallback);
+        g_PrevUserCallbackMousebutton = glfwSetMouseButtonCallback(window, ImGui_ImplGlfw_MouseButtonCallback);
+        g_PrevUserCallbackScroll = glfwSetScrollCallback(window, ImGui_ImplGlfw_ScrollCallback);
+        g_PrevUserCallbackKey = glfwSetKeyCallback(window, ImGui_ImplGlfw_KeyCallback);
+        g_PrevUserCallbackChar = glfwSetCharCallback(window, ImGui_ImplGlfw_CharCallback);
     }
 
     g_ClientApi = client_api;

examples/imgui_impl_glfw.h

@@ -25,10 +25,8 @@ IMGUI_IMPL_API bool     ImGui_ImplGlfw_InitForVulkan(GLFWwindow* window, bool in
 IMGUI_IMPL_API void     ImGui_ImplGlfw_Shutdown();
 IMGUI_IMPL_API void     ImGui_ImplGlfw_NewFrame();
 
-// GLFW callbacks are installed by default if you call the InitXXX function with 'install_callbacks=true'.
-// If you already have GLFW callbacks installed by your application, call the InitXXX function with install_callbacks=false,
-// then call the functions yourselves from your own GLFW callbacks. 
-// You may also handle inputs yourself and use those as a reference.
+// InitXXX function with 'install_callbacks=true': install GLFW callbacks. They will call user's previously installed callbacks, if any.
+// InitXXX function with 'install_callbacks=false': do not install GLFW callbacks. You will need to call them yourself from your own GLFW callbacks.
 IMGUI_IMPL_API void     ImGui_ImplGlfw_MouseButtonCallback(GLFWwindow* window, int button, int action, int mods);
 IMGUI_IMPL_API void     ImGui_ImplGlfw_ScrollCallback(GLFWwindow* window, double xoffset, double yoffset);
 IMGUI_IMPL_API void     ImGui_ImplGlfw_KeyCallback(GLFWwindow* window, int key, int scancode, int action, int mods);