Backends: GLFW, Emscripten: fixes for canvas resizing. (#6751)

backends/imgui_impl_glfw.cpp

@@ -20,6 +20,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2023-12-18: Emscripten: Change the size of the GLFW window according to the size of the canvas
 //  2023-10-05: Inputs: Added support for extra ImGuiKey values: F13 to F24 function keys.
 //  2023-07-18: Inputs: Revert ignoring mouse data on GLFW_CURSOR_DISABLED as it can be used differently. User may set ImGuiConfigFLags_NoMouse if desired. (#5625, #6609)
 //  2023-06-12: Accept glfwGetTime() not returning a monotonically increasing value. This seems to happens on some Windows setup when peripherals disconnect, and is likely to also happen on browser + Emscripten. (#6491)
@@ -126,6 +127,9 @@ struct ImGui_ImplGlfw_Data
     ImVec2                  LastValidMousePos;
     bool                    InstalledCallbacks;
     bool                    CallbacksChainForAllWindows;
+#ifdef __EMSCRIPTEN__
+    const char*             CanvasSelector;
+#endif
 
     // Chain GLFW callbacks: our callbacks will call the user's previously installed callbacks, if any.
     GLFWwindowfocusfun      PrevUserCallbackWindowFocus;
@@ -807,6 +811,49 @@ void ImGui_ImplGlfw_NewFrame()
     ImGui_ImplGlfw_UpdateGamepads();
 }
 
+#ifdef __EMSCRIPTEN__
+static EM_BOOL ImGui_ImplGlfw_OnCanvasSizeChange(int event_type, const EmscriptenUiEvent* event, void* user_data)
+{
+    ImGui_ImplGlfw_Data* bd = (ImGui_ImplGlfw_Data *) user_data;
+
+    double canvas_width, canvas_height;
+    emscripten_get_element_css_size(bd->CanvasSelector, &canvas_width, &canvas_height);
+
+    glfwSetWindowSize(bd->Window, (int)canvas_width, (int)canvas_height);
+
+    return true;
+}
+
+static EM_BOOL ImGui_ImplGlfw_OnFullscreenChange(int event_type, const EmscriptenFullscreenChangeEvent* event, void* user_data)
+{
+    ImGui_ImplGlfw_Data* bd = (ImGui_ImplGlfw_Data *) user_data;
+
+    double canvas_width, canvas_height;
+    emscripten_get_element_css_size(bd->CanvasSelector, &canvas_width, &canvas_height);
+
+    glfwSetWindowSize(bd->Window, (int)canvas_width, (int)canvas_height);
+
+    return true;
+}
+
+/**
+ * @param canvas_selector A CSS selector, the event listener is applied to the first element that matches the query.
+ */
+void ImGui_ImplGlfw_SetEmscriptenCanvasSelector(const char *canvas_selector)
+{
+    IM_ASSERT(canvas_selector != nullptr);
+    ImGui_ImplGlfw_Data* bd = ImGui_ImplGlfw_GetBackendData();
+    IM_ASSERT(bd != nullptr && "Did you call ImGui_ImplGlfw_InitForXXX()?");
+    bd->CanvasSelector = canvas_selector;
+
+    emscripten_set_resize_callback(EMSCRIPTEN_EVENT_TARGET_WINDOW, bd, false, ImGui_ImplGlfw_OnCanvasSizeChange);
+    emscripten_set_fullscreenchange_callback(EMSCRIPTEN_EVENT_TARGET_DOCUMENT, bd, false, ImGui_ImplGlfw_OnFullscreenChange);
+
+    // Change the size of the GLFW window according to the size of the canvas
+    ImGui_ImplGlfw_OnCanvasSizeChange(EMSCRIPTEN_EVENT_RESIZE, {}, bd);
+}
+#endif
+
 //-----------------------------------------------------------------------------
 
 #if defined(__clang__)

backends/imgui_impl_glfw.h

@@ -30,6 +30,11 @@ IMGUI_IMPL_API bool     ImGui_ImplGlfw_InitForOther(GLFWwindow* window, bool ins
 IMGUI_IMPL_API void     ImGui_ImplGlfw_Shutdown();
 IMGUI_IMPL_API void     ImGui_ImplGlfw_NewFrame();
 
+// Emscripten related initialization phase methods
+#ifdef __EMSCRIPTEN__
+IMGUI_IMPL_API void     ImGui_ImplGlfw_SetEmscriptenCanvasSelector(const char* canvas_selector);
+#endif
+
 // GLFW callbacks install
 // - When calling Init with 'install_callbacks=true': ImGui_ImplGlfw_InstallCallbacks() is called. GLFW callbacks will be installed for you. They will chain-call user's previously installed callbacks, if any.
 // - When calling Init with 'install_callbacks=false': GLFW callbacks won't be installed. You will need to call individual function yourself from your own GLFW callbacks.

examples/example_emscripten_wgpu/main.cpp

@@ -26,6 +26,8 @@ static WGPUSwapChain     wgpu_swap_chain = nullptr;
 static int               wgpu_swap_chain_width = 0;
 static int               wgpu_swap_chain_height = 0;
 
+const char* canvas_selector = "#canvas";
+
 // Forward declarations
 static void MainLoopStep(void* window);
 static bool InitWGPU();
@@ -76,6 +78,7 @@ int main(int, char**)
 
     // Setup Platform/Renderer backends
     ImGui_ImplGlfw_InitForOther(window, true);
+    ImGui_ImplGlfw_SetEmscriptenCanvasSelector(canvas_selector);
     ImGui_ImplWGPU_Init(wgpu_device, 3, wgpu_preferred_fmt, WGPUTextureFormat_Undefined);
 
     // Load Fonts

examples/example_glfw_opengl3/Makefile.emscripten

@@ -59,7 +59,7 @@ endif
 CPPFLAGS += -I$(IMGUI_DIR) -I$(IMGUI_DIR)/backends
 #CPPFLAGS += -g
 CPPFLAGS += -Wall -Wformat -Os $(EMS)
-# LDFLAGS += --shell-file ../libs/emscripten/shell_minimal.html
+LDFLAGS += --shell-file ../libs/emscripten/shell_minimal.html
 LDFLAGS += $(EMS)
 
 ##---------------------------------------------------------------------

examples/example_glfw_opengl3/main.cpp

@@ -26,9 +26,13 @@
 
 // This example can also compile and run with Emscripten! See 'Makefile.emscripten' for details.
 #ifdef __EMSCRIPTEN__
+#include <emscripten.h>
+#include <emscripten/html5.h>
 #include "../libs/emscripten/emscripten_mainloop_stub.h"
 #endif
 
+const char* canvas_selector = "#canvas";
+
 static void glfw_error_callback(int error, const char* description)
 {
     fprintf(stderr, "GLFW Error %d: %s\n", error, description);
@@ -84,6 +88,9 @@ int main(int, char**)
 
     // Setup Platform/Renderer backends
     ImGui_ImplGlfw_InitForOpenGL(window, true);
+#ifdef __EMSCRIPTEN__
+    ImGui_ImplGlfw_SetEmscriptenCanvasSelector(canvas_selector);
+#endif
     ImGui_ImplOpenGL3_Init(glsl_version);
 
     // Load Fonts