[wpigui] Reload fonts to scale rather than preloading (#4712)

wpigui/src/main/native/cpp/wpigui.cpp

@@ -115,6 +115,47 @@ void gui::DestroyContext() {
   gContext = nullptr;
 }
 
+static void UpdateFontScale() {
+  // Scale based on OS window content scaling
+  float windowScale = 1.0;
+#ifndef __APPLE__
+  glfwGetWindowContentScale(gContext->window, &windowScale, nullptr);
+#endif
+  // map to closest font size: 0 = 0.5x, 1 = 0.75x, 2 = 1.0x, 3 = 1.25x,
+  // 4 = 1.5x, 5 = 1.75x, 6 = 2x
+  int fontScale =
+      gContext->userScale + static_cast<int>((windowScale - 1.0) * 4);
+  if (fontScale < 0) {
+    fontScale = 0;
+  }
+  if (gContext->fontScale != fontScale) {
+    gContext->reloadFonts = true;
+    gContext->fontScale = fontScale;
+  }
+}
+
+// the range is based on 13px being the "nominal" 100% size and going from
+// ~0.5x (7px) to ~2.0x (25px)
+static void ReloadFonts() {
+  auto& io = ImGui::GetIO();
+  io.Fonts->Clear();
+  gContext->fonts.clear();
+  float size = 7.0f + gContext->fontScale * 3.0f;
+  bool first = true;
+  for (auto&& makeFont : gContext->makeFonts) {
+    if (makeFont.second) {
+      ImFontConfig cfg;
+      std::snprintf(cfg.Name, sizeof(cfg.Name), "%s", makeFont.first);
+      ImFont* font = makeFont.second(io, size, &cfg);
+      if (first) {
+        ImGui::GetIO().FontDefault = font;
+        first = false;
+      }
+      gContext->fonts.emplace_back(font);
+    }
+  }
+}
+
 bool gui::Initialize(const char* title, int width, int height,
                      ImGuiConfigFlags configFlags) {
   gContext->title = title;
@@ -268,20 +309,9 @@ bool gui::Initialize(const char* title, int width, int height,
   SetStyle(static_cast<Style>(gContext->style));
 
   // Load Fonts
-  // this range is based on 13px being the "nominal" 100% size and going from
-  // ~0.5x (7px) to ~2.0x (25px)
-  for (auto&& makeFont : gContext->makeFonts) {
-    if (makeFont.second) {
-      auto& font = gContext->fonts.emplace_back();
-      for (int i = 0; i < Font::kScaledLevels; ++i) {
-        float size = 7.0f + i * 3.0f;
-        ImFontConfig cfg;
-        std::snprintf(cfg.Name, sizeof(cfg.Name), "%s-%d", makeFont.first,
-                      static_cast<int>(size));
-        font.scaled[i] = makeFont.second(io, size, &cfg);
-      }
-    }
-  }
+  UpdateFontScale();
+  ReloadFonts();
+  gContext->reloadFonts = false;  // init renderer will do this
 
   if (!PlatformInitRenderer()) {
     return false;
@@ -296,6 +326,11 @@ void gui::Main() {
     // Poll and handle events (inputs, window resize, etc.)
     glfwPollEvents();
     gContext->isPlatformRendering = true;
+    UpdateFontScale();
+    if (gContext->reloadFonts) {
+      ReloadFonts();
+      // PlatformRenderFrame() will clear reloadFonts flag
+    }
     PlatformRenderFrame();
     gContext->isPlatformRendering = false;
 
@@ -336,18 +371,6 @@ void gui::CommonRenderFrame() {
   // Start the Dear ImGui frame
   ImGui::NewFrame();
 
-  // Scale based on OS window content scaling
-  float windowScale = 1.0;
-#ifndef __APPLE__
-  glfwGetWindowContentScale(gContext->window, &windowScale, nullptr);
-#endif
-  // map to closest font size: 0 = 0.5x, 1 = 0.75x, 2 = 1.0x, 3 = 1.25x,
-  // 4 = 1.5x, 5 = 1.75x, 6 = 2x
-  gContext->fontScale = std::clamp(
-      gContext->userScale + static_cast<int>((windowScale - 1.0) * 4), 0,
-      Font::kScaledLevels - 1);
-  ImGui::GetIO().FontDefault = gContext->fonts[0].scaled[gContext->fontScale];
-
   for (size_t i = 0; i < gContext->earlyExecutors.size(); ++i) {
     auto& execute = gContext->earlyExecutors[i];
     if (execute) {
@@ -431,10 +454,6 @@ int gui::AddFont(
   return gContext->makeFonts.size() - 1;
 }
 
-ImFont* gui::GetFont(int font) {
-  return gContext->fonts[font].scaled[gContext->fontScale];
-}
-
 void gui::SetStyle(Style style) {
   gContext->style = static_cast<int>(style);
   switch (style) {
@@ -501,14 +520,11 @@ void gui::EmitViewMenu() {
     }
 
     if (ImGui::BeginMenu("Zoom")) {
-      for (int i = 0; i < Font::kScaledLevels && (25 * (i + 2)) <= 200; ++i) {
+      for (int i = 0; i < kFontScaledLevels && (25 * (i + 2)) <= 200; ++i) {
         char label[20];
         std::snprintf(label, sizeof(label), "%d%%", 25 * (i + 2));
         bool selected = gContext->userScale == i;
-        bool enabled = (gContext->fontScale - gContext->userScale + i) >= 0 &&
-                       (gContext->fontScale - gContext->userScale + i) <
-                           Font::kScaledLevels;
-        if (ImGui::MenuItem(label, nullptr, &selected, enabled)) {
+        if (ImGui::MenuItem(label, nullptr, &selected)) {
           gContext->userScale = i;
         }
       }

wpigui/src/main/native/directx11/wpigui_directx11.cpp

@@ -134,6 +134,11 @@ bool gui::PlatformInitRenderer() {
 }
 
 void gui::PlatformRenderFrame() {
+  if (gContext->reloadFonts) {
+    ImGui_ImplDX11_InvalidateDeviceObjects();
+    ImGui_ImplDX11_CreateDeviceObjects();
+    gContext->reloadFonts = false;
+  }
   ImGui_ImplDX11_NewFrame();
 
   CommonRenderFrame();

wpigui/src/main/native/include/wpigui_internal.h

@@ -26,10 +26,7 @@ struct SavedSettings {
   int style = 0;
 };
 
-struct Font {
-  static constexpr int kScaledLevels = 9;
-  ImFont* scaled[kScaledLevels];
-};
+constexpr int kFontScaledLevels = 9;
 
 struct Context : public SavedSettings {
   std::atomic_bool exit{false};
@@ -56,12 +53,14 @@ struct Context : public SavedSettings {
   std::vector<std::function<void()>> lateExecutors;
 
   int fontScale = 2;  // updated by main loop
-  std::vector<Font> fonts;
+  std::vector<ImFont*> fonts;
 
   std::vector<GLFWimage> icons;
 
   std::string iniPath = "imgui.ini";
   bool resetOnExit = false;
+
+  bool reloadFonts = false;  // reload fonts in next PlatformRenderFrame()
 };
 
 extern Context* gContext;

wpigui/src/main/native/metal/wpigui_metal.mm

@@ -84,6 +84,12 @@ void gui::PlatformRenderFrame() {
     id <MTLRenderCommandEncoder> renderEncoder = [commandBuffer renderCommandEncoderWithDescriptor:renderPassDescriptor];
     [renderEncoder pushDebugGroup:@"WPI GUI"];
 
+    if (gContext->reloadFonts) {
+      ImGui_ImplMetal_DestroyFontsTexture();
+      ImGui_ImplMetal_CreateFontsTexture(gPlatformContext->layer.device);
+      gContext->reloadFonts = false;
+    }
+
     // Start the Dear ImGui frame
     ImGui_ImplMetal_NewFrame(renderPassDescriptor);
 

wpigui/src/main/native/opengl2/wpigui_opengl2.cpp

@@ -51,6 +51,11 @@ bool gui::PlatformInitRenderer() {
 }
 
 void gui::PlatformRenderFrame() {
+  if (gContext->reloadFonts) {
+    ImGui_ImplOpenGL2_DestroyFontsTexture();
+    ImGui_ImplOpenGL2_CreateFontsTexture();
+    gContext->reloadFonts = false;
+  }
   ImGui_ImplOpenGL2_NewFrame();
 
   CommonRenderFrame();

wpigui/src/main/native/opengl3/wpigui_opengl3.cpp

@@ -76,6 +76,11 @@ bool gui::PlatformInitRenderer() {
 }
 
 void gui::PlatformRenderFrame() {
+  if (gContext->reloadFonts) {
+    ImGui_ImplOpenGL3_DestroyFontsTexture();
+    ImGui_ImplOpenGL3_CreateFontsTexture();
+    gContext->reloadFonts = false;
+  }
   ImGui_ImplOpenGL3_NewFrame();
 
   CommonRenderFrame();