Example apps: accumulate mouse wheel to accodomate for slow framerate.

examples/directx11_example/main.cpp

@@ -317,7 +317,7 @@ LRESULT WINAPI MsgProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
         io.MouseDown[1] = false; 
         return true;
     case WM_MOUSEWHEEL:
-        io.MouseWheel = GET_WHEEL_DELTA_WPARAM(wParam) > 0 ? +1.0f : -1.0f;
+        io.MouseWheel += GET_WHEEL_DELTA_WPARAM(wParam) > 0 ? +1.0f : -1.0f;
         return true;
     case WM_MOUSEMOVE:
         // Mouse position, in pixels (set to -1,-1 if no mouse / on another screen, etc.)

examples/directx9_example/main.cpp

@@ -153,7 +153,7 @@ LRESULT WINAPI MsgProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
         io.MouseDown[1] = false; 
         return true;
     case WM_MOUSEWHEEL:
-        io.MouseWheel = GET_WHEEL_DELTA_WPARAM(wParam) > 0 ? +1.0f : -1.0f;
+        io.MouseWheel += GET_WHEEL_DELTA_WPARAM(wParam) > 0 ? +1.0f : -1.0f;
         return true;
     case WM_MOUSEMOVE:
         // Mouse position, in pixels (set to -1,-1 if no mouse / on another screen, etc.)

examples/opengl_example/main.cpp

@@ -114,7 +114,7 @@ static void glfw_mouse_button_callback(GLFWwindow* window, int button, int actio
 static void glfw_scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
 {
     ImGuiIO& io = ImGui::GetIO();
-    io.MouseWheel = (float)yoffset; // Use fractional mouse wheel, 1.0 unit 5 lines.
+    io.MouseWheel += (float)yoffset; // Use fractional mouse wheel, 1.0 unit 5 lines.
 }
 
 static void glfw_key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
@@ -258,7 +258,6 @@ int main(int argc, char** argv)
     {
         ImGuiIO& io = ImGui::GetIO();
         mousePressed[0] = mousePressed[1] = false;
-        io.MouseWheel = 0;
         glfwPollEvents();
         UpdateImGui();