imgui_extras.h

#pragma once
#include <imgui.h>

namespace ImEx {

struct ScopedDisableItem
{
    ScopedDisableItem(bool disable, float disabledAlpha = 0.5f);
    ~ScopedDisableItem();

    void Release();

private:
    bool    m_Disable       = false;
    float   m_LastAlpha     = 1.0f;
};
    
} // namespace ImEx {


inline ImEx::ScopedDisableItem::ScopedDisableItem(bool disable, float disabledAlpha)
    : m_Disable(disable)
{
    if (!m_Disable)
        return;

    auto wasDisabled = (ImGui::GetCurrentWindow()->DC.ItemFlags & ImGuiItemFlags_Disabled) == ImGuiItemFlags_Disabled;

    ImGui::PushItemFlag(ImGuiItemFlags_Disabled, true);

    auto& stale = ImGui::GetStyle();
    m_LastAlpha = stale.Alpha;

    // Don't override alpha if we're already in disabled context.
    if (!wasDisabled)
        stale.Alpha = disabledAlpha;
}

inline ImEx::ScopedDisableItem::~ScopedDisableItem()
{
    Release();
}

inline void ImEx::ScopedDisableItem::Release()
{
    if (!m_Disable)
        return;

    auto& stale = ImGui::GetStyle();
    stale.Alpha = m_LastAlpha;

    ImGui::PopItemFlag();

    m_Disable = false;
}