ppdnode/lib/context_wrapper.h

#pragma once

#include "imgui.h"
#include "imgui_internal.h"

inline static void CopyIOEvents(ImGuiContext *src, ImGuiContext *dst,
                                ImVec2 origin, float scale) {
  dst->InputEventsQueue = src->InputEventsTrail;
  for (ImGuiInputEvent &e : dst->InputEventsQueue) {
    if (e.Type == ImGuiInputEventType_MousePos) {
      e.MousePos.PosX = (e.MousePos.PosX - origin.x) / scale;
      e.MousePos.PosY = (e.MousePos.PosY - origin.y) / scale;
    }
  }
}

inline static void AppendDrawData(ImDrawList *src, ImVec2 origin, float scale) {
  // TODO optimize if vtx_start == 0 || if idx_start == 0
  ImDrawList *dl = ImGui::GetWindowDrawList();
  const int vtx_start = dl->VtxBuffer.size();
  const int idx_start = dl->IdxBuffer.size();
  dl->VtxBuffer.resize(dl->VtxBuffer.size() + src->VtxBuffer.size());
  dl->IdxBuffer.resize(dl->IdxBuffer.size() + src->IdxBuffer.size());
  dl->CmdBuffer.reserve(dl->CmdBuffer.size() + src->CmdBuffer.size());
  dl->_VtxWritePtr = dl->VtxBuffer.Data + vtx_start;
  dl->_IdxWritePtr = dl->IdxBuffer.Data + idx_start;
  const ImDrawVert *vtx_read = src->VtxBuffer.Data;
  const ImDrawIdx *idx_read = src->IdxBuffer.Data;
  for (int i = 0, c = src->VtxBuffer.size(); i < c; ++i) {
    dl->_VtxWritePtr[i].uv = vtx_read[i].uv;
    dl->_VtxWritePtr[i].col = vtx_read[i].col;
    dl->_VtxWritePtr[i].pos = vtx_read[i].pos * scale + origin;
  }
  for (int i = 0, c = src->IdxBuffer.size(); i < c; ++i) {
    dl->_IdxWritePtr[i] = idx_read[i] + vtx_start;
  }
  for (auto cmd : src->CmdBuffer) {
    cmd.IdxOffset += idx_start;
    IM_ASSERT(cmd.VtxOffset == 0);
    cmd.ClipRect.x = cmd.ClipRect.x * scale + origin.x;
    cmd.ClipRect.y = cmd.ClipRect.y * scale + origin.y;
    cmd.ClipRect.z = cmd.ClipRect.z * scale + origin.x;
    cmd.ClipRect.w = cmd.ClipRect.w * scale + origin.y;
    dl->CmdBuffer.push_back(cmd);
  }

  dl->_VtxCurrentIdx += src->VtxBuffer.size();
  dl->_VtxWritePtr = dl->VtxBuffer.Data + dl->VtxBuffer.size();
  dl->_IdxWritePtr = dl->IdxBuffer.Data + dl->IdxBuffer.size();
}

struct ContainedContextConfig {
  bool extra_window_wrapper = false;
  ImVec2 size = {0.f, 0.f};
  ImU32 color = IM_COL32_WHITE;
  bool zoom_enabled = true;
  float zoom_min = 0.3f;
  float zoom_max = 2.f;
  float zoom_divisions = 10.f;
  float zoom_smoothness = 5.f;
  float default_zoom = 1.f;
  ImGuiKey reset_zoom_key = ImGuiKey_R;
  ImGuiMouseButton scroll_button = ImGuiMouseButton_Middle;
};

class ContainedContext {
public:
  ~ContainedContext();
  ContainedContextConfig &config() { return m_config; }
  void begin();
  void end();
  [[nodiscard]] float scale() const { return m_scale; }
  [[nodiscard]] const ImVec2 &origin() const { return m_origin; }
  [[nodiscard]] bool hovered() const { return m_hovered; }
  [[nodiscard]] const ImVec2 &scroll() const { return m_scroll; }
  ImGuiContext *getRawContext() { return m_ctx; }

private:
  ContainedContextConfig m_config;

  ImVec2 m_origin;
  ImVec2 m_pos;
  ImGuiContext *m_ctx = nullptr;
  ImGuiContext *m_original_ctx = nullptr;

  bool m_anyWindowHovered = false;
  bool m_anyItemActive = false;
  bool m_hovered = false;

  float m_scale = m_config.default_zoom, m_scaleTarget = m_config.default_zoom;
  ImVec2 m_scroll = {0.f, 0.f}, m_scrollTarget = {0.f, 0.f};
};

inline ContainedContext::~ContainedContext() {
  if (m_ctx)
    ImGui::DestroyContext(m_ctx);
}

inline void ContainedContext::begin() {
  ImGui::PushID(this);
  ImGui::PushStyleColor(ImGuiCol_ChildBg, m_config.color);
  ImGui::BeginChild("view_port", m_config.size, 0, ImGuiWindowFlags_NoMove);
  ImGui::PopStyleColor();
  //    m_size = ImGui::GetWindowSize();
  m_pos = ImGui::GetWindowPos();

  ImVec2 size = ImGui::GetContentRegionAvail();
  m_origin = ImGui::GetCursorScreenPos();
  m_original_ctx = ImGui::GetCurrentContext();
  const ImGuiStyle &orig_style = ImGui::GetStyle();
  if (!m_ctx)
    m_ctx = ImGui::CreateContext(ImGui::GetIO().Fonts);
  ImGui::SetCurrentContext(m_ctx);
  ImGuiStyle &new_style = ImGui::GetStyle();
  new_style = orig_style;

  CopyIOEvents(m_original_ctx, m_ctx, m_origin, m_scale);

  ImGui::GetIO().DisplaySize = size / m_scale;
  ImGui::GetIO().ConfigInputTrickleEventQueue = false;
  ImGui::NewFrame();

  if (!m_config.extra_window_wrapper)
    return;
  ImGui::SetNextWindowPos(ImVec2(0, 0), ImGuiCond_Appearing);
  ImGui::SetNextWindowSize(ImGui::GetMainViewport()->WorkSize);
  ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(0, 0));
  ImGui::Begin("viewport_container", nullptr,
               ImGuiWindowFlags_NoDecoration | ImGuiWindowFlags_NoBackground |
                   ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoScrollbar |
                   ImGuiWindowFlags_NoScrollWithMouse);
  ImGui::PopStyleVar();
}

inline void ContainedContext::end() {
  m_anyWindowHovered = ImGui::IsWindowHovered(ImGuiHoveredFlags_AnyWindow);
  if (m_config.extra_window_wrapper && ImGui::IsWindowHovered())
    m_anyWindowHovered = false;

  m_anyItemActive = ImGui::IsAnyItemActive();

  if (m_config.extra_window_wrapper)
    ImGui::End();

  ImGui::Render();

  ImDrawData *draw_data = ImGui::GetDrawData();

  ImGui::SetCurrentContext(m_original_ctx);
  m_original_ctx = nullptr;

  for (int i = 0; i < draw_data->CmdListsCount; ++i)
    AppendDrawData(draw_data->CmdLists[i], m_origin, m_scale);

  m_hovered = ImGui::IsWindowHovered(ImGuiHoveredFlags_ChildWindows) &&
              !m_anyWindowHovered;

  // Zooming
  if (m_config.zoom_enabled && m_hovered && ImGui::GetIO().MouseWheel != 0.f) {
    m_scaleTarget += ImGui::GetIO().MouseWheel / m_config.zoom_divisions;
    m_scaleTarget =
        m_scaleTarget < m_config.zoom_min ? m_config.zoom_min : m_scaleTarget;
    m_scaleTarget =
        m_scaleTarget > m_config.zoom_max ? m_config.zoom_max : m_scaleTarget;

    if (m_config.zoom_smoothness == 0.f) {
      m_scroll += (ImGui::GetMousePos() - m_pos) / m_scaleTarget -
                  (ImGui::GetMousePos() - m_pos) / m_scale;
      m_scale = m_scaleTarget;
    }
  }
  if (abs(m_scaleTarget - m_scale) >= 0.015f / m_config.zoom_smoothness) {
    float cs = (m_scaleTarget - m_scale) / m_config.zoom_smoothness;
    m_scroll += (ImGui::GetMousePos() - m_pos) / (m_scale + cs) -
                (ImGui::GetMousePos() - m_pos) / m_scale;
    m_scale += (m_scaleTarget - m_scale) / m_config.zoom_smoothness;

    if (abs(m_scaleTarget - m_scale) < 0.015f / m_config.zoom_smoothness) {
      m_scroll += (ImGui::GetMousePos() - m_pos) / m_scaleTarget -
                  (ImGui::GetMousePos() - m_pos) / m_scale;
      m_scale = m_scaleTarget;
    }
  }

  // Zoom reset
  if (ImGui::IsKeyPressed(m_config.reset_zoom_key, false))
    m_scaleTarget = m_config.default_zoom;

  // Scrolling
  if (m_hovered && !m_anyItemActive &&
      ImGui::IsMouseDragging(m_config.scroll_button, 0.f)) {
    m_scroll += ImGui::GetIO().MouseDelta / m_scale;
    m_scrollTarget = m_scroll;
  }

  ImGui::EndChild();
  ImGui::PopID();
}