GUI: prepare for new pattern renderer

likely two stages, depending on how efficient the first one is

stage 1:
- no more Selectables
- using ImDrawList to draw the pattern
  - perhaps even bypassing that and directly firing quads at the draw queue

stage 2:
- using textures and tiles to draw the pattern

src/gui/newPattern.cpp

@@ -0,0 +1,102 @@
+/**
+ * Furnace Tracker - multi-system chiptune tracker
+ * Copyright (C) 2021-2025 tildearrow and contributors
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+// for suck's fake Clang extension!
+#define _USE_MATH_DEFINES
+#include "gui.h"
+#include "../ta-log.h"
+#include "imgui_internal.h"
+#include "IconsFontAwesome4.h"
+#include "furIcons.h"
+#include "misc/cpp/imgui_stdlib.h"
+#include "guiConst.h"
+#include "../utfutils.h"
+#include <fmt/printf.h>
+
+void FurnaceGUI::drawPatternNew() {
+  if (nextWindow==GUI_WINDOW_PATTERN) {
+    patternOpen=true;
+    ImGui::SetNextWindowFocus();
+    nextWindow=GUI_WINDOW_NOTHING;
+  }
+  if (!patternOpen) return;
+
+  if (e->isPlaying() && followPattern) {
+    if (oldRowChanged || !e->isStepping()) {
+      if (e->isStepping()) pendingStepUpdate=1;
+      cursor.y=oldRow;
+      cursor.order=curOrder;
+      if (selStart.xCoarse==selEnd.xCoarse && selStart.xFine==selEnd.xFine && selStart.y==selEnd.y && selStart.order==selEnd.order && !selecting) {
+        selStart=cursor;
+        selEnd=cursor;
+      }
+    }
+  }
+  sel1=selStart;
+  sel2=selEnd;
+  if (sel2.order<sel1.order) {
+    sel2.order^=sel1.order;
+    sel1.order^=sel2.order;
+    sel2.order^=sel1.order;
+    sel2.y^=sel1.y;
+    sel1.y^=sel2.y;
+    sel2.y^=sel1.y;
+  } else if (sel2.order==sel1.order && sel2.y<sel1.y) {
+    sel2.y^=sel1.y;
+    sel1.y^=sel2.y;
+    sel2.y^=sel1.y;
+  }
+  if (sel2.xCoarse<sel1.xCoarse) {
+    sel2.xCoarse^=sel1.xCoarse;
+    sel1.xCoarse^=sel2.xCoarse;
+    sel2.xCoarse^=sel1.xCoarse;
+
+    sel2.xFine^=sel1.xFine;
+    sel1.xFine^=sel2.xFine;
+    sel2.xFine^=sel1.xFine;
+  } else if (sel2.xCoarse==sel1.xCoarse && sel2.xFine<sel1.xFine) {
+    sel2.xFine^=sel1.xFine;
+    sel1.xFine^=sel2.xFine;
+    sel2.xFine^=sel1.xFine;
+  }
+
+  //ImVec2 origWinPadding=ImGui::GetStyle().WindowPadding;
+  ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding,ImVec2(0.0f,0.0f));
+  if (mobileUI) {
+    patWindowPos=(portrait?ImVec2(0.0f,(mobileMenuPos*-0.65*canvasH)+(0.12*canvasW)):ImVec2((0.16*canvasH)+0.5*canvasW*mobileMenuPos,0.0f));
+    patWindowSize=(portrait?ImVec2(canvasW,canvasH-(0.16*canvasW)-(0.12*canvasW)-(pianoOpen?(0.4*canvasW):0.0f)):ImVec2(canvasW-(0.16*canvasH),canvasH-(pianoOpen?(0.3*canvasH):0.0f)));
+    ImGui::SetNextWindowPos(patWindowPos);
+    ImGui::SetNextWindowSize(patWindowSize);
+  }
+  if (ImGui::Begin("PatternNew",&patternOpen,globalWinFlags|(settings.avoidRaisingPattern?ImGuiWindowFlags_NoBringToFrontOnFocus:0)|((settings.cursorFollowsWheel && !selecting)?ImGuiWindowFlags_NoScrollWithMouse:0),_("Pattern"))) {
+    if (!mobileUI) {
+      patWindowPos=ImGui::GetWindowPos();
+      patWindowSize=ImGui::GetWindowSize();
+    }
+
+    ImGui::Text("The pattern view goes here.");
+
+    ImGui::PushFont(patFont);
+    ImGui::PopFont();
+  }
+  ImGui::PopStyleVar();
+  if (ImGui::IsWindowFocused(ImGuiFocusedFlags_ChildWindows)) curWindow=GUI_WINDOW_PATTERN;
+  ImGui::End();
+}
+