Clipper: add ForceDisplayRangeByIndices (ocornut#3841, ocornut#3578)

This partially reverts commit 6a7e2c7.

docs/CHANGELOG.txt

@@ -57,9 +57,11 @@ Other Changes:
 - Clipper: currently focused item is automatically included in clipper range.
   Fixes issue where e.g. drag and dropping an item and scrolling ensure the item source location is
   still submitted. (#3841, #1725) [@GamingMinds-DanielC, @ocornut]
+- Cliooer: added ForceDisplayRangeByIndices() to force a given item (or several) to be stepped out
+  during a clipping operation. (#3841) [@@GamingMinds-DanielC]
 - Clipper: rework so gamepad/keyboard navigation doesn't create spikes in number of items requested
   by the clipper to display. (#3841)
-- Clipper: Fixed content height declaration slightly mismatching the value of when not using a clipper.
+- Clipper: fixed content height declaration slightly mismatching the value of when not using a clipper.
   (an additional ItemSpacing.y was declared, affecting scrollbar range).
 - Backends: Vulkan: Call vkCmdSetScissor() at the end of render with a full-viewport to reduce
   likehood of issues with people using VK_DYNAMIC_STATE_SCISSOR in their app without calling

docs/TODO.txt

@@ -142,7 +142,6 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - plot: option/feature: draw unit
  - plot: add a helper e.g. Plot(char* label, float value, float time_span=2.0f) that stores values and Plot them for you - probably another function name. and/or automatically allow to plot ANY displayed value (more reliance on stable ID)
 
- - clipper: ability to force display 1 item in the list would be convenient (for patterns where we need to set active id etc.) (#3841) (can resurrect ForceDisplayRangeXXX functions removed)
  - clipper: ability to disable the clipping through a simple flag/bool.
  - clipper: ability to run without knowing full count in advance.
  - clipper: horizontal clipping support. (#2580)

imgui.cpp

@@ -2411,6 +2411,15 @@ void ImGuiListClipper::End()
     }
 }
 
+void ImGuiListClipper::ForceDisplayRangeByIndices(int item_min, int item_max)
+{
+    ImGuiListClipperData* data = (ImGuiListClipperData*)TempData;
+    IM_ASSERT(DisplayStart < 0); // Only allowed after Begin() and if there has not been a specified range yet.
+    IM_ASSERT(item_min <= item_max);
+    if (item_min < item_max)
+        data->Ranges.push_back(ImGuiListClipperRange::FromIndices(item_min, item_max));
+}
+
 bool ImGuiListClipper::Step()
 {
     ImGuiContext& g = *GImGui;

imgui.h

@@ -64,7 +64,7 @@ Index of this file:
 // Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals. Work in progress versions typically starts at XYY99 then bounce up to XYY00, XYY01 etc. when release tagging happens)
 #define IMGUI_VERSION               "1.86 WIP"
-#define IMGUI_VERSION_NUM           18508
+#define IMGUI_VERSION_NUM           18509
 #define IMGUI_CHECKVERSION()        ImGui::DebugCheckVersionAndDataLayout(IMGUI_VERSION, sizeof(ImGuiIO), sizeof(ImGuiStyle), sizeof(ImVec2), sizeof(ImVec4), sizeof(ImDrawVert), sizeof(ImDrawIdx))
 #define IMGUI_HAS_TABLE
 
@@ -2207,6 +2207,9 @@ struct ImGuiListClipper
     IMGUI_API void  End();             // Automatically called on the last call of Step() that returns false.
     IMGUI_API bool  Step();            // Call until it returns false. The DisplayStart/DisplayEnd fields will be set and you can process/draw those items.
 
+    // Call ForceDisplayRangeByIndices() before first call to Step() if you need a range of items to be displayed regardless of visibility.
+    IMGUI_API void  ForceDisplayRangeByIndices(int item_min, int item_max); // item_max is exclusive e.g. use (42, 42+1) to make item 42 always visible BUT due to alignment/padding of certain items it is likely that an extra item may be included on either end of the display range.
+
 #ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
     inline ImGuiListClipper(int items_count, float items_height = -1.0f) { memset(this, 0, sizeof(*this)); ItemsCount = -1; Begin(items_count, items_height); } // [removed in 1.79]
 #endif