Internals: made ScrollbarEx() use ImS64 to facilitate use with larger…

… ranges (not fully tested) + clipper tweaks (#3609, #3962 + ocornut/imgui_club#20)

This does NOT fix all problems with large ranges and floating point precision, it merely attenuate them.

docs/CHANGELOG.txt

@@ -72,6 +72,7 @@ Other Changes:
   by the clipper to display. (#3841)
 - Clipper: fixed content height declaration slightly mismatching the value of when not using a clipper.
   (an additional ItemSpacing.y was declared, affecting scrollbar range).
+- Clipper: minor and incomplete changes to tame down precision issues on very large ranges (#3609, #3962).
 - Drag and Drop: BeginDragDropSource() with ImGuiDragDropFlags_SourceAllowNullID doesn't lose
   tooltip when scrolling. (#143)
 - Metrics: Added a node showing windows in submission order and showing the Begin() stack.

imgui.cpp

@@ -2348,8 +2348,9 @@ static void ImGuiListClipper_SeekCursorAndSetupPrevLine(float pos_y, float line_
 static void ImGuiListClipper_SeekCursorForItem(ImGuiListClipper* clipper, int item_n)
 {
     // StartPosY starts from ItemsFrozen hence the subtraction
+    // Perform the add and multiply with double to allow seeking through larger ranges
     ImGuiListClipperData* data = (ImGuiListClipperData*)clipper->TempData;
-    float pos_y = clipper->StartPosY + (item_n - data->ItemsFrozen) * clipper->ItemsHeight;
+    float pos_y = (float)((double)clipper->StartPosY + (double)(item_n - data->ItemsFrozen) * clipper->ItemsHeight);
     ImGuiListClipper_SeekCursorAndSetupPrevLine(pos_y, clipper->ItemsHeight);
 }
 
@@ -2520,8 +2521,10 @@ bool ImGuiListClipper::Step()
         for (int i = 0; i < data->Ranges.Size; i++)
             if (data->Ranges[i].PosToIndexConvert)
             {
-                data->Ranges[i].Min = ImClamp(already_submitted + (int)ImFloor((data->Ranges[i].Min - window->DC.CursorPos.y) / ItemsHeight) + data->Ranges[i].PosToIndexOffsetMin, already_submitted, ItemsCount - 1);
-                data->Ranges[i].Max = ImClamp(already_submitted + (int)ImCeil((data->Ranges[i].Max - window->DC.CursorPos.y) / ItemsHeight) + 0 + data->Ranges[i].PosToIndexOffsetMax, data->Ranges[i].Min + 1, ItemsCount);
+                int m1 = (int)(((double)data->Ranges[i].Min - window->DC.CursorPos.y) / ItemsHeight);
+                int m2 = (int)((((double)data->Ranges[i].Max - window->DC.CursorPos.y) / ItemsHeight) + 0.999999f);
+                data->Ranges[i].Min = ImClamp(already_submitted + m1 + data->Ranges[i].PosToIndexOffsetMin, already_submitted, ItemsCount - 1);
+                data->Ranges[i].Max = ImClamp(already_submitted + m2 + data->Ranges[i].PosToIndexOffsetMax, data->Ranges[i].Min + 1, ItemsCount);
                 data->Ranges[i].PosToIndexConvert = false;
             }
         ImGuiListClipper_SortAndFuseRanges(data->Ranges, data->StepNo);

imgui_internal.h

@@ -2707,7 +2707,7 @@ namespace ImGui
     IMGUI_API bool          CollapseButton(ImGuiID id, const ImVec2& pos);
     IMGUI_API bool          ArrowButtonEx(const char* str_id, ImGuiDir dir, ImVec2 size_arg, ImGuiButtonFlags flags = 0);
     IMGUI_API void          Scrollbar(ImGuiAxis axis);
-    IMGUI_API bool          ScrollbarEx(const ImRect& bb, ImGuiID id, ImGuiAxis axis, float* p_scroll_v, float avail_v, float contents_v, ImDrawFlags flags);
+    IMGUI_API bool          ScrollbarEx(const ImRect& bb, ImGuiID id, ImGuiAxis axis, ImS64* p_scroll_v, ImS64 avail_v, ImS64 contents_v, ImDrawFlags flags);
     IMGUI_API bool          ImageButtonEx(ImGuiID id, ImTextureID texture_id, const ImVec2& size, const ImVec2& uv0, const ImVec2& uv1, const ImVec2& padding, const ImVec4& bg_col, const ImVec4& tint_col);
     IMGUI_API ImRect        GetWindowScrollbarRect(ImGuiWindow* window, ImGuiAxis axis);
     IMGUI_API ImGuiID       GetWindowScrollbarID(ImGuiWindow* window, ImGuiAxis axis);

imgui_widgets.cpp

@@ -896,7 +896,9 @@ void ImGui::Scrollbar(ImGuiAxis axis)
     }
     float size_avail = window->InnerRect.Max[axis] - window->InnerRect.Min[axis];
     float size_contents = window->ContentSize[axis] + window->WindowPadding[axis] * 2.0f;
-    ScrollbarEx(bb, id, axis, &window->Scroll[axis], size_avail, size_contents, rounding_corners);
+    ImS64 scroll = (ImS64)window->Scroll[axis];
+    ScrollbarEx(bb, id, axis, &scroll, (ImS64)size_avail, (ImS64)size_contents, rounding_corners);
+    window->Scroll[axis] = (float)scroll;
 }
 
 // Vertical/Horizontal scrollbar
@@ -905,7 +907,7 @@ void ImGui::Scrollbar(ImGuiAxis axis)
 // - We store values as normalized ratio and in a form that allows the window content to change while we are holding on a scrollbar
 // - We handle both horizontal and vertical scrollbars, which makes the terminology not ideal.
 // Still, the code should probably be made simpler..
-bool ImGui::ScrollbarEx(const ImRect& bb_frame, ImGuiID id, ImGuiAxis axis, float* p_scroll_v, float size_avail_v, float size_contents_v, ImDrawFlags flags)
+bool ImGui::ScrollbarEx(const ImRect& bb_frame, ImGuiID id, ImGuiAxis axis, ImS64* p_scroll_v, ImS64 size_avail_v, ImS64 size_contents_v, ImDrawFlags flags)
 {
     ImGuiContext& g = *GImGui;
     ImGuiWindow* window = g.CurrentWindow;
@@ -936,22 +938,22 @@ bool ImGui::ScrollbarEx(const ImRect& bb_frame, ImGuiID id, ImGuiAxis axis, floa
     // Calculate the height of our grabbable box. It generally represent the amount visible (vs the total scrollable amount)
     // But we maintain a minimum size in pixel to allow for the user to still aim inside.
     IM_ASSERT(ImMax(size_contents_v, size_avail_v) > 0.0f); // Adding this assert to check if the ImMax(XXX,1.0f) is still needed. PLEASE CONTACT ME if this triggers.
-    const float win_size_v = ImMax(ImMax(size_contents_v, size_avail_v), 1.0f);
-    const float grab_h_pixels = ImClamp(scrollbar_size_v * (size_avail_v / win_size_v), style.GrabMinSize, scrollbar_size_v);
+    const ImS64 win_size_v = ImMax(ImMax(size_contents_v, size_avail_v), (ImS64)1);
+    const float grab_h_pixels = ImClamp(scrollbar_size_v * ((float)size_avail_v / (float)win_size_v), style.GrabMinSize, scrollbar_size_v);
     const float grab_h_norm = grab_h_pixels / scrollbar_size_v;
 
     // Handle input right away. None of the code of Begin() is relying on scrolling position before calling Scrollbar().
     bool held = false;
     bool hovered = false;
     ButtonBehavior(bb, id, &hovered, &held, ImGuiButtonFlags_NoNavFocus);
 
-    float scroll_max = ImMax(1.0f, size_contents_v - size_avail_v);
-    float scroll_ratio = ImSaturate(*p_scroll_v / scroll_max);
+    const ImS64 scroll_max = ImMax((ImS64)1, size_contents_v - size_avail_v);
+    float scroll_ratio = ImSaturate((float)*p_scroll_v / (float)scroll_max);
     float grab_v_norm = scroll_ratio * (scrollbar_size_v - grab_h_pixels) / scrollbar_size_v; // Grab position in normalized space
     if (held && allow_interaction && grab_h_norm < 1.0f)
     {
-        float scrollbar_pos_v = bb.Min[axis];
-        float mouse_pos_v = g.IO.MousePos[axis];
+        const float scrollbar_pos_v = bb.Min[axis];
+        const float mouse_pos_v = g.IO.MousePos[axis];
 
         // Click position in scrollbar normalized space (0.0f->1.0f)
         const float clicked_v_norm = ImSaturate((mouse_pos_v - scrollbar_pos_v) / scrollbar_size_v);
@@ -971,10 +973,10 @@ bool ImGui::ScrollbarEx(const ImRect& bb_frame, ImGuiID id, ImGuiAxis axis, floa
         // Apply scroll (p_scroll_v will generally point on one member of window->Scroll)
         // It is ok to modify Scroll here because we are being called in Begin() after the calculation of ContentSize and before setting up our starting position
         const float scroll_v_norm = ImSaturate((clicked_v_norm - g.ScrollbarClickDeltaToGrabCenter - grab_h_norm * 0.5f) / (1.0f - grab_h_norm));
-        *p_scroll_v = IM_ROUND(scroll_v_norm * scroll_max);//(win_size_contents_v - win_size_v));
+        *p_scroll_v = (ImS64)(scroll_v_norm * scroll_max);
 
         // Update values for rendering
-        scroll_ratio = ImSaturate(*p_scroll_v / scroll_max);
+        scroll_ratio = ImSaturate((float)*p_scroll_v / (float)scroll_max);
         grab_v_norm = scroll_ratio * (scrollbar_size_v - grab_h_pixels) / scrollbar_size_v;
 
         // Update distance to grab now that we have seeked and saturated