Sliders: An initial click within the knob/grab doesn't shift its position. (#1946, #5328) + Adjust default GrabMinSize.

docs/CHANGELOG.txt

@@ -78,6 +78,7 @@ Other Changes:
 - Layout: Fixed mixing up SameLine() and SetCursorPos() together from creating situations where line
   height would be emitted from the wrong location (e.g. 'ItemA+SameLine()+SetCursorPos()+ItemB' would
   emit ItemA worth of height from the position of ItemB, which is not necessarily aligned with ItemA).
+- Sliders: An initial click within the knob/grab doesn't shift its position. (#1946, #5328)
 - Sliders, Drags: Fixed dragging when using hexadecimal display format string. (#5165, #3133)
 - Sliders, Drags: Fixed manual input when using hexadecimal display format string. (#5165, #3133)
 - InputScalar: Fixed manual input when using %03d style width in display format string. (#5165, #3133)
@@ -109,6 +110,7 @@ Other Changes:
   level of a popup with a child menu opened.
 - Menus: Menus emitted from the main/scrolling layer are not part of the same menuset as menus emitted
   from the menu-bar, avoiding  accidental hovering from one to the other. (#3496, #4797) [@rokups]
+- Style: Adjust default value of GrabMinSize from 10.0f to 12.0f.
 - Stack Tool: Added option to copy item path to clipboard. (#4631)
 - Settings: Fixed out-of-bounds read when .ini file on disk is empty. (#5351) [@quantum5]
 - Settings: Fixed some SetNextWindowPos/SetNextWindowSize API calls not marking settings as dirty.

imgui.cpp

@@ -1062,7 +1062,7 @@ ImGuiStyle::ImGuiStyle()
     ColumnsMinSpacing       = 6.0f;             // Minimum horizontal spacing between two columns. Preferably > (FramePadding.x + 1).
     ScrollbarSize           = 14.0f;            // Width of the vertical scrollbar, Height of the horizontal scrollbar
     ScrollbarRounding       = 9.0f;             // Radius of grab corners rounding for scrollbar
-    GrabMinSize             = 10.0f;            // Minimum width/height of a grab box for slider/scrollbar
+    GrabMinSize             = 12.0f;            // Minimum width/height of a grab box for slider/scrollbar
     GrabRounding            = 0.0f;             // Radius of grabs corners rounding. Set to 0.0f to have rectangular slider grabs.
     LogSliderDeadzone       = 4.0f;             // The size in pixels of the dead-zone around zero on logarithmic sliders that cross zero.
     TabRounding             = 4.0f;             // Radius of upper corners of a tab. Set to 0.0f to have rectangular tabs.

imgui.h

@@ -65,7 +65,7 @@ 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               "1.88 WIP"
-#define IMGUI_VERSION_NUM           18731
+#define IMGUI_VERSION_NUM           18732
 #define IMGUI_CHECKVERSION()        ImGui::DebugCheckVersionAndDataLayout(IMGUI_VERSION, sizeof(ImGuiIO), sizeof(ImGuiStyle), sizeof(ImVec2), sizeof(ImVec4), sizeof(ImDrawVert), sizeof(ImDrawIdx))
 #define IMGUI_HAS_TABLE
 

imgui_internal.h

@@ -1773,6 +1773,7 @@ struct ImGuiContext
     ImU32                   ColorEditLastColor;                 // RGB value with alpha set to 0.
     ImVec4                  ColorPickerRef;                     // Initial/reference color at the time of opening the color picker.
     ImGuiComboPreviewData   ComboPreviewData;
+    float                   SliderGrabClickOffset;
     float                   SliderCurrentAccum;                 // Accumulated slider delta when using navigation controls.
     bool                    SliderCurrentAccumDirty;            // Has the accumulated slider delta changed since last time we tried to apply it?
     bool                    DragCurrentAccumDirty;
@@ -1944,6 +1945,7 @@ struct ImGuiContext
         ColorEditOptions = ImGuiColorEditFlags_DefaultOptions_;
         ColorEditLastHue = ColorEditLastSat = 0.0f;
         ColorEditLastColor = 0;
+        SliderGrabClickOffset = 0.0f;
         SliderCurrentAccum = 0.0f;
         SliderCurrentAccumDirty = false;
         DragCurrentAccumDirty = false;

imgui_widgets.cpp

@@ -2760,8 +2760,17 @@ bool ImGui::SliderBehaviorT(const ImRect& bb, ImGuiID id, ImGuiDataType data_typ
             else
             {
                 const float mouse_abs_pos = g.IO.MousePos[axis];
+                if (g.ActiveIdIsJustActivated)
+                {
+                    float grab_t = ScaleRatioFromValueT<TYPE, SIGNEDTYPE, FLOATTYPE>(data_type, *v, v_min, v_max, is_logarithmic, logarithmic_zero_epsilon, zero_deadzone_halfsize);
+                    if (axis == ImGuiAxis_Y)
+                        grab_t = 1.0f - grab_t;
+                    const float grab_pos = ImLerp(slider_usable_pos_min, slider_usable_pos_max, grab_t);
+                    const bool clicked_around_grab = (mouse_abs_pos >= grab_pos - grab_sz * 0.5f - 1.0f) && (mouse_abs_pos <= grab_pos + grab_sz * 0.5f + 1.0f); // No harm being extra generous here.
+                    g.SliderGrabClickOffset = (clicked_around_grab && is_floating_point) ? mouse_abs_pos - grab_pos : 0.0f;
+                }
                 if (slider_usable_sz > 0.0f)
-                    clicked_t = ImSaturate((mouse_abs_pos - slider_usable_pos_min) / slider_usable_sz);
+                    clicked_t = ImSaturate((mouse_abs_pos - g.SliderGrabClickOffset - slider_usable_pos_min) / slider_usable_sz);
                 if (axis == ImGuiAxis_Y)
                     clicked_t = 1.0f - clicked_t;
                 set_new_value = true;