Style: Added style.TabMinWidthForUnselectedCloseButton settings.

Set to 0.0f (default) to always make a close button appear on hover (same as Chrome, VS).
Set to FLT_MAX to only display a close button when selected (merely hovering is not enough).
Set to an intermediary value to toggle behavior based on width (same as Firefox).

docs/CHANGELOG.txt

@@ -46,6 +46,10 @@ Other Changes:
   flag was also set, and _OpenOnArrow is frequently set along with _OpenOnDoubleClick).
 - TreeNode: Fixed bug where dragging a payload over a TreeNode() with either _OpenOnDoubleClick
   or _OpenOnArrow would open the node. (#143)
+- Style: Added style.TabMinWidthForUnselectedCloseButton settings.
+  Set to 0.0f (default) to always make a close button appear on hover (same as Chrome, VS).
+  Set to FLT_MAX to only display a close button when selected (merely hovering is not enough).
+  Set to an intermediary value to toggle behavior based on width (same as Firefox).
 - Backends: Win32: Support for #define NOGDI, won't try to call GetDeviceCaps(). (#3137, #2327)
 - Backends: OpenGL: Fixed handling of GL 4.5+ glClipControl(GL_UPPER_LEFT) by inverting the
   projection matrix top and bottom values. (#3143, #3146) [@u3shit]

imgui.cpp

@@ -1028,6 +1028,7 @@ ImGuiStyle::ImGuiStyle()
     GrabRounding            = 0.0f;             // Radius of grabs corners rounding. Set to 0.0f to have rectangular slider grabs.
     TabRounding             = 4.0f;             // Radius of upper corners of a tab. Set to 0.0f to have rectangular tabs.
     TabBorderSize           = 0.0f;             // Thickness of border around tabs.
+    TabMinWidthForUnselectedCloseButton = 0.0f; // Minimum width for close button to appears on an unselected tab when hovered. Set to 0.0f to always show when hovering, set to FLT_MAX to never show close button unless selected.
     ColorButtonPosition     = ImGuiDir_Right;   // Side of the color button in the ColorEdit4 widget (left/right). Defaults to ImGuiDir_Right.
     ButtonTextAlign         = ImVec2(0.5f,0.5f);// Alignment of button text when button is larger than text.
     SelectableTextAlign     = ImVec2(0.0f,0.0f);// Alignment of selectable text. Defaults to (0.0f, 0.0f) (top-left aligned). It's generally important to keep this left-aligned if you want to lay multiple items on a same line.
@@ -1064,6 +1065,8 @@ void ImGuiStyle::ScaleAllSizes(float scale_factor)
     GrabMinSize = ImFloor(GrabMinSize * scale_factor);
     GrabRounding = ImFloor(GrabRounding * scale_factor);
     TabRounding = ImFloor(TabRounding * scale_factor);
+    if (TabMinWidthForUnselectedCloseButton != FLT_MAX)
+        TabMinWidthForUnselectedCloseButton = ImFloor(TabMinWidthForUnselectedCloseButton * scale_factor);
     DisplayWindowPadding = ImFloor(DisplayWindowPadding * scale_factor);
     DisplaySafeAreaPadding = ImFloor(DisplaySafeAreaPadding * scale_factor);
     MouseCursorScale = ImFloor(MouseCursorScale * scale_factor);

imgui.h

@@ -1393,6 +1393,7 @@ struct ImGuiStyle
     float       GrabRounding;               // Radius of grabs corners rounding. Set to 0.0f to have rectangular slider grabs.
     float       TabRounding;                // Radius of upper corners of a tab. Set to 0.0f to have rectangular tabs.
     float       TabBorderSize;              // Thickness of border around tabs.
+    float       TabMinWidthForUnselectedCloseButton; // Minimum width for close button to appears on an unselected tab when hovered. Set to 0.0f to always show when hovering, set to FLT_MAX to never show close button unless selected.
     ImGuiDir    ColorButtonPosition;        // Side of the color button in the ColorEdit4 widget (left/right). Defaults to ImGuiDir_Right.
     ImVec2      ButtonTextAlign;            // Alignment of button text when button is larger than text. Defaults to (0.5f, 0.5f) (centered).
     ImVec2      SelectableTextAlign;        // Alignment of selectable text. Defaults to (0.0f, 0.0f) (top-left aligned). It's generally important to keep this left-aligned if you want to lay multiple items on a same line.

imgui_internal.h

@@ -1827,7 +1827,7 @@ namespace ImGui
     IMGUI_API bool          TabItemEx(ImGuiTabBar* tab_bar, const char* label, bool* p_open, ImGuiTabItemFlags flags);
     IMGUI_API ImVec2        TabItemCalcSize(const char* label, bool has_close_button);
     IMGUI_API void          TabItemBackground(ImDrawList* draw_list, const ImRect& bb, ImGuiTabItemFlags flags, ImU32 col);
-    IMGUI_API bool          TabItemLabelAndCloseButton(ImDrawList* draw_list, const ImRect& bb, ImGuiTabItemFlags flags, ImVec2 frame_padding, const char* label, ImGuiID tab_id, ImGuiID close_button_id);
+    IMGUI_API bool          TabItemLabelAndCloseButton(ImDrawList* draw_list, const ImRect& bb, ImGuiTabItemFlags flags, ImVec2 frame_padding, const char* label, ImGuiID tab_id, ImGuiID close_button_id, bool is_contents_visible);
 
     // Render helpers
     // AVOID USING OUTSIDE OF IMGUI.CPP! NOT FOR PUBLIC CONSUMPTION. THOSE FUNCTIONS ARE A MESS. THEIR SIGNATURE AND BEHAVIOR WILL CHANGE, THEY NEED TO BE REFACTORED INTO SOMETHING DECENT.

imgui_widgets.cpp

@@ -7090,6 +7090,7 @@ bool    ImGui::TabItemEx(ImGuiTabBar* tab_bar, const char* label, bool* p_open,
         tab_bar->NextSelectedTabId = id;
 
     // Lock visibility
+    // (Note: tab_contents_visible != tab_selected... because CTRL+TAB operations may preview some tabs without selecting them!)
     bool tab_contents_visible = (tab_bar->VisibleTabId == id);
     if (tab_contents_visible)
         tab_bar->VisibleTabWasSubmitted = true;
@@ -7195,7 +7196,7 @@ bool    ImGui::TabItemEx(ImGuiTabBar* tab_bar, const char* label, bool* p_open,
 
     // Render tab label, process close button
     const ImGuiID close_button_id = p_open ? window->GetID((void*)((intptr_t)id + 1)) : 0;
-    bool just_closed = TabItemLabelAndCloseButton(display_draw_list, bb, flags, tab_bar->FramePadding, label, id, close_button_id);
+    bool just_closed = TabItemLabelAndCloseButton(display_draw_list, bb, flags, tab_bar->FramePadding, label, id, close_button_id, tab_contents_visible);
     if (just_closed && p_open != NULL)
     {
         *p_open = false;
@@ -7270,13 +7271,21 @@ void ImGui::TabItemBackground(ImDrawList* draw_list, const ImRect& bb, ImGuiTabI
 
 // Render text label (with custom clipping) + Unsaved Document marker + Close Button logic
 // We tend to lock style.FramePadding for a given tab-bar, hence the 'frame_padding' parameter.
-bool ImGui::TabItemLabelAndCloseButton(ImDrawList* draw_list, const ImRect& bb, ImGuiTabItemFlags flags, ImVec2 frame_padding, const char* label, ImGuiID tab_id, ImGuiID close_button_id)
+bool ImGui::TabItemLabelAndCloseButton(ImDrawList* draw_list, const ImRect& bb, ImGuiTabItemFlags flags, ImVec2 frame_padding, const char* label, ImGuiID tab_id, ImGuiID close_button_id, bool is_contents_visible)
 {
     ImGuiContext& g = *GImGui;
     ImVec2 label_size = CalcTextSize(label, NULL, true);
     if (bb.GetWidth() <= 1.0f)
         return false;
 
+    // In Style V2 we'll have full override of all colors per state (e.g. focused, selected)
+    // But right now if you want to alter text color of tabs this is what you need to do.
+#if 0
+    const float backup_alpha = g.Style.Alpha;
+    if (!is_contents_visible)
+        g.Style.Alpha *= 0.7f;
+#endif
+
     // Render text label (with clipping + alpha gradient) + unsaved marker
     const char* TAB_UNSAVED_MARKER = "*";
     ImRect text_pixel_clip_bb(bb.Min.x + frame_padding.x, bb.Min.y + frame_padding.y, bb.Max.x - frame_padding.x, bb.Max.y);
@@ -7296,8 +7305,9 @@ bool ImGui::TabItemLabelAndCloseButton(ImDrawList* draw_list, const ImRect& bb,
     bool close_button_pressed = false;
     bool close_button_visible = false;
     if (close_button_id != 0)
-        if (g.HoveredId == tab_id || g.HoveredId == close_button_id || g.ActiveId == close_button_id)
+        if (is_contents_visible || bb.GetWidth() >= g.Style.TabMinWidthForUnselectedCloseButton)
-            close_button_visible = true;
+            if (g.HoveredId == tab_id || g.HoveredId == close_button_id || g.ActiveId == close_button_id)
+                close_button_visible = true;
     if (close_button_visible)
     {
         ImGuiItemHoveredDataBackup last_item_backup;
@@ -7318,6 +7328,11 @@ bool ImGui::TabItemLabelAndCloseButton(ImDrawList* draw_list, const ImRect& bb,
     float ellipsis_max_x = close_button_visible ? text_pixel_clip_bb.Max.x : bb.Max.x - 1.0f;
     RenderTextEllipsis(draw_list, text_ellipsis_clip_bb.Min, text_ellipsis_clip_bb.Max, text_pixel_clip_bb.Max.x, ellipsis_max_x, label, NULL, &label_size);
 
+#if 0
+    if (!is_contents_visible)
+        g.Style.Alpha = backup_alpha;
+#endif
+
     return close_button_pressed;
 }