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diff --git a/src/ui/modifiers.cpp b/src/ui/modifiers.cpp
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+// SPDX-License-Identifier: GPL-2.0-or-later
+/** @file
+ * Modifiers for inkscape
+ *
+ * The file provides a definition of all the ways shift/ctrl/alt modifiers
+ * are used in Inkscape, and allows users to customise them in keys.xml
+ *
+ *//*
+ * Authors:
+ * 2020 Martin Owens <doctormo@geek-2.com>
+ *
+ * Copyright (C) 2018 Authors
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#include <cstring>
+#include <string>
+#include <bitset>
+#include <glibmm/i18n.h>
+
+#include "modifiers.h"
+#include "ui/tools/tool-base.h"
+
+namespace Inkscape {
+namespace Modifiers {
+
+Modifier::Lookup Modifier::_modifier_lookup;
+
+// these must be in the same order as the * enum in "modifiers.h"
+decltype(Modifier::_modifiers) Modifier::_modifiers {
+    // Canvas modifiers
+    {Type::CANVAS_PAN_Y, new Modifier("canvas-pan-y", _("Vertical pan"), _("Pan/Scroll up and down"), ALWAYS, CANVAS, SCROLL)},
+    {Type::CANVAS_PAN_X, new Modifier("canvas-pan-x", _("Horizontal pan"), _("Pan/Scroll left and right"), SHIFT, CANVAS, SCROLL)},
+    {Type::CANVAS_ZOOM, new Modifier("canvas-zoom", _("Canvas zoom"), _("Zoom in and out with scroll wheel"), CTRL, CANVAS, SCROLL)},
+    {Type::CANVAS_ROTATE, new Modifier("canvas-rotate", _("Canvas rotate"), _("Rotate the canvas with scroll wheel"), SHIFT | CTRL, CANVAS, SCROLL)},
+
+    // Select tool modifiers (minus transforms)
+    {Type::SELECT_ADD_TO, new Modifier("select-add-to", _("Add to selection"), _("Add items to existing selection"), SHIFT, SELECT, CLICK)},
+    {Type::SELECT_IN_GROUPS, new Modifier("select-in-groups", _("Select inside groups"), _("Ignore groups when selecting items"), CTRL, SELECT, CLICK)},
+    {Type::SELECT_TOUCH_PATH, new Modifier("select-touch-path", _("Select with touch-path"), _("Draw a band around items to select them"), ALT, SELECT, DRAG)},
+    {Type::SELECT_ALWAYS_BOX, new Modifier("select-always-box", _("Select with box"), _("Don't drag items, select more with a box"), SHIFT, SELECT, DRAG)},
+    {Type::SELECT_FIRST_HIT, new Modifier("select-first-hit", _("Select the first"), _("Drag the first item the mouse hits"), CTRL, SELECT, DRAG)},
+    {Type::SELECT_FORCE_DRAG, new Modifier("select-force-drag", _("Forced Drag"), _("Drag objects even if the mouse isn't over them"), ALT, SELECT, DRAG)},
+    {Type::SELECT_CYCLE, new Modifier("select-cycle", _("Cycle through objects"), _("Scroll through objects under the cursor"), ALT, SELECT, SCROLL)},
+
+    // Transform handle modifiers (applies to multiple tools)
+    {Type::MOVE_CONFINE, new Modifier("move-confine", _("Move one axis only"), _("When dragging items, confine to either x or y axis"), CTRL, MOVE, DRAG)},
+    {Type::MOVE_INCREMENT, new Modifier("move-increment", _("Move in increments"), _("Move the objects by set increments when dragging"), ALT, MOVE, DRAG)},
+    {Type::MOVE_SNAPPING, new Modifier("move-snapping", _("No Move Snapping"), _("Disable snapping when moving objects"), SHIFT, MOVE, DRAG)},
+    {Type::TRANS_CONFINE, new Modifier("trans-confine", _("Keep aspect ratio"), _("When resizing objects, confine the aspect ratio"), CTRL, TRANSFORM, DRAG)},
+    {Type::TRANS_INCREMENT, new Modifier("trans-increment", _("Transform in increments"), _("Scale, rotate or skew by set increments"), ALT, TRANSFORM, DRAG)},
+    {Type::TRANS_OFF_CENTER, new Modifier("trans-off-center", _("Transform around center"), _("When scaling, scale selection symmetrically around its rotation center. When rotating/skewing, transform relative to opposite corner/edge."), SHIFT, TRANSFORM, DRAG)},
+    {Type::TRANS_SNAPPING, new Modifier("trans-snapping", _("No Transform Snapping"), _("Disable snapping when transforming object."), SHIFT, TRANSFORM, DRAG)},
+    // Center handle click: seltrans.cpp:734 SHIFT
+    // Align handle click: seltrans.cpp:1365 SHIFT
+};
+
+decltype(Modifier::_category_names) Modifier::_category_names {
+    {NO_CATEGORY, _("No Category")},
+    {CANVAS, _("Canvas")},
+    {SELECT, _("Selection")},
+    {MOVE, _("Movement")},
+    {TRANSFORM, _("Transformations")},
+};
+
+
+/**
+ * Given a Trigger, find which modifier is active (category lookup)
+ *
+ * @param  trigger - The Modifier::Trigger category in the form "CANVAS | DRAG".
+ * @param  button_state - The Gdk button state from an event.
+ * @return - Returns the best matching modifier id by the most number of keys.
+ */
+Type Modifier::which(Trigger trigger, int button_state)
+{
+    // Record each active modifier with it's weight
+    std::map<Type, unsigned long> scales;
+    for (auto const& [key, val] : _modifiers) {
+        if (val->get_trigger() == trigger) {
+            if(val->active(button_state)) {
+                scales[key] = val->get_weight();
+            }
+        }
+    }
+    // Sort the weightings
+    using pair_type = decltype(scales)::value_type;
+    auto sorted = std::max_element
+    (
+        std::begin(scales), std::end(scales),
+        [] (const pair_type & p1, const pair_type & p2) {
+            return p1.second < p2.second;
+        }
+    );
+    return sorted->first;
+}
+
+/**
+  * List all the modifiers available. Used in UI listing.
+  *
+  * @return a vector of Modifier objects.
+  */
+std::vector<Modifier *>
+Modifier::getList () {
+
+    std::vector<Modifier *> modifiers;
+    // Go through the dynamic modifier table
+    for( auto const& [key, val] : _modifiers ) {
+        modifiers.push_back(val);
+    }
+
+    return modifiers;
+};
+
+/**
+ * Test if this modifier is currently active.
+ *
+ * @param  button_state - The GDK button state from an event
+ * @return a boolean, true if the modifiers for this action are active.
+ */
+bool Modifier::active(int button_state)
+{
+    // TODO:
+    //  * ALT key is sometimes MOD1, MOD2 etc, if we find other ALT keys, set the ALT bit
+    //  * SUPER key could be HYPER or META, these cases need to be considered.
+    auto and_mask = get_and_mask();
+    auto not_mask = get_not_mask();
+    auto active = Key::ALL_MODS & button_state;
+    // Check that all keys in AND mask are pressed, and NONE of the NOT mask are.
+    return and_mask != NEVER && ((active & and_mask) == and_mask) && (not_mask == NOT_SET || (active & not_mask) == 0);
+}
+
+/**
+ * Generate a label for any modifier keys based on the mask
+ *
+ * @param  mask - The Modifier Mask such as {SHIFT & CTRL}
+ * @return a string of the keys needed for this mask to be true.
+ */
+std::string generate_label(KeyMask mask, std::string sep)
+{
+    auto ret = std::string();
+    if(mask == NOT_SET) {
+        return "-";
+    }
+    if(mask == NEVER) {
+        ret.append("[NEVER]");
+        return ret;
+    }
+    if(mask & CTRL) ret.append("Ctrl");
+    if(mask & SHIFT) {
+        if(!ret.empty()) ret.append(sep);
+        ret.append("Shift");
+    }
+    if(mask & ALT) {
+        if(!ret.empty()) ret.append(sep);
+        ret.append("Alt");
+    }
+    if(mask & SUPER) {
+        if(!ret.empty()) ret.append(sep);
+        ret.append("Super");
+    }
+    if(mask & HYPER) {
+        if(!ret.empty()) ret.append(sep);
+        ret.append("Hyper");
+    }
+    if(mask & META) {
+        if(!ret.empty()) ret.append(sep);
+        ret.append("Meta");
+    }
+    return ret;
+}
+
+/**
+ * Calculate the weight of this mask based on how many bits are set.
+ *
+ * @param  mask - The Modifier Mask such as {SHIFT & CTRL}
+ * @return count of all modifiers being pressed (or excluded)
+ */
+unsigned long calculate_weight(KeyMask mask)
+{
+
+    if (mask < 0)
+        return 0;
+    std::bitset<sizeof(mask)> bit_mask(mask);
+    return bit_mask.count();
+}
+
+/**
+ * Set the responsive tooltip for this tool, given the selected types.
+ *
+ * @param message_context - The desktop's message context for showing tooltips
+ * @param event - The current event status (which keys are pressed)
+ * @param num_args - Number of Modifier::Type arguments to follow.
+ * @param ... - One or more Modifier::Type arguments.
+ */
+void responsive_tooltip(Inkscape::MessageContext *message_context, GdkEvent *event, int num_args, ...)
+{
+    std::string ctrl_msg = "<b>Ctrl</b>: ";
+    std::string shift_msg = "<b>Shift</b>: ";
+    std::string alt_msg = "<b>Alt</b>: ";
+
+    // NOTE: This will hide any keys changed to SUPER or multiple keys such as CTRL+SHIFT
+    va_list args;
+    va_start(args, num_args);
+    for(int i = 0; i < num_args; i++) {
+        auto modifier = Modifier::get(va_arg(args, Type));
+        auto name = std::string(_(modifier->get_name()));
+        switch (modifier->get_and_mask()) {
+            case CTRL:
+                ctrl_msg += name + ", ";
+                break;
+            case SHIFT:
+                shift_msg += name + ", ";
+                break;
+            case ALT:
+                alt_msg += name + ", ";
+                break;
+            default:
+                g_warning("Unhandled responsivle tooltip: %s", name.c_str());
+        }
+    }
+    va_end(args);
+    ctrl_msg.erase(ctrl_msg.size() - 2);
+    shift_msg.erase(shift_msg.size() - 2);
+    alt_msg.erase(alt_msg.size() - 2);
+
+    Inkscape::UI::Tools::sp_event_show_modifier_tip(message_context, event,
+        ctrl_msg.c_str(), shift_msg.c_str(), alt_msg.c_str());
+}
+
+} // namespace Modifiers
+} // namespace Inkscape
+
+/*
+  Local Variables:
+  mode:c++
+  c-file-style:"stroustrup"
+  c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
+  indent-tabs-mode:nil
+  fill-column:99
+  End:
+*/
+// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:fileencoding=utf-8:textwidth=99 :