Implement zooming using Ctrl + Mouse wheel in the GridMap editor

The minimum value of the slider was changed to 0.2 as zooming
works in increments of 0.2. This way, the value can go back to 1
after you've reached the slider's minimum value.

(cherry picked from commit 4c1b2171b0d2ebff568460a06a24287c0b994dc2)

modules/gridmap/grid_map_editor_plugin.cpp

@@ -840,15 +840,33 @@ void GridMapEditor::_text_changed(const String &p_text) {
 
 void GridMapEditor::_sbox_input(const Ref<InputEvent> &p_ie) {
 
-	Ref<InputEventKey> k = p_ie;
+	const Ref<InputEventKey> k = p_ie;
 
 	if (k.is_valid() && (k->get_scancode() == KEY_UP || k->get_scancode() == KEY_DOWN || k->get_scancode() == KEY_PAGEUP || k->get_scancode() == KEY_PAGEDOWN)) {
 
+		// Forward the key input to the ItemList so it can be scrolled
 		mesh_library_palette->call("_gui_input", k);
 		search_box->accept_event();
 	}
 }
 
+void GridMapEditor::_mesh_library_palette_input(const Ref<InputEvent> &p_ie) {
+
+	const Ref<InputEventMouseButton> mb = p_ie;
+
+	// Zoom in/out using Ctrl + mouse wheel
+	if (mb.is_valid() && mb->is_pressed() && mb->get_command()) {
+
+		if (mb->is_pressed() && mb->get_button_index() == BUTTON_WHEEL_UP) {
+			size_slider->set_value(size_slider->get_value() + 0.2);
+		}
+
+		if (mb->is_pressed() && mb->get_button_index() == BUTTON_WHEEL_DOWN) {
+			size_slider->set_value(size_slider->get_value() - 0.2);
+		}
+	}
+}
+
 void GridMapEditor::_icon_size_changed(float p_value) {
 	mesh_library_palette->set_icon_scale(p_value);
 	update_palette();
@@ -1183,6 +1201,7 @@ void GridMapEditor::_bind_methods() {
 
 	ClassDB::bind_method("_text_changed", &GridMapEditor::_text_changed);
 	ClassDB::bind_method("_sbox_input", &GridMapEditor::_sbox_input);
+	ClassDB::bind_method("_mesh_library_palette_input", &GridMapEditor::_mesh_library_palette_input);
 	ClassDB::bind_method("_icon_size_changed", &GridMapEditor::_icon_size_changed);
 	ClassDB::bind_method("_menu_option", &GridMapEditor::_menu_option);
 	ClassDB::bind_method("_configure", &GridMapEditor::_configure);
@@ -1311,7 +1330,7 @@ GridMapEditor::GridMapEditor(EditorNode *p_editor) {
 
 	size_slider = memnew(HSlider);
 	size_slider->set_h_size_flags(SIZE_EXPAND_FILL);
-	size_slider->set_min(0.1f);
+	size_slider->set_min(0.2f);
 	size_slider->set_max(4.0f);
 	size_slider->set_step(0.1f);
 	size_slider->set_value(1.0f);
@@ -1325,6 +1344,7 @@ GridMapEditor::GridMapEditor(EditorNode *p_editor) {
 	mesh_library_palette = memnew(ItemList);
 	add_child(mesh_library_palette);
 	mesh_library_palette->set_v_size_flags(SIZE_EXPAND_FILL);
+	mesh_library_palette->connect("gui_input", this, "_mesh_library_palette_input");
 
 	info_message = memnew(Label);
 	info_message->set_text(TTR("Give a MeshLibrary resource to this GridMap to use its meshes."));

modules/gridmap/grid_map_editor_plugin.h

@@ -214,6 +214,7 @@ class GridMapEditor : public VBoxContainer {
 
 	void _text_changed(const String &p_text);
 	void _sbox_input(const Ref<InputEvent> &p_ie);
+	void _mesh_library_palette_input(const Ref<InputEvent> &p_ie);
 
 	void _icon_size_changed(float p_value);