operator.py

# -*- coding: utf-8 -*-
# operator.py: interaction with Blender and the user

from re import compile as re_compile
from math import pi, ceil
import bpy
import bl_operators
import bmesh
import mathutils

from .unfolder import Unfolder, UnfoldError, default_priority_effect
from .svg import Svg
from .pdf import Pdf


global_paper_sizes = [
    ('USER', "User defined", "User defined paper size"),
    ('A4', "A4", "International standard paper size"),
    ('A3', "A3", "International standard paper size"),
    ('US_LETTER', "Letter", "North American paper size"),
    ('US_LEGAL', "Legal", "North American paper size")
]


def first_letters(text):
    """Iterator over the first letter of each word"""
    for match in first_letters.pattern.finditer(text):
        yield text[match.start()]
first_letters.pattern = re_compile("((?<!\w)\w)|\d")


def init_exporter(self, properties):
    self.page_size = mathutils.Vector((properties.output_size_x, properties.output_size_y))
    self.style = properties.style
    margin = properties.output_margin
    self.margin = mathutils.Vector((margin, margin))
    self.pure_net = (properties.texture_type == 'NONE')
    self.do_create_stickers = properties.do_create_stickers
    self.text_size = properties.sticker_width
    self.angle_epsilon = properties.angle_epsilon


class Unfold(bpy.types.Operator):
    """Blender Operator: unfold the selected object."""

    bl_idname = "mesh.unfold"
    bl_label = "Unfold"
    bl_description = "Mark seams so that the mesh can be exported as a paper model"
    bl_options = {'REGISTER', 'UNDO'}
    edit: bpy.props.BoolProperty(default=False, options={'HIDDEN'})
    priority_effect_convex: bpy.props.FloatProperty(
        name="Priority Convex", description="Priority effect for edges in convex angles",
        default=default_priority_effect['CONVEX'], soft_min=-1, soft_max=10, subtype='FACTOR')
    priority_effect_concave: bpy.props.FloatProperty(
        name="Priority Concave", description="Priority effect for edges in concave angles",
        default=default_priority_effect['CONCAVE'], soft_min=-1, soft_max=10, subtype='FACTOR')
    priority_effect_length: bpy.props.FloatProperty(
        name="Priority Length", description="Priority effect of edge length",
        default=default_priority_effect['LENGTH'], soft_min=-10, soft_max=1, subtype='FACTOR')
    do_create_uvmap: bpy.props.BoolProperty(
        name="Create UVMap", description="Create a new UV Map showing the islands and page layout", default=False)
    object = None

    @classmethod
    def poll(cls, context):
        return context.active_object and context.active_object.type == "MESH"

    def draw(self, context):
        layout = self.layout
        col = layout.column()
        col.active = not self.object or len(self.object.data.uv_layers) < 8
        col.prop(self.properties, "do_create_uvmap")
        layout.label(text="Edge Cutting Factors:")
        col = layout.column(align=True)
        col.label(text="Face Angle:")
        col.prop(self.properties, "priority_effect_convex", text="Convex")
        col.prop(self.properties, "priority_effect_concave", text="Concave")
        layout.prop(self.properties, "priority_effect_length", text="Edge Length")

    def execute(self, context):
        sce = bpy.context.scene
        settings = sce.paper_model
        recall_mode = context.object.mode
        bpy.ops.object.mode_set(mode='EDIT')

        self.object = context.object

        cage_size = mathutils.Vector((settings.output_size_x, settings.output_size_y))
        priority_effect = {
            'CONVEX': self.priority_effect_convex,
            'CONCAVE': self.priority_effect_concave,
            'LENGTH': self.priority_effect_length}
        try:
            unfolder = Unfolder(self.object)
            unfolder.do_create_uvmap = self.do_create_uvmap
            scale = sce.unit_settings.scale_length / settings.scale
            unfolder.prepare(cage_size, priority_effect, scale, settings.limit_by_page)
            unfolder.mesh.mark_cuts()
        except UnfoldError as error:
            self.report(type={'ERROR_INVALID_INPUT'}, message=error.args[0])
            error.mesh_select()
            del unfolder
            bpy.ops.object.mode_set(mode=recall_mode)
            return {'CANCELLED'}
        mesh = self.object.data
        mesh.update()
        if mesh.paper_island_list:
            unfolder.copy_island_names(mesh.paper_island_list)
        island_list = mesh.paper_island_list
        attributes = {item.label: (item.abbreviation, item.auto_label, item.auto_abbrev) for item in island_list}
        island_list.clear()  # remove previously defined islands
        for island in unfolder.mesh.islands:
            # add islands to UI list and set default descriptions
            list_item = island_list.add()
            # add faces' IDs to the island
            for face in island.faces:
                lface = list_item.faces.add()
                lface.id = face.index
            list_item["label"] = island.label
            list_item["abbreviation"], list_item["auto_label"], list_item["auto_abbrev"] = attributes.get(
                island.label,
                (island.abbreviation, True, True))
            island_item_changed(list_item, context)
            mesh.paper_island_index = -1

        del unfolder
        bpy.ops.object.mode_set(mode=recall_mode)
        return {'FINISHED'}


class ClearAllSeams(bpy.types.Operator):
    """Blender Operator: clear all seams of the active Mesh and all its unfold data"""

    bl_idname = "mesh.clear_all_seams"
    bl_label = "Clear All Seams"
    bl_description = "Clear all the seams and unfolded islands of the active object"

    @classmethod
    def poll(cls, context):
        return context.active_object and context.active_object.type == 'MESH'

    def execute(self, context):
        ob = context.active_object
        mesh = ob.data

        for edge in mesh.edges:
            edge.use_seam = False
        mesh.paper_island_list.clear()

        return {'FINISHED'}


def page_size_preset_changed(self, context):
    """Update the actual document size to correct values"""
    if hasattr(self, "limit_by_page") and not self.limit_by_page:
        return
    if self.page_size_preset == 'A4':
        self.output_size_x = 0.210
        self.output_size_y = 0.297
    elif self.page_size_preset == 'A3':
        self.output_size_x = 0.297
        self.output_size_y = 0.420
    elif self.page_size_preset == 'US_LETTER':
        self.output_size_x = 0.216
        self.output_size_y = 0.279
    elif self.page_size_preset == 'US_LEGAL':
        self.output_size_x = 0.216
        self.output_size_y = 0.356


class PaperModelStyle(bpy.types.PropertyGroup):
    line_styles = [
        ('SOLID', "Solid (----)", "Solid line"),
        ('DOT', "Dots (. . .)", "Dotted line"),
        ('DASH', "Short Dashes (- - -)", "Solid line"),
        ('LONGDASH', "Long Dashes (-- --)", "Solid line"),
        ('DASHDOT', "Dash-dotted (-- .)", "Solid line")
    ]
    outer_color: bpy.props.FloatVectorProperty(
        name="Outer Lines", description="Color of net outline",
        default=(0.0, 0.0, 0.0, 1.0), min=0, max=1, subtype='COLOR', size=4)
    outer_style: bpy.props.EnumProperty(
        name="Outer Lines Drawing Style", description="Drawing style of net outline",
        default='SOLID', items=line_styles)
    line_width: bpy.props.FloatProperty(
        name="Base Lines Thickness", description="Base thickness of net lines, each actual value is a multiple of this length",
        default=1e-4, min=0, soft_max=5e-3, precision=5, step=1e-2, subtype="UNSIGNED", unit="LENGTH")
    outer_width: bpy.props.FloatProperty(
        name="Outer Lines Thickness", description="Relative thickness of net outline",
        default=3, min=0, soft_max=10, precision=1, step=10, subtype='FACTOR')
    use_outbg: bpy.props.BoolProperty(
        name="Highlight Outer Lines", description="Add another line below every line to improve contrast",
        default=True)
    outbg_color: bpy.props.FloatVectorProperty(
        name="Outer Highlight", description="Color of the highlight for outer lines",
        default=(1.0, 1.0, 1.0, 1.0), min=0, max=1, subtype='COLOR', size=4)
    outbg_width: bpy.props.FloatProperty(
        name="Outer Highlight Thickness", description="Relative thickness of the highlighting lines",
        default=5, min=0, soft_max=10, precision=1, step=10, subtype='FACTOR')

    convex_color: bpy.props.FloatVectorProperty(
        name="Inner Convex Lines", description="Color of lines to be folded to a convex angle",
        default=(0.0, 0.0, 0.0, 1.0), min=0, max=1, subtype='COLOR', size=4)
    convex_style: bpy.props.EnumProperty(
        name="Convex Lines Drawing Style", description="Drawing style of lines to be folded to a convex angle",
        default='DASH', items=line_styles)
    convex_width: bpy.props.FloatProperty(
        name="Convex Lines Thickness", description="Relative thickness of concave lines",
        default=2, min=0, soft_max=10, precision=1, step=10, subtype='FACTOR')
    concave_color: bpy.props.FloatVectorProperty(
        name="Inner Concave Lines", description="Color of lines to be folded to a concave angle",
        default=(0.0, 0.0, 0.0, 1.0), min=0, max=1, subtype='COLOR', size=4)
    concave_style: bpy.props.EnumProperty(
        name="Concave Lines Drawing Style", description="Drawing style of lines to be folded to a concave angle",
        default='DASHDOT', items=line_styles)
    concave_width: bpy.props.FloatProperty(
        name="Concave Lines Thickness", description="Relative thickness of concave lines",
        default=2, min=0, soft_max=10, precision=1, step=10, subtype='FACTOR')
    freestyle_color: bpy.props.FloatVectorProperty(
        name="Freestyle Edges", description="Color of lines marked as Freestyle Edge",
        default=(0.0, 0.0, 0.0, 1.0), min=0, max=1, subtype='COLOR', size=4)
    freestyle_style: bpy.props.EnumProperty(
        name="Freestyle Edges Drawing Style", description="Drawing style of Freestyle Edges",
        default='SOLID', items=line_styles)
    freestyle_width: bpy.props.FloatProperty(
        name="Freestyle Edges Thickness", description="Relative thickness of Freestyle edges",
        default=2, min=0, soft_max=10, precision=1, step=10, subtype='FACTOR')
    use_inbg: bpy.props.BoolProperty(
        name="Highlight Inner Lines", description="Add another line below every line to improve contrast",
        default=True)
    inbg_color: bpy.props.FloatVectorProperty(
        name="Inner Highlight", description="Color of the highlight for inner lines",
        default=(1.0, 1.0, 1.0, 1.0), min=0, max=1, subtype='COLOR', size=4)
    inbg_width: bpy.props.FloatProperty(
        name="Inner Highlight Thickness", description="Relative thickness of the highlighting lines",
        default=2, min=0, soft_max=10, precision=1, step=10, subtype='FACTOR')

    sticker_color: bpy.props.FloatVectorProperty(
        name="Tabs Fill", description="Fill color of sticking tabs",
        default=(0.9, 0.9, 0.9, 1.0), min=0, max=1, subtype='COLOR', size=4)
    text_color: bpy.props.FloatVectorProperty(
        name="Text Color", description="Color of all text used in the document",
        default=(0.0, 0.0, 0.0, 1.0), min=0, max=1, subtype='COLOR', size=4)
bpy.utils.register_class(PaperModelStyle)


class ExportPaperModel(bpy.types.Operator):
    """Blender Operator: save the selected object's net and optionally bake its texture"""

    bl_idname = "export_mesh.paper_model"
    bl_label = "Export Paper Model"
    bl_description = "Export the selected object's net and optionally bake its texture"
    bl_options = {'PRESET'}

    filepath: bpy.props.StringProperty(
        name="File Path", description="Target file to save the SVG", options={'SKIP_SAVE'})
    filename: bpy.props.StringProperty(
        name="File Name", description="Name of the file", options={'SKIP_SAVE'})
    directory: bpy.props.StringProperty(
        name="Directory", description="Directory of the file", options={'SKIP_SAVE'})
    page_size_preset: bpy.props.EnumProperty(
        name="Page Size", description="Size of the exported document",
        default='A4', update=page_size_preset_changed, items=global_paper_sizes)
    output_size_x: bpy.props.FloatProperty(
        name="Page Width", description="Width of the exported document",
        default=0.210, soft_min=0.105, soft_max=0.841, subtype="UNSIGNED", unit="LENGTH")
    output_size_y: bpy.props.FloatProperty(
        name="Page Height", description="Height of the exported document",
        default=0.297, soft_min=0.148, soft_max=1.189, subtype="UNSIGNED", unit="LENGTH")
    output_margin: bpy.props.FloatProperty(
        name="Page Margin", description="Distance from page borders to the printable area",
        default=0.005, min=0, soft_max=0.1, step=0.1, subtype="UNSIGNED", unit="LENGTH")
    texture_type: bpy.props.EnumProperty(
        name="Textures", description="Source of a texture for the model",
        default='NONE', items=[
            ('NONE', "No Texture", "Export the net only"),
            ('TEXTURE', "From Materials", "Render the diffuse color and all painted textures"),
            ('AMBIENT_OCCLUSION', "Ambient Occlusion", "Render the Ambient Occlusion pass"),
            ('RENDER', "Full Render", "Render the material in actual scene illumination"),
            ('SELECTED_TO_ACTIVE', "Selected to Active", "Render all selected surrounding objects as a texture")
        ])
    output_layers: bpy.props.EnumProperty(
        name="Layers", description="Separation of drawings by meaning",
        default='ONESIDE', items=[
            ('ONESIDE', "Single Sided", "All layers exported on top of each other"),
            ('TWOSIDE', "Two Sided", "Texture exported to odd pages, drawing to even pages"),
            ('SEPARATE', "Separate", "Texture and drawing exported as two separate documents"),
        ])
    do_create_stickers: bpy.props.BoolProperty(
        name="Create Tabs", description="Create gluing tabs around the net (useful for paper)",
        default=True)
    do_create_numbers: bpy.props.BoolProperty(
        name="Create Numbers", description="Enumerate edges to make it clear which edges should be sticked together",
        default=True)
    sticker_width: bpy.props.FloatProperty(
        name="Tabs and Text Size", description="Width of gluing tabs and their numbers",
        default=0.005, soft_min=0, soft_max=0.05, step=0.1, subtype="UNSIGNED", unit="LENGTH")
    angle_epsilon: bpy.props.FloatProperty(
        name="Hidden Edge Angle", description="Folds with angle below this limit will not be drawn",
        default=pi/360, min=0, soft_max=pi/4, step=0.01, subtype="ANGLE", unit="ROTATION")
    output_dpi: bpy.props.FloatProperty(
        name="Resolution (DPI)", description="Resolution of images in pixels per inch",
        default=90, min=1, soft_min=30, soft_max=600, subtype="UNSIGNED")
    bake_samples: bpy.props.IntProperty(
        name="Samples", description="Number of samples to render for each pixel",
        default=64, min=1, subtype="UNSIGNED")
    file_format: bpy.props.EnumProperty(
        name="Document Format", description="File format of the exported net",
        default='PDF', items=[
            ('PDF', "PDF", "Adobe Portable Document Format 1.4"),
            ('SVG', "SVG", "W3C Scalable Vector Graphics"),
        ])
    image_packing: bpy.props.EnumProperty(
        name="Image Packing Method", description="Method of attaching baked image(s) to the SVG",
        default='ISLAND_EMBED', items=[
            ('PAGE_LINK', "Single Linked", "Bake one image per page of output and save it separately"),
            ('ISLAND_LINK', "Linked", "Bake images separately for each island and save them in a directory"),
            ('ISLAND_EMBED', "Embedded", "Bake images separately for each island and embed them into the SVG")
        ])
    nesting_method: bpy.props.EnumProperty(
        name="Nesting Method", description="How to pack islands onto a page",
        default='BOX', items=[
            ('BOX', "Bounding Box", "Built-in Blender method with bounding boxes"),
            ('CCOR', "Raster", "Cross-correlation of rasterized shapes"),
        ])
    scale: bpy.props.FloatProperty(
        name="Scale", description="Divisor of all dimensions when exporting",
        default=1, soft_min=1.0, soft_max=100.0, subtype='FACTOR', precision=1)
    do_create_uvmap: bpy.props.BoolProperty(
        name="Create UVMap",
        description="Create a new UV Map showing the islands and page layout",
        default=False, options={'SKIP_SAVE'})
    ui_expanded_document: bpy.props.BoolProperty(
        name="Show Document Settings Expanded",
        description="Shows the box 'Document Settings' expanded in user interface",
        default=True, options={'SKIP_SAVE'})
    ui_expanded_style: bpy.props.BoolProperty(
        name="Show Style Settings Expanded",
        description="Shows the box 'Colors and Style' expanded in user interface",
        default=False, options={'SKIP_SAVE'})
    ui_expanded_development: bpy.props.BoolProperty(
        name="Show Development Settings Expanded",
        description="Shows the box 'Colors and Style' expanded in user interface",
        default=False, options={'SKIP_SAVE'})
    style: bpy.props.PointerProperty(type=PaperModelStyle)

    unfolder = None

    @classmethod
    def poll(cls, context):
        return context.active_object and context.active_object.type == 'MESH'

    def prepare(self, context):
        sce = context.scene
        self.recall_mode = context.object.mode
        bpy.ops.object.mode_set(mode='EDIT')

        self.object = context.active_object
        self.unfolder = Unfolder(self.object)
        cage_size = mathutils.Vector((sce.paper_model.output_size_x, sce.paper_model.output_size_y))
        unfolder_scale = sce.unit_settings.scale_length/self.scale
        self.unfolder.prepare(cage_size, scale=unfolder_scale, limit_by_page=sce.paper_model.limit_by_page)
        if sce.paper_model.use_auto_scale:
            self.scale = ceil(self.get_scale_ratio(sce))

    def recall(self):
        self.unfolder = None
        bpy.ops.object.mode_set(mode=self.recall_mode)

    def invoke(self, context, event):
        self.scale = context.scene.paper_model.scale
        try:
            self.prepare(context)
        except UnfoldError as error:
            self.report(type={'ERROR_INVALID_INPUT'}, message=error.args[0])
            error.mesh_select()
            self.recall()
            return {'CANCELLED'}
        wm = context.window_manager
        self.filename = f"{self.object.name}"
        wm.fileselect_add(self)
        return {'RUNNING_MODAL'}

    def execute(self, context):
        try:
            if not self.unfolder:
                self.prepare(context)
            self.unfolder.do_create_uvmap = self.do_create_uvmap
            if self.object.data.paper_island_list:
                self.unfolder.copy_island_names(self.object.data.paper_island_list)
            exporter_class = Svg if self.properties.file_format == 'SVG' else Pdf
            exporter = exporter_class(self.properties)
            # TODO make the constructor meaningful enough so that init_exporter is not necessary
            init_exporter(exporter, self.properties)
            self.unfolder.save(self.properties, exporter)
            self.report({'INFO'}, "Saved a {}-page document".format(len(self.unfolder.mesh.pages)))
            return {'FINISHED'}
        except UnfoldError as error:
            self.report(type={'ERROR_INVALID_INPUT'}, message=error.args[0])
            return {'CANCELLED'}
        finally:
            self.recall()
            self.unfolder = None

    def get_scale_ratio(self, sce):
        margin = self.output_margin + self.sticker_width
        if min(self.output_size_x, self.output_size_y) <= 2 * margin:
            return False
        output_inner_size = mathutils.Vector((self.output_size_x - 2*margin, self.output_size_y - 2*margin))
        ratio = self.unfolder.mesh.largest_island_ratio(output_inner_size)
        return ratio * sce.unit_settings.scale_length / self.scale

    def draw(self, context):
        layout = self.layout
        layout.prop(self.properties, "do_create_uvmap")
        layout.prop(self.properties, "scale", text="Scale: 1/")
        scale_ratio = self.get_scale_ratio(context.scene)
        if scale_ratio > 1:
            layout.label(
                text="An island is roughly {:.1f}x bigger than page".format(scale_ratio),
                icon="ERROR")
        elif scale_ratio > 0:
            layout.label(text="Largest island is roughly 1/{:.1f} of page".format(1 / scale_ratio))

        if context.scene.unit_settings.scale_length != 1:
            layout.label(
                text="Unit scale {:.1f} makes page size etc. not display correctly".format(
                    context.scene.unit_settings.scale_length), icon="ERROR")
        box = layout.box()
        row = box.row(align=True)
        row.prop(
            self.properties, "ui_expanded_document", text="",
            icon=('TRIA_DOWN' if self.ui_expanded_document else 'TRIA_RIGHT'), emboss=False)
        row.label(text="Document Settings")

        if self.ui_expanded_document:
            box.prop(self.properties, "file_format", text="Format")
            box.prop(self.properties, "page_size_preset")
            col = box.column(align=True)
            col.active = self.page_size_preset == 'USER'
            col.prop(self.properties, "output_size_x")
            col.prop(self.properties, "output_size_y")
            box.prop(self.properties, "output_margin")
            col = box.column()
            col.prop(self.properties, "do_create_stickers")
            col.prop(self.properties, "do_create_numbers")
            col = box.column()
            col.active = self.do_create_stickers or self.do_create_numbers
            col.prop(self.properties, "sticker_width")
            box.prop(self.properties, "angle_epsilon")

            box.prop(self.properties, "texture_type")
            col = box.column()
            col.active = (self.texture_type != 'NONE')
            if len(self.object.data.uv_layers) >= 8:
                col.label(text="No UV slots left, No Texture is the only option.", icon='ERROR')
            elif context.scene.render.engine != 'CYCLES' and self.texture_type != 'NONE':
                col.label(text="Cycles will be used for texture baking.", icon='ERROR')
            row = col.row()
            row.active = self.texture_type in ('AMBIENT_OCCLUSION', 'RENDER', 'SELECTED_TO_ACTIVE')
            row.prop(self.properties, "bake_samples")
            col.prop(self.properties, "output_dpi")
            row = col.row()
            row.active = self.file_format == 'SVG'
            row.prop(self.properties, "image_packing", text="Images")

        box = layout.box()
        row = box.row(align=True)
        row.prop(
            self.properties, "ui_expanded_style", text="",
            icon=('TRIA_DOWN' if self.ui_expanded_style else 'TRIA_RIGHT'), emboss=False)
        row.label(text="Colors and Style")

        if self.ui_expanded_style:
            box.prop(self.style, "line_width", text="Default line width")
            col = box.column()
            col.prop(self.style, "outer_color")
            col.prop(self.style, "outer_width", text="Relative width")
            col.prop(self.style, "outer_style", text="Style")
            col = box.column()
            col.active = self.texture_type != 'NONE'
            col.prop(self.style, "use_outbg", text="Outer Lines Highlight:")
            sub = col.column()
            sub.active = self.texture_type != 'NONE' and self.style.use_outbg
            sub.prop(self.style, "outbg_color", text="")
            sub.prop(self.style, "outbg_width", text="Relative width")
            col = box.column()
            col.prop(self.style, "convex_color")
            col.prop(self.style, "convex_width", text="Relative width")
            col.prop(self.style, "convex_style", text="Style")
            col = box.column()
            col.prop(self.style, "concave_color")
            col.prop(self.style, "concave_width", text="Relative width")
            col.prop(self.style, "concave_style", text="Style")
            col = box.column()
            col.prop(self.style, "freestyle_color")
            col.prop(self.style, "freestyle_width", text="Relative width")
            col.prop(self.style, "freestyle_style", text="Style")
            col = box.column()
            col.active = self.texture_type != 'NONE'
            col.prop(self.style, "use_inbg", text="Inner Lines Highlight:")
            sub = col.column()
            sub.active = self.texture_type != 'NONE' and self.style.use_inbg
            sub.prop(self.style, "inbg_color", text="")
            sub.prop(self.style, "inbg_width", text="Relative width")
            col = box.column()
            col.active = self.do_create_stickers
            col.prop(self.style, "sticker_color")
            box.prop(self.style, "text_color")

        if 0:
            box = layout.box()
            row = box.row(align=True)
            row.prop(
                self.properties, "ui_expanded_development", text="",
                icon=('TRIA_DOWN' if self.ui_expanded_development else 'TRIA_RIGHT'), emboss=False)
            row.label(text="Development")
    
            if self.ui_expanded_development:
                box.prop(self.properties, "nesting_method", text="Format")


def menu_func_export(self, context):
    self.layout.operator("export_mesh.paper_model", text="Paper Model (.pdf/.svg)")


def menu_func_unfold(self, context):
    self.layout.operator("mesh.unfold", text="Unfold")


class SelectIsland(bpy.types.Operator):
    """Blender Operator: select all faces of the active island"""

    bl_idname = "mesh.select_paper_island"
    bl_label = "Select Island"
    bl_description = "Select an island of the paper model net"

    operation: bpy.props.EnumProperty(
        name="Operation", description="Operation with the current selection",
        default='ADD', items=[
            ('ADD', "Add", "Add to current selection"),
            ('REMOVE', "Remove", "Remove from selection"),
            ('REPLACE', "Replace", "Select only the ")
        ])

    @classmethod
    def poll(cls, context):
        return context.active_object and context.active_object.type == 'MESH' and context.mode == 'EDIT_MESH'

    def execute(self, context):
        ob = context.active_object
        me = ob.data
        bm = bmesh.from_edit_mesh(me)
        island = me.paper_island_list[me.paper_island_index]
        faces = {face.id for face in island.faces}
        edges = set()
        verts = set()
        if self.operation == 'REPLACE':
            for face in bm.faces:
                selected = face.index in faces
                face.select = selected
                if selected:
                    edges.update(face.edges)
                    verts.update(face.verts)
            for edge in bm.edges:
                edge.select = edge in edges
            for vert in bm.verts:
                vert.select = vert in verts
        else:
            selected = (self.operation == 'ADD')
            for index in faces:
                face = bm.faces[index]
                face.select = selected
                edges.update(face.edges)
                verts.update(face.verts)
            for edge in edges:
                edge.select = any(face.select for face in edge.link_faces)
            for vert in verts:
                vert.select = any(edge.select for edge in vert.link_edges)
        bmesh.update_edit_mesh(me, loop_triangles=False, destructive=False)
        return {'FINISHED'}


class VIEW3D_PT_paper_model_tools(bpy.types.Panel):
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'UI'
    bl_category = 'Paper'
    bl_label = "Unfold"

    def draw(self, context):
        layout = self.layout
        sce = context.scene
        obj = context.active_object
        mesh = obj.data if obj and obj.type == 'MESH' else None

        layout.operator("mesh.unfold")

        if context.mode == 'EDIT_MESH':
            row = layout.row(align=True)
            row.operator("mesh.mark_seam", text="Mark Seam").clear = False
            row.operator("mesh.mark_seam", text="Clear Seam").clear = True
        else:
            layout.operator("mesh.clear_all_seams")


class VIEW3D_PT_paper_model_settings(bpy.types.Panel):
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'UI'
    bl_category = 'Paper'
    bl_label = "Export"

    def draw(self, context):
        layout = self.layout
        sce = context.scene
        obj = context.active_object
        mesh = obj.data if obj and obj.type == 'MESH' else None

        layout.operator("export_mesh.paper_model")
        props = sce.paper_model
        layout.prop(props, "use_auto_scale")
        sub = layout.row()
        sub.active = not props.use_auto_scale
        sub.prop(props, "scale", text="Model Scale:  1/")

        layout.prop(props, "limit_by_page")
        col = layout.column()
        col.active = props.limit_by_page
        col.prop(props, "page_size_preset")
        sub = col.column(align=True)
        sub.active = props.page_size_preset == 'USER'
        sub.prop(props, "output_size_x")
        sub.prop(props, "output_size_y")


class DATA_PT_paper_model_islands(bpy.types.Panel):
    bl_space_type = 'PROPERTIES'
    bl_region_type = 'WINDOW'
    bl_context = "data"
    bl_label = "Paper Model Islands"
    COMPAT_ENGINES = {'BLENDER_RENDER', 'BLENDER_EEVEE', 'BLENDER_WORKBENCH'}

    def draw(self, context):
        layout = self.layout
        sce = context.scene
        obj = context.active_object
        mesh = obj.data if obj and obj.type == 'MESH' else None

        layout.operator("mesh.unfold", icon='FILE_REFRESH')
        if mesh and mesh.paper_island_list:
            layout.label(
                text="1 island:" if len(mesh.paper_island_list) == 1 else
                "{} islands:".format(len(mesh.paper_island_list)))
            layout.template_list(
                'UI_UL_list', 'paper_model_island_list', mesh,
                'paper_island_list', mesh, 'paper_island_index', rows=1, maxrows=5)
            sub = layout.split(align=True)
            sub.operator("mesh.select_paper_island", text="Select").operation = 'ADD'
            sub.operator("mesh.select_paper_island", text="Deselect").operation = 'REMOVE'
            sub.prop(sce.paper_model, "sync_island", icon='UV_SYNC_SELECT', toggle=True)
            if mesh.paper_island_index >= 0:
                list_item = mesh.paper_island_list[mesh.paper_island_index]
                sub = layout.column(align=True)
                sub.prop(list_item, "auto_label")
                sub.prop(list_item, "label")
                sub.prop(list_item, "auto_abbrev")
                row = sub.row()
                row.active = not list_item.auto_abbrev
                row.prop(list_item, "abbreviation")
        else:
            layout.box().label(text="Not unfolded")


def label_changed(self, context):
    """The label of an island was changed"""
    # accessing properties via [..] to avoid a recursive call after the update
    self["auto_label"] = not self.label or self.label.isspace()
    island_item_changed(self, context)


def island_item_changed(self, context):
    """The labelling of an island was changed"""
    def increment(abbrev, collisions):
        letters = "ABCDEFGHIJKLMNPQRSTUVWXYZ123456789"
        while abbrev in collisions:
            if len(abbrev) < 3:
                abbrev += letters[0]
            else:
                abbrev = abbrev.rstrip(letters[-1])
                abbrev = abbrev[:-1] + letters[letters.find(abbrev[-1]) + 1]
        return abbrev

    # accessing properties via [..] to avoid a recursive call after the update
    island_list = context.active_object.data.paper_island_list
    if self.auto_label:
        self["label"] = ""  # avoid self-conflict
        number = 1
        while any(item.label == "Island {}".format(number) for item in island_list):
            number += 1
        self["label"] = "Island {}".format(number)
    if self.auto_abbrev:
        self["abbreviation"] = ""  # avoid self-conflict
        abbrev = "".join(first_letters(self.label))[:3].upper()
        self["abbreviation"] = increment(abbrev, {item.abbreviation for item in island_list})
    elif len(self.abbreviation) > 3:
        self["abbreviation"] = self.abbreviation[:3]
    self.name = "[{}] {} ({} {})".format(
        self.abbreviation, self.label, len(self.faces), "faces" if len(self.faces) > 1 else "face")


def island_index_changed(self, context):
    """The active island was changed"""
    if context.scene.paper_model.sync_island and SelectIsland.poll(context):
        bpy.ops.mesh.select_paper_island(operation='REPLACE')


class FaceList(bpy.types.PropertyGroup):
    id: bpy.props.IntProperty(name="Face ID")


class IslandList(bpy.types.PropertyGroup):
    faces: bpy.props.CollectionProperty(
        name="Faces", description="Faces belonging to this island", type=FaceList)
    label: bpy.props.StringProperty(
        name="Label", description="Label on this island",
        default="", update=label_changed)
    abbreviation: bpy.props.StringProperty(
        name="Abbreviation", description="Three-letter label to use when there is not enough space",
        default="", update=island_item_changed)
    auto_label: bpy.props.BoolProperty(
        name="Auto Label", description="Generate the label automatically",
        default=True, update=island_item_changed)
    auto_abbrev: bpy.props.BoolProperty(
        name="Auto Abbreviation", description="Generate the abbreviation automatically",
        default=True, update=island_item_changed)


class PaperModelSettings(bpy.types.PropertyGroup):
    sync_island: bpy.props.BoolProperty(
        name="Sync", description="Keep faces of the active island selected",
        default=False, update=island_index_changed)
    limit_by_page: bpy.props.BoolProperty(
        name="Limit Island Size", description="Do not create islands larger than given dimensions",
        default=False, update=page_size_preset_changed)
    page_size_preset: bpy.props.EnumProperty(
        name="Page Size", description="Maximal size of an island",
        default='A4', update=page_size_preset_changed, items=global_paper_sizes)
    output_size_x: bpy.props.FloatProperty(
        name="Width", description="Maximal width of an island",
        default=0.2, soft_min=0.105, soft_max=0.841, subtype="UNSIGNED", unit="LENGTH")
    output_size_y: bpy.props.FloatProperty(
        name="Height", description="Maximal height of an island",
        default=0.29, soft_min=0.148, soft_max=1.189, subtype="UNSIGNED", unit="LENGTH")
    use_auto_scale: bpy.props.BoolProperty(
        name="Automatic Scale", description="Scale the net automatically to fit on paper",
        default=True)
    scale: bpy.props.FloatProperty(
        name="Scale", description="Divisor of all dimensions when exporting",
        default=1, soft_min=1.0, soft_max=100.0, subtype='FACTOR', precision=1,
        update=lambda settings, _: settings.__setattr__('use_auto_scale', False))