ui.py

        col.prop(raym, "depth")
        col.prop(raym, "distance", text="Max Dist")
        col.separator()
        sub = col.split(factor=0.4)
        sub.active = raym.distance > 0.0
        sub.label(text="Fade To:")
        sub.prop(raym, "fade_to", text="")

        col = split.column()
        col.label(text="Gloss:")
        col.prop(raym, "gloss_factor", text="Amount")
        sub = col.column()
        sub.active = raym.gloss_factor < 1.0
        sub.prop(raym, "gloss_threshold", text="Threshold")
        sub.prop(raym, "gloss_samples", text="Noise")
        sub.prop(raym, "gloss_anisotropic", text="Anisotropic")


class MATERIAL_PT_POV_transp(MaterialButtonsPanel, Panel):
    """Use this class to define pov material transparency (alpha) buttons."""

    bl_label = "Transparency"
    COMPAT_ENGINES = {'POVRAY_RENDER'}

    @classmethod
    def poll(cls, context):
        mat = context.material
        engine = context.scene.render.engine
        return (
            check_material(mat)
            and (mat.pov.type in {'SURFACE', 'WIRE'})
            and (engine in cls.COMPAT_ENGINES)
        )

    def draw_header(self, context):
        mat = context.material

        if simple_material(mat):
            self.layout.prop(mat.pov, "use_transparency", text="")

    def draw(self, context):
        layout = self.layout

        base_mat = context.material
        mat = context.material  # FORMERLY active_node_mat(context.material)
        rayt = mat.pov_raytrace_transparency

        if simple_material(base_mat):
            row = layout.row()
            row.active = mat.pov.use_transparency
            row.prop(mat.pov, "transparency_method", expand=True)

        split = layout.split()
        split.active = base_mat.pov.use_transparency

        col = split.column()
        col.prop(mat.pov, "alpha")
        row = col.row()
        row.active = (base_mat.pov.transparency_method != 'MASK') and (
            not mat.pov.use_shadeless
        )
        row.prop(mat.pov, "specular_alpha", text="Specular")

        col = split.column()
        col.active = not mat.pov.use_shadeless
        col.prop(rayt, "fresnel")
        sub = col.column()
        sub.active = rayt.fresnel > 0.0
        sub.prop(rayt, "fresnel_factor", text="Blend")

        if base_mat.pov.transparency_method == 'RAYTRACE':
            layout.separator()
            split = layout.split()
            split.active = base_mat.pov.use_transparency

            col = split.column()
            col.prop(rayt, "ior")
            col.prop(rayt, "filter")
            col.prop(rayt, "falloff")
            col.prop(rayt, "depth_max")
            col.prop(rayt, "depth")

            col = split.column()
            col.label(text="Gloss:")
            col.prop(rayt, "gloss_factor", text="Amount")
            sub = col.column()
            sub.active = rayt.gloss_factor < 1.0
            sub.prop(rayt, "gloss_threshold", text="Threshold")
            sub.prop(rayt, "gloss_samples", text="Samples")


class MATERIAL_PT_POV_reflection(MaterialButtonsPanel, Panel):
    """Use this class to define more pov specific reflectivity buttons."""

    bl_label = "POV-Ray Reflection"
    bl_parent_id = "MATERIAL_PT_POV_raytrace_mirror"
    COMPAT_ENGINES = {'POVRAY_RENDER'}

    @classmethod
    def poll(cls, context):
        engine = context.scene.render.engine
        mat = context.material
        ob = context.object
        return (
            mat
            and mat.pov.type == "SURFACE"
            and (engine in cls.COMPAT_ENGINES)
            and not (mat.pov.material_use_nodes or mat.use_nodes)
        )

    def draw(self, context):
        layout = self.layout
        mat = context.material
        col = layout.column()
        col.prop(mat.pov, "irid_enable")
        if mat.pov.irid_enable:
            col = layout.column()
            col.prop(mat.pov, "irid_amount", slider=True)
            col.prop(mat.pov, "irid_thickness", slider=True)
            col.prop(mat.pov, "irid_turbulence", slider=True)
        col.prop(mat.pov, "conserve_energy")
        col2 = col.split().column()

        if not mat.pov_raytrace_mirror.use:
            col2.label(text="Please Check Mirror settings :")
        col2.active = mat.pov_raytrace_mirror.use
        col2.prop(mat.pov, "mirror_use_IOR")
        if mat.pov.mirror_use_IOR:
            col2.alignment = 'CENTER'
            col2.label(text="The current Raytrace ")
            col2.label(text="Transparency IOR is: " + str(mat.pov.ior))
        col2.prop(mat.pov, "mirror_metallic")


'''
#group some native Blender (SSS) and POV (Fade)settings under such a parent panel?
class MATERIAL_PT_POV_interior(MaterialButtonsPanel, Panel):
    bl_label = "POV-Ray Interior"
    bl_idname = "material.pov_interior"
    #bl_parent_id = "material.absorption"
    COMPAT_ENGINES = {'POVRAY_RENDER'}
    @classmethod
    def poll(cls, context):
        engine = context.scene.render.engine
        mat=context.material
        ob = context.object
        return mat and mat.pov.type == "SURFACE" and (engine in cls.COMPAT_ENGINES) and not (mat.pov.material_use_nodes or mat.use_nodes)


    def draw_header(self, context):
        mat = context.material
'''


class MATERIAL_PT_POV_fade_color(MaterialButtonsPanel, Panel):
    """Use this class to define pov fading (absorption) color buttons."""

    bl_label = "POV-Ray Absorption"
    COMPAT_ENGINES = {'POVRAY_RENDER'}
    # bl_parent_id = "material.pov_interior"

    @classmethod
    def poll(cls, context):
        engine = context.scene.render.engine
        mat = context.material
        ob = context.object
        return (
            mat
            and mat.pov.type == "SURFACE"
            and (engine in cls.COMPAT_ENGINES)
            and not (mat.pov.material_use_nodes or mat.use_nodes)
        )

    def draw_header(self, context):
        mat = context.material

        self.layout.prop(mat.pov, "interior_fade_color", text="")

    def draw(self, context):
        layout = self.layout
        mat = context.material
        # layout.active = mat.pov.interior_fade_color
        if mat.pov.interior_fade_color != (0.0, 0.0, 0.0):
            layout.label(text="Raytrace transparency")
            layout.label(text="depth max Limit needs")
            layout.label(text="to be non zero to fade")

        pass


class MATERIAL_PT_POV_caustics(MaterialButtonsPanel, Panel):
    """Use this class to define pov caustics buttons."""

    bl_label = "Caustics"
    COMPAT_ENGINES = {'POVRAY_RENDER'}

    @classmethod
    def poll(cls, context):
        engine = context.scene.render.engine
        mat = context.material
        ob = context.object
        return (
            mat
            and mat.pov.type == "SURFACE"
            and (engine in cls.COMPAT_ENGINES)
            and not (mat.pov.material_use_nodes or mat.use_nodes)
        )

    def draw_header(self, context):
        mat = context.material
        if mat.pov.caustics_enable:
            self.layout.prop(
                mat.pov, "caustics_enable", text="", icon="PMARKER_SEL"
            )
        else:
            self.layout.prop(
                mat.pov, "caustics_enable", text="", icon="PMARKER"
            )

    def draw(self, context):

        layout = self.layout

        mat = context.material
        layout.active = mat.pov.caustics_enable
        col = layout.column()
        if mat.pov.caustics_enable:
            col.prop(mat.pov, "refraction_caustics")
            if mat.pov.refraction_caustics:

                col.prop(mat.pov, "refraction_type", text="")

                if mat.pov.refraction_type == "1":
                    col.prop(mat.pov, "fake_caustics_power", slider=True)
                elif mat.pov.refraction_type == "2":
                    col.prop(mat.pov, "photons_dispersion", slider=True)
                    col.prop(mat.pov, "photons_dispersion_samples", slider=True)
            col.prop(mat.pov, "photons_reflection")

            if (
                not mat.pov.refraction_caustics
                and not mat.pov.photons_reflection
            ):
                col = layout.column()
                col.alignment = 'CENTER'
                col.label(text="Caustics override is on, ")
                col.label(text="but you didn't chose any !")


class MATERIAL_PT_strand(MaterialButtonsPanel, Panel):
    """Use this class to define Blender strand antialiasing buttons."""

    bl_label = "Strand"
    bl_options = {'DEFAULT_CLOSED'}
    COMPAT_ENGINES = {'POVRAY_RENDER'}

    @classmethod
    def poll(cls, context):
        mat = context.material
        engine = context.scene.render.engine
        return (
            mat
            and (mat.pov.type in {'SURFACE', 'WIRE', 'HALO'})
            and (engine in cls.COMPAT_ENGINES)
        )

    def draw(self, context):
        layout = self.layout

        mat = context.material  # don't use node material
        tan = mat.strand

        split = layout.split()

        col = split.column()
        sub = col.column(align=True)
        sub.label(text="Size:")
        sub.prop(tan, "root_size", text="Root")
        sub.prop(tan, "tip_size", text="Tip")
        sub.prop(tan, "size_min", text="Minimum")
        sub.prop(tan, "use_blender_units")
        sub = col.column()
        sub.active = not mat.pov.use_shadeless
        sub.prop(tan, "use_tangent_shading")
        col.prop(tan, "shape")

        col = split.column()
        col.label(text="Shading:")
        col.prop(tan, "width_fade")
        ob = context.object
        if ob and ob.type == 'MESH':
            col.prop_search(
                tan, "uv_layer", ob.data, "tessface_uv_textures", text=""
            )
        else:
            col.prop(tan, "uv_layer", text="")
        col.separator()
        sub = col.column()
        sub.active = not mat.pov.use_shadeless
        sub.label(text="Surface diffuse:")
        sub = col.column()
        sub.prop(tan, "blend_distance", text="Distance")


class MATERIAL_PT_POV_replacement_text(MaterialButtonsPanel, Panel):
    """Use this class to define pov custom code declared name field."""

    bl_label = "Custom POV Code"
    COMPAT_ENGINES = {'POVRAY_RENDER'}

    def draw(self, context):
        layout = self.layout

        mat = context.material

        col = layout.column()
        col.label(text="Replace properties with:")
        col.prop(mat.pov, "replacement_text", text="")


class TEXTURE_MT_POV_specials(Menu):
    """Use this class to define pov texture slot operations buttons."""

    bl_label = "Texture Specials"
    COMPAT_ENGINES = {'POVRAY_RENDER'}

    def draw(self, context):
        layout = self.layout

        layout.operator("texture.slot_copy", icon='COPYDOWN')
        layout.operator("texture.slot_paste", icon='PASTEDOWN')


class WORLD_TEXTURE_SLOTS_UL_POV_layerlist(UIList):
    """Use this class to show pov texture slots list."""  # XXX Not used yet

    index: bpy.props.IntProperty(name='index')
    def draw_item(
        self, context, layout, data, item, icon, active_data, active_propname
    ):
        world = context.scene.world  # .pov
        active_data = world.pov
        # tex = context.texture #may be needed later?

        # We could write some code to decide which icon to use here...
        custom_icon = 'TEXTURE'

        ob = data
        slot = item
        # ma = slot.name
        # draw_item must handle the three layout types... Usually 'DEFAULT' and 'COMPACT' can share the same code.
        if self.layout_type in {'DEFAULT', 'COMPACT'}:
            # You should always start your row layout by a label (icon + text), or a non-embossed text field,
            # this will also make the row easily selectable in the list! The later also enables ctrl-click rename.
            # We use icon_value of label, as our given icon is an integer value, not an enum ID.
            # Note "data" names should never be translated!
            if slot:
                layout.prop(
                    item, "texture", text="", emboss=False, icon='TEXTURE'
                )
            else:
                layout.label(text="New", translate=False, icon_value=icon)
        # 'GRID' layout type should be as compact as possible (typically a single icon!).
        elif self.layout_type in {'GRID'}:
            layout.alignment = 'CENTER'
            layout.label(text="", icon_value=icon)


class MATERIAL_TEXTURE_SLOTS_UL_POV_layerlist(UIList):
    """Use this class to show pov texture slots list."""

    #    texture_slots:
    index: bpy.props.IntProperty(name='index')
    # foo  = random prop
    def draw_item(
        self, context, layout, data, item, icon, active_data, active_propname
    ):
        ob = data
        slot = item
        # ma = slot.name
        # draw_item must handle the three layout types... Usually 'DEFAULT' and 'COMPACT' can share the same code.
        if self.layout_type in {'DEFAULT', 'COMPACT'}:
            # You should always start your row layout by a label (icon + text), or a non-embossed text field,
            # this will also make the row easily selectable in the list! The later also enables ctrl-click rename.
            # We use icon_value of label, as our given icon is an integer value, not an enum ID.
            # Note "data" names should never be translated!
            if slot:
                layout.prop(
                    item, "texture", text="", emboss=False, icon='TEXTURE'
                )
            else:
                layout.label(text="New", translate=False, icon_value=icon)
        # 'GRID' layout type should be as compact as possible (typically a single icon!).
        elif self.layout_type in {'GRID'}:
            layout.alignment = 'CENTER'
            layout.label(text="", icon_value=icon)

# Rewrite an existing class to modify.
# register but not unregistered because
# the modified parts concern only POVRAY_RENDER
class TEXTURE_PT_context(TextureButtonsPanel, Panel):
    bl_label = ""
    bl_context = "texture"
    bl_options = {'HIDE_HEADER'}
    COMPAT_ENGINES = {'POVRAY_RENDER', 'BLENDER_EEVEE', 'BLENDER_WORKBENCH'}

    @classmethod
    def poll(cls, context):
        return (
            (context.scene.texture_context
            not in('MATERIAL','WORLD','LIGHT','PARTICLES','LINESTYLE')
            or context.scene.render.engine != 'POVRAY_RENDER')
        )
    def draw(self, context):
        layout = self.layout
        tex = context.texture
        space = context.space_data
        pin_id = space.pin_id
        use_pin_id = space.use_pin_id
        user = context.texture_user

        col = layout.column()

        if not (use_pin_id and isinstance(pin_id, bpy.types.Texture)):
            pin_id = None

        if not pin_id:
            col.template_texture_user()

        if user or pin_id:
            col.separator()

            if pin_id:
                col.template_ID(space, "pin_id")
            else:
                propname = context.texture_user_property.identifier
                col.template_ID(user, propname, new="texture.new")

            if tex:
                col.separator()

                split = col.split(factor=0.2)
                split.label(text="Type")
                split.prop(tex, "type", text="")

class TEXTURE_PT_POV_context_texture(TextureButtonsPanel, Panel):
    """Use this class to show pov texture context buttons."""

    bl_label = ""
    bl_options = {'HIDE_HEADER'}
    COMPAT_ENGINES = {'POVRAY_RENDER'}

    @classmethod
    def poll(cls, context):
        engine = context.scene.render.engine
        return engine in cls.COMPAT_ENGINES
        # if not (hasattr(context, "pov_texture_slot") or hasattr(context, "texture_node")):
        #     return False
        return (
            context.material
            or context.scene.world
            or context.light
            or context.texture
            or context.line_style
            or context.particle_system
            or isinstance(context.space_data.pin_id, ParticleSettings)
            or context.texture_user
        ) and (engine in cls.COMPAT_ENGINES)

    def draw(self, context):
        layout = self.layout

        scene = context.scene
        mat = context.view_layer.objects.active.active_material
        wld = context.scene.world

        layout.prop(scene, "texture_context", expand=True)
        if scene.texture_context == 'MATERIAL' and mat is not None:

            row = layout.row()
            row.template_list(
                "MATERIAL_TEXTURE_SLOTS_UL_POV_layerlist",
                "",
                mat,
                "pov_texture_slots",
                mat.pov,
                "active_texture_index",
                rows=2,
                maxrows=16,
                type="DEFAULT"
            )
            col = row.column(align=True)
            col.operator("pov.textureslotadd", icon='ADD', text='')
            col.operator("pov.textureslotremove", icon='REMOVE', text='')
            #todo: recreate for pov_texture_slots?
            #col.operator("texture.slot_move", text="", icon='TRIA_UP').type = 'UP'
            #col.operator("texture.slot_move", text="", icon='TRIA_DOWN').type = 'DOWN'
            col.separator()

            if mat.pov_texture_slots:
                index = mat.pov.active_texture_index
                slot = mat.pov_texture_slots[index]
                povtex = slot.texture#slot.name
                tex = bpy.data.textures[povtex]
                col.prop(tex, 'use_fake_user', text='')
                #layout.label(text='Linked Texture data browser:')
                propname = slot.texture_search
                # if slot.texture was a pointer to texture data rather than just a name string:
                # layout.template_ID(povtex, "texture", new="texture.new")

                layout.prop_search(
                    slot, 'texture_search', bpy.data, 'textures', text='', icon='TEXTURE'
                )
                try:
                    bpy.context.tool_settings.image_paint.brush.texture = bpy.data.textures[slot.texture_search]
                    bpy.context.tool_settings.image_paint.brush.mask_texture = bpy.data.textures[slot.texture_search]
                except KeyError:
                    # texture not hand-linked by user
                    pass

                if tex:
                    layout.separator()
                    split = layout.split(factor=0.2)
                    split.label(text="Type")
                    split.prop(tex, "type", text="")

            # else:
            # for i in range(18):  # length of material texture slots
            # mat.pov_texture_slots.add()
        elif scene.texture_context == 'WORLD' and wld is not None:

            row = layout.row()
            row.template_list(
                "WORLD_TEXTURE_SLOTS_UL_POV_layerlist",
                "",
                wld,
                "pov_texture_slots",
                wld.pov,
                "active_texture_index",
                rows=2,
                maxrows=16,
                type="DEFAULT"
            )
            col = row.column(align=True)
            col.operator("pov.textureslotadd", icon='ADD', text='')
            col.operator("pov.textureslotremove", icon='REMOVE', text='')

            #todo: recreate for pov_texture_slots?
            #col.operator("texture.slot_move", text="", icon='TRIA_UP').type = 'UP'
            #col.operator("texture.slot_move", text="", icon='TRIA_DOWN').type = 'DOWN'
            col.separator()

            if wld.pov_texture_slots:
                index = wld.pov.active_texture_index
                slot = wld.pov_texture_slots[index]
                povtex = slot.texture#slot.name
                tex = bpy.data.textures[povtex]
                col.prop(tex, 'use_fake_user', text='')
                #layout.label(text='Linked Texture data browser:')
                propname = slot.texture_search
                # if slot.texture was a pointer to texture data rather than just a name string:
                # layout.template_ID(povtex, "texture", new="texture.new")

                layout.prop_search(
                    slot, 'texture_search', bpy.data, 'textures', text='', icon='TEXTURE'
                )
                try:
                    bpy.context.tool_settings.image_paint.brush.texture = bpy.data.textures[slot.texture_search]
                    bpy.context.tool_settings.image_paint.brush.mask_texture = bpy.data.textures[slot.texture_search]
                except KeyError:
                    # texture not hand-linked by user
                    pass

                if tex:
                    layout.separator()
                    split = layout.split(factor=0.2)
                    split.label(text="Type")
                    split.prop(tex, "type", text="")

# Commented out below is a reminder of what existed in Blender Internal
# attributes need to be recreated
'''
        slot = getattr(context, "texture_slot", None)
        node = getattr(context, "texture_node", None)
        space = context.space_data

        #attempt at replacing removed space_data
        mtl = getattr(context, "material", None)
        if mtl != None:
            spacedependant = mtl
        wld = getattr(context, "world", None)
        if wld != None:
            spacedependant = wld
        lgt = getattr(context, "light", None)
        if lgt != None:
            spacedependant = lgt


        #idblock = context.particle_system.settings

        tex = getattr(context, "texture", None)
        if tex != None:
            spacedependant = tex



        scene = context.scene
        idblock = scene.pov#pov_context_tex_datablock(context)
        pin_id = space.pin_id

        #spacedependant.use_limited_texture_context = True

        if space.use_pin_id and not isinstance(pin_id, Texture):
            idblock = id_tex_datablock(pin_id)
            pin_id = None

        if not space.use_pin_id:
            layout.row().prop(spacedependant, "texture_context", expand=True)
            pin_id = None

        if spacedependant.texture_context == 'OTHER':
            if not pin_id:
                layout.template_texture_user()
            user = context.texture_user
            if user or pin_id:
                layout.separator()

                row = layout.row()

                if pin_id:
                    row.template_ID(space, "pin_id")
                else:
                    propname = context.texture_user_property.identifier
                    row.template_ID(user, propname, new="texture.new")

                if tex:
                    split = layout.split(factor=0.2)
                    if tex.use_nodes:
                        if slot:
                            split.label(text="Output:")
                            split.prop(slot, "output_node", text="")
                    else:
                        split.label(text="Type:")
                        split.prop(tex, "type", text="")
            return

        tex_collection = (pin_id is None) and (node is None) and (spacedependant.texture_context not in ('LINESTYLE','OTHER'))

        if tex_collection:

            pov = getattr(context, "pov", None)
            active_texture_index = getattr(spacedependant, "active_texture_index", None)
            print (pov)
            print(idblock)
            print(active_texture_index)
            row = layout.row()

            row.template_list("TEXTURE_UL_texslots", "", idblock, "texture_slots",
                              idblock, "active_texture_index", rows=2, maxrows=16, type="DEFAULT")

            # row.template_list("WORLD_TEXTURE_SLOTS_UL_List", "texture_slots", world,
                              # world.texture_slots, world, "active_texture_index", rows=2)

            col = row.column(align=True)
            col.operator("texture.slot_move", text="", icon='TRIA_UP').type = 'UP'
            col.operator("texture.slot_move", text="", icon='TRIA_DOWN').type = 'DOWN'
            col.menu("TEXTURE_MT_POV_specials", icon='DOWNARROW_HLT', text="")

        if tex_collection:
            layout.template_ID(idblock, "active_texture", new="texture.new")
        elif node:
            layout.template_ID(node, "texture", new="texture.new")
        elif idblock:
            layout.template_ID(idblock, "texture", new="texture.new")

        if pin_id:
            layout.template_ID(space, "pin_id")

        if tex:
            split = layout.split(factor=0.2)
            if tex.use_nodes:
                if slot:
                    split.label(text="Output:")
                    split.prop(slot, "output_node", text="")
            else:
                split.label(text="Type:")
'''


class TEXTURE_PT_colors(TextureButtonsPanel, Panel):
    """Use this class to show pov color ramps."""

    bl_label = "Colors"
    bl_options = {'DEFAULT_CLOSED'}
    COMPAT_ENGINES = {'POVRAY_RENDER'}

    def draw(self, context):
        layout = self.layout

        tex = context.texture

        layout.prop(tex, "use_color_ramp", text="Ramp")
        if tex.use_color_ramp:
            layout.template_color_ramp(tex, "color_ramp", expand=True)

        split = layout.split()

        col = split.column()
        col.label(text="RGB Multiply:")
        sub = col.column(align=True)
        sub.prop(tex, "factor_red", text="R")
        sub.prop(tex, "factor_green", text="G")
        sub.prop(tex, "factor_blue", text="B")

        col = split.column()
        col.label(text="Adjust:")
        col.prop(tex, "intensity")
        col.prop(tex, "contrast")
        col.prop(tex, "saturation")

        col = layout.column()
        col.prop(tex, "use_clamp", text="Clamp")


# Texture Slot Panels #


class TEXTURE_OT_POV_texture_slot_add(Operator):
    """Use this class for the add texture slot button."""

    bl_idname = "pov.textureslotadd"
    bl_label = "Add"
    bl_description = "Add texture_slot"
    bl_options = {'REGISTER', 'UNDO'}
    COMPAT_ENGINES = {'POVRAY_RENDER'}

    def execute(self, context):
        idblock = pov_context_tex_datablock(context)
        tex = bpy.data.textures.new(name='Texture', type='IMAGE')
        #tex.use_fake_user = True
        #mat = context.view_layer.objects.active.active_material
        slot = idblock.pov_texture_slots.add()
        slot.name = tex.name
        slot.texture = tex.name
        slot.texture_search = tex.name
        # Switch paint brush and paint brush mask
        # to this texture so settings remain contextual
        bpy.context.tool_settings.image_paint.brush.texture = tex
        bpy.context.tool_settings.image_paint.brush.mask_texture = tex
        idblock.pov.active_texture_index = (len(idblock.pov_texture_slots)-1)

        #for area in bpy.context.screen.areas:
            #if area.type in ['PROPERTIES']:
                #area.tag_redraw()


        return {'FINISHED'}


class TEXTURE_OT_POV_texture_slot_remove(Operator):
    """Use this class for the remove texture slot button."""

    bl_idname = "pov.textureslotremove"
    bl_label = "Remove"
    bl_description = "Remove texture_slot"
    bl_options = {'REGISTER', 'UNDO'}
    COMPAT_ENGINES = {'POVRAY_RENDER'}

    def execute(self, context):
        idblock = pov_context_tex_datablock(context)
        #mat = context.view_layer.objects.active.active_material
        tex_slot = idblock.pov_texture_slots.remove(idblock.pov.active_texture_index)
        if idblock.pov.active_texture_index > 0:
            idblock.pov.active_texture_index -= 1
        try:
            tex = idblock.pov_texture_slots[idblock.pov.active_texture_index].texture
        except IndexError:
            # No more slots
            return {'FINISHED'}
        # Switch paint brush to previous texture so settings remain contextual
        # if 'tex' in locals(): # Would test is the tex variable is assigned / exists
        bpy.context.tool_settings.image_paint.brush.texture = bpy.data.textures[tex]
        bpy.context.tool_settings.image_paint.brush.mask_texture = bpy.data.textures[tex]

        return {'FINISHED'}

class TextureSlotPanel(TextureButtonsPanel):
    """Use this class to show pov texture slots panel."""

    COMPAT_ENGINES = {'POVRAY_RENDER'}

    @classmethod
    def poll(cls, context):
        if not hasattr(context, "pov_texture_slot"):
            return False

        engine = context.scene.render.engine
        return TextureButtonsPanel.poll(cls, context) and (
            engine in cls.COMPAT_ENGINES
        )


class TEXTURE_PT_POV_type(TextureButtonsPanel, Panel):
    """Use this class to define pov texture type buttons."""

    bl_label = "POV Textures"
    COMPAT_ENGINES = {'POVRAY_RENDER'}
    bl_options = {'HIDE_HEADER'}

    def draw(self, context):
        layout = self.layout
        world = context.world
        tex = context.texture

        split = layout.split(factor=0.2)
        split.label(text="Pattern")
        split.prop(tex.pov, "tex_pattern_type", text="")

        # row = layout.row()
        # row.template_list("WORLD_TEXTURE_SLOTS_UL_List", "texture_slots", world,
        # world.texture_slots, world, "active_texture_index")


class TEXTURE_PT_POV_preview(TextureButtonsPanel, Panel):
    """Use this class to define pov texture preview panel."""

    bl_label = "Preview"
    COMPAT_ENGINES = {'POVRAY_RENDER'}
    bl_options = {'HIDE_HEADER'}

    @classmethod
    def poll(cls, context):
        engine = context.scene.render.engine
        if not hasattr(context, "pov_texture_slot"):
            return False
        tex = context.texture
        mat = bpy.context.active_object.active_material
        return (
            tex
            and (tex.pov.tex_pattern_type != 'emulator')
            and (engine in cls.COMPAT_ENGINES)
        )

    def draw(self, context):
        tex = context.texture
        slot = getattr(context, "pov_texture_slot", None)
        idblock = pov_context_tex_datablock(context)
        layout = self.layout
        # if idblock:
        # layout.template_preview(tex, parent=idblock, slot=slot)
        if tex.pov.tex_pattern_type != 'emulator':
            layout.operator("tex.preview_update")
        else:
            layout.template_preview(tex, slot=slot)


class TEXTURE_PT_POV_parameters(TextureButtonsPanel, Panel):
    """Use this class to define pov texture pattern buttons."""

    bl_label = "POV Pattern Options"
    bl_options = {'HIDE_HEADER'}
    COMPAT_ENGINES = {'POVRAY_RENDER'}

    def draw(self, context):
        mat = bpy.context.active_object.active_material
        layout = self.layout
        tex = context.texture
        align = True
        if tex is not None and tex.pov.tex_pattern_type != 'emulator':
            if tex.pov.tex_pattern_type == 'agate':
                layout.prop(
                    tex.pov, "modifier_turbulence", text="Agate Turbulence"
                )
            if tex.pov.tex_pattern_type in {'spiral1', 'spiral2'}:
                layout.prop(tex.pov, "modifier_numbers", text="Number of arms")
            if tex.pov.tex_pattern_type == 'tiling':
                layout.prop(tex.pov, "modifier_numbers", text="Pattern number")
            if tex.pov.tex_pattern_type == 'magnet':
                layout.prop(tex.pov, "magnet_style", text="Magnet style")
            if tex.pov.tex_pattern_type == 'quilted':
                row = layout.row(align=align)
                row.prop(tex.pov, "modifier_control0", text="Control0")
                row.prop(tex.pov, "modifier_control1", text="Control1")
            if tex.pov.tex_pattern_type == 'brick':
                col = layout.column(align=align)
                row = col.row()
                row.prop(tex.pov, "brick_size_x", text="Brick size X")
                row.prop(tex.pov, "brick_size_y", text="Brick size Y")
                row = col.row()
                row.prop(tex.pov, "brick_size_z", text="Brick size Z")
                row.prop(tex.pov, "brick_mortar", text="Brick mortar")
            if tex.pov.tex_pattern_type in {'julia', 'mandel', 'magnet'}:
                col = layout.column(align=align)
                if tex.pov.tex_pattern_type == 'julia':
                    row = col.row()
                    row.prop(tex.pov, "julia_complex_1", text="Complex 1")
                    row.prop(tex.pov, "julia_complex_2", text="Complex 2")
                if (
                    tex.pov.tex_pattern_type == 'magnet'
                    and tex.pov.magnet_style == 'julia'
                ):
                    row = col.row()
                    row.prop(tex.pov, "julia_complex_1", text="Complex 1")
                    row.prop(tex.pov, "julia_complex_2", text="Complex 2")
                row = col.row()
                if tex.pov.tex_pattern_type in {'julia', 'mandel'}:
                    row.prop(tex.pov, "f_exponent", text="Exponent")
                if tex.pov.tex_pattern_type == 'magnet':
                    row.prop(tex.pov, "magnet_type", text="Type")
                row.prop(tex.pov, "f_iter", text="Iterations")
                row = col.row()
                row.prop(tex.pov, "f_ior", text="Interior")
                row.prop(tex.pov, "f_ior_fac", text="Factor I")
                row = col.row()
                row.prop(tex.pov, "f_eor", text="Exterior")
                row.prop(tex.pov, "f_eor_fac", text="Factor E")
            if tex.pov.tex_pattern_type == 'gradient':
                layout.label(text="Gradient orientation:")
                column_flow = layout.column_flow(columns=3, align=True)
                column_flow.prop(tex.pov, "grad_orient_x", text="X")
                column_flow.prop(tex.pov, "grad_orient_y", text="Y")
                column_flow.prop(tex.pov, "grad_orient_z", text="Z")
            if tex.pov.tex_pattern_type == 'pavement':
                layout.prop(
                    tex.pov, "pave_sides", text="Pavement:number of sides"
                )
                col = layout.column(align=align)
                column_flow = col.column_flow(columns=3, align=True)
                column_flow.prop(tex.pov, "pave_tiles", text="Tiles")
                if tex.pov.pave_sides == '4' and tex.pov.pave_tiles == 6:
                    column_flow.prop(tex.pov, "pave_pat_35", text="Pattern")
                if tex.pov.pave_sides == '6' and tex.pov.pave_tiles == 5:
                    column_flow.prop(tex.pov, "pave_pat_22", text="Pattern")
                if tex.pov.pave_sides == '4' and tex.pov.pave_tiles == 5:
                    column_flow.prop(tex.pov, "pave_pat_12", text="Pattern")
                if tex.pov.pave_sides == '3' and tex.pov.pave_tiles == 6:
                    column_flow.prop(tex.pov, "pave_pat_12", text="Pattern")
                if tex.pov.pave_sides == '6' and tex.pov.pave_tiles == 4:
                    column_flow.prop(tex.pov, "pave_pat_7", text="Pattern")
                if tex.pov.pave_sides == '4' and tex.pov.pave_tiles == 4:
                    column_flow.prop(tex.pov, "pave_pat_5", text="Pattern")
                if tex.pov.pave_sides == '3' and tex.pov.pave_tiles == 5:
                    column_flow.prop(tex.pov, "pave_pat_4", text="Pattern")
                if tex.pov.pave_sides == '6' and tex.pov.pave_tiles == 3:
                    column_flow.prop(tex.pov, "pave_pat_3", text="Pattern")
                if tex.pov.pave_sides == '3' and tex.pov.pave_tiles == 4:
                    column_flow.prop(tex.pov, "pave_pat_3", text="Pattern")
                if tex.pov.pave_sides == '4' and tex.pov.pave_tiles == 3:
                    column_flow.prop(tex.pov, "pave_pat_2", text="Pattern")
                if tex.pov.pave_sides == '6' and tex.pov.pave_tiles == 6:
                    column_flow.label(text="!!! 5 tiles!")
                column_flow.prop(tex.pov, "pave_form", text="Form")
            if tex.pov.tex_pattern_type == 'function':
                layout.prop(tex.pov, "func_list", text="Functions")
            if (
                tex.pov.tex_pattern_type == 'function'
                and tex.pov.func_list != "NONE"
            ):
                func = None
                if tex.pov.func_list in {"f_noise3d", "f_ph", "f_r", "f_th"}:
                    func = 0
                if tex.pov.func_list in {
                    "f_comma",
                    "f_crossed_trough",
                    "f_cubic_saddle",
                    "f_cushion",
                    "f_devils_curve",
                    "f_enneper",
                    "f_glob",
                    "f_heart",
                    "f_hex_x",
                    "f_hex_y",
                    "f_hunt_surface",
                    "f_klein_bottle",
                    "f_kummer_surface_v1",
                    "f_lemniscate_of_gerono",
                    "f_mitre",
                    "f_nodal_cubic",
                    "f_noise_generator",
                    "f_odd",
                    "f_paraboloid",
                    "f_pillow",
                    "f_piriform",
                    "f_quantum",
                    "f_quartic_paraboloid",
                    "f_quartic_saddle",
                    "f_sphere",
                    "f_steiners_roman",
                    "f_torus_gumdrop",
                    "f_umbrella",
                }:
                    func = 1
                if tex.pov.func_list in {
                    "f_bicorn",
                    "f_bifolia",
                    "f_boy_surface",
                    "f_superellipsoid",
                    "f_torus",
                }:
                    func = 2