space_view3d_panel_measure.py

# ##### BEGIN GPL LICENSE BLOCK #####
#
#  This program is free software; you can redistribute it and/or
#  modify it under the terms of the GNU General Public License
#  as published by the Free Software Foundation; either version 2
#  of the License, or (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software Foundation,
#  Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
#
# ##### END GPL LICENSE BLOCK #####
#
# Uses volume calculation and manifold check code (GPL2+) from:
# http://www.shapeways.com/forum/index.php?t=msg&goto=3639
# Shapeways Volume Calculator by Benjamin Lauritzen (Loonsbury)
#
# #################################

bl_info = {
    "name": "Measure Panel",
    "author": "Buerbaum Martin (Pontiac), TNae (Normal patch)," \
        " Benjamin Lauritzen (Loonsbury; Volume code)," \
        " Alessandro Sala (patch: Units in 3D View)",
    "version": (0, 8, 6),
    "blender": (2, 6, 0),
    "location": "View3D > Properties > Measure Panel",
    "description": "Measure distances between objects",
    "warning": "Script needs repairs",
    "wiki_url": "http://wiki.blender.org/index.php/Extensions:2.5/Py/" \
        "Scripts/3D_interaction/Panel_Measure",
    "tracker_url": "https://projects.blender.org/tracker/index.php?" \
        "func=detail&aid=21445",
    "category": "3D View"}

"""
Measure panel

This script displays in OBJECT MODE:
* The distance of the 3D cursor to the origin of the
  3D space (if NOTHING is selected).
* The distance of the 3D cursor to the center of an object
  (if exactly ONE object is selected).
* The distance between 2 object centers
  (if exactly TWO objects are selected).
* The surface area of any selected mesh object.
* The average normal of the mesh surface of any selected mesh object.
* The volume of any selected mesh object.

Display in EDIT MODE (Local and Global space supported):
* The distance of the 3D cursor to the origin
  (in Local space it is the object center instead).
* The distance of the 3D cursor to a selected vertex.
* The distance between 2 selected vertices.

Usage:

This functionality can be accessed via the
"Properties" panel in 3D View ([N] key).

It's very helpful to use one or two "Empty" objects with
"Snap during transform" enabled for fast measurement.

More links:
http://gitorious.org/blender-scripts/blender-measure-panel-script
http://blenderartists.org/forum/showthread.php?t=177800
"""

import bpy
from bpy.props import *
from mathutils import Vector, Matrix
import bgl
import blf
from bpy_extras.view3d_utils import location_3d_to_region_2d
from bpy_extras.mesh_utils import ngon_tesselate


# Precicion for display of float values.
PRECISION = 4

# Name of the custom properties as stored in the scene.
COLOR_LOCAL = (1.0, 0.5, 0.0, 0.8)
COLOR_GLOBAL = (0.5, 0.0, 1.0, 0.8)


# Returns a tuple describing the current measuring system
# and formatting options.
# Returned data is meant to be passed to formatDistance().
# Original by Alessandro Sala (Feb, 12th 2012)
def getUnitsInfo():
        scale = bpy.context.scene.unit_settings.scale_length
        unit_system = bpy.context.scene.unit_settings.system
        separate_units = bpy.context.scene.unit_settings.use_separate
        if unit_system == 'METRIC':
                scale_steps = ((1000, 'km'), (1, 'm'), (1 / 100, 'cm'),
                    (1 / 1000, 'mm'), (1 / 1000000, '\u00b5m'))
        elif unit_system == 'IMPERIAL':
                scale_steps = ((1760, 'mi'), (1, 'yd'), (1 / 3, '\''),
                    (1 / 36, '"'), (1 / 36000, 'thou'))
                scale *= 1.0936133
        else:
                scale_steps = ((1, ' BU'),)
                separate_units = False

        return (scale, scale_steps, separate_units)


# Converts a distance from BU into the measuring system
# described by units_info.
# Original by Alessandro Sala (Feb, 12th 2012)
def convertDistance(val, units_info):
        scale, scale_steps, separate_units = units_info
        sval = val * scale
        rsval = round(sval, PRECISION)
        idx = 0
        while idx < len(scale_steps) - 1:
                if rsval >= scale_steps[idx][0]:
                        break
                idx += 1
        factor, suffix = scale_steps[idx]
        sval /= factor
        if not separate_units or idx == len(scale_steps) - 1:
                dval = str(round(sval, PRECISION)) + suffix
        else:
                ival = int(sval)
                dval = str(ival) + suffix
                fval = sval - ival
                idx += 1
                while idx < len(scale_steps):
                        fval *= scale_steps[idx - 1][0] / scale_steps[idx][0]
                        if fval >= 1:
                                dval += ' ' \
                                    + str(round(fval, 1)) \
                                    + scale_steps[idx][1]
                                break
                        idx += 1

        return dval


# Returns a single selected object.
# Returns None if more than one (or nothing) is selected.
# Note: Ignores the active object.
def getSingleObject(context):
    if len(context.selected_objects) == 1:
        return context.selected_objects[0]

    return None


# Returns a list with 2 3D points (Vector) and a color (RGBA)
# depending on the current view mode and the selection.
def getMeasurePoints(context):
    sce = context.scene

    # Get a single selected object (or nothing).
    obj = getSingleObject(context)

    if context.mode == 'EDIT_MESH':
        obj = context.active_object

        if obj and obj.type == 'MESH' and obj.data:
            # Get mesh data from Object.
            mesh = obj.data

            # Get the selected vertices.
            # @todo: Better (more efficient) way to do this?
            verts_selected = [v for v in mesh.vertices if v.select == 1]

            if len(verts_selected) == 0:
                # Nothing selected.
                # We measure the distance from...
                # local  ... the object center to the 3D cursor.
                # global ... the origin to the 3D cursor.
                cur_loc = sce.cursor_location
                obj_loc = obj.matrix_world.to_translation()

                # Convert to local space, if needed.
                if measureLocal(sce):
                    p1 = cur_loc
                    p2 = obj_loc
                    return (p1, p2, COLOR_GLOBAL)

                else:
                    p1 = Vector((0.0, 0.0, 0.0))
                    p2 = cur_loc
                    return (p1, p2, COLOR_GLOBAL)

            elif len(verts_selected) == 1:
                # One vertex selected.
                # We measure the distance from the
                # selected vertex object to the 3D cursor.
                cur_loc = sce.cursor_location
                vert_loc = verts_selected[0].co.copy()

                # Convert to local or global space.
                if measureLocal(sce):
                    p1 = vert_loc
                    p2 = cur_loc
                    return (p1, p2, COLOR_LOCAL)

                else:
                    p1 = obj.matrix_world * vert_loc
                    p2 = cur_loc
                    return (p1, p2, COLOR_GLOBAL)

            elif len(verts_selected) == 2:
                # Two vertices selected.
                # We measure the distance between the
                # two selected vertices.
                obj_loc = obj.matrix_world.to_translation()
                vert1_loc = verts_selected[0].co.copy()
                vert2_loc = verts_selected[1].co.copy()

                # Convert to local or global space.
                if measureLocal(sce):
                    p1 = vert1_loc
                    p2 = vert2_loc
                    return (p1, p2, COLOR_LOCAL)

                else:
                    p1 = obj.matrix_world * vert1_loc
                    p2 = obj.matrix_world * vert2_loc
                    return (p1, p2, COLOR_GLOBAL)

            else:
                return None

    elif context.mode == 'OBJECT':
        # We are working in object mode.

        if len(context.selected_objects) > 2:
            return None
        elif len(context.selected_objects) == 2:
            # 2 objects selected.
            # We measure the distance between the 2 selected objects.
            obj1, obj2 = context.selected_objects
            obj1_loc = obj1.matrix_world.to_translation()
            obj2_loc = obj2.matrix_world.to_translation()
            return (obj1_loc, obj2_loc, COLOR_GLOBAL)

        elif obj:
            # One object selected.
            # We measure the distance from the object to the 3D cursor.
            cur_loc = sce.cursor_location
            obj_loc = obj.matrix_world.to_translation()
            return (obj_loc, cur_loc, COLOR_GLOBAL)

        elif not context.selected_objects:
            # Nothing selected.
            # We measure the distance from the origin to the 3D cursor.
            p1 = Vector((0.0, 0.0, 0.0))
            p2 = sce.cursor_location
            return (p1, p2, COLOR_GLOBAL)

        else:
            return None


# Return the length of an edge (in global space if "obj" is set).
# Respects the scaling (via the "obj.matrix_world" parameter).
def edgeLengthGlobal(edge, obj, globalSpace):
    v1, v2 = edge.vertices

    # Get vertex data
    v1 = obj.data.vertices[v1]
    v2 = obj.data.vertices[v2]

    if globalSpace:
        mat = obj.matrix_world
        # Apply transform matrix to vertex coordinates.
        v1 = mat * v1.co
        v2 = mat * v2.co
    else:
        v1 = v1.co
        v2 = v2.co

    return (v1 - v2).length


# Calculate the edge length of a mesh object.
# *) Set selectedOnly=1 if you only want to count selected edges.
# *) Set globalSpace=1 if you want to calculate
#    the global edge length (object mode).
# Note: Be sure you have updated the mesh data before
#       running this with selectedOnly=1!
# @todo Support other object types (surfaces, etc...)?
def objectEdgeLength(obj, selectedOnly, globalSpace):
    if obj and obj.type == 'MESH' and obj.data:
        edgeTotal = 0

        mesh = obj.data

        # Count the length of all edges.
        for ed in mesh.edges:
            if not selectedOnly or ed.select:
                edgeTotal += edgeLengthGlobal(ed, obj, globalSpace)

        return edgeTotal

    # We can not calculate a length for this object.
    return -1


# Return the area of a face (in global space).
# @note Copies the functionality of the following functions,
# but also respects the scaling (via the "obj.matrix_world" parameter):
# @sa: rna_mesh.c:rna_MeshFace_area_get
# @sa: math_geom.c:area_quad_v3
# @sa: math_geom.c:area_tri_v3
# @sa: math_geom.c:area_poly_v3
# @todo Fix calculation of "n" for n-gons?
def polyAreaGlobal(poly, obj):
    mesh = obj.data
    mat = obj.matrix_world.copy()
    norm = poly.normal

    area = 0.0

    if len(poly.vertices) > 3:
        # Tesselate the polygon into multiple tris
        tris = ngon_tesselate(mesh, poly.vertices)

        for tri in tris:
            # Get vertex data
            v1, v2, v3 = tri

            # Get indices from original poly
            v1 = poly.vertices[v1]
            v2 = poly.vertices[v2]
            v3 = poly.vertices[v3]

            # Get vertex information from indices
            v1 = mesh.vertices[v1]
            v2 = mesh.vertices[v2]
            v3 = mesh.vertices[v3]

            # Apply transform matrix to vertex coordinates.
            v1 = mat * v1.co
            v2 = mat * v2.co
            v3 = mat * v3.co

            # Calculate area for the new tri
            vec1 = v3 - v2
            vec2 = v1 - v2

            n = vec1.cross(vec2)

            area += n.length / 2.0

    elif len(poly.vertices) == 3:
        # Triangle

        # Get vertex indices
        v1, v2, v3 = poly.vertices

        # Get vertex data
        v1 = mesh.vertices[v1]
        v2 = mesh.vertices[v2]
        v3 = mesh.vertices[v3]

        # Apply transform matrix to vertex coordinates.
        v1 = mat * v1.co
        v2 = mat * v2.co
        v3 = mat * v3.co

        vec1 = v3 - v2
        vec2 = v1 - v2

        n = vec1.cross(vec2)

        area = n.length / 2.0

    # Apply world matrix to normal as well.
    norm = mat * norm

    return area, norm


# Calculate the surface area of a mesh object.
# *) Set selectedOnly=1 if you only want to count selected faces.
# *) Set globalSpace=1 if you want to calculate
#    the global surface area (object mode).
# Note: Be sure you have updated the mesh data before
#       running this with selectedOnly=1!
# @todo Support other object types (surfaces, etc...)?
def objectSurfaceArea(obj, selectedOnly, globalSpace):
    if obj and obj.type == 'MESH' and obj.data:
        areaTotal = 0
        normTotal = Vector((0.0, 0.0, 0.0))

        mesh = obj.data

        # Count the area of all the faces.
        for poly in mesh.polygons:
            if not selectedOnly or poly.select:
                if globalSpace:
                    a, n = polyAreaGlobal(poly, obj)
                    areaTotal += a
                    normTotal += n
                else:
                    areaTotal += poly.area
                    normTotal += poly.normal

        return areaTotal, normTotal

    # We can not calculate an area for this object.
    return -1, Vector((0.0, 0.0, 0.0))


# Calculate the volume of a mesh object.
# Copyright Loonsbury (loonsbury@yahoo.com)
def objectVolume(obj, globalSpace):
    if obj and obj.type == 'MESH' and obj.data:

        # Check if mesh is non-manifold
        if not checkManifold(obj):
            return -1

        # Check if mesh has n-gons
        if checkNgon(obj):
            return -2

        mesh = obj.data

        volTot = 0

        for poly in mesh.polygons:
            fzn = poly.normal.z

            if len(poly.vertices) == 4:
                v1, v2, v3, v4 = poly.vertices
            else:
                v1, v2, v3 = poly.vertices

            v1 = mesh.vertices[v1]
            v2 = mesh.vertices[v2]
            v3 = mesh.vertices[v3]

            # Scaled vert coordinates with object XYZ offsets for
            # selection extremes/sizing.
            if globalSpace:
                x1 = v1.co[0] * obj.scale[0] + obj.location[0]
                y1 = v1.co[1] * obj.scale[1] + obj.location[1]
                z1 = v1.co[2] * obj.scale[2] + obj.location[2]

                x2 = v2.co[0] * obj.scale[0] + obj.location[0]
                y2 = v2.co[1] * obj.scale[1] + obj.location[1]
                z2 = v2.co[2] * obj.scale[2] + obj.location[2]

                x3 = v3.co[0] * obj.scale[0] + obj.location[0]
                y3 = v3.co[1] * obj.scale[1] + obj.location[1]
                z3 = v3.co[2] * obj.scale[2] + obj.location[2]

            else:
                x1, y1, z1 = v1.co
                x2, y2, z2 = v2.co
                x3, y3, z3 = v3.co

            pa = 0.5 * abs(
                (x1 * (y3 - y2))
                + (x2 * (y1 - y3))
                + (x3 * (y2 - y1)))
            volume = ((z1 + z2 + z3) / 3.0) * pa

            # Allowing for quads
            if len(poly.vertices) == 4:
                # Get vertex data
                v4 = mesh.vertices[v4]

                if globalSpace:
                    x4 = v4.co[0] * obj.scale[0] + obj.location[0]
                    y4 = v4.co[1] * obj.scale[1] + obj.location[1]
                    z4 = v4.co[2] * obj.scale[2] + obj.location[2]

                else:
                    x4, y4, z4 = v4.co

                pa = 0.5 * abs(
                    (x1 * (y4 - y3))
                    + (x3 * (y1 - y4))
                    + (x4 * (y3 - y1)))

                volume += ((z1 + z3 + z4) / 3.0) * pa

            if fzn < 0:
                fzn = -1

            elif fzn > 0:
                fzn = 1

            else:
                fzn = 0

            volTot += fzn * volume

        return volTot

#    else:
#        print obj.name, ': Object must be a mesh!'        # TODO

    return -3


# Manifold Checks
# Copyright Loonsbury (loonsbury@yahoo.com)
def checkManifold(obj):
    if obj and obj.type == 'MESH' and obj.data:
        mesh = obj.data

        mc = dict([(ed.key, 0) for ed in mesh.edges])     # TODO

        for p in mesh.polygons:
            for ek in p.edge_keys:
                mc[ek] += 1
                if mc[ek] > 2:
                    return 0

        mt = [e[1] for e in mc.items()]
        mt.sort()

        if mt[0] < 2:
            return 0

        if mt[len(mt) - 1] > 2:
            return 0

        return 1

    else:
        return -1


# Check if a mesh has n-gons (polygon with more than 4 edges).
def checkNgon(obj):
    if obj and obj.type == 'MESH' and obj.data:
        mesh = obj.data

        for p in mesh.polygons:
            if len(p.vertices) > 4:
                return 1

        return 0

    else:
        return -1


# User friendly access to the "space" setting.
def measureGlobal(sce):
    return (sce.measure_panel_transform == "measure_global")


# User friendly access to the "space" setting.
def measureLocal(sce):
    return (sce.measure_panel_transform == "measure_local")


def draw_measurements_callback(self, context):
    sce = context.scene

    draw = 0
    if hasattr(sce, "measure_panel_draw"):
        draw = sce.measure_panel_draw

    # 2D drawing code example
    #bgl.glBegin(bgl.GL_LINE_STRIP)
    #bgl.glVertex2i(0, 0)
    #bgl.glVertex2i(80, 100)
    #bgl.glEnd()

    # Get measured 3D points and colors.
    line = getMeasurePoints(context)
    if line and draw:
        p1, p2, color = line

        # Get and convert the Perspective Matrix of the current view/region.
        view3d = bpy.context
        region = view3d.region_data
        perspMatrix = region.perspective_matrix
        tempMat = [perspMatrix[j][i] for i in range(4) for j in range(4)]
        perspBuff = bgl.Buffer(bgl.GL_FLOAT, 16, tempMat)

        # ---
        # Store previous OpenGL settings.
        # Store MatrixMode
        MatrixMode_prev = bgl.Buffer(bgl.GL_INT, [1])
        bgl.glGetIntegerv(bgl.GL_MATRIX_MODE, MatrixMode_prev)
        MatrixMode_prev = MatrixMode_prev[0]

        # Store projection matrix
        ProjMatrix_prev = bgl.Buffer(bgl.GL_DOUBLE, [16])
        bgl.glGetFloatv(bgl.GL_PROJECTION_MATRIX, ProjMatrix_prev)

        # Store Line width
        lineWidth_prev = bgl.Buffer(bgl.GL_FLOAT, [1])
        bgl.glGetFloatv(bgl.GL_LINE_WIDTH, lineWidth_prev)
        lineWidth_prev = lineWidth_prev[0]

        # Store GL_BLEND
        blend_prev = bgl.Buffer(bgl.GL_BYTE, [1])
        bgl.glGetFloatv(bgl.GL_BLEND, blend_prev)
        blend_prev = blend_prev[0]

        line_stipple_prev = bgl.Buffer(bgl.GL_BYTE, [1])
        bgl.glGetFloatv(bgl.GL_LINE_STIPPLE, line_stipple_prev)
        line_stipple_prev = line_stipple_prev[0]

        # Store glColor4f
        color_prev = bgl.Buffer(bgl.GL_FLOAT, [4])
        bgl.glGetFloatv(bgl.GL_COLOR, color_prev)

        # ---
        # Prepare for 3D drawing
        bgl.glLoadIdentity()
        bgl.glMatrixMode(bgl.GL_PROJECTION)
        bgl.glLoadMatrixf(perspBuff)

        bgl.glEnable(bgl.GL_BLEND)
        bgl.glEnable(bgl.GL_LINE_STIPPLE)

        # ---
        # Draw 3D stuff.
        width = 1
        bgl.glLineWidth(width)
        # X
        bgl.glColor4f(1, 0, 0, 0.8)
        bgl.glBegin(bgl.GL_LINE_STRIP)
        bgl.glVertex3f(p1[0], p1[1], p1[2])
        bgl.glVertex3f(p2[0], p1[1], p1[2])
        bgl.glEnd()
        # Y
        bgl.glColor4f(0, 1, 0, 0.8)
        bgl.glBegin(bgl.GL_LINE_STRIP)
        bgl.glVertex3f(p1[0], p1[1], p1[2])
        bgl.glVertex3f(p1[0], p2[1], p1[2])
        bgl.glEnd()
        # Z
        bgl.glColor4f(0, 0, 1, 0.8)
        bgl.glBegin(bgl.GL_LINE_STRIP)
        bgl.glVertex3f(p1[0], p1[1], p1[2])
        bgl.glVertex3f(p1[0], p1[1], p2[2])
        bgl.glEnd()

        # Dist
        width = 2
        bgl.glLineWidth(width)
        bgl.glColor4f(color[0], color[1], color[2], color[3])
        bgl.glBegin(bgl.GL_LINE_STRIP)
        bgl.glVertex3f(p1[0], p1[1], p1[2])
        bgl.glVertex3f(p2[0], p2[1], p2[2])
        bgl.glEnd()

        # ---
        # Restore previous OpenGL settings
        bgl.glLoadIdentity()
        bgl.glMatrixMode(MatrixMode_prev)
        bgl.glLoadMatrixf(ProjMatrix_prev)
        bgl.glLineWidth(lineWidth_prev)
        if not blend_prev:
            bgl.glDisable(bgl.GL_BLEND)
        if not line_stipple_prev:
            bgl.glDisable(bgl.GL_LINE_STIPPLE)
        bgl.glColor4f(color_prev[0],
            color_prev[1],
            color_prev[2],
            color_prev[3])

        # ---
        # Draw (2D) text
        # We do this after drawing the lines so
        # we can draw it OVER the line.
        coord_2d = location_3d_to_region_2d(context.region,
                                            context.space_data.region_3d,
                                            p1.lerp(p2, 0.5),
                                            )
        OFFSET_LINE = 10   # Offset the text a bit to the right.
        OFFSET_Y = 15      # Offset of the lines.
        OFFSET_VALUE = 30  # Offset of value(s) from the text.
        dist = (p1 - p2).length

        # Write distance value into the scene property,
        # so we can display it in the panel & refresh the panel.
        if hasattr(sce, "measure_panel_dist"):
            sce.measure_panel_dist = dist
            context.area.tag_redraw()

        texts = [("Dist:", dist),
            ("X:", abs(p1[0] - p2[0])),
            ("Y:", abs(p1[1] - p2[1])),
            ("Z:", abs(p1[2] - p2[2]))]

        # Draw all texts
        # @todo Get user pref for text color in 3D View
        bgl.glColor4f(1.0, 1.0, 1.0, 1.0)
        blf.size(0, 12, 72)  # Prevent font size to randomly change.

        uinfo = getUnitsInfo()

        loc_x = coord_2d[0] + OFFSET_LINE
        loc_y = coord_2d[1]
        for t in texts:
            text = t[0]

            value = convertDistance(t[1], uinfo)

            blf.position(0, loc_x, loc_y, 0)
            blf.draw(0, text)
            blf.position(0, loc_x + OFFSET_VALUE, loc_y, 0)
            blf.draw(0, value)

            loc_y -= OFFSET_Y

    if sce.measure_panel_calc_edge_length:
        if context.mode == 'EDIT_MESH':
            obj = context.active_object

            length_total = objectEdgeLength(obj, True, measureGlobal(sce))

            sce.measure_panel_edge_length = length_total

        elif context.mode == 'OBJECT':
            length_total = -1

            for o in context.selected_objects:
                if o.type == 'MESH':
                    length = objectEdgeLength(o, False, measureGlobal(sce))

                    if length >= 0:
                        if length_total < 0:
                            length_total = 0

                        length_total += length

            sce.measure_panel_edge_length = length_total

    # Handle mesh surface area calulations
    if sce.measure_panel_calc_area:
        # Get a single selected object (or nothing).
        obj = getSingleObject(context)

        if context.mode == 'EDIT_MESH':
            obj = context.active_object

            if obj and obj.type == 'MESH' and obj.data:
                # "Note: a Mesh will return the selection state of the mesh
                # when EditMode was last exited. A Python script operating
                # in EditMode must exit EditMode before getting the current
                # selection state of the mesh."
                # http://www.blender.org/documentation/249PythonDoc/
                # /Mesh.MVert-class.html#sel
                # We can only provide this by existing & re-entering EditMode.
                # @todo: Better way to do this?

                # Get mesh data from Object.
                mesh = obj.data

                # Get transformation matrix from object.
                ob_mat = obj.matrix_world
                # Also make an inversed copy! of the matrix.
                ob_mat_inv = ob_mat.copy()
                Matrix.invert(ob_mat_inv)

                # Get the selected vertices.
                # @todo: Better (more efficient) way to do this?
                verts_selected = [v for v in mesh.vertices if v.select == 1]

                if len(verts_selected) >= 3:
                    # Get selected faces
                    # @todo: Better (more efficient) way to do this?
                    polys_selected = [f for f in mesh.polygons
                        if f.select == 1]

                    if len(polys_selected) > 0:
                        area, normal = objectSurfaceArea(obj, True,
                            measureGlobal(sce))
                        if area >= 0.0:
                            sce.measure_panel_area1 = area
                            sce.measure_panel_normal1 = normal

        elif context.mode == 'OBJECT':
            # We are working in object mode.

            if len(context.selected_objects) > 2:
                return
# @todo Make this work again.
#                # We have more that 2 objects selected...
#
#                mesh_objects = [o for o in context.selected_objects
#                    if o.type == 'MESH']

#                if len(mesh_objects) > 0:
#                    # ... and at least one of them is a mesh.
#
#                    for o in mesh_objects:
#                        area = objectSurfaceArea(o, False,
#                            measureGlobal(sce))
#                        if area >= 0:
#                            #row.label(text=o.name, icon='OBJECT_DATA')
#                            #row.label(text=str(round(area, PRECISION))
#                            #    + " BU^2")

            elif len(context.selected_objects) == 2:
                # 2 objects selected.

                obj1, obj2 = context.selected_objects

                # Calculate surface area of the objects.
                area1, normal1 = objectSurfaceArea(obj1, False,
                    measureGlobal(sce))
                area2, normal2 = objectSurfaceArea(obj2, False,
                    measureGlobal(sce))
                sce.measure_panel_area1 = area1
                sce.measure_panel_area2 = area2
                sce.measure_panel_normal1 = normal1
                sce.measure_panel_normal2 = normal2

            elif obj:
                # One object selected.

                # Calculate surface area of the object.
                area, normal = objectSurfaceArea(obj, False,
                    measureGlobal(sce))

                sce.measure_panel_area1 = area
                sce.measure_panel_normal1 = normal

    if sce.measure_panel_calc_volume:
        obj = getSingleObject(context)

        if context.mode == 'OBJECT':
            # We are working in object mode.

            #if len(context.selected_objects) > 2:       # TODO

            #el
            if len(context.selected_objects) == 2:
                # 2 objects selected.

                obj1, obj2 = context.selected_objects

                # Calculate surface area of the objects.
                volume1 = objectVolume(obj1, measureGlobal(sce))
                volume2 = objectVolume(obj2, measureGlobal(sce))

                sce.measure_panel_volume1 = volume1
                sce.measure_panel_volume2 = volume2

            elif obj:
                # One object selected.

                # Calculate surface area of the object.
                volume1 = objectVolume(obj, measureGlobal(sce))

                sce.measure_panel_volume1 = volume1


class VIEW3D_OT_display_measurements(bpy.types.Operator):
    '''Display the measurements made in the 'Measure' panel'''
    bl_idname = "view3d.display_measurements"
    bl_label = "Display the measurements made in the" \
        " 'Measure' panel in the 3D View"
    bl_options = {'REGISTER'}

    def modal(self, context, event):
        context.area.tag_redraw()

        return {'FINISHED'}

    def execute(self, context):
        if context.area.type == 'VIEW_3D':
            mgr_ops = context.window_manager.operators.values()
            if not self.bl_idname in [op.bl_idname for op in mgr_ops]:
                # Add the region OpenGL drawing callback
                for WINregion in context.area.regions:
                    if WINregion.type == 'WINDOW':
                        context.window_manager.modal_handler_add(self)
                        self._handle = WINregion.callback_add(
                            draw_measurements_callback,
                            (self, context),
                            'POST_PIXEL')

                        print("Measure panel display callback added")

                        return {'RUNNING_MODAL'}

            return {'CANCELLED'}

        else:
            self.report({'WARNING'}, "View3D not found, cannot run operator")
            return {'CANCELLED'}


class VIEW3D_OT_activate_measure_panel(bpy.types.Operator):
    bl_label = "Activate"
    bl_idname = "view3d.activate_measure_panel"
    bl_description = "Activate the callback needed to draw the lines"
    bl_options = {'REGISTER'}

    def invoke(self, context, event):

        # Execute operator (this adds the callback)
        # if it wasn't done yet.
        bpy.ops.view3d.display_measurements()
        return {'FINISHED'}


class VIEW3D_OT_reenter_editmode(bpy.types.Operator):
    bl_label = "Re-enter EditMode"
    bl_idname = "view3d.reenter_editmode"
    bl_description = "Update mesh data of an active mesh object " \
        "(this is done by exiting and re-entering mesh edit mode)"
    bl_options = {'REGISTER'}

    def invoke(self, context, event):

        # Get the active object.
        obj = context.active_object

        if obj and obj.type == 'MESH' and context.mode == 'EDIT_MESH':
            # Exit and re-enter mesh EditMode.
            bpy.ops.object.mode_set(mode='OBJECT')
            bpy.ops.object.mode_set(mode='EDIT')
            return {'FINISHED'}

        return {'CANCELLED'}


class VIEW3D_PT_measure(bpy.types.Panel):
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'UI'
    bl_label = "Measure"
    bl_options = {'DEFAULT_CLOSED'}

    @classmethod
    def poll(cls, context):
        # Only display this panel in the object and edit mode 3D view.
        if (context.area.type == 'VIEW_3D' and
            (context.mode == 'EDIT_MESH'
            or context.mode == 'OBJECT')):
            return 1

        return 0

    def draw_header(self, context):
        layout = self.layout
        sce = context.scene

        # Force a redraw.
        # This prevents the lines still be drawn after
        # disabling the "measure_panel_draw" checkbox.
        # @todo Better solution?
        context.area.tag_redraw()

        mgr_ops = context.window_manager.operators.values()
        if (not "VIEW3D_OT_display_measurements"
            in [op.bl_idname for op in mgr_ops]):
            layout.operator("view3d.activate_measure_panel",
                        text="Activate")

        context.area.tag_redraw()

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

        # Get a single selected object (or nothing).
        obj = getSingleObject(context)

        drawTansformButtons = 1

        if context.mode == 'EDIT_MESH':
            obj = context.active_object

            row = layout.row()
            row.operator("view3d.reenter_editmode",
                text="Update selection")
#               @todo
#                description="The calculated values can" \
#                    " not be updated in mesh edit mode" \
#                    " automatically. Press this button" \
#                    " to do this manually, after you changed" \
#                    " the selection")

            if obj and obj.type == 'MESH' and obj.data:
                # "Note: a Mesh will return the selection state of the mesh
                # when EditMode was last exited. A Python script operating
                # in EditMode must exit EditMode before getting the current
                # selection state of the mesh."
                # http://www.blender.org/documentation/249PythonDoc/
                # /Mesh.MVert-class.html#sel
                # We can only provide this by existing & re-entering EditMode.
                # @todo: Better way to do this?

                # Get mesh data from Object.