Tutorial for mesh distortion in Blender Python

examples/scripts/blender/distort_mesh.py

@@ -0,0 +1,264 @@
+#!/usr/bin/env python3
+
+# In Blender, perform mesh modifications.
+#
+# Usage:
+#   This script is to be run from within the Blender GUI. Tested in Blender
+#   2.92.
+#   distort_mesh.py <mesh_path> <object_prefix> [distort_extent] [method]
+#   where
+#   mesh_path: Absolute path to mesh file
+#   object_prefix: Prefix of object name in Scene Collection in Blender. The
+#     prefix instead of the name is required, because if the script is
+#     repeatedly run, Blender will append numerical suffixes .001, .002, etc.
+#     to the object name.
+#   distort_extent: A floating point number in the range of [0, 1]
+#   method: A list of strings. Distortion operations, in order of desired
+#     execution.
+#
+#   Example from command line:
+#   $ blender -b -P distort_mesh.py -- /path/to/mesh.obj object_prefix 0.005 "['subdiv_mod', 'vert_rand', 'edge_subdiv']"
+#
+#   Example from Blender Scripting GUI Python command line:
+#   >>> file_path = '/path/to/mesh.dae'
+#   >>> object_prefix = 'Cube'
+#   >>> distort_extent = 0.005  # float in range [0, 1]
+#   >>> method = ['subdiv_mod', 'vert_rand', 'edge_subdiv']
+#   >>> sys.argv = [file_path, object_prefix, distort_extent, method]
+#   >>> exec(open('/path/to/distort_mesh.py').read());
+#
+
+import bpy
+
+import os
+import sys
+
+import numpy as np
+
+
+def find_target_object(object_prefix):
+
+    target_obj = None
+    object_name = None
+
+    # Find the object that matches the name prefix. Assume the first one.
+    for obj in bpy.data.objects:
+        if obj.name.startswith(object_prefix):
+            target_obj = bpy.data.objects[obj.name]
+            object_name = obj.name
+            break
+    if target_obj == None:
+        print('ERROR: Object with prefix [{}] not found'.format(object_prefix))
+        return None
+
+    return target_obj, object_name
+
+
+# shading: 'WIREFRAME', 'SOLID', 'MATERIAL', or 'RENDERED'
+def viewport_shading(shading):
+    print('Changing viewport shading to {}...'.format(shading))
+    areas = bpy.context.workspace.screens[0].areas
+    for ar in areas:
+        for spc in ar.spaces:
+            if spc.type == 'VIEW_3D':
+                spc.shading.type = shading
+
+
+def subdivision_modifier(obj, levels=2):
+
+    if levels == 0:
+        print('Subdivision modifier level is 0, skipping')
+        return
+
+    print('Applying subdivision modifier with level {}...'.format(levels))
+
+    viewport_shading('WIREFRAME')
+
+    # Select the object
+    obj.select_set(True)
+    # Set active object, otherwise incorrect context
+    bpy.context.view_layer.objects.active = obj
+
+    # subdivision modifier
+    mod = obj.modifiers.new(name='Subdivision', type='SUBSURF')
+
+    mod.subdivision_type = 'SIMPLE'
+    mod.show_only_control_edges = False
+    mod.levels = levels
+
+    print(bpy.ops.object.modifier_apply(modifier='Subdivision'))
+
+
+# Randomize mesh vertices
+# offset (float in [-inf, inf], (optional)): Amount, Distance to offset. Meters
+# uniform (float in [0, 1], (optional)): Uniform, Increase for uniform offset
+#     distance
+# normal (float in [0, 1], (optional)): Normal, Align offset direction to
+#     normals
+# seed (int in [0, 10000], (optional)): Random Seed
+def mesh_vert_randomize(obj, offset=0.0, uniform=0.0, normal=1.0, seed=0):
+
+    print('Applying mesh vertex randomization with offset {}...'.format(offset))
+
+    # Set active object, otherwise incorrect context
+    bpy.context.view_layer.objects.active = obj
+
+    # Go into Edit mode
+    bpy.ops.object.mode_set(mode='EDIT')
+
+    bpy.ops.mesh.select_all(action='SELECT')
+
+    # Offset is in meters
+    print(bpy.ops.transform.vertex_random(offset=offset, uniform=uniform,
+        normal=normal, seed=seed))
+
+    # Go back to object mode
+    bpy.ops.object.mode_set(mode='OBJECT')
+
+
+def edge_subdivide(obj, ncuts=1, smooth=1.0):
+
+    print('Applying edge subdivide with number of cuts {}...'.format(ncuts))
+
+    # Set active object, otherwise incorrect context
+    bpy.context.view_layer.objects.active = obj
+
+    # Go into Edit mode
+    bpy.ops.object.mode_set(mode='EDIT')
+
+    bpy.ops.mesh.select_all(action='SELECT')
+
+    print(bpy.ops.mesh.subdivide(number_cuts=ncuts, smoothness=smooth,
+        ngon=True, quadcorner='STRAIGHT_CUT', fractal=0.0,
+        fractal_along_normal=0.0, seed=0))
+
+    # Go back to object mode
+    bpy.ops.object.mode_set(mode='OBJECT')
+
+
+# file_path: Full path to input file
+# object_prefix: Prefix of the mesh name found in the 3D model file
+# distort_extent: relative scale, in range [0.0, 1.0]
+# method: List of strings, a subset of those defined in METHODS
+def distort(file_path, object_prefix, distort_extent, method):
+
+    # Sanity checks
+    if not os.path.exists(file_path):
+        print('ERROR: File does not exist: [{}]'.format(file_path))
+        return
+    if distort_extent < 0.0 or distort_extent > 1.0:
+        print('ERROR: distort_extent ({}) must be in range [0.0, 1.0]'.format(
+            distort_extent))
+        return
+    if not isinstance(method, list):
+        print('ERROR: method parameter "%s" must be specified as a list' % method)
+        return
+
+    # Clear scene
+    bpy.ops.object.select_all(action='SELECT')
+    bpy.ops.object.delete()
+
+    # Open file
+    if file_path.lower().endswith('dae'):
+        bpy.ops.wm.collada_import(filepath=file_path)
+    elif file_path.lower().endswith('obj'):
+        bpy.ops.import_scene.obj(filepath=file_path, axis_forward='X',
+            axis_up='Z')
+    else:
+        print('ERROR: Only COLLADA (.dae) and OBJ formats are supported for importing at the moment.')
+        return
+
+    objs = find_target_object(object_prefix)
+    if objs is None:
+        print('Error detected. Aborting')
+        return
+    target_obj, object_name = objs
+
+    print('Distorting mesh [{}] for relative extent {} out of [0, 1]...'.format(
+        object_name, distort_extent))
+
+    METHODS = ['subdiv_mod', 'vert_rand', 'edge_subdiv']
+    for step in method:
+
+        if not step in METHODS:
+            print('ERROR: Unrecognized step {}'.format(step))
+            print('Available steps are:')
+            for m in METHODS:
+                print(m)
+            print('Aborting')
+            break
+
+        if step == 'subdiv_mod':
+            # Figure out levels magnitude
+            SUBDIV_LVL_MIN = 0
+            # This might need tuning
+            SUBDIV_LVL_MAX = 4
+            # Must be integer
+            subdiv_lvl = round(SUBDIV_LVL_MIN + (
+                (SUBDIV_LVL_MAX - SUBDIV_LVL_MIN) * distort_extent))
+
+            subdivision_modifier(target_obj, subdiv_lvl)
+
+        elif step == 'vert_rand':
+            # Meters
+            VERT_RAND_MIN = 0
+            # Set max in terms of object dimensions. This might need tuning.
+            VERT_RAND_MAX = 10 * np.max(target_obj.dimensions)
+
+            # Figure out offset magnitude
+            vert_rand_amt = VERT_RAND_MIN + (
+                (VERT_RAND_MAX - VERT_RAND_MIN) * distort_extent)
+
+            mesh_vert_randomize(target_obj, vert_rand_amt, uniform=0.0,
+                normal=1.0, seed=0)
+
+        elif step == 'edge_subdiv':
+
+            edge_subdivide(target_obj)
+
+    # Export result to file
+    out_path = os.path.splitext(file_path)[0] + '_distort' + \
+        os.path.splitext(file_path)[1]
+    # NOTE: COLLADA is not exporting texture correctly, not sure why.
+    # NOTE: collada_export() does not expose relative path option.
+    if out_path.lower().endswith('dae'):
+        bpy.ops.wm.collada_export(filepath=out_path)
+    elif out_path.lower().endswith('obj'):
+        bpy.ops.export_scene.obj(filepath=out_path, path_mode='RELATIVE',
+            axis_forward='X', axis_up='Z')
+    else:
+        print('ERROR: Only COLLADA (.dae) and OBJ formats are supported for exporting at the moment.')
+        return
+
+    print('Exported result to [{}]'.format(out_path))
+
+
+if __name__ == '__main__':
+    # Default values
+    distort_extent = 0.1
+    method = ['subdiv_mod', 'vert_rand', 'edge_subdiv']
+
+    # Parse everything after `--`
+    argStartI = 0
+    for i in range(len(sys.argv)):
+        if sys.argv[i] == '--':
+            argStartI = i + 1
+            break
+
+    # Parse args
+    if len(sys.argv) - argStartI < 2:
+        print('ERROR: Mesh name prefix not provided. No object to distort.')
+    else:
+        file_path = sys.argv[argStartI]
+        object_prefix = sys.argv[argStartI + 1]
+        if len(sys.argv) - argStartI > 1:
+            distort_extent = float(sys.argv[argStartI + 2])
+        if len(sys.argv) - argStartI > 2:
+            # If arg is not already a list (happens when script run from
+            # bash command line, for example, as opposed to Blender Python
+            # prompt), convert string literal of a list, to a list.
+            if type(sys.argv[argStartI + 3]) != list:
+                import ast
+                method = ast.literal_eval(sys.argv[argStartI + 3])
+
+        distort(file_path, object_prefix, distort_extent, method)

tutorials.md.in

@@ -32,8 +32,9 @@ Gazebo @IGN_DESIGNATION_CAP@ library and how to use the library effectively.
 * \subpage collada_world_exporter "Collada World Exporter": Export an entire world to a single Collada mesh.
 * \subpage underwater_vehicles "Underwater Vehicles": Understand how to simulate underwater vehicles.
 * \subpage particle_emitter "Particle emitter": Using particle emitters in simulation
-* \subpage blender_sdf_exporter "Blender SDF Exporter": Use a blender script to export a model to the SDF format.
-* \subpage model_and_optimize_meshes  "Model and optimize meshes": Some recomendations when creating meshes  in blender for simulations.
+* \subpage blender_sdf_exporter "Blender SDF Exporter": Use a Blender script to export a model to the SDF format.
+* \subpage model_and_optimize_meshes "Model and optimize meshes": Some recomendations when creating meshes in Blender for simulations.
+* \subpage blender_distort_meshes "Blender mesh distortion": Use a Blender Python script to programmatically deform and distort meshes to customized extents.
 * \subpage model_command "Model Command": Use the CLI to get information about the models in a simulation.
 * \subpage test_fixture "Test Fixture": Writing automated CI tests
 * \subpage model_photo_shoot "Model Photo Shoot" Taking perspective, top, front, and side pictures of a model.