计算机图形学流体模拟 blender 渲染脚本

做流体模拟的时候，想要复现别人的成果，但是别人的代码都是每帧输出 ply 格式的文件，渲染部分需要自己完成

看了一下，似乎用 blender 是最简单的，于是记录一下过程中用到的代码

Blender 版本 4.0

批量导入 ply

假设所有 ply 文件都和 blend 文件位于同一目录

ply 文件的文件名格式是 00001.ply, 00002.ply, 000123.ply 之类，编号表示帧数

希望导入所有 ply 文件，都放在一个 collection 里面，并且只连接到这个 collection

import bpy 
import os

in_dir = bpy.path.abspath("//")
filters = []  # files to ignore
files_number = 0

def only_link_to_one_collection(obj, collection):
    for other_col in obj.users_collection:
        other_col.objects.unlink(obj)
    if obj.name not in collection.objects:
        collection.objects.link(obj)
        
def import_ply(path, filters):
    need_file_items = []
    need_file_names = []

    filterDict = {}
    for item in filters:
        filterDict[item] = True;

    file_lst = os.listdir(path)
    
    for item in file_lst:
        fileName, fileExtension = os.path.splitext(item)
        if fileExtension == ".ply" and (not item in filterDict):
            need_file_items.append(item)
            need_file_names.append(fileName)
    
    fluid_mesh_collection = bpy.data.collections.new(name='FluidMesh')
    bpy.context.scene.collection.children.link(fluid_mesh_collection)
    
    files_number = len(need_file_items)
    for i in range(files_number):
        item = need_file_items[i]
        itemName = need_file_names[i]
        ufilename = path + "\\" + item
        bpy.ops.wm.ply_import(filepath=ufilename)
        cur_obj = bpy.data.objects[itemName]
        if (cur_obj):
            only_link_to_one_collection(cur_obj, fluid_mesh_collection)
            cur_obj.hide_set(False)
            cur_obj.hide_render = True

import_ply(in_dir, filters)

Mesh 预处理

删除没有使用到的材质

import bpy

toRemove = [block for block in bpy.data.materials if block.users == 0]
for block in toRemove:
    bpy.data.materials.remove(block)

添加 Glass BSDF 材质

import bpy

fluid_mat = bpy.data.materials.new("FluidMat")
fluid_mat.use_nodes = True

principled_node = fluid_mat.node_tree.nodes.get("Principled BSDF")
fluid_mat.node_tree.nodes.remove(principled_node)

glass_node = fluid_mat.node_tree.nodes.new("ShaderNodeBsdfGlass")
glass_node.location = (0, 0)

glass_node.inputs[0].default_value = (0.730, 0.927, 1.0, 1.0)
glass_node.inputs[1].default_value = 0.0
glass_node.inputs[2].default_value = 1.333

output_node = fluid_mat.node_tree.nodes.get("Material Output")
output_node.location = (200, 0)

fluid_mat.node_tree.links.new(glass_node.outputs[0], output_node.inputs[0])

for obj in bpy.data.collections['FluidMesh'].all_objects:
    obj.active_material = fluid_mat

重定位 Mesh

具体怎么修改位置和旋转的，是根据你代码里面具体是怎么设置流体域的

import bpy

for obj in bpy.data.collections['FluidMesh'].all_objects:
    obj.rotation_euler[0] = 1.5708  # 90d
    obj.location = (-4, 4, 0)

清理旧的动画

import bpy

for obj in bpy.data.collections['FluidMesh'].all_objects:
    obj.animation_data_clear()

制作动画帧

Hide_Render 动画

import bpy

for obj in bpy.data.collections['FluidMesh'].all_objects:
    mesh_name = obj.name
    i = int(mesh_name)
    
    obj.hide_viewport = True
    obj.hide_render = True
    obj.keyframe_insert("hide_viewport", frame=0)
    obj.keyframe_insert("hide_render", frame=0)
    
    obj.hide_viewport = False
    obj.hide_render = False
    obj.keyframe_insert("hide_viewport", frame=i+1)
    obj.keyframe_insert("hide_render", frame=i+1)
    
    obj.hide_viewport = True
    obj.hide_render = True
    obj.keyframe_insert("hide_viewport", frame=i+2)
    obj.keyframe_insert("hide_render", frame=i+2)

输出渲染动画

地面、天光等创建暂时不写脚本里，手动创建

选择光追渲染，才有好看的效果。选 eevee 的话，光线都没有从玻璃里面折射出来，所以玻璃都是一片黑的

fps 的设置也是根据流体计算时设置的 dt 来的

import bpy
import math

camera = bpy.data.objects['Camera']
camera.location = (20, -20, 20)
camera.rotation_euler = (math.radians(60), 0, math.radians(45))

bpy.context.scene.render.engine = 'CYCLES'
bpy.context.scene.cycles.device = 'GPU'
bpy.context.scene.cycles.samples = 256

bpy.context.scene.render.resolution_x = 1080
bpy.context.scene.render.resolution_y = 720
bpy.context.scene.render.fps = 30

bpy.context.scene.render.filepath = bpy.path.abspath("//fluid_anim.mkv")
bpy.context.scene.render.image_settings.file_format = 'FFMPEG'

bpy.context.scene.frame_start = 1
bpy.context.scene.frame_end = len(bpy.data.collections['FluidMesh'].all_objects)+1

bpy.ops.render.render(animation=True)

效果