前言
原理之前在这篇文档讲过，纯属于自嗨产物，大概只有自己能看得懂写了啥。然后根据这个思路实现。这篇主要目的就是复习下节点编辑器。maya节点编辑器的手感真的稀烂。
- 这个系列都是挖的国外的某个教程，不太适合我这种彩笔，操作真的飞快。
代码实现
我还是觉得代码最清晰，先放代码
def add_ik_stretch(side, part, ik_chain, base_ctrl, local_ctrl, world_ctrl,primary_axis):
base_name = side +'_' + part
# start to end distance
limb_dist = cmds.createNode('distanceBetween', name=base_name+'_DIST')
# cinditon node
limb_cnd = cmds.createNode('condition', name=base_name+'CND')
# allocate locater, get transform node
start_LOC = cmds.spaceLocator(name=base_name+'_start_LOC')[0]
end_LOC = cmds.spaceLocator(name=base_name+'_end_LOC')[0]
stretch_mdn = cmds.createNode('multiplyDivide', name=base_name+'_stretch_MDN')
# calculate section length
length_a = distance_between(ik_chain[0],ik_chain[1])
length_b = distance_between(ik_chain[1], ik_chain[2])
total_length = length_b + length_a
# measure start-end desired direct distance
# move the loc first
cmds.pointConstraint(base_ctrl, start_LOC, maintainOffset=False)
cmds.pointConstraint(local_ctrl, end_LOC, maintainOffset=False)
connectAttr(start_LOC, 'worldMatrix[0]', limb_dist, 'inMatrix1')
connectAttr(end_LOC, 'worldMatrix[0]', limb_dist, 'inMatrix2')
# length ratio
connectAttr(limb_dist, 'distance', stretch_mdn,'input1X')
cmds.setAttr(stretch_mdn+'.input2X', total_length)#set devision
cmds.setAttr(stretch_mdn+'.operation', 2)
connectAttr(limb_dist,'distance',limb_cnd,'firstTerm')
connectAttr(stretch_mdn,'outputX', limb_cnd,'colorIfTrueR')
cmds.setAttr(limb_cnd+'.secondTerm', total_length)
cmds.setAttr(limb_cnd+'.operation',3)
# switch stretch
cmds.addAtter(world_ctrl, attributeType='double', min=0, max=1,
defaultValue=1, keyable=True, longName='stretch')
up_name = 'up' + part.title()
lo_name = 'lo' + part.title()
cmds.addAtter(world_ctrl, attributeType='double',
defaultValue=1, keyable=True, longName='up_name')
cmds.addAtter(world_ctrl, attributeType='double',
defaultValue=1, keyable=True, longName='lo_name')
stretch_bta = cmds.createNode('blendTwoAttr', name = base_name+'_BTA')
cmds.setAttr(stretch_bta+'.input[0]', 1)
connectAttr(limb_cnd,'outColorR',stretch_bta,'input[1]')
connectAttr(world_ctrl,'stretch',stretch_bta,'attributesBlender')
up_pma = cmds.createNode('plusMinusAverage', name=up_name+'_PMA')
lo_pma = cmds.createNode('plusMinusAverage', name=lo_name + '_PMA')
connectAttr(world_ctrl, up_name, up_pma, 'input1D[0]')
connectAttr(world_ctrl, lo_name, lo_pma, 'input1D[0]')
connectAttr(stretch_bta, 'output', up_pma, 'input1D[1]')
connectAttr(stretch_bta, 'output', lo_pma, 'input1D[1]')
cmds.setAttr(up_pma+'.input1D[2]', -1)
cmds.setAttr(lo_pma + '.input1D[2]', -1)
connectAttr(up_pma,'output1D',
ik_chain[0],'scale'+primary_axis[-1])
connectAttr(lo_pma,'output1D',
ik_chain[1],'scale'+primary_axis[-1])
return_dict = {
'measure_locs': [start_LOC, end_LOC],
'total_length': total_length,
'mdn': stretch_mdn,
'cnd': limb_cnd}
return return_dict
过程解释
获取effectors变换信息
我们首先创建两个个定位器，将定位器移动到start以及end effector的位置。
start_effector位置事先被base_ctrl(start_effector)记录了
同理end_effector被local_ctrl记录了，这个local_ctrl的作用是控制手，不过这里没有增加手的关节。
- 移动locator到effectors
cmds.pointConstraint(base_ctrl, start_LOC, maintainOffset=False)
cmds.pointConstraint(local_ctrl, end_LOC, maintainOffset=False)
计算一些距离数值
- 得到effector之间的距离，effector的距离是我们期望将原始的IKhandeler拉长的target，这个数字比较关键
limb_dist.distance
# start to end distance
limb_dist = cmds.createNode('distanceBetween', name=base_name+'_DIST')
···
connectAttr(start_LOC, 'worldMatrix[0]', limb_dist, 'inMatrix1')
connectAttr(end_LOC, 'worldMatrix[0]', limb_dist, 'inMatrix2')
-
模型上臂和下臂的距离和他们的总和
total_lengthlength_a = distance_between(ik_chain[0],ik_chain[1]) length_b = distance_between(ik_chain[1], ik_chain[2]) total_length = length_b + length_a
获得拉伸stretch比例
tips：下面的函数connectAttr（）是我自己重写的cmds的方法，作用都是一样的
stretch_mdn = cmds.createNode('multiplyDivide', name=base_name+'_stretch_MDN')
···
# length ratio
connectAttr(limb_dist, 'distance', stretch_mdn,'input1X')
cmds.setAttr(stretch_mdn+'.input2X', total_length)#set devision
cmds.setAttr(stretch_mdn+'.operation', 2)
是加上就是stretch ratio = effectors的距离/模型手臂长，这个部分用了’multiplyDivide’这个节点完成。就很麻烦，要是要实现实时计算就必须用节点，除非是一直固定不变的值，比如模型手臂长这种constant我们可以离线计算
stretch比例的条件分支切换
# cinditon node
limb_cnd = cmds.createNode('condition', name=base_name+'CND')
···
connectAttr(limb_dist,'distance',limb_cnd,'firstTerm')
connectAttr(stretch_mdn,'outputX', limb_cnd,'colorIfTrueR')
cmds.setAttr(limb_cnd+'.secondTerm', total_length)
cmds.setAttr(limb_cnd+'.operation',3)
这个道理是： effectors距离>=模型手臂总长时，启用之前计算的strech ratio，否则就是1
为end effctor添加几个属性
我们这里添加新属性是在local_ctrl的父控制器world_ctrl上，这俩玩意的pivot世界位置是一样的
# switch stretch
cmds.addAtter(world_ctrl, attributeType='double', min=0, max=1,
defaultValue=1, keyable=True, longName='stretch')
up_name = 'up' + part.title()
lo_name = 'lo' + part.title()
cmds.addAtter(world_ctrl, attributeType='double',
defaultValue=1, keyable=True, longName='up_name')
cmds.addAtter(world_ctrl, attributeType='double',
defaultValue=1, keyable=True, longName='lo_name')
- stretch：IK整体拉伸还是不拉伸的混合比例
- up Arm: 上臂的拉伸程度因子
- lo Arm：下臂同理
实现关节拉伸
stretch_bta = cmds.createNode('blendTwoAttr', name = base_name+'_BTA')
cmds.setAttr(stretch_bta+'.input[0]', 1)
connectAttr(limb_cnd,'outColorR',stretch_bta,'input[1]')
connectAttr(world_ctrl,'stretch',stretch_bta,'attributesBlender')
- 一个坑点：纯节点编辑器下，BTA节点的input都是要激活的，不激活不能输入constant进去。
input[0]=1代表world_ctrlde stretch系数为0，采取不变措施
-
获得部件的拉伸以及实现上下骨架缩放
up_pma = cmds.createNode('plusMinusAverage', name=up_name+'_PMA')
lo_pma = cmds.createNode('plusMinusAverage', name=lo_name + '_PMA')
connectAttr(world_ctrl, up_name, up_pma, 'input1D[0]')
connectAttr(world_ctrl, lo_name, lo_pma, 'input1D[0]')
connectAttr(stretch_bta, 'output', up_pma, 'input1D[1]')
connectAttr(stretch_bta, 'output', lo_pma, 'input1D[1]')
cmds.setAttr(up_pma+'.input1D[2]', -1)
cmds.setAttr(lo_pma + '.input1D[2]', -1)
我们将已经按上图得到经过上下手臂的缩放因子衰减的stretch ratio用于IK关节的scale实现拉伸
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connectAttr(up_pma,'output1D',
ik_chain[0],'scale'+primary_axis[-1])
connectAttr(lo_pma,'output1D',
ik_chain[1],'scale'+primary_axis[-1])
结尾
以上就是大致的梳理过程还有很多细节没说，怕自己搞忘了，我也放上了节点编辑器版本的同功能mb文件，2020以上才能打开。
