Maya Frustum Cutter

maya_frustum_cutter.py

"""
Select the camera you want to cut from, then the geometry you want
to be cut.
"""
import maya.cmds as cmds
import pymel.core as pm


def cut_to_frustum(camera, geometry):
    # Gather relevant camera attributes.
    focalLength = cmds.getAttr(camera + ".focalLength")
    horizontalAperture = cmds.getAttr(camera + ".cameraAperture")[0][0]
    nearClipping = cmds.getAttr(camera + ".nearClipPlane")
    farClipping = cmds.getAttr(camera + ".farClipPlane")

    # Calculate ratios.
    plane = horizontalAperture * 25.4
    nearScaleValue = nearClipping * plane / focalLength

    # Build geometry.
    cube_transform, cube_shape = cmds.polyCube(
        w=1,
        h=1,
        d=farClipping-nearClipping,
        sy=1,
        sx=1,
        sz=1,
        ax=[0, 1, 0],
        ch=1,
        name=camera.replace("Shape", "Frustrum")
    )

    cmds.setAttr(
        cube_transform + ".translateZ",
        nearClipping + (farClipping-nearClipping) * 0.5
    )
    cmds.makeIdentity(apply=True, t=1, r=1, s=1, n=0, pn=1)
    cmds.setAttr(cube_transform + ".rotatePivotZ", 0)
    cmds.setAttr(cube_transform + ".scalePivotZ", 0)
    cmds.setAttr(cube_transform + ".rotateY", 180)

    # Use expressions to update frustum geo as FOV and apertures are changed.
    scaleX = (
        "{}.scaleZ*{}.farClipPlane*{}.horizontalFilmAperture*25.4*0.94"
        "/{}.focalLength".format(cube_transform, camera, camera, camera)
    )
    scaleY = (
        "{}.scaleZ*{}.farClipPlane*{}.verticalFilmAperture*25.4"
        "/{}.focalLength".format(cube_transform, camera, camera, camera)
    )

    cmds.move(0, 0, 0, cube_transform + ".f[2]", absolute=True)
    cmds.scale(nearScaleValue, 0, 1, cube_transform + ".f[2]", pivot=[0, 0, 0])
    cmds.expression(
        s="{}.scaleX = {};{}.scaleY = {};".format(
            cube_transform, scaleX, cube_transform, scaleY
        ),
        n="{}_Expr".format(cube_transform)
    )

    cmds.parent(cube_transform, camera.getTransform().name(), relative=True)
    cmds.parent(cube_transform, world=True)

    # Difference operation.
    pm.polyCBoolOp(
        cube_transform,
        geometry,
        operation=2,
        constructionHistory=False,
        preserveColor=0,
        classification=1,
        name=geometry.name()
    )


with pm.UndoChunk():
    selection = pm.ls(selection=True)
    cut_to_frustum(selection[0].getShape(), selection[1])