[Maya - python] Super weird behaviour of M3dView

Coding
#1

Hi!
I’m having this problem with Maya M3dView class. I’m creating a super simple widget with this code:


def get_preview_window():
    win = cmds.window()
    layout = cmds.paneLayout()
    
    model_editor = cmds.modelPanel()
    cmds.setParent("..")
    cmds.setParent("..")
    cmds.showWindow(win)
    
get_preview_window()

Now I’m trying to grab a screenshot from this with this code:


import ctypes
import maya.OpenMaya as om
import maya.OpenMayaUI as omui
from PySide.QtGui import QImage

view = omui.M3dView.active3dView()
width = view.portWidth()
height = view.portHeight()
img = om.MImage()
view.readColorBuffer(img, False)
ptr = ctypes.cast(img.pixels().__long__(), ctypes.POINTER(ctypes.c_char))
ptrAsStr = ctypes.string_at(ptr, width * height * 4)
qimg = QImage(ptrAsStr, width, height, QImage.Format_ARGB32)
qimg = qimg.mirrored(horizontal=False, vertical=True)
qimg.save('C:/screenshot.png')

Now - the thing is that the grabbed image has a proper size of an embedded viewport (the one created with mel) but the actual image comes from the main viewport (“modelPanel4”) so it’s cropped and it’s completely not what I want.
Can anyone help me with that? :confused:

PS. One IMPORTANT thing - it stops to work when you open the viewport window, navigate it and then try to grab it. If you grab it right after creation everything works just fine.

#2

active3dView() returns a class, but is it a static object, or does it change when the active viewport changes? Does the active viewport change while the script is operating?

#3

Ok - I’ve forgot to post a reply here. It’s a Maya 2016 viewport 2.0 bug. In previous Maya versions it’s working properly, and in 2016 it works fine with legacy viewport. Already reported to Autodesk. Took me 2 days to figure out that it’s a bug :confused:

Btw - active3dView() is a static method that returns you an instance of the M3dView class. However you can change your active screen after obtaining it, it still points to the viewport gathered with active3dView().

#4

Ok - the problem was actually with the floating/fixed point pixel buffers. MImage by default is kByte and the viewport 2.0 is kFloat.
Now, whenever I’ve passed a kByte MImage to M3dView::readColorBuffer() the image buffer was actually filled with some random data that by some strange accident made some sense (output image contained a part of a different viewport so it was hard to determine that it was in fact a trash, I’ve figured it out because calling MImage::create gave the same results as readColorBuffer). Passing the MImage created as kFloat to the readColorBuffer fixes this issue so the code below works just fine.


#------------------------------
# grab active Model editor view to QImage
#------------------------------
import ctypes
import maya.OpenMaya as om
import maya.OpenMayaUI as omui
from PySide.QtGui import QImage, QWidget
from shiboken import wrapInstance
import uuid

view = omui.M3dView.active3dView()
model_editor_qwidget = wrapInstance(long(view.widget()), QWidget)

view.refresh(True, True)
img = om.MImage()
if view.getRendererName() == view.kViewport2Renderer:
    print "Saving float point viewport"
    img.create(view.portWidth(), view.portHeight(), 4, om.MImage.kFloat)
    view.readColorBuffer(img)
    img.convertPixelFormat(om.MImage.kByte )
else:
    print "Saving fixed point viewport"
    view.readColorBuffer(img)

pixels_size = view.portWidth() * view.portHeight() * bg_image.depth()
pixels_pointer = bg_image.pixels()
# --------------------------------------- convert the frame buffer to str
pp = uuid.ctypes.cast(pixels_pointer.__long__(), uuid.ctypes.POINTER(uuid.ctypes.c_char))
pixels_string = uuid.ctypes.string_at(pp, pixels_size)

# ------------------------------------------ make the QImage from the str
image = QImage(pixels_string, width, height, QImage.Format_RGB32).mirrored(horizontal=False, vertical=True)
image.save("c:/qimage.png", "PNG")

I am aware that this whole viewport capture method is currently obsolete. I think that before the release of the next Maya version I’ll have to invent “the proper way” of capturing viewports with python. Meanwhile a great “thank you” to the Autodesk API team for the tip about the MImage bit depth, I would NEVER figure it on myself.

PS. Even if I’ve had Floating Point Render Target disabled in the hardwareRenderGlobals the VP2.0 readColorBuffer still needs a floating point MImage.

#5

I am currently bumping my head on a similar issue, and im wondering if you (or anyone) ever managed to
capture the viewport using the new “proper” way ?
any snippet would help

  • capture a specific viewport , possibly with specific resolution, and save an image file (png, jpg, exr)
  • capture the image even when the viewport is not refreshing (off screen render)