Screenshots have an alpha layer, weird.

Scripting Issues
1

I tried taking a screenshot of my game with the following code:

    def takeScreenShot(self):
        file_name = Filename('whatever.png'))
        self.win.saveScreenshot(file_name)

It works, but when I opened the result I saw little squares where objects with an alpha layer were:

The little squares aren’t put there by panda of course, they’re there because my image viewer puts them there to show me the transparency. So the picture above is actually a screenshot of the screenshot seen in my image viewer.

Questions: How does it work ? Does it make sense for a screenshot to have some transparency ?

I could avoid the problem by using jpg or bmp, but I like png for its lossless compression.

2

It’s the alpha channel of the framebuffer. You could disable it by disabling alpha writes, or by requesting a framebuffer without alpha channel (framebuffer-alpha #f). Alternatively, you could use the alternate lower-level screenshot method that saves to a PNMImage, and then remove the alpha channel from the PNMImage, and write that to disk.

3

Oh, thanks, that makes sense :slight_smile:.

I chose to take the PNMImage way. Although I am not doing any post-processing, I don’t want to limit my options in the future by removing frame buffer planes.

This code works very well, no more little squares.

#! /usr/bin/python
"""
Module screenshot.

Save screenshots to disk using threads.
"""
import threading
from panda3d.core import PNMImage #@UnresolvedImport

def _shoot(screen, file_name):
    print "Screenshot..."
    screen.write(file_name)
    print "...taken", file_name

def take(win, file_name):
    screen = PNMImage()
    if win.getScreenshot(screen):
        screen.removeAlpha()
        t = threading.Thread(target=_shoot, args=(screen, file_name))
        t.start()
    else:
        print "Screenshot derped."


Thanks!

Question: what could cause win.getScreenshot(screen) to return False?

4

I’d guess the function might return None if taking a picture of the buffer or saving it fails.