IDLE: Turn on DPI awareness on Windows

[terryjreedy]

BPO	33656
Nosy	@terryjreedy, @pfmoore, @ronaldoussoren, @taleinat, @tjguk, @zware, @serhiy-storchaka, @zooba, @efahl, @miss-islington
PRs	bpo-33656: On Windows, add API call saying that tk scales for DPI. #7137 bpo-33656: Add entry to What's New 3.7 #7638 [3.7] bpo-33656: On Windows, add API call saying that tk scales for DPI (GH-7137) #7639 [3.6] bpo-33656: On Windows, add API call saying that tk scales for DPI (GH-7137) #7640 [3.7] bpo-33656: Add entry to What's New 3.7. (GH-7638) #7641 bpo-33656: Add enum name for argument of Windows call. #7642 [3.7] bpo-33656: Add enum name for argument of Windows call. (GH-7642) #7643 [3.6] bpo-33656: Add enum name for argument of Windows call. (GH-7642) #7644 bpo-33656: Mention color in idlelib/NEWS.txt entry. #7646 [3.7] bpo-33656: Mention color in idlelib/NEWS.txt entry. (GH-7646) #7647 [3.6] bpo-33656: Mention color in idlelib/NEWS.txt entry. (GH-7646) #7648 bpo-33656: Move pyshell ctypes import inside try block. #9858 [3.7] bpo-33656: Move pyshell ctypes import inside try block. (GH-9858) #9862 [3.6] bpo-33656: Move pyshell ctypes import inside try block. (GH-9858) #9863

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/terryjreedy'
closed_at = <Date 2018-10-14.00:41:17.759>
created_at = <Date 2018-05-26.23:14:50.803>
labels = ['3.8', 'expert-IDLE', 'type-feature', '3.7']
title = 'IDLE: Turn on DPI awareness on Windows'
updated_at = <Date 2018-10-14.00:41:17.758>
user = 'https://github.com/terryjreedy'

bugs.python.org fields:

activity = <Date 2018-10-14.00:41:17.758>
actor = 'terry.reedy'
assignee = 'terry.reedy'
closed = True
closed_date = <Date 2018-10-14.00:41:17.759>
closer = 'terry.reedy'
components = ['IDLE']
creation = <Date 2018-05-26.23:14:50.803>
creator = 'terry.reedy'
dependencies = []
files = []
hgrepos = []
issue_num = 33656
keywords = ['patch']
message_count = 38.0
messages = ['317775', '317776', '318040', '318053', '318056', '318068', '318069', '319130', '319148', '319150', '319152', '319159', '319184', '319185', '319192', '319326', '319327', '319328', '319329', '319330', '319331', '319332', '319334', '319336', '319340', '319345', '319346', '319348', '319362', '319403', '319407', '319411', '319426', '327676', '327680', '327681', '327683', '327685']
nosy_count = 10.0
nosy_names = ['terry.reedy', 'paul.moore', 'ronaldoussoren', 'taleinat', 'tim.golden', 'zach.ware', 'serhiy.storchaka', 'steve.dower', 'eric.fahlgren', 'miss-islington']
pr_nums = ['7137', '7638', '7639', '7640', '7641', '7642', '7643', '7644', '7646', '7647', '7648', '9858', '9862', '9863']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue33656'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']

[terryjreedy]

On IDLE-dev today, Elisha Paine, from Ranelagh School in England, wrote:
'''
I love IDLE (so simple and lightweight compared with other IDEs) and was just wondering if you could add the following code into pyshell.py (as I have done on mine) because, as you will be able to tell, it sets DPI awareness (and on my set-up makes the text a lot clearer)

import ctypes
try: ctypes.windll.shcore.SetProcessDpiAwareness (True)
except: pass
'''
On my Win 10 system with a 2560 x 1440 27" monitor, the text is noticeably sharper, some colors are brighter, and some characters are better formed.  The main effect seems to be from properly lining up vertical and horizontal lines with the pixels.  Lines that are supposed to be 1 or 2 pixels wide are just that, instead of bleeding over onto additional rows or columns.

By comparing IDLE's shell with Windows consoles with the same font and text, both for Command Prompt and Python x.y consoles, I determined that the Windows consoles have DPI awareness on. The text is longer with it off and some character shapes, such as for 2 and 3, don't match, whereas text length and shape matches perfectly with it on.

At least some other apps also have DPO awareness on. With the patch, the Open and Save As dialogs opened opened by from IDLE, via the tkinter/tk function, match those opened by Firefox. Without the patch, not.

I like the improvement and with 3.7.0rc1 delayed, would like to get it in now. My question for you Windows experts is 1. Is the above exactly the right thing? and 2. Should it be unconditional, or is there a possible downside? Do consoles always have DPI awareness, or is it conditional on the monitor?

I will make a PR as soon as I post this and get an issue number.

[terryjreedy]

I changed the bare except: to 'except AttributeError:'. If ctypes.windll.shcore.SetProcessDpiAwareness exists, can calling it with True ever fail?

[ronaldoussoren]

I'm not a Windows expert, but looking that the API description [1] the patch is not entirely correct.

The API takes an integer with 3 valid values, the patch effectively passes the value 1 (which means the application claims to be DPI aware, but won't scale itself when the DPI changes for some reason).

The API can fail, but that shouldn't cause an exception as ctypes won't automaticly convert error return values to exceptions.

P.S. The pull request seems to contain an unrelated change as well.

[1] https://msdn.microsoft.com/en-us/library/windows/desktop/dn302122(v=vs.85).aspx

[zware]

Does Tcl/Tk have a function for this, and/or should we expose this as a function in Tkinter? Do other platforms (macOS, X/Wayland) have similar functions?

[serhiy-storchaka]

Perhaps the argument should be 2 for supporting multi-display configuration. Currently I can't do this, but will test this recipe with Hi-DPI monitor and multiple displays after 1-2 weeks.

[terryjreedy]

Thanks for the comments:

Ronald: I agree that an int should be passed. I understand your ctype comment as saying that an attribute error before making the call should be the only possible exception.

I should have explained the 'unrelated change' to the one entry box. With the default size of 20, it no longer fits properly after the change. Adding an explicit size was the easiest fix for something that is only present for test and demonstration purposes. A better fix, which is not needed for this issue, would probably be to add a 'expand=True' or something, somewhere else.

I checked all the other panes on the settings dialog and the other major dialog boxes and found no problems.

Zack: I had the same question. Now that I know that IDLE as a tk app *can* look 'sharp', the current fuzzyness is annoying. I would not be surprised if it contributes to some of the negative opinions about IDLE.

Tk tries to look 'native' and this seems to be the main thing missing. To me, the only obvious reason for tk to not use this setting as default
is that is can mess up spacing on current windows. But to me, it definitely should be available.

I don't know if other systems have such a setting, or any need for such. I will ask an someone who uses IDLE both in Windows and Ubuntu on the same machine to compare.

Serhiy: I have a space monitor and I believe my graphics card will allow me to attach one, so I may give it a try.

The linked article recommends "that you set the process-default DPI awareness via application manifest." I don't currently know what this
means. It appears that making one call before any tkinter calls is the right thing to do if any call is to be made.

The call does not appear to be available on Windows 7 or 8.0.

[terryjreedy]

Eryk Sun commented on the PR.

[terryjreedy]

Elisha wrote and I quoted: '[the call] sets DPI awareness'. After reading https://msdn.microsoft.com/en-us/library/windows/desktop/dn280512(v=vs.85).aspx PROCESS_DPI_AWARENESS, what the call sets is the system's idea of what DPI awareness the app/process has. As I understand,
0 means 'App assumes DPI = 96, so if it is not, system must adjust.'
1 means 'App reads DPI at startup (somehow) and adjust to that value, but does not adapt to monitor change, so system must.'
2 means 'App reads DPI at startup and again after monitor change (somehow), so system should leave it alone.'
The correct value to pass is the one that best describes what the app does. I believe that 0 is wrong and 1 more likely than 2.

My own experience and Elisha's report that IDLE looks better (at any resolution setting) matches others. For instance,
https://stackoverflow.com/questions/41315873/attempting-to-resolve-blurred-tkinter-text-scaling-on-windows-10-high-dpi-disp
Three people describe fuzzy tk text as a well-known problem, fixed by SetProcessDpiAwareness(1).

https://wiki.tcl.tk/8484 tk has a scaling function that gets and sets a scaling factor, dpi/72 = pixels per printer point. "The initial value for the scaling factor is set when the application starts, based on properties of the installed monitor." This also suggests to me also that default 0 for awareness is wrong value. Users (apps) can changes this, but I see no suggestion that monitor changes are tracked.

[efahl]

https://msdn.microsoft.com/en-us/library/windows/desktop/mt748620(v=vs.85).aspx gives the syntax for adding dpiAwareness to the Windows manifest.

[terryjreedy]

As reported on bpo-26698, which was originally opened as an IDLE issue, but which I turned into a tkinter issue, one can also sharpen text buy opening python(w).exe properties, Compatibility tab, clicking [Change high DPI settings], and then checking [] Override high DPI scaling behavior while leaving the default 'Application'. The effect is the same as 'SetProcessDpiAwareness (1)' -- or (2) if monitor is not changed.