Add support for the "blink" graphic rendition attribute #7490

j4james · 2020-08-31T23:33:16Z

This PR adds support for the blink graphic rendition attribute. When a
character is output with this attribute set, it "blinks" at a regular
interval, by cycling its color between the normal rendition and a dimmer
shade of that color.

The majority of the blinking mechanism is encapsulated in a new
BlinkingState class, which is shared between the Terminal and Conhost
implementations. This class keeps track of the position in the blinking
cycle, which determines whether characters are rendered as normal or
faint.

In Windows Terminal, the state is stored in the Terminal class, and in
Conhost it's stored in the CONSOLE_INFORMATION class. In both cases,
the IsBlinkingFaint method is used to determine the current blinking
rendition, and that is passed on as a parameter to the
TextAttribute::CalculateRgbColors method when these classes are
looking up attribute colors.

Prior to calculating the colors, the current attribute is also passed to
the RecordBlinkingUsage method, which keeps track of whether there are
actually any blink attributes in use. This is used to determine whether
the screen needs to be refreshed when the blinking cycle toggles between
the normal and faint renditions.

The refresh itself is handled by the ToggleBlinkingRendition method,
which is triggered by a timer. In Conhost this is just piggybacking on
the existing cursor blink timer, but in Windows Terminal it needs to
have its own separate timer, since the cursor timer is reset whenever a
key is pressed, which is not something we want for attribute blinking.

Although the ToggleBlinkingRendition is called at the same rate as the
cursor blinking, we actually only want the cells to blink at half that
frequency. We thus have a counter that cycles through four phases, and
blinking is rendered as faint for two of those four. Then every two
cycles - when the state changes - a redraw is triggered, but only if
there are actually blinking attributes in use (as previously recorded).

As mentioned earlier, the blinking frequency is based on the cursor
blink rate, so that means it'll automatically be disabled if a user has
set their cursor blink rate to none. It can also be disabled by turning
off the Show animations in Windows option. In Conhost these settings
take effect immediately, but in Windows Terminal they only apply when a
new tab is opened.

This PR also adds partial support for the SGR 6 rapid blink
attribute. This is not used by DEC terminals, but was defined in the
ECMA/ANSI standards. It's not widely supported, but many terminals just
it implement it as an alias for the regular SGR 5 blink attribute, so
that's what I've done here too.

Validation Steps Performed

I've checked the Graphic rendition test pattern in Vttest, and
compared our representation of the blink attribute to that of an actual
DEC VT220 terminal as seen on YouTube. With the right color scheme
it's a reasonably close match.

Closes #7388

j4james · 2020-09-01T01:02:03Z

For comparison with the DEC VT220 video mentioned above, here's a gif of the Terminal output with an appropriate color scheme, and with retro effects enabled:

src/host/settings.hpp

PankajBhojwani · 2020-09-01T16:42:02Z

Thanks for this, it looks amazing

Had a question - should we initialize our own timer if the user has disabled cursor blinking (but has enabled animations)? I'm wondering about the use case where someone does not want their cursor to blink but still wants text with this attribute to blink.

src/renderer/base/BlinkingState.cpp

j4james · 2020-09-01T18:43:40Z

Had a question - should we initialize our own timer if the user has disabled cursor blinking (but has enabled animations)? I'm wondering about the use case where someone does not want their cursor to blink but still wants text with this attribute to blink.

I've essentially replied to this in the comments above. But I should also point out that there have been quite a few concerns raised about the accessibility implications of this feature. So if there's any hint from the user that they don't like blinking (e.g. setting the cursor blink rate to none), I think it's probably better to be on the safe side and assume they don't want any blinking at all.

But again, I'm OK being overridden on this point if you all disagree.

skyline75489 · 2020-09-02T02:46:54Z

@j4james FYI Dustin and Mike are currently out of the office right now. I'm sure they'd love to review a PR like this when they're available.

src/cascadia/TerminalControl/TermControl.cpp

…king attributes as faint.

…to redraw the screen.

src/renderer/base/BlinkingState.cpp

DHowett · 2020-09-18T20:20:14Z

src/host/consoleInformation.cpp

+// - The color values of the attribute's foreground and background.
+std::pair<COLORREF, COLORREF> CONSOLE_INFORMATION::LookupAttributeColors(const TextAttribute& attr) const noexcept
+{
+    _blinkingState.RecordBlinkingUsage(attr);


clever clearing it during a render cycle on-blink and using the function that resolves the color to tell whether we should keep blinking.

It took me a little bit to understand what was going on (and why I was worried that we would keep doing a full redraw every other cursor blink for all eternity), but... I like it.

It might want to be documented in a comment (sorry if it already has: I'm reading bottom-up).

Yeah, I've tried to explain this in the doc comment for RecordBlinkingUsage and then there's more detail in the internal comments of ToggleBlinkingRendition as well.

src/host/CursorBlinker.cpp

src/cascadia/TerminalControl/TermControl.cpp

DHowett · 2020-09-18T20:22:33Z

Sorry to take so long to review this!

miniksa

Excellent. Thank you, as always, James. I appreciate the choices you made here.

ghost · 2020-09-21T23:21:16Z

Hello @DHowett!

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This PR adds support for the _blink_ graphic rendition attribute. When a character is output with this attribute set, it "blinks" at a regular interval, by cycling its color between the normal rendition and a dimmer shade of that color. The majority of the blinking mechanism is encapsulated in a new `BlinkingState` class, which is shared between the Terminal and Conhost implementations. This class keeps track of the position in the blinking cycle, which determines whether characters are rendered as normal or faint. In Windows Terminal, the state is stored in the `Terminal` class, and in Conhost it's stored in the `CONSOLE_INFORMATION` class. In both cases, the `IsBlinkingFaint` method is used to determine the current blinking rendition, and that is passed on as a parameter to the `TextAttribute::CalculateRgbColors` method when these classes are looking up attribute colors. Prior to calculating the colors, the current attribute is also passed to the `RecordBlinkingUsage` method, which keeps track of whether there are actually any blink attributes in use. This is used to determine whether the screen needs to be refreshed when the blinking cycle toggles between the normal and faint renditions. The refresh itself is handled by the `ToggleBlinkingRendition` method, which is triggered by a timer. In Conhost this is just piggybacking on the existing cursor blink timer, but in Windows Terminal it needs to have its own separate timer, since the cursor timer is reset whenever a key is pressed, which is not something we want for attribute blinking. Although the `ToggleBlinkingRendition` is called at the same rate as the cursor blinking, we actually only want the cells to blink at half that frequency. We thus have a counter that cycles through four phases, and blinking is rendered as faint for two of those four. Then every two cycles - when the state changes - a redraw is triggered, but only if there are actually blinking attributes in use (as previously recorded). As mentioned earlier, the blinking frequency is based on the cursor blink rate, so that means it'll automatically be disabled if a user has set their cursor blink rate to none. It can also be disabled by turning off the _Show animations in Windows_ option. In Conhost these settings take effect immediately, but in Windows Terminal they only apply when a new tab is opened. This PR also adds partial support for the `SGR 6` _rapid blink_ attribute. This is not used by DEC terminals, but was defined in the ECMA/ANSI standards. It's not widely supported, but many terminals just it implement it as an alias for the regular `SGR 5` blink attribute, so that's what I've done here too. ## Validation Steps Performed I've checked the _Graphic rendition test pattern_ in Vttest, and compared our representation of the blink attribute to that of an actual DEC VT220 terminal as seen on [YouTube]. With the right color scheme it's a reasonably close match. [YouTube]: https://www.youtube.com/watch?v=03Pz5AmxbE4&t=1m55s Closes #7388 (cherry picked from commit d1671a0)

ghost · 2020-09-22T16:01:36Z

🎉Windows Terminal Preview v1.4.2652.0 has been released which incorporates this pull request.:tada:

Handy links:

ghost added Area-VT Virtual Terminal sequence support Issue-Task It's a feature request, but it doesn't really need a major design. Product-Conhost For issues in the Console codebase Product-Terminal The new Windows Terminal. labels Aug 31, 2020

skyline75489 reviewed Sep 1, 2020

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src/host/settings.hpp Outdated Show resolved Hide resolved

PankajBhojwani reviewed Sep 1, 2020

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src/renderer/base/BlinkingState.cpp Show resolved Hide resolved

skyline75489 reviewed Sep 2, 2020

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src/cascadia/TerminalControl/TermControl.cpp Show resolved Hide resolved

DHowett requested a review from miniksa September 11, 2020 00:55

j4james added 8 commits September 17, 2020 21:43

Extend the CalculateRgbColors method to support the rendering of blin…

8a089e0

…king attributes as faint.

Add a class to track the blinking state determining whether and when …

a1aba2c

…to redraw the screen.

Add the blinking functionality to the conhost renderer.

eb3c886

Add the blinking functionality to the Terminal renderer.

71a9113

Interpret the rapid blink attribute as an alias of blink.

42b291e

Disable blinking when SPI_GETCLIENTAREAANIMATION is false.

232c12a

Appease the spell-check bot.

b7c2d8f

Move the conhost blinking state from Settings to CONSOLE_INFORMATION.

a3f25a4

j4james force-pushed the feature-sgr-blink branch from 2a48218 to a3f25a4 Compare September 17, 2020 22:04

DHowett approved these changes Sep 18, 2020

View reviewed changes

Use the appropriate TRUE value for BOOL variables and fix typo.

b2cb13a

miniksa approved these changes Sep 21, 2020

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DHowett added the AutoMerge Marked for automatic merge by the bot when requirements are met label Sep 21, 2020

ghost merged commit d1671a0 into microsoft:master Sep 21, 2020

ghost mentioned this pull request Sep 22, 2020

Add support for the "blink" graphic rendition attribute #7388

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j4james deleted the feature-sgr-blink branch October 15, 2020 20:57

liudonghua123 mentioned this pull request Jun 7, 2023

why the output of curl has some blink effects while web version does not have. chubin/wttr.in#887

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Add support for the "blink" graphic rendition attribute #7490

Add support for the "blink" graphic rendition attribute #7490

j4james commented Aug 31, 2020 •

edited by DHowett

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ghost commented Sep 22, 2020

Add support for the "blink" graphic rendition attribute #7490

Add support for the "blink" graphic rendition attribute #7490

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j4james commented Aug 31, 2020 • edited by DHowett Loading

Validation Steps Performed

j4james commented Sep 1, 2020

PankajBhojwani commented Sep 1, 2020

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skyline75489 commented Sep 2, 2020

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ghost commented Sep 22, 2020

j4james commented Aug 31, 2020 •

edited by DHowett

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