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[PR #7490] Add support for the "blink" graphic rendition attribute #26935

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opened 2026-01-31 09:18:59 +00:00 by claunia · 0 comments
claunia commented 2026-01-31 09:18:59 +00:00
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Original Pull Request: https://github.com/microsoft/terminal/pull/7490

State: closed
Merged: Yes

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

**Original Pull Request:** https://github.com/microsoft/terminal/pull/7490 **State:** closed **Merged:** Yes --- 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
claunia added the pull-request label 2026-01-31 09:18:59 +00:00
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Reference: starred/terminal#26935
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