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index.md (3891B) |
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1 Synchronized rendering |
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2 ====================== |
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3 |
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4 Summary |
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5 ------- |
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6 Better draw timing to reduce flicker/tearing and improve animation smoot… |
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7 |
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8 Background |
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9 ---------- |
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10 |
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11 Terminals have to guess when to draw and refresh the screen. This is bec… |
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12 the terminal doesn't know whether the application has completed a "batch… |
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13 output, or whether it's about to have more output right after the refres… |
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14 |
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15 This means that sometimes the terminal draws before the application has |
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16 completed an output "batch", and usually this results in flicker or tear… |
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17 |
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18 In st, the parameters which control the timing are `xfps` and `actionfps… |
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19 `xfps` determines how long st waits before drawing after interactive X e… |
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20 (KB/mouse), and `actionfps` determines the draw frequency for output whi… |
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21 doesn't follow X events - i.e. unattended output - e.g. during animation. |
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22 |
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23 |
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24 Part 1: auto-sync |
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25 ----------------- |
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26 |
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27 *NOTE*: this patch (part 1) is not required if you use st-master. It was |
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28 merged upsream on 2020-05-10 and will be included in the next release. |
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29 |
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30 This patch replaces the timing algorithm and uses a range instead of fix… |
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31 timing values. The range gives it the flexibility to choose when to draw… |
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32 it tries to draw once an output "batch" is complete, i.e. when there's s… |
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33 idle period where no new output arrived. Typically this eliminates flick… |
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34 tearing almost completely. |
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35 |
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36 The range is defined with the new configuration values `minlatency` and |
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37 `maxlatency` (which replace xfps/actionfps), and you should ensure they'… |
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38 your `config.h` file. |
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39 |
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40 This range has equal effect for both X events and unattended output; it … |
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41 care what the trigger was, and only cares when idle arrives. Interactive… |
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42 usually arrives very quickly so latency is near `minlatency`, while for |
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43 animation it might take longer until the application completes its outpu… |
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44 `maxlatency` is almost never reached, except e.g. during `cat huge.txt` … |
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45 idle never happens until the whole file was printed. |
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46 |
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47 Note that the interactive timing (mouse/KB) was fine before this patch, … |
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48 main improvement is for animation e.g. `mpv --vo=tct`, `cava`, terminal … |
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49 etc, but interactive timing also benefits from this flexibility. |
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50 |
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51 Part 2: application-sync |
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52 ------------------------ |
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53 |
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54 The problem of draw timing is not unique to st. All terminals have to de… |
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55 with it, and a new suggested standard tries to solve it. It's called |
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56 "Synchronized Updates" and it allows the application to tell the termina… |
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57 the output "batch" is complete so that the terminal knows not to draw pa… |
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58 output - hence "application sync". |
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59 |
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60 The suggestion - by iTerm2 author - is available here: |
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61 https://gitlab.com/gnachman/iterm2/-/wikis/synchronized-updates-spec |
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62 |
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63 This patch adds synchronized-updates/application-sync support in st. It |
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64 requires the auto-sync patch above installed first. This patch has no ef… |
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65 except when an application uses the synchronized-update escape sequences. |
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66 |
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67 Note that currently there are very few terminals or applications which s… |
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68 it, but one application which does support it is `tmux` since 2020-04-18… |
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69 this patch nearly all cursor flicker is eliminated in tmux, and tmux det… |
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70 it automatically via terminfo and enables it when st is installed correc… |
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71 |
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72 |
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73 Download |
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74 -------- |
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75 Part 1 is independent, but part 2 needs part 1 first. Both files are git |
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76 patches and can be applied with either `git am` or with `patch`. Both fi… |
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77 add values at `config.def.h`, and part 2 also updates `st.info`. |
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78 |
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79 * Part 1 (merged upstream): [st-autosync-0.8.3.diff](st-autosync-0.8.3.d… |
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80 * Part 2 (st 0.8.3): [st-appsync-0.8.3.diff](st-appsync-0.8.3.diff) |
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81 * Part 2 (st master 2020-06-17 or later): |
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82 [st-appsync-20200618-b27a383.diff](st-appsync-20200618-b27a383.diff) |
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83 |
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84 |
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85 Author |
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86 ------ |
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87 * Avi Halachmi (:avih) - [https://github.com/avih](https://github.com/av… |
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88 Contact email is available inside the patch files. |
