Grease Pencil eraser acts as though full pressure was applied when tablet stylus is released #108573

New Issue

henryb · 2023-06-04T08:21:54+02:00

henryb commented

2023-06-04 08:21:54 +02:00

System Information
Graphics card: GTX 980
Reproduced on these operating systems:

Windows 10
Arch Linux 6.3.1 (KDE Plasma 5.27)

Reproduced using these drawing tablets:

HUION H610PRO V2
HUION Q11K

Blender Version
Broken: Reproduced in 3.5.1 and 4.0 (locally compiled 7372b3bdda)
Worked: Before 74f291cdea (2016-01-11)

Short description of error
Erasing lightly with a pressure-sensitive tablet is made difficult by a bug that erases a large area (as if the stylus was pressed down with maximum pressure) whenever the stylus is released:

This is the code that introduced this issue (added in 74f291cdea for #47101)
Removing it completely resolves this issue:

  /* Hack for pressure sensitive eraser on D+RMB when using a tablet:
   * The pen has to float over the tablet surface, resulting in
   * zero pressure (#47101). Ignore pressure values if floating
   * (i.e. "effectively zero" pressure), and only when the "active"
   * end is the stylus (i.e. the default when not eraser)
   */
  if (p->paintmode == GP_PAINTMODE_ERASER) {
    if ((event->tablet.active != EVT_TABLET_ERASER) && (p->pressure < 0.001f)) {
      p->pressure = 1.0f;
    }
  }

A sample of what I observed by logging pen pressure events while reproducing the issue:

tablet.active: 1, p->pressure: 0.399948
tablet.active: 1, p->pressure: 0.326324
tablet.active: 1, p->pressure: 0.246231
tablet.active: 1, p->pressure: 0.168350
tablet.active: 1, p->pressure: 0.097900
tablet.active: 1, p->pressure: 0.038330
tablet.active: 1, p->pressure: 0.000000

When I release my stylus, an event of type EVT_TABLET_STYLUS (1) with a pressure value at (or very close to) 0.0f is sent. This triggers the above conditional that sets p->pressure to 1.0f (full pressure), causing the issue.

Exact steps for others to reproduce the error
In the attached .blend file:
Using a pressure sensitive drawing tablet, lightly use the Grease Pencil eraser tool to erase the strokes, then release your stylus.
(If your drawing tablet sends an event with a pressure value lighter than 0.001, the issue will occur)

Question: Is #47101 still relevant and applicable?

I'm not sure I fully understand the use-case that was effected by #47101 or whether it is even still applicable to Blender today, 8 years later.
If someone can shed some light on what the intended behavior of 74f291cdea is and whether it is still needed, I will happily work on a pull request to reconcile this issue (or simply remove the conditional if it is no longer applicable)

**System Information** Graphics card: GTX 980 Reproduced on these operating systems: - Windows 10 - Arch Linux 6.3.1 (KDE Plasma 5.27) Reproduced using these drawing tablets: - HUION H610PRO V2 - HUION Q11K **Blender Version** Broken: Reproduced in 3.5.1 and 4.0 (locally compiled 7372b3bdda350) Worked: Before 74f291cdea979 (2016-01-11) **Short description of error** Erasing lightly with a pressure-sensitive tablet is made difficult by a bug that erases a large area (as if the stylus was pressed down with maximum pressure) whenever the stylus is released: <video src="/attachments/f4ae6259-0b87-4069-8365-3fcd49d52203" title="pen_pressure_release_bug.mp4" controls></video> This is the code that introduced this issue (added in 74f291cdea979 for #47101) Removing it completely resolves this issue: ```cpp /* Hack for pressure sensitive eraser on D+RMB when using a tablet: * The pen has to float over the tablet surface, resulting in * zero pressure (#47101). Ignore pressure values if floating * (i.e. "effectively zero" pressure), and only when the "active" * end is the stylus (i.e. the default when not eraser) */ if (p->paintmode == GP_PAINTMODE_ERASER) { if ((event->tablet.active != EVT_TABLET_ERASER) && (p->pressure < 0.001f)) { p->pressure = 1.0f; } } ``` A sample of what I observed by logging pen pressure events while reproducing the issue: ``` tablet.active: 1, p->pressure: 0.399948 tablet.active: 1, p->pressure: 0.326324 tablet.active: 1, p->pressure: 0.246231 tablet.active: 1, p->pressure: 0.168350 tablet.active: 1, p->pressure: 0.097900 tablet.active: 1, p->pressure: 0.038330 tablet.active: 1, p->pressure: 0.000000 ``` When I **release** my stylus, an event of type `EVT_TABLET_STYLUS` (`1`) with a pressure value at (or very close to) `0.0f` is sent. This triggers the above conditional that sets `p->pressure` to `1.0f` (full pressure), causing the issue. **Exact steps for others to reproduce the error** In the attached .blend file: Using a pressure sensitive drawing tablet, lightly use the Grease Pencil eraser tool to erase the strokes, then release your stylus. (If your drawing tablet sends an event with a pressure value lighter than `0.001`, the issue will occur) ## Question: Is #47101 still relevant and applicable? I'm not sure I fully understand the use-case that was effected by #47101 or whether it is even still applicable to Blender today, 8 years later. If someone can shed some light on what the intended behavior of 74f291cdea979 is and whether it is still needed, I will happily work on a pull request to reconcile this issue (or simply remove the conditional if it is no longer applicable)

pen_pressure_release_bug.mp4

927 KiB

pen_pressure_release_bug.blend

1.0 MiB

henryb added the

labels 2023-06-04 08:21:55 +02:00