Implement Software Cursors

Kazekai · February 10, 2016, 2:02am

I’ve noticed some brushes will stop resizing if you make the brush too big, Is there a way to make the cursor track the brush size no matter how big it gets? It’s hard to tell how big my strokes are until I place them.

achadwick · February 10, 2016, 4:30pm

You’re seeing a hard limit there: our existing “hardware” cursors can only get so big, and we use those because they’re the fastest kind. These are the cursors used almost everywhere else, and they’re faster because they’re stored as a little texture in the GPU, no need to redraw as you move.

It may be time for a change to more flexible “software” cursors, though they’ll be laggy compared to the real deal. Perhaps a hybrid approach, with hardware small-circles . o O but a combination hardware mini-crosshair and software big-circle ( + ) would work OK?

github.com/mypaint/mypaint

Implement Software Cursors

opened 04:05PM - 30 Oct 15 UTC

achadwick

type.Enhancement cat.UX cat.UI

A common complaint from users is that the freehand cursor size doesn't grow beyo…nd a certain size. That's because there's a hardware-determined upper limit to its diameter, normally 64, 128 or 256 pixels. There is also a hardware bug present on some systems that disrupts the (software-controlled) hardware cursor: #166. It would be good if MyPaint could go with a simple, small hardware cursor for locating the cursor in freehand mode - perhaps the existing crosshair one - with a circle showing the brush radius rendered directly to the canvas under it. In the past, I've attempted to make something like this as a _complete_ replacement for the existing cursor, but the result is laggy and generally feels unresponsive. Perhaps a combination of approaches would be best? I note that GIMP does something very similar. Other open cursor-related issues that would be helped or made closable addressing this, or which would need looking at as a consequence: #355, #449, #421, #357, #311 (!), #83, #384.

Kazekai · February 10, 2016, 11:19pm

I dunno, I’m not too knowledgeable to the technical stuff, I just know that the other programs I’ve used in the past did with little issue and they didn’t lag for me, but the cursor problem is pretty common in open-source software for some reason, I guess because everyone pools their knowledge.

It isn’t really a big deal or anything if major changes have to be made for it, I just found it a bit strange because I’m coming off commercial software. I can probably adapt to it with practice.

bleke · April 10, 2016, 10:52pm

Could we have an outline of the brush shape in the cursor? Or at least a line showing the angle of the brush?

See also my request here http://community.mypaint.org/t/flat-brush/285 about easily change the brush rotation.

calsioro · April 23, 2016, 11:34pm

Just a thought:
Maybe doing a switch from soft to hard cursor when you start drawing would solve a possible lag, if there’s any (maybe it’s just premature optimization?).

That way you have feedback from the cursor when not drawing, and from the effect when drawing.

achadwick · April 27, 2016, 11:37am

Yeah, that’s a possibility. Some mini-ring that reflects the tilt maybe? So let’s talk UX for this. Here’s the back-and-forth in my head…

Let’s say the user is zoomed all the way in and using a huge brush
They’re gonna want to see where their cursor is centred.
- Perhaps the outline ring will be bigger than their screen.
- So maybe the ring is software and they get a little + cursor to show the centre?
That little hardware “+” might be hidden if it’s bigger than the ring though
- Or replaced with a hardware cursor ring? We’re taking about 32 or 48 pixels here, hardware issues won’t really apply.
It’ll update quickly even if the ring lags.
- Eyes focus on centres of things when doing. Ppl have real tunnel vision!
- But where you’re not focused, you spot motion better. Blame our evolution for this. There might be a leopard lurking where you’re not looking directly!
- Perhaps the inevitable software/hardware lag won’t be that disturbing if artists are fixating on the middle “+”. It’s worth testing.
Some users are very particular about the look of the drawing cursor.
Need to keep redraws minimal to avoid lag.
Is there a good algorithm for deciding what tiles need redraws based on a ring shape (probably an elliptical one, angled for tilt)
The rendering cache we already have will help a lot during these redraws.

While the stylus is in contact with the drawing surface, do we need the same level of visual cursor feedback as when the stylus is hovering? I think a lot of the feedback here is provided by the brushstroke itself rendering. We could diminish the cursor to just the “+”, just a maximum-sized hardware ring-and-“+”, or nothing at all.

bleke · April 27, 2016, 12:21pm

For me personally, the cursor is mostly important so that I can see where to begin the stroke.

It can be useful during the stroke too, when the stroke lags behind the stylus. Some sort of indicator would be sufficient for that.

Perhaps we could have a hardware ring as long as the brush size is within the maximum sized ring. If the brush is larger, then use a + with no ring.

calsioro · April 27, 2016, 10:42pm

Ok, that seems hard…
Related: intersection - Ellipsoid v. Box collision detection - Game Development Stack Exchange
It’s about ellipse-rectangle collision detection, but the interesting idea is to apply an inverse matrix transform to everything, making the ellipse transform into a circle, and the rectangles become quadrilaterals.
That way you could check if all 4 points are either inside or outside the circle, which is just distance from the center (all that after filtering by bounding box or whatever).

I don’t see this as a deal breaker, just a minor inconvenience.