feat: Arc canvas

[Vinci10]

Description:

As per #856 issue

This PR adds a new canvas.Arc object to Fyne, enabling the drawing of filled arcs and annular sectors (ring segments) with optional stroke and rounded corners. The Arc object supports:

• Customizable fill color and stroke (color and width)
• Configurable inner radius (for rings/annular sectors)
• Start and end angles (in degrees, positive is counter-clockwise, negative is clockwise)
• Corner radius for rounded arc ends
• Full circle and partial arc rendering
• Public API with Since: 2.7 annotation

Use cases:

• Doughnut and Pie Charts
• Loading indicator
• Progress indicator

Examples:

Checklist:

• Tests included.
• Lint and formatter run with no errors.
• Tests all pass.

Where applicable:

• Public APIs match existing style and have Since: line.
• Any breaking changes have a deprecation path or have been discussed.
• Check for binary size increases when importing new modules.

Known limitations:

• macOS test failures (to be investigated) Done
• corner radius not implemented yet in software painter Done

[andydotxyz]

Thanks so much this is completely epic!

Just FYI I ran the Darwin test locally to show what is failing and here is a comparison of the draw vs expected:

One thought - if the curved corners are not supported in software this could be landed without them and that could be added later (if that's easier for you).

Thanks so much :)

[Vinci10]

Thank you for sharing failed data. I was able to fix macos unit tests.

[andydotxyz]

Thank you for sharing failed data. I was able to fix macos unit tests.

Thanks for this. Just one thing remains:

arc.CornerRadius = 0 // rounded corners are supported in gl painter but not yet in software painter

is this fixed, or should it land without CornerRadius initially?

[Vinci10]

It's not fixed. I can't figure out how to implement it properly.
If CornerRadius doesn't work in the software painter, does it only affect unit tests? If that's not a problem, it can be added later.

[dweymouth]

I'm not entirely sure whether any platform actually uses the software painter in "production", but nonetheless as Andy mentioned, we can land it without CornerRadius at all and implement it in a follow-up for all painters. Regardless of if the software painter is only used in tests, I don't think we want to introduce a known difference between the painters.

You can probably even leave the corner radius handling code in the GL painters, and just always set the uniform to 0 for now, and remove the public CornerRadius property from the Arc struct.

[andydotxyz]

I'm not entirely sure whether any platform actually uses the software painter in "production",

The new "noos"/tinygo/tamago addition will be using it in prod.
Plus other devs like those building for reMarkable will be using the software driver.

[Vinci10]

Thanks for update. I implemented rounded corners in software painter. Please check from your end whether the new canvas works fine and let me know if something should be fixed/changed.

[dweymouth]

It looks like this has merge conflicts, probably with #5884. They shouldn't be too hard to resolve though, that linked PR introduced a helper function for passing uniforms to GL where it avoids the GL call if the uniform is being set to the same value.

[coveralls]

coverage: 61.745% (-0.5%) from 62.216%
when pulling e46a6b9 on Vinci10:feature/arc_canvas
into 34b5b8b on fyne-io:develop.

[Vinci10]

Conflicts resolved. Now I see some check failing Coverage decreased (-0.5%) to 61.704%. Not sure how to fix it.

[andydotxyz]

Conflicts resolved. Now I see some check failing Coverage decreased (-0.5%) to 61.704%. Not sure how to fix it.

The only thing that stands out in the report is that markup_renderer does not have tests for the new arc.
(Yes it's a bit silly because it is then used everywhere - but the analysis is per-package I think)

[Vinci10]

Conflicts resolved. Now I see some check failing Coverage decreased (-0.5%) to 61.704%. Not sure how to fix it.

The only thing that stands out in the report is that markup_renderer does not have tests for the new arc. (Yes it's a bit silly because it is then used everywhere - but the analysis is per-package I think)

Oh ok. Right it is tested but in canvas_test package and not directly but via test.AssertObjectRendersToMarkup

[Vinci10]

The code I used to create the simple Doughnut and Pie Charts (may help during testing)

type Slice struct {
	Value float32
	Color color.Color
}

func NewPieChart(cornerRadius, innerRadius, pad, strokeWidth float32, varyInnerRadius bool, data []Slice) *fyne.Container {
	total := float32(0)
	for _, s := range data {
		total += s.Value
	}

	objects := make([]fyne.CanvasObject, len(data))
	start := float32(-90) // 0° = right; we start at top (-90°)

	for i, s := range data {
		angle := 360 * s.Value / total
		end := start + angle

		// vary inner radius per slice for visual effect
		inner := innerRadius
		if varyInnerRadius && innerRadius > 0 {
			variation := innerRadius * (0.8 + 0.4*float32(i%3)/2)
			inner = variation
		}

		arc := &canvas.Arc{
			InnerRadius:  inner,
			StartAngle:   start + pad,
			EndAngle:     end,
			FillColor:    s.Color,
			CornerRadius: cornerRadius,
			StrokeColor:  color.White,
			StrokeWidth:  strokeWidth,
		}
		objects[i] = arc
		start = end
	}

	return container.NewStack(objects...)
}

// -- And the simple charts --

// Pie chart data:
data := []Slice{
    {Value: 30, Color: color.NRGBA{R: 255, G: 99, B: 71, A: 255}},  // Tomato Red
    {Value: 20, Color: color.NRGBA{R: 50, G: 205, B: 50, A: 255}},  // Lime Green
    {Value: 25, Color: color.NRGBA{R: 255, G: 120, B: 0, A: 255}},  // Orange
    {Value: 15, Color: color.NRGBA{R: 255, G: 215, B: 0, A: 255}},  // Gold
    {Value: 10, Color: color.NRGBA{R: 138, G: 43, B: 226, A: 255}}, // Blue Violet
}

chart := NewPieChart(15, 80, 8, 0, true, data)
chart2 := NewPieChart(0, 0, 0, 0, false, data)
chart3 := NewPieChart(0, 90, 1, 0, false, data)
chart4 := NewPieChart(20, 80, 1, 2, true, data)

[andydotxyz]

Oh ok. Right it is tested but in canvas_test package and not directly but via test.AssertObjectRendersToMarkup

I'd say that is usage, not test - and the coveralls report is showing the same. See test/markup_renderer_test.go