Circles don't look sharp

[abique]

It feels to me that the painting could look better:

Using skia.

[Enyium]

That's right. Rounded Rectangle corners aren't antialiased well enough.

SlintPad example (change the circle's size via the handles in the corners).

To compare this with an SVG <circle>, visit https://developer.mozilla.org/en-US/docs/Web/SVG/Element/circle, click "Play" on the circle preview and paste the following JavaScript code to make the circle change its size together with your mouse position:

const svg = document.getElementsByTagName('svg')[0];
const circle = document.getElementsByTagName('circle')[0];

svg.addEventListener('mousemove', function(event) {
    const rect = svg.getBoundingClientRect();
    const viewBox = svg.viewBox.baseVal;
    
    const scaleX = viewBox.width / rect.width;
    const scaleY = viewBox.height / rect.height;

    const cx = parseFloat(circle.getAttribute('cx'));
    const cy = parseFloat(circle.getAttribute('cy'));
    
    const mouseX = (event.clientX - rect.left) * scaleX;
    const mouseY = (event.clientY - rect.top) * scaleY;

    const dx = mouseX - cx;
    const dy = mouseY - cy;

    const newRadius = Math.sqrt(dx * dx + dy * dy);
    circle.setAttribute('r', newRadius);
});

[tronical]

I'm having difficulties reproducing this with skia (as @abique originally tagged it as). Running @Enyium 's example with Skia on my desktop (note that Slintpad doesn't use Skia) I get this result:

That looks alright, doesn't it?

[tronical]

In contrast, this is the result with FemtoVG:

This isn't quite as nice as Skia, the quality of the anti-aliasing is not as good.

[tronical]

I'll re-tag this with femtovg as renderer tagged, instead of Skia.

For both renderers we explicitly enable anti-aliasing when drawing rounded rects, so I think if anything this ties to the renderer's anti-aliasing qualities in general.

[Enyium]

Yeah, I'm sorry, Skia renders the circle very well in a native Windows 10 window. I can't make out any quality differences to the SVG circle.

Even the software renderer seems on par with Skia in this regard.

FemtoVG circles have lower quality:

[tronical]

Thanks for confirming :)

[abique]

Did you try with non hi-dpi monitor?

[abique]

Try rendering to bitmap and compare with what cairo can do.

[abique]

I think skia can do a 4x oversampling right?