nvgArc does some ugly overdraw

[mulle-nat]

I suspect, that when the area to fill gets less than a pixel, something goes awry at the very top of the circle hole:

In this special case, it can be mitigated with nvgIntersectScissor.

For reference this is how it's drawn (it uses a few "UIKit"isms, that should be easy to understand)

void drawSplitRectWithHole(NVGcontext* vg, CGRect rect, CGFloat x, CGFloat radius)
{
    CGFloat y = CGRectGetMidY( rect);
    CGFloat angle = asinf( rect.size.height / (2 * radius));

    nvgSave( vg);
    //nvgIntersectScissor( vg, rect.origin.x, rect.origin.y, rect.size.width, rect.size.height);

    // Draw the left part
    nvgBeginPath(vg);
    nvgMoveTo(vg, CGRectGetMinX( rect), CGRectGetMinY( rect));
    nvgLineTo(vg, x - radius * cosf(angle), CGRectGetMinY( rect));
    nvgArc(vg, x, y, radius, M_PI_f + angle, M_PI_f - angle, NVG_CCW);
    nvgLineTo(vg, CGRectGetMinX( rect), CGRectGetMaxY( rect));
    nvgClosePath(vg);
    nvgFillColor( vg, CGColorMakeIndigo());
    nvgFill(vg);

    // Draw the right part 
    nvgBeginPath(vg);
    nvgMoveTo(vg, x + radius * cosf(angle), CGRectGetMinY( rect));
    nvgLineTo(vg, CGRectGetMaxX( rect), CGRectGetMinY( rect));
    nvgLineTo(vg, CGRectGetMaxX( rect), CGRectGetMaxY( rect));
    nvgLineTo(vg, x + radius * cosf(angle), CGRectGetMaxY( rect));
    nvgArc(vg, x, y, radius, angle, -angle, NVG_CCW);
    nvgClosePath(vg);
    nvgFillColor( vg, CGColorMakeOrange());
    nvgFill(vg);

    nvgRestore( vg);
}

[memononen]

This is unfortunately due to the antialiasing algorithm used by nanovg.

An alternative is to use MSAA, one of the examples shows how to set that up.

[mulle-nat]

Thanks, I wasn't aware that I could use MSAA to replace nanovg edge antialiasing. I am trying to use MSAA (4) as the default now and EdgeAntialiasing as a fallback option.

It seems though, that there is more to do than just adding glfwWindowHint( GLFW_SAMPLES, 4). For example at my current understanding (being mostly this stackoverflow.) nvgluCreateFramebuffer doesn't seem to be coded to be MSAA aware. I am also not sure how this will pertain to textures, so I have no real feel for how much more work this will be.

Just to get a better understanding of things:

• Is the anti aliasing algorithm used by nanovg "fixable" in any shape or form ?
• Would I expect that MSAA is available on major mobile and desktop platforms ?
• Does MSAA really take up 4 times the GPU memory for everything, it feels like this might get too expensive for mobile platforms.