Painting

A component can draw itself with a Painter and still take part in layout and styling.

Paint functions

Give a component paint(Painter&) instead of render. It lays out and styles like any other component, and the painter draws inside its resolved bounds.

struct Swatch {
    Color color;

    void paint(Painter& painter) const {
        const Rect b = painter.bounds();
        painter.rect(b, color, CornerRadius::all(6.f));
        painter.line({ b.x, b.y }, { b.x + b.width, b.y + b.height },
            1.f, Color::WHITE);
    }

private:
    friend StyleAccess;

    Styles m_styles { width = 48_px, height = 48_px };
};

The painter draws rectangles, lines, polygons, shadows, text and images.

Animation

Animation runs on frames. A Frame& parameter gives the current frame's time, and requesting another frame keeps the animation going:

struct Pulse {
    void paint(Painter& painter, Frame& frame) const {
        const auto t = 0.5 + 0.5 * std::sin(frame.time().seconds() * 3.0);
        painter.rect(Color::BLUE_VIOLET.set_a(static_cast<float>(t)));
        frame.request();
    }
};

When a component stops requesting frames, Barton stops redrawing until something changes.

Viewports

Embedded wgpu viewports are being built now. This section will cover them once they land.