public abstract class ScrollSurface

A painted component that scrolls on two axes, under an optional pinned header row and pinned header column.

A view that draws thousands of items itself – a calendar, a Gantt chart, a diagram – cannot afford a component per item, and so cannot use a scrollable Container. This class does for such a view what a scrollable container does for components: panning and the fling after it, the mouse wheel, pinch to zoom, auto scrolling while something is dragged near an edge, and telling a tap from a double tap, a drag and a long press. The view only says how big its content is and paints it.

class Sheet extends ScrollSurface {
    protected void layoutSurface(int width, int height) {
        setHeaderSize(80, 30);
    }
    protected int getContentWidth() { return 5000; }
    protected int getContentHeight() { return 20000; }
    protected void paintContent(Graphics g, int x, int y) {
        // the content's origin is at x, y; only the visible part is clipped in
    }
}

Regions

The component is divided into the content, which scrolls on both axes; the top header, which scrolls only horizontally with it; the left header, which scrolls only vertically; and the corner where the two meet, which does not scroll. Each is painted clipped to its own region. paintOverlay paints last, over all four. A view without headers leaves their size at zero.

Edits

A drag either pans or edits. When a drag or a long press begins, the surface asks editStarted whether it begins an edit, telling it what kind of gesture it is (EditTrigger). From then on the pointer goes to editMoved and, when it lifts, to editEnded. isDragEdits decides whether a plain drag may start an edit anywhere, which is the default where there is a mouse, or only on things made to be dragged (EditTrigger.HANDLE_DRAG), which leaves a finger free to pan.

Bounded and unbounded content

By default the scroll position stays inside the content. A surface whose content has no edges, such as an infinite canvas, turns that off with setBounded(false) and reads the moves through scrollChanged.