joinstyle

joinStyle is a parameter used in computer graphics and vector‑drawing APIs to define how two line segments are rendered where they meet. It determines the shape of the junction, influencing both visual appearance and the extent of the painted area. Commonly supported joinStyle values are miter, round, and bevel. A miter join extends the outer edges of the strokes until they intersect, producing a sharp corner; it is often limited by a miter‑limit ratio to prevent excessively long spikes. A round join creates a circular arc that smoothly connects the segments, yielding a softer corner. A bevel join truncates the corner with a straight line, forming a flattened diagonal.

joinStyle is specified in many graphics libraries. In Java’s java.awt.BasicStroke, the constructor accepts an integer constant such as BasicStroke.JOIN_MITER, JOIN_ROUND, or JOIN_BEVEL. In SVG, the analogous attribute is stroke-linejoin, and in CSS it can be set with border‑join (though support varies). PDF graphics operators also include a join parameter as part of the graphics state.

Choosing a joinStyle affects the perceived thickness and continuity of stroked paths, especially at acute angles. Designers may select round joins for a more organic look, bevel joins for a clean, angular style, or miter joins for precise corners where space permits. The default join style in most implementations is miter, often with a default miter‑limit of 10. Adjusting the joinStyle alongside line‑cap styles and stroke width allows fine control over the aesthetic of vector outlines.