Drawspan

Drawspan is a low-level graphics primitive used in rasterization to render a horizontal sequence of pixels on a single scan line. A span is defined by a fixed y coordinate and a start and end x coordinate, typically inclusive. In software renderers and some GPU pipelines designed around scanline filling, drawspan is the operation that paints the pixels within [x_min, x_max] on row y with a given color, shade, or texture.

A drawspan may carry additional attributes such as alpha, depth, or texture coordinates. It is often issued after clipping against the viewport and, in three-dimensional rendering, possibly after depth testing or masking. In polygon filling, the rasterizer computes edge intersections to generate spans between consecutive edge pairs and then issues drawspan calls to fill those spans. For sprites and textured blits, a span may be drawn with per-pixel texture mapping or shading; implementations optimize through bulk memory writes and by skipping spans outside the clipped region.

Variants include colored spans (solid color), shaded spans (color interpolation across the span), and textured spans (texture mapping along the span). Some graphics APIs expose a drawspan operation as part of a software renderer’s API, while GPU pipelines implement similar functionality through rasterization stages that produce fragments written to the framebuffer.

See also: scanline rasterization, polygon fill, rasterization, spans, framebuffer, z-buffer, alpha blending.