Rasterposition

Rasterposition, usually written as two words, refers to a specific position on the output device (the window or frame buffer) that serves as the origin for raster operations. In graphics APIs such as OpenGL, it is the position at which subsequent raster-based rendering—such as bitmaps or pixel blocks—begins.

In OpenGL, the raster position is defined by glRasterPos* calls. The coordinates you provide are transformed by the current modelview and projection matrices, then by the viewport transform, to produce a window-space position. The raster position also carries the current raster attributes, including color, depth, and texture coordinates, effectively behaving like a special vertex for raster operations. If the transformed position has a non-positive w value (or yields NaN or infinite values), the raster position becomes invalid and raster operations will be ignored until a new valid position is specified.

Validity and behavior are important: a valid raster position allows commands such as glBitmap and glDrawPixels to render starting at that position, with the initial horizontal position typically advancing according to the operation’s size. Because the position is projection-dependent, changes to the projection or modelview matrices can render a previously valid raster position invalid.

Extensions and alternatives: some systems provide a window-space variant, such as glWindowPos* (via GL_ARB_window_pos and related extensions), which sets the position directly in window coordinates without performing the usual transformation pipeline.

See also: glDrawPixels, glBitmap, glRasterPos, glWindowPos.