% notcurses_render(3) % nick black % v1.1.0 # NAME notcurses_render - sync the physical display to the virtual ncplanes # SYNOPSIS **#include ** **int notcurses_render(struct notcurses* nc);** **char* notcurses_at_yx(struct notcurses* nc, int yoff, int xoff, cell* c);** # DESCRIPTION **notcurses_render** syncs the physical display to the context's prepared ncplanes. It is necessary to call **notcurses_render** to generate any visible output; the various notcurses_output(3) calls only draw to the virtual ncplanes. Most of the notcurses statistics are updated as a result of a render (see notcurses_stats(3)). A render operation consists of two logical phases: generation of the rendered scene, and blitting this scene to the terminal (these two phases might actually be interleaved, streaming the output as it is rendered). All ncplanes are locked while generating the frame. Frame generation requires determining an extended grapheme cluster, foreground color, background color, and style for each cell of the physical terminal. Writing the scene requires synthesizing a set of UTF-8-encoded characters and escape codes appropriate for the terminal (relying on terminfo(5)), and writing this sequence to the output **FILE**. If the **renderfp** value was not NULL in the original call to notcurses_init(3), the frame will be written to that **FILE** as well. This write does not affect statistics. Each cell can be rendered in isolation, though synthesis of the stream carries dependencies between cells. ## Cell rendering algorithm Recall that there is a total ordering on the N ncplanes, and that the standard plane always exists, with geometry equal to the physical screen. Each cell of the physical screen is thus intersected by some totally ordered subset of planes **P0**, **P1**...**Pi**, where 0 < **i** ≤ **N**. At each cell, rendering starts at the topmost intersecting plane **P0**. The algorithm descends until either: * it has locked in an extended grapheme cluster, and fore/background colors, or * all **i** planes have been examined At each plane **P**, we consider a cell **C**. This cell is the intersecting cell, unless that cell has no EGC. In that case, **C** is the plane's default cell. * If we have not yet determined an EGC, and **C** has a non-zero EGC, use the EGC and style of **C**. * If we have not yet locked in a foreground color, and **C** is not foreground-transparent, use the foreground color of **C** (see [BUGS][] below). If **C** is **CELL_ALPHA_OPAQUE**, lock the color in. * If we have not yet locked in a background color, and **C** is not background-transparent, use the background color of **C** (see [BUGS][] below). If **C** is **CELL_ALPHA_OPAQUE**, lock the color in. If the algorithm concludes without an EGC, the cell is rendered with no glyph and a default background. If the algorithm concludes without a color locked in, the color as computed thus far is used. # RETURN VALUES On success, 0 is returned. On failure, a non-zero value is returned. A success will result in the **renders** stat being increased by 1. A failure will result in the **failed_renders** stat being increased by 1. # BUGS In addition to the RGB colors, it is possible to use the "default foreground color" and "default background color" inherited from the terminal. Since notcurses doesn't know what these colors are, they are not considered for purposes of color blending. # SEE ALSO **notcurses(3)**, **notcurses_cell(3)**, **notcurses_ncplane(3)**, **notcurses_output(3)**, **notcurses_stats(3)**, **console_codes(4)**, **utf-8(7)**