notcurses_render(3)

NAME
notcurses_render - sync the physical display to a virtual pile

SYNOPSIS
#include <notcurses/notcurses.h>

int ncpile_render(struct ncplane* n);

int ncpile_rasterize(struct ncplane* n);

int notcurses_render(struct notcurses* nc);

char* notcurses_at_yx(struct notcurses* nc, unsigned yoff, unsigned xoff, uint16_t* styles, uint64_t* channels);

int ncpile_render_to_file(struct ncplane* p, FILE* fp);

int ncpile_render_to_buffer(struct ncplane* p, char** buf, size_t* buflen);

DESCRIPTION
Rendering reduces a pile of ncplanes to a single plane, proceeding from the top to the bottom along a pile's z-axis. The result is a matrix of nccells (see notcurses_cell). Rasterizing takes this matrix, together with the current state of the visual area, and produces a stream of optimized control sequences and EGCs for the terminal. By writing this stream to the terminal, the physical display is synced to some pile's planes.

ncpile_render performs the first of these tasks for the pile of which n is a part. The output is maintained internally; calling ncpile_render again on the same pile will replace this state with a fresh render. Multiple piles can be concurrently rendered. ncpile_rasterize performs rasterization, and writes the result to the terminal. It is a blocking call, and only one rasterization operation may proceed at a time. notcurses_render calls ncpile_render and ncpile_rasterize on the standard plane, for backwards compatibility. It is an exclusive blocking call.

It is necessary to call ncpile_rasterize or 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)), and screen geometry is refreshed (similarly to notcurses_refresh(3)) following the render.

While notcurses_render is called, you must not call any other functions modifying the same pile. Other piles may be freely accessed and modified. The pile being rendered may be accessed, but not modified.

ncpile_render_to_buffer performs the render and raster processes of ncpile_render and ncpile_rasterize, but does not write the resulting buffer to the terminal. The user is responsible for writing the buffer to the terminal in its entirety. If there is an error, subsequent frames will be out of sync, and notcurses_refresh(3) must be called.

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). 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.

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 NCALPHA_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 NCALPHA_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.

notcurses_at_yx retrieves a cell as rendered. The EGC in that cell is copied and returned; it must be free(3)d by the caller. If the cell is a secondary column of a wide glyph, the glyph is still returned.

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.

notcurses_at_yx returns a heap-allocated copy of the cell's EGC on success, and NULL on failure.

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_input(3), notcurses_output(3), notcurses_plane(3), notcurses_refresh(3), notcurses_stats(3), notcurses_visual(3), console_codes(4), utf-8(7)

AUTHORS
nick black nickblack@linux.com