Clipping seems not working with `gmt text -G+n` when text position is assigned using `-F+c[justify]`

[mkononets]

Clipping seems not working with gmt text -G+n when text position is assigned using -F+c[justify]

gmt begin text-clipping png
  gmt plot -T -R0/1/0/1 -JX5c
  gmt text -F+f10p,Helvetica+cMC+jMC+t'Test text' -G+n -C20%+tO -N
  gmt basemap -BWStr -Bxafg -Byafg
  gmt clip -C
  gmt text -F+f10p,Helvetica+cMC+jMC+t'Test text' -Gred@90 -C20%+tO
gmt end show

Providing coordinates on the input enables clipping, that is, the gridlines behind the text label got clipped, see below.

gmt begin text-clipping png
  gmt plot -T -R0/1/0/1 -JX5c
  echo 0.5 0.5 | gmt text -F+f10p,Helvetica+jMC+t'Test text' -G+n -C20%+tO -N
  gmt basemap -BWStr -Bxafg -Byafg
  gmt clip -C
  gmt text -F+f10p,Helvetica+cMC+jMC+t'Test text' -Gred@90 -C20%+tO
gmt end show

gmt 6.6.0 on linux, same with versions 6.5.0 and 6.3.0 FWIW.

[anbj]

(It looks like the link to 'clip -C' (https://docs.generic-mapping-tools.org/dev/text.html#g) refers to the wrong -C (text module); it's supposed to link to -C in the clip module I think.)

[joa-quim]

By Claude's

● Now it's clear.

  Issue #8929: Root Cause

  The bug is in pstext.c, in the Ctrl->F.no_input early-return branch (lines 911-986).

  What happens

  When using -F+cMC+t'Test text' (text and position fully specified on the command line, no input data), the code enters the no_input branch at line 911.
  This branch:

  1. Computes the position from +cMC (line 923)
  2. Plots the text box and/or text directly (lines 955-977)
  3. Returns at line 986

  The problem: this branch completely ignores Ctrl->G.mode. It never collects the text into the c_x/c_y/c_txt/c_angle/c_just/c_font arrays, and never
  calls PSL_plottextline() with PSL_TXT_CLIP_ON to activate the clipping path.

  Why the workaround works

  When coordinates are piped in (echo 0.5 0.5 | gmt text -F+jMC+t'Test text' -G+n ...), the code takes the main loop path (lines 1059-1443) instead. In
  that path, when Ctrl->G.mode is set (line 1422), text info is collected into arrays, and after the loop ends, PSL_plottextline() is called at line 1495
  with PSL_TXT_CLIP_ON to properly set up the clipping path.

  The fix

  The no_input branch (lines 911-986) needs to handle Ctrl->G.mode. Instead of directly plotting and returning, when Ctrl->G.mode is set it should:
  1. Collect the text info into the clipping arrays (like lines 1422-1435 do)
  2. Call PSL_plottextline() with PSL_TXT_CLIP_ON (like lines 1466-1495 do)

  Or more simply, the no_input path could be refactored to feed into the same clipping logic that the main path uses.