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print_img: correct off-center print area via per-device pin_offset

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On the PT-P900W the print area is not centered on the 560-pin printhead:
its center sits at pin 272 rather than the head center (pin 280), a fixed
8-pin offset that is constant across all tape widths. Centering the raster
data on the head therefore prints ~0.5mm off-center (measured as a constant
~1mm margin delta across 12/18/36mm tapes, confirmed against the spec).

Add a pin_offset field to _pt_dev_info (0 = centered, the default for all
existing printers) and apply it in print_img. Set it to -8 for the
PT-P900Wc, which reproduces the spec left-margin exactly for every tape
width ((560-print_area)/2 - 8 = documented left margin).

Reference: Brother "Software Developer's Manual - Raster Command Reference,
PT-P900/P900W/P950NW", section 2.3.5 "Raster line" (per-tape left/right
margin and print-area pin counts for the 560-pin head).
https://download.brother.com/welcome/docp100407/cv_ptp900_eng_raster_102.pdf
This commit is contained in:
Tobias Klausmann
2026-07-18 08:01:24 +02:00
committed by Dominic Radermacher
parent 9af6276135
commit 921206cd5f
3 changed files with 19 additions and 3 deletions
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include/ptouch.h
+5
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@@ -57,6 +57,11 @@ struct _pt_dev_info {
int dpi; /* Dots per inch of the printhead */
//size_t bytes_per_line;
int flags;
/* Pins to shift the print area from the centre of the printhead.
On some models the print area is not centred on the head; see the
Brother "Software Developer's Manual - Raster Command Reference,
PT-P900/P900W/P950NW", section 2.3.5 "Raster line". 0 = centred. */
int pin_offset;
};
typedef struct _pt_dev_info *pt_dev_info;