- API: add new zint_symbol dpmm field for output resolution (BMP/

EMF/PCX/PNG/TIF only, i.e. excluding EPS, GIF & SVG)
- Add support for specifying scale by X-dimension and resolution
  with new option `--scalexdimdp` for CLI/Tcl & new API function
  `ZBarcode_Scale_From_XdimDp()` (+ `ZBarcode_XdimDp_From_Scale()`
  & `ZBarcode_Default_Xdim()`) and new GUI popup; manual: document
- BMP/EMF/PCX/PNG/TIF: use new `dpmm` resolution field (for EMF
  following Inkscape)
- backend_qt: add `dpmm()`, `vectorWidth()`, `vectorHeight()`,
  `noPng()`, `getVersion()`, `takesGS1AIData()`, & `XdimDp` stuff
  incl. new `QZintXdimDp` struct for passing around scale vars &
  use in `getAsCLI()`; add comments
- Raise `scale` limit to 200 (from 100) to allow for large dpmm
- output: create directories & subdirectories as necessary for
  output path using new function `out_fopen()` and use in BMP/EMF/
  EPS/GIF/PCX/PNG/SVG/TIF
- DPLEIT/DPIDENT: format HRT according to (incomplete)
  documentation, and set default height to 72X (from 50X)
- CODE128B renamed to CODE128AB as can use subsets A and/or B
- CODABAR: fix minimum height calc
- EMF: fix indexing of handles (zero-based not 1-based)
- GUI: fix symbology zap (previous technique of clearing and
  re-loading settings without doing a sync no longer works);
  fix UPCEAN guard descent enable
- MAILMARK: better error message if input < 14 characters
- GUI: add "Default" button for DAFT tracker ratio & enable/disable
  various default buttons; use new `takesGS1AIData()` to
  enable/disable GS1-specific checkboxes
- CLI: use new `validate_float()` to parse float options (7
  significant digits allowed only, no scientific notation)
- DATAMATRIX/GRIDMATRIX/PDF417/QR/ULTRA: micro-optimize structapp
  ID parse
- library/CLI: fiddle with static asserts (make CHAR_BIT sensitive,
  supposedly)
- win32/README: update building libpng (assembly removed)
- README.linux: document incompatibility of Qt6 >= 6.3
- manual: expand Barcode Studio waffle
- test suite: change range separator to hyphen and allow multiple
  excludes

backend/png.c

@@ -33,6 +33,7 @@
 #ifndef ZINT_NO_PNG
 
 #include <errno.h>
+#include <math.h>
 #include <stdio.h>
 #ifdef _MSC_VER
 #include <fcntl.h>
@@ -42,6 +43,7 @@
 #include <zlib.h>
 #include <setjmp.h>
 #include "common.h"
+#include "output.h"
 
 /* Note if change this need to change "backend/tests/test_png.c" definition also */
 struct wpng_error_type {
@@ -232,7 +234,7 @@ INTERNAL int png_pixel_plot(struct zint_symbol *symbol, unsigned char *pixelbuf)
 #endif
         outfile = stdout;
     } else {
-        if (!(outfile = fopen(symbol->outfile, "wb"))) {
+        if (!(outfile = out_fopen(symbol->outfile, "wb"))) {
             sprintf(symbol->errtxt, "632: Could not open output file (%d: %.30s)", errno, strerror(errno));
             return ZINT_ERROR_FILE_ACCESS;
         }
@@ -279,6 +281,11 @@ INTERNAL int png_pixel_plot(struct zint_symbol *symbol, unsigned char *pixelbuf)
         png_set_compression_strategy(png_ptr, compression_strategy);
     }
 
+    if (symbol->dpmm) {
+        int resolution = (int) roundf(stripf(symbol->dpmm * 1000.0f)); /* pixels per metre */
+        png_set_pHYs(png_ptr, info_ptr, resolution, resolution, PNG_RESOLUTION_METER);
+    }
+
     /* set Header block */
     png_set_IHDR(png_ptr, info_ptr, symbol->bitmap_width, symbol->bitmap_height,
             bit_depth, PNG_COLOR_TYPE_PALETTE, PNG_INTERLACE_NONE,