Refactor fluid: make fl_write_png() public

The new function fl_write_png() was moved to its own file and is now
publicly available ("exported") so other programs can use it.

This function was used in fluid to write a window screenshot (.png)
together with a template (.fl) to preferences storage.

4 files changed, 148 insertions, 2 deletions

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 274df8e02..0efbfede4 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -1,7 +1,7 @@
 #
 # CMakeLists.txt to build the FLTK library using CMake (www.cmake.org)
 #
-# Copyright 1998-2020 by Bill Spitzak and others.
+# Copyright 1998-2021 by Bill Spitzak and others.
 #
 # This library is free software. Distribution and use rights are outlined in
 # the file "COPYING" which should have been included with this file.  If this
@@ -424,6 +424,7 @@ set (GLCPPFILES
 
 set (IMGCPPFILES
   fl_images_core.cxx
+  fl_write_png.cxx
   Fl_BMP_Image.cxx
   Fl_File_Icon2.cxx
   Fl_GIF_Image.cxx
diff --git a/src/Makefile b/src/Makefile
index 1415be133..0b7b89a92 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -1,7 +1,7 @@
 #
 # Library Makefile for the Fast Light Tool Kit (FLTK).
 #
-# Copyright 1998-2020 by Bill Spitzak and others.
+# Copyright 1998-2021 by Bill Spitzak and others.
 #
 # This library is free software. Distribution and use rights are outlined in
 # the file "COPYING" which should have been included with this file.  If this
@@ -210,6 +210,7 @@ GLCPPFILES += $(GLCPPFILES_$(BUILD))
 
 IMGCPPFILES = \
 	fl_images_core.cxx \
+	fl_write_png.cxx \
 	Fl_BMP_Image.cxx \
 	Fl_File_Icon2.cxx \
 	Fl_GIF_Image.cxx \
diff --git a/src/fl_write_png.cxx b/src/fl_write_png.cxx
new file mode 100644
index 000000000..e3fa56034
--- /dev/null
+++ b/src/fl_write_png.cxx
@@ -0,0 +1,136 @@
+//
+// Fl_PNG_Image support functions for the Fast Light Tool Kit (FLTK).
+//
+// Copyright 2021 by Bill Spitzak and others.
+//
+// This library is free software. Distribution and use rights are outlined in
+// the file "COPYING" which should have been included with this file.  If this
+// file is missing or damaged, see the license at:
+//
+//     https://www.fltk.org/COPYING.php
+//
+// Please see the following page on how to report bugs and issues:
+//
+//     https://www.fltk.org/bugs.php
+//
+
+#include <config.h>
+#include <FL/Fl_PNG_Image.H>
+#include <FL/Fl_RGB_Image.H>
+#include <FL/fl_string.h>
+#include <FL/fl_utf8.h> // fl_fopen()
+#include <stdio.h>
+
+// PNG library include files
+
+extern "C" {
+#if defined(HAVE_LIBPNG) && defined(HAVE_LIBZ)
+#include <zlib.h>
+#ifdef HAVE_PNG_H
+#include <png.h>
+#else
+#include <libpng/png.h>
+#endif // HAVE_PNG_H
+#endif // HAVE_LIBPNG && HAVE_LIBZ
+} // extern "C"
+
+/**
+  \file fl_write_png.cxx
+
+  PNG image support functions.
+
+*/
+
+/**
+  Write a RGB(A) image to a PNG image file.
+
+  This is a very basic and restricted function to create a PNG image file
+  from an RGB image (Fl_RGB_Image).
+
+  The image data must be aligned w/o gaps, i.e. ld() \b MUST be zero or
+  equal to data_w() * data_h().
+
+  The image file is always written with the original image size data_w()
+  and data_h(), even if the image has been scaled.
+
+  Image depth 3 (RGB) and 4 (RGBA) are supported.
+
+  \note Behavior of grayscale images (depth 1 and 2) is currently undefined
+    and may or may not work. There is no error handling except for opening
+    the file. This function may be changed in the future.
+
+  \param[in]  filename  Output filename, extension should be '.png'
+  \param[in]  img       RGB image to be written
+
+  \return     success (0) or error code
+
+  \retval      0        success, file has been written
+  \retval     -1        png or zlib library not available
+  \retval     -2        file open error
+
+  \see fl_write_png(const char *, int, int, int, const unsigned char *)
+*/
+
+int fl_write_png(const char *filename, Fl_RGB_Image *img) {
+  return fl_write_png(filename,
+                      img->data_w(), img->data_h(), img->d(),
+                      (const unsigned char *)img->data()[0]);
+}
+
+/**
+  Write raw image data to a PNG image file.
+
+  This is a very basic and restricted function to create a PNG image file
+  from raw image data, e.g. a screenshot.
+
+  The image data must be aligned w/o gaps after each row.
+
+  For further restrictions and return values please see
+  fl_write_png(const char *filename, Fl_RGB_Image *img).
+
+  \param[in]  filename  Output filename, extension should be '.png'
+  \param[in]  w         Image data width
+  \param[in]  h         Image data height
+  \param[in]  d         Image depth (3 = RGB, 4 = RGBA)
+  \param[in]  pixels    Image data (\p w * \p h * \p d bytes)
+
+  \return     success (0) or error code, see ...
+
+  \see fl_write_png(const char *filename, Fl_RGB_Image *img)
+ */
+int fl_write_png(const char *filename, int w, int h, int d, const unsigned char *pixels) {
+
+#if defined(HAVE_LIBPNG) && defined(HAVE_LIBZ)
+
+  FILE *fp;
+
+  if ((fp = fl_fopen(filename, "wb")) == NULL) {
+    return -2;
+  }
+
+  png_structp pptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, 0, 0, 0);
+  png_infop iptr = png_create_info_struct(pptr);
+  png_bytep ptr = (png_bytep)pixels;
+
+  png_init_io(pptr, fp);
+  png_set_IHDR(pptr, iptr, w, h, 8,
+               PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE,
+               PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
+  png_set_sRGB(pptr, iptr, PNG_sRGB_INTENT_PERCEPTUAL);
+
+  png_write_info(pptr, iptr);
+
+  for (int i = h; i > 0; i--, ptr += w * d) {
+    png_write_row(pptr, ptr);
+  }
+
+  png_write_end(pptr, iptr);
+  png_destroy_write_struct(&pptr, &iptr);
+
+  fclose(fp);
+  return 0;
+
+#else
+  return -1;
+#endif
+}
diff --git a/src/makedepend b/src/makedepend
index 328e057cc..137bc943d 100644
--- a/src/makedepend
+++ b/src/makedepend
@@ -3502,6 +3502,14 @@ Fl_Wizard.o: ../FL/Fl_Widget.H
 Fl_Wizard.o: ../FL/Fl_Window.H
 Fl_Wizard.o: ../FL/Fl_Wizard.H
 Fl_Wizard.o: ../FL/platform_types.h
+fl_write_png.o: ../config.h
+fl_write_png.o: ../FL/Fl_Export.H
+fl_write_png.o: ../FL/Fl_Image.H
+fl_write_png.o: ../FL/Fl_PNG_Image.H
+fl_write_png.o: ../FL/Fl_RGB_Image.H
+fl_write_png.o: ../FL/fl_string.h
+fl_write_png.o: ../FL/fl_types.h
+fl_write_png.o: ../FL/fl_utf8.h
 Fl_x.o: ../config.h
 Fl_x.o: ../FL/abi-version.h
 Fl_x.o: ../FL/Enumerations.H