src/lib/pngwrite.c 1.1

Index: src/lib/pngwrite.c
===================================================================
RCS file: src/lib/pngwrite.c
diff -N src/lib/pngwrite.c
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ src/lib/pngwrite.c	5 Aug 2009 23:34:31 -0000	1.1
@@ -0,0 +1,114 @@
+/* pngwrite.c - write out a memGfx to a PNG file, using the reference library libpng */
+/* (libpng is available from sourceforge and included in many open source distros,
+ *  has a wide-open license intended to encourage usage of the PNG format, and the lib
+ *  has been under development and testing for 14 years -- http://libpng.org/) */
+
+#ifdef USE_PNG
+
+#include "common.h"
+#include "memgfx.h"
+#ifdef SETJMP_H
+//.crap!;
+#endif
+#include "png.h"
+
+static char const rcsid[] = "$Id$";
+
+static void pngAbort(png_structp png, png_const_charp errorMessage)
+/* type png_error wrapper around errAbort */
+{
+errAbort((char *)errorMessage);
+}
+
+static void pngWarn(png_structp png, png_const_charp warningMessage)
+/* type png_error wrapper around warn */
+{
+warn((char *)warningMessage);
+}
+
+boolean mgSaveToPng(FILE *png_file, struct memGfx *mg, boolean useAlpha)
+/* Save PNG to an already open file.
+ * If useAlpha, then the first color in memgfx's colormap/palette is
+ * assumed to be the image background color, and pixels of that color
+ * are made transparent. */
+/* Reference: http://libpng.org/pub/png/libpng-1.2.5-manual.html */
+{
+if (!png_file || !mg)
+    errAbort("mgSaveToPng: caller screwed up: png_file=[%lld], mg=[%lld]",
+	     (long long int)png_file, (long long int)mg);
+png_structp png = png_create_write_struct(PNG_LIBPNG_VER_STRING,
+					  NULL, // don't need pointer to data for err/warn handlers
+					  pngAbort, pngWarn);
+if (!png)
+    {
+    errAbort("png_write_struct failed");
+    return FALSE;
+    }
+png_infop info = png_create_info_struct(png);
+if (!info)
+    {
+    errAbort("png create_info_struct failed");
+    png_destroy_write_struct(&png, NULL);
+    return FALSE;
+    }
+
+// If setjmp returns nonzero, it means png_error is returning control here.
+// But that should not happen because png_error should call pngAbort which calls errAbort.
+if (setjmp(png_jmpbuf(png)))
+    {
+    png_destroy_write_struct(&png, &info);
+    fclose(png_file);
+    errAbort("pngwrite: setjmp nonzero.  "
+	     "why didn't png_error..pngAbort..errAbort stop execution before this errAbort?");
+    return FALSE;
+    }
+
+// Configure PNG output params:
+png_init_io(png, png_file);
+png_set_IHDR(png, info, mg->width, mg->height, 8, // 8=bit_depth
+	     PNG_COLOR_TYPE_PALETTE, PNG_INTERLACE_NONE,
+	     PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
+png_set_PLTE(png, info,
+	     (png_color *)(mg->colorMap), // png_color is same as struct rgbColor!
+	     mg->colorsUsed);
+if (useAlpha)
+    {
+    // First palette color is assumed to be background/transparent, so
+    // that's the only one we need in the parallel array opacities[].
+    png_byte opacities[] = {0};
+    int num_opacities = ArraySize(opacities);
+    png_color_16p nonPalette_opacities_values = NULL; // n/a for us, we're using palette
+    png_set_tRNS(png, info, opacities, num_opacities, nonPalette_opacities_values);
+    }
+
+// Write header/params, write pixels, close and clean up.
+// PNG wants a 2D array of pointers to byte offsets into palette/colorMap.
+// mg has a 1D array of byte offsets.  Make row pointers for PNG:
+png_byte **row_pointers = needMem(mg->height * sizeof(png_byte *));
+int i;
+for (i = 0;  i < mg->height;  i++)
+    row_pointers[i] = &(mg->pixels[i*mg->width]);
+png_set_rows(png, info, row_pointers);
+png_write_png(png, info, PNG_TRANSFORM_IDENTITY, // no transform
+	      NULL); // unused as of PNG 1.2
+png_destroy_write_struct(&png, &info);
+return TRUE;
+}
+
+void mgSavePng(struct memGfx *mg, char *filename, boolean useAlpha)
+/* Save memory bitmap to filename as a PNG.
+ * If useAlpha, then the first color in memgfx's colormap/palette is
+ * assumed to be the image background color, and pixels of that color
+ * are made transparent. */
+{
+FILE *pngFile = mustOpen(filename, "wb");
+if (!mgSaveToPng(pngFile, mg, useAlpha))
+    {
+    remove(filename);
+    errAbort("Couldn't save %s", filename);
+    }
+if (fclose(pngFile) != 0)
+    errnoAbort("fclose failed");
+}
+
+#endif//def USE_PNG