+
+/* Demonstration of user chunk support of the sTER and vpAg chunks */
+#if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
+
+/* (sTER is a public chunk not yet understood by libpng. vpAg is a private
+chunk used in ImageMagick to store "virtual page" size). */
+
+static png_uint_32 user_chunk_data[4];
+
+ /* 0: sTER mode + 1
+ * 1: vpAg width
+ * 2: vpAg height
+ * 3: vpAg units
+ */
+
+static int read_user_chunk_callback(png_struct *png_ptr,
+ png_unknown_chunkp chunk)
+{
+ png_uint_32
+ *user_chunk_data;
+
+ /* Return one of the following: */
+ /* return (-n); chunk had an error */
+ /* return (0); did not recognize */
+ /* return (n); success */
+
+ /* The unknown chunk structure contains the chunk data:
+ * png_byte name[5];
+ * png_byte *data;
+ * png_size_t size;
+ *
+ * Note that libpng has already taken care of the CRC handling.
+ */
+
+ if (chunk->name[0] == 115 && chunk->name[1] == 84 && /* s T */
+ chunk->name[2] == 69 && chunk->name[3] == 82) /* E R */
+ {
+ /* Found sTER chunk */
+ if (chunk->size != 1)
+ return (-1); /* Error return */
+ if (chunk->data[0] != 0 && chunk->data[0] != 1)
+ return (-1); /* Invalid mode */
+ user_chunk_data=(png_uint_32 *) png_get_user_chunk_ptr(png_ptr);
+ user_chunk_data[0]=chunk->data[0]+1;
+ return (1);
+ }
+ if (chunk->name[0] != 118 || chunk->name[1] != 112 || /* v p */
+ chunk->name[2] != 65 || chunk->name[3] != 103) /* A g */
+ return (0); /* Did not recognize */
+
+ /* Found ImageMagick vpAg chunk */
+
+ if (chunk->size != 9)
+ return (-1); /* Error return */
+
+ user_chunk_data=(png_uint_32 *) png_get_user_chunk_ptr(png_ptr);
+
+ user_chunk_data[1]=png_get_uint_31(png_ptr, chunk->data);
+ user_chunk_data[2]=png_get_uint_31(png_ptr, chunk->data + 4);
+ user_chunk_data[3]=(png_uint_32)chunk->data[8];
+
+ return (1);
+
+}
+#endif
+/* END of code to demonstrate user chunk support */
+
projects / wxWidgets.git / blobdiff