Add an option to embed image size in its name to PNG-to-C script.

When a PNG image exists in several sizes it makes sense to use its size as a
suffix to distinguish the different versions, so update the png2c script to
optionally allow to do this.

Current implementation simply checks the PNG header directly to avoid any
extra dependencies.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66502 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

misc/scripts/png2c.py

@@ -13,8 +13,11 @@ import os.path
 import re
 import array
 
-USAGE = """png2c - Embed a PNG in a C header file (like XPM)
-Usage: png2c [file ..] Output input PNG files as C structures on stdout"""
+USAGE = """Usage: png2c [-s] [file...]
+Output input PNG files as C arrays to standard output. Used to embed PNG images
+in C code (like XPM but with full alpha channel support).
+
+  -s    embed the image size in the image names in generated code."""
 
 if len(sys.argv) < 2:
         print USAGE
@@ -22,11 +25,17 @@ if len(sys.argv) < 2:
 
 r = re.compile("^([a-zA-Z._][a-zA-Z._0-9]*)[.][pP][nN][gG]$")
 
+with_size = 0
+size_suffix = ''
 for path in sys.argv[1:]:
+        if path == '-s':
+            with_size = 1
+            continue
+
         filename = os.path.basename(path).replace('-','_')
         m = r.match(filename)
-        # Allow only filenames that make sense
-        # as C variable names
+
+        # Allow only filenames that make sense as C variable names
         if not(m):
                 print "Skipped file (unsuitable filename): " + filename
                 continue
@@ -35,9 +44,26 @@ for path in sys.argv[1:]:
         bytes = array.array('B', open(path, "rb").read())
         count = len(bytes)
 
+        # Check that it's actually a PNG to avoid problems when loading it
+        # later.
+        #
+        # Each PNG file starts with a 8 byte signature that should be followed
+        # by IHDR chunk which is always 13 bytes in length so the first 16
+        # bytes are fixed (or at least we expect them to be).
+        if bytes[0:16].tostring() != '\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR':
+                print '"%s" doesn\'t seem to be a valid PNG file.' % filename
+                continue
+
+        # Try to naively get its size if necessary
+        if with_size:
+                width = bytes[19] + 16*bytes[18] + 256*bytes[17] + 4096*bytes[16]
+                height = bytes[23] + 16*bytes[22] + 256*bytes[21] + 4096*bytes[20]
+                size_suffix = "_%dx%d" % (width, height)
+
         # Create the C header
         text = "/* %s - %d bytes */\n" \
-               "static const unsigned char %s_png[] = {\n" % (filename, count, m.group(1))
+               "static const unsigned char %s%s_png[] = {\n" % (
+                    filename, count, m.group(1), size_suffix)
 
         # Iterate the characters, we want
         # lines like:
@@ -51,10 +77,10 @@ for path in sys.argv[1:]:
                 # Then the hex data (up to 8 values per line)
                 text += "0x%02x" % (byte)
                 # Separate all but the last values
-                if (i + 1) < count:
-                        text += ", "
                 if (i % 8) == 7:
-                        text += '\n'
+                        text += ',\n'
+                elif (i + 1) < count:
+                        text += ", "
                 i += 1
 
         # Now conclude the C source