On Thu, 2007-01-11 at 08:50 -0600, John Hunter wrote: > >>>>> "Steve" == Steve Chaplin <[EMAIL PROTECTED]> writes: > > Steve> On Mon, 2007-01-08 at 11:24 -0500, Darren Dale wrote: > >> I only had a short time to work with backend_gtkcairo, but a > >> couple of things caught my attention. mathtext support seemed > >> to need some improvement, it looked like it was rendered as an > >> image rather than as text. Also, imshow(rand(100,100)) looked > >> very different with gtkcairo and gtkagg, (maybe because the > >> rgba ordering is different in agg and cairo? I'm not sure this > >> is even the case, I'm taking a stab in the dark.) > > Steve> cairo mathtext uses a method copied from gdk/gtk and does > Steve> render an image. It needs updating to render text. > > Steve> imshow does look different on cairo and agg, and yes, It > Steve> looks like an image format problem. cairo uses ARGB32 with > Steve> pre-multiplied alpha, and the ARGB order depends on whether > Steve> the machine is little- of big-endian. > > I am confused by what you mean about the ARGB order depending on > endianess. ARGB defines the order, and each color is one byte, so > where is the ambiguity? Do you mean that depending on endianness, > cairo will use other orderings than ARGB? > > In _image.cpp we provide a few buffer methods for various pixel > orderings, eg buffer_argb32. We may need to provide additional > orderings for cairo, and call the right one depending on the platform.
This is the official definition from the manual: CAIRO_FORMAT_ARGB32 each pixel is a 32-bit quantity, with alpha in the upper 8 bits, then red, then green, then blue. The 32-bit quantities are stored native-endian. Pre-multiplied alpha is used. (That is, 50% transparent red is 0x80800000, not 0x80ff0000.) What I think this means is: cairo ARGB32 is stored not as 4 8-bit quantities, but as one 32-bit int. On big-endian systems the byte order is ARGB, as you would expect, but on little-endian systems (like a PC) the byte order is BGRA. I imagine the reason is that its easier/faster to read/write one 32-bit int than it is to read/write four bytes. Steve Send instant messages to your online friends http://au.messenger.yahoo.com ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Matplotlib-devel mailing list Matplotlib-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-devel
