Experimental change to pixmap rendering. Switch from using NSImage to NSBitmapImageRef to store the image. This is closer to the core backing store used to display images. Using this I was able to avoid using lockFocus on the images and instead set the graphics context manually allowing us to draw directly on the backing image. However NSBitmapImageRef is a more simple format and didn't work with the flipped Y axis... so... I had to perform some voodoo to get the flipping to work with the graphics context. Not sure it is 100% right.

/* XPM */
static char * kill_xpm[] = {
/* width height num_colors chars_per_pixel */
"15 15 6 1",
/* colors */
" 	c white",
".	c #5f5f5f",
"X	c gray75",
"o	c black",
"O	c gray40",
"+	c gray70",
/* pixels */
"              .",
" XXXXXXXXXXXX..",
" XoO++++++OoX..",
" XOoO++++OoOX..",
" X+OoO++OoO+X..",
" X++OoOOoO++X..",
" X+++OooO+++X..",
" X+++OooO+++X..",
" X++OoOOoO++X..",
" X+OoO++OoO+X..",
" XOoO++++OoOX..",
" XoO++++++OoX..",
" XXXXXXXXXXXX..",
" ..............",
"..............."};