Improve and simplify line segment rendering on Win32, especially the

2005-06-23  Tor Lillqvist  <tml@novell.com>

	Improve and simplify line segment rendering on Win32, especially
	the implementation of GDK_CAP_NOT_LAST, and dashed lines. Fixes
	bug #306396.

	* gdk/win32/gdkprivate-win32.h (GdkGCWin32): Save the GdkGC's
	line_style, cap_style and join_style as such in the
	GdkGCWin32. Don't need to keep the pen_double_dash flag, we can
	check the line_style.

	* gdk/win32/gdkgc-win32.c (fixup_pen): New internal function. Sets
	up the GDI pen type, style, end cap and join attributes to use
	based on the pen width, GDK line style, end cap style, and join
	style.

	For a narrow (zero-width) GDK pen with the GDK_CAP_NOT_LAST end
	cap style, which typically are used for XOR drawing where it is
	essential that the last pixel is not drawn, use a GDI cosmetic
	pen. Only for a cosmetic pen does GDI not draw the last pixel. I
	deduced this by experimetation, the documentation is rather vague.

	For other GDK pens use a geometric GDI pen. If the width is 0 or 1
	and the GDK end cap style is GDK_CAP_BUTT, and the line style is
	GDK_LINE_SOLID, use PS_ENDCAP_ROUND. This ensures that also
	single-pixel length lines are drawn. (For sngle-pixel width lines
	roundness as such is of course irrelevant.) For dashed lines, use
	PS_ENDCAP_FLAT.

	For wide lines use PS_ENDCAP_FLAT, _ROUND or _SQUARE,
	respectively, for GDK_CAP_BUTT, GDK_CAP_ROUND and GDK_CAP_PROJECTING.

	For one pixel on-off dashed lines, use PS_ALTERNATE, it seems to
	work better than PS_USERSTYLE. For other dashed lines, use
	PS_USERSTYLE and the dashes as set by the user (or the default
	four-pixel on-off style).

	(gdk_win32_gc_values_to_win32values, gdk_win32_gc_set_dashes):
	Call fixup_pen() to do the pen settings after modifying some of
	the GDK GC attributes that affect pens.

	* gdk/win32/gdkdrawable-win32.c (render_line_horizontal,
	render_line_vertical, draw_segments): Check GdkGCWin32::line_style
	instead of the the removed pen_double_dash member. Don't use
	PATCOPY unconditionally in the PatBlt() call, use a raster ope
	code that depends on the GC function in use.

	(draw_rectangle, draw_segments, draw_lines): Be more careful in
	deciding when to do the manual dash rendering.

	(draw_segments): Don't do any manual "last point" drawing at
	all. The above changes takes care of narrow line segments being
	drawn correctly in most cases, at least on NT-based Windows.

gdk/win32/gdkprivate-win32.h

@@ -274,10 +274,12 @@ struct _GdkGCWin32
   gint graphics_exposures;
   gint pen_width;
   DWORD pen_style;
+  GdkLineStyle line_style;
+  GdkCapStyle cap_style;
+  GdkJoinStyle join_style;
   DWORD *pen_dashes;		/* use for PS_USERSTYLE or step-by-step rendering */
   gint pen_num_dashes;
   gint pen_dash_offset;
-  gboolean pen_double_dash;
   HBRUSH pen_hbrbg;
 
   /* Following fields are valid while the GC exists as a Windows DC */