Don't make the global bitmap a friend of the screen bitmap, instead allocate it so

that alpha blitting and Cairo operations work correctly.  Running NetSurf on a 16-bit
screen is now possible without bits of the display missing or obliterated, however it
does suffer a small performance hit.

svn path=/trunk/netsurf/; revision=8331

amiga/gui.c

@@ -509,7 +509,7 @@ void ami_openscreen(void)
 			if(screenmodereq = AllocAslRequest(ASL_ScreenModeRequest,NULL))
 			{
 				AslRequestTags(screenmodereq,
-						ASLSM_MinDepth,24,
+						ASLSM_MinDepth,16,
 						ASLSM_MaxDepth,32,
 						TAG_DONE);
 
@@ -593,8 +593,7 @@ void gui_init2(int argc, char** argv)
 		if(!option_direct_render)
 		{
 			glob.bm = p96AllocBitMap(scrn->Width,scrn->Width,32,
-						BMF_CLEAR | BMF_DISPLAYABLE | BMF_INTERLEAVED,
-						scrn->RastPort.BitMap,RGBFB_A8R8G8B8);
+						BMF_INTERLEAVED, NULL, RGBFB_A8R8G8B8);
 
 			if(!glob.bm) warn_user("NoMemory","");
 

amiga/gui_options.c

@@ -498,7 +498,7 @@ void ami_gui_opts_open(void)
         	 	           						GA_RelVerify, TRUE,
 												GA_Disabled,screenmodedisabled,
 												GETSCREENMODE_DisplayID,screenmodeid,
-												GETSCREENMODE_MinDepth, 24,
+												GETSCREENMODE_MinDepth, 16,
 												GETSCREENMODE_MaxDepth, 32,
 											GetScreenModeEnd,
 											LAYOUT_AddChild, gow->gadgets[GID_OPTS_SCREENNAME] = StringObject,