reduce software cursor flickering

the software cursor starts flickering and reacts bumby if a process
spends most of its time with drawlock acquired because the timer interrupt
thats supposed to redraw the cursor fails to acquire the lock at the time
the timer fires.

instead of trying to draw the cursor on the screen from a timer interrupt
30 times per second, devmouse now creates a process calling cursoron() and
cursoroff() when the cursor needs to be redrawn. this allows the swcursor
to schedule a redraw while holding the drawlock in swcursoravoid() and
cursoron()/cursoroff() are now able to wait for a qlock (drawlock) because
they get called from process context.

the overall responsiveness is also improved with this change as the cursor
redraw rate isnt limited to 30 times a second anymore.

1 files changed, 133 insertions, 0 deletions

diff --git a/sys/src/9/port/swcursor.c b/sys/src/9/port/swcursor.c
new file mode 100644
index 000000000..55ea014d0
--- /dev/null
+++ b/sys/src/9/port/swcursor.c
@@ -0,0 +1,133 @@
+#include	"u.h"
+#include	"../port/lib.h"
+#include	"mem.h"
+#include	"dat.h"
+#include	"fns.h"
+#include	"../port/error.h"
+
+#define	Image	IMAGE
+#include	<draw.h>
+#include	<memdraw.h>
+#include	<cursor.h>
+#include	"screen.h"
+
+extern Memimage* gscreen;
+
+/*
+ * Software cursor. 
+ */
+static Memimage*	swback;		/* screen under cursor */
+static Memimage*	swimg;		/* cursor image */
+static Memimage*	swmask;		/* cursor mask */
+static Memimage*	swimg1;
+static Memimage*	swmask1;
+
+static Point		swoffset;
+static Rectangle	swrect;		/* screen rectangle in swback */
+static Point		swvispt;	/* actual cursor location */
+static int		swvisible;	/* is the cursor visible? */
+
+/*
+ * called with drawlock locked for us, most of the time.
+ * kernel prints at inopportune times might mean we don't
+ * hold the lock, but memimagedraw is now reentrant so
+ * that should be okay: worst case we get cursor droppings.
+ */
+void
+swcursorhide(void)
+{
+	if(swvisible == 0)
+		return;
+	if(swback == nil || gscreen == nil)
+		return;
+	swvisible = 0;
+	memimagedraw(gscreen, swrect, swback, ZP, memopaque, ZP, S);
+	flushmemscreen(swrect);
+}
+
+void
+swcursoravoid(Rectangle r)
+{
+	if(swvisible && rectXrect(r, swrect)){
+		swcursorhide();
+		mouseredraw();	/* schedule cursor redraw after we release drawlock */
+	}
+}
+
+void
+swcursordraw(Point p)
+{
+	if(swvisible)
+		return;
+	if(swback == nil || swimg1 == nil || swmask1 == nil || gscreen == nil)
+		return;
+	assert(!canqlock(&drawlock));
+	swvispt = addpt(swoffset, p);
+	swrect = rectaddpt(Rect(0,0,16,16), swvispt);
+	memimagedraw(swback, swback->r, gscreen, swvispt, memopaque, ZP, S);
+	memimagedraw(gscreen, swrect, swimg1, ZP, swmask1, ZP, SoverD);
+	flushmemscreen(swrect);
+	swvisible = 1;
+}
+
+void
+swcursorload(Cursor *curs)
+{
+	uchar *ip, *mp;
+	int i, j, set, clr;
+
+	if(swimg == nil || swmask == nil || swimg1 == nil || swmask1 == nil)
+		return;
+	/*
+	 * Build cursor image and mask.
+	 * Image is just the usual cursor image
+	 * but mask is a transparent alpha mask.
+	 * 
+	 * The 16x16x8 memimages do not have
+	 * padding at the end of their scan lines.
+	 */
+	ip = byteaddr(swimg, ZP);
+	mp = byteaddr(swmask, ZP);
+	for(i=0; i<32; i++){
+		set = curs->set[i];
+		clr = curs->clr[i];
+		for(j=0x80; j; j>>=1){
+			*ip++ = set&j ? 0x00 : 0xFF;
+			*mp++ = (clr|set)&j ? 0xFF : 0x00;
+		}
+	}
+	swoffset = curs->offset;
+	memimagedraw(swimg1, swimg1->r, swimg, ZP, memopaque, ZP, S);
+	memimagedraw(swmask1, swmask1->r, swmask, ZP, memopaque, ZP, S);
+
+	mouseredraw();
+}
+
+void
+swcursorinit(void)
+{
+	if(gscreen == nil)
+		return;
+
+	if(swback){
+		freememimage(swback);
+		freememimage(swmask);
+		freememimage(swmask1);
+		freememimage(swimg);
+		freememimage(swimg1); 
+	}
+	swback = allocmemimage(Rect(0,0,32,32), gscreen->chan);
+	swmask = allocmemimage(Rect(0,0,16,16), GREY8);
+	swmask1 = allocmemimage(Rect(0,0,16,16), GREY1);
+	swimg = allocmemimage(Rect(0,0,16,16), GREY8);
+	swimg1 = allocmemimage(Rect(0,0,16,16), GREY1);
+	if(swback == nil || swmask == nil || swmask1 == nil || swimg == nil || swimg1 == nil){
+		print("software cursor: allocmemimage fails\n");
+		return;
+	}
+	memfillcolor(swback, DTransparent);
+	memfillcolor(swmask, DOpaque);
+	memfillcolor(swmask1, DOpaque);
+	memfillcolor(swimg, DBlack);
+	memfillcolor(swimg1, DBlack);
+}