From d46d43f863908e38a9cda7e9d50e8eb39cb6cc13 Mon Sep 17 00:00:00 2001
From: Liam Girdwood <lgirdwood@gmail.com>
Date: Sat, 5 Jul 2008 11:56:04 +0100
Subject: [PATCH] sky: grid - working fast EQU grid. Zoom broken at low FOV.

---
 src/sky/grid.c       | 680 +++++++++++----------------------------------------
 src/sky/projection.c |   4 +-
 src/sky/projection.h |   6 +
 3 files changed, 149 insertions(+), 541 deletions(-)

diff --git a/src/sky/grid.c b/src/sky/grid.c
index 7c189dc..bbafc4c 100644
--- a/src/sky/grid.c
+++ b/src/sky/grid.c
@@ -67,503 +67,87 @@ static const gdouble grid_dms_dec[] = {
 	1.0,
 };
 
-/* get grid RA step size for projection in arcsecs */
-static gdouble get_ra_step_delta(struct projection *proj)
-{
-	gint i;
-	
-	for (i = 0; i < nsize(grid_hms_ra); i++) {
-		if (proj->fov / 1.1 > grid_hms_ra[i] / 3600.0)
-			return grid_hms_ra[i] / 3600.0;
-	}
-	return grid_hms_ra[i] / 3600.0;
-}
-
-/* get grid DEC step size for projection in arcsecs */
-static gdouble get_dec_step_delta(struct projection *proj)
-{
-	gint i;
-	
-	for (i = 0; i < nsize(grid_dms_dec); i++) {
-		if (proj->fov / 1.1 > grid_dms_dec[i] / 3600.0)
-			return grid_dms_dec[i] / 3600.0;
-	}
-	return grid_dms_dec[i] / 3600.0;
-}
-
-/* clip DEC grid to current projection FOV */
-static void clip_dec_equ_grid(struct projection *proj, gdouble step_size,
-	gdouble *south, gdouble *north)
-{
-	*south = proj->centre_dec - proj->fov / 2.0;
-	if (*south <= -90.0)
-		*south = -90.0 + step_size;
-	else
-		*south = floor(*south / step_size) * step_size;
-	
-	*north = proj->centre_dec + proj->fov / 2.0;
-	if (*north >= 90.0)
-		*north = 90.0 - step_size;
-	else
-		*north = floor(*north / step_size) * step_size;
-}
-
-/* clip RA grid to current projection FOV */
-static void clip_ra_equ_grid(struct projection *proj, gdouble step_size,
-	gdouble *start, gdouble *end)
+static inline int is_tile_visible(struct projection *proj, gint ra, gint dec)
 {
 	struct render_object robject;
-	struct ln_equ_posn pos[4];
-	gdouble start_, end_;
-	gint i;
-	
-	/* get RA at each projection corner */
-	robject.coord[0].x = 0;
-	robject.coord[0].y = 0;
-	robject.coord[0].posn = &pos[0];
-	proj->trans->proj_to_sky_hrz(proj, &robject.coord[0]);
-	if (pos[0].ra < 0.0)
-		pos[0].ra += 360.0;
-	else if (pos[0].ra >= 360.0)
-		pos[0].ra -= 360.0;
-		
-	robject.coord[0].x = proj->sky_width;
-	robject.coord[0].y = 0;
-	robject.coord[0].posn = &pos[1];
-	proj->trans->proj_to_sky_hrz(proj, &robject.coord[0]);
-	if (pos[1].ra < 0.0)
-		pos[1].ra += 360.0;
-	else if (pos[1].ra >= 360.0)
-		pos[1].ra -= 360.0;
-		
-	robject.coord[0].x = 0;
-	robject.coord[0].y = proj->sky_height;
-	robject.coord[0].posn = &pos[2];
-	proj->trans->proj_to_sky_hrz(proj, &robject.coord[0]);
-	if (pos[2].ra < 0.0)
-		pos[2].ra += 360.0;
-	else if (pos[2].ra >= 360.0)
-		pos[2].ra -= 360.0;
-		
-	robject.coord[0].x = proj->sky_width;
-	robject.coord[0].y = proj->sky_height;
-	robject.coord[0].posn = &pos[3];
-	proj->trans->proj_to_sky_hrz(proj, &robject.coord[0]);
-	if (pos[3].ra < 0.0)
-		pos[3].ra += 360.0;
-	else if (pos[3].ra >= 360.0)
-		pos[3].ra -= 360.0;
-		
-	/* get highest and lowest RA from corners */
-	start_ = 360.0;
-	end_ = 0.0;
-	for (i = 0; i < 4; i++) {
-		printf("pos %d ra %3.2f dec %3.2f\n",i,  pos[i].ra, pos[i].dec);
-		if (start_ > pos[i].ra)
-			start_ = pos[i].ra;
-		if (end_ < pos[i].ra)
-			end_ = pos[i].ra;
-	} 
-	
-	start_ = floor(start_ / step_size) * step_size;
-	if (start_ < 0.0)
-		start_ += 360.0;
-	else if (start_ >= 360.0)
-		start_ -= 360.0;
-
-	end_ = ceil(end_ / step_size) * step_size;
-	if (end_ < 0.0)
-		end_ += 360.0;
-	else if (end_ >= 360.0)
-		end_ -= 360.0;
-	
-	if (start_ > end_) {
-		*start = end_;
-		*end = start_;
-	} else {
-		*start = start_;
-		*end = end_;
-	}
+	struct ln_equ_posn pos;
 	
-printf("start %3.2f end %3.2f\n", *start, *end);	
+	pos.ra = ra * 15.0;
+	pos.dec = -90 + dec * 10.0;
+	robject.coord[0].posn = &pos;
+	proj->trans->sky_to_proj_equ(proj, &robject.coord[0]);
+	return projection_is_visible0(proj, &robject);
 }
 
-/* should we render a line of this radius as an arc or a straight line */ 
-static inline gint is_arc_line(struct projection *proj, gdouble radius)
+static inline void mark_neighbour_tiles(struct projection *proj, 
+	gint ra, gint dec)
 {
-	/* magic number - must refine */
-	if (radius > proj->sky_width * ARC_MAGIC || 
-		radius < proj->sky_width * -ARC_MAGIC) {
-		//printf("%s rad %f\n", __func__, radius);
-		return 1;
-	}
-	return 0;
+	gint ra_start = ra - 1, ra_end = ra + 1;
+	gint dec_start = dec - 1, dec_end = dec + 1;
+	
+	if (ra_start < 0)
+		ra_start = GRID_RA_TILES -1;
+	if (ra_end == GRID_RA_TILES)
+		ra_end = 0;
+	if (dec_start < 0)
+		dec_start = 0;
+	if (dec_end == GRID_DEC_TILES)
+		dec_end = GRID_DEC_TILES - 1;
+	 
+	proj->grid_tile[ra_start][dec_start] = 1;
+	proj->grid_tile[ra_end][dec_start] = 1;
+	proj->grid_tile[ra_start][dec_end] = 1;
+	proj->grid_tile[ra_end][dec_end] = 1;
+	proj->grid_tile[ra][dec_start] = 1;
+	proj->grid_tile[ra][dec_end] = 1;
+	proj->grid_tile[ra_start][dec] = 1;
+	proj->grid_tile[ra_end][dec] = 1;
 }
 
-/* is this arc visible in projection */
-static gint is_arc_visible(struct projection *proj, gdouble x, gdouble y, 
-	gdouble radius)
+static void get_visible_tiles(struct projection *proj)
 {
-	gdouble x1, y1, x2, y2;
+	gint ra, dec;
 	
-	/* sanity check */
-	if (radius == FP_NAN 
-		|| radius == FP_INFINITE 
-		|| radius == -FP_INFINITE) {
-		return 0;
+	/* clear all tiles first */
+	for (ra = 0; ra < GRID_RA_TILES; ra++) {
+		for (dec = 0; dec < GRID_DEC_TILES; dec++) {
+			proj->grid_tile[ra][dec] = 0;
+		}
 	}
-		
-	/* create clip area sky size + radius */
-	x1 = -radius;
-	y1 = -radius;
-	x2 = proj->sky_width + radius;
-	y2 = proj->sky_height + radius;
-		
-	/* are we inside ? */
-	if (x >= x1 && x <= x2 && y >= y1 && y <= y2)
-		return 1;
-		
-	return 0;
-}
-
-static inline void do_ra_line(struct render_object *robject, 
-	struct projection *proj, gdouble x, gdouble y, gdouble my)
-{
-	gdouble x1, y1, x2, y2;
-	
-	x1 = x - my * y;
-	y1 = 0;
-	x2 = my * (proj->sky_height - y) + x;
-	y2 = proj->sky_height;
-	
-	cairo_move_to(robject->cr, x1, y1);
-	cairo_line_to(robject->cr, x2, y2);
-}
-
-/* draw a straight RA grid line */
-static inline void draw_ra_line(struct render_object *robject, 
-	struct projection *proj, gdouble step)
-{
-	struct ln_equ_posn pos1, pos2;
-	gdouble my;
-	
-	/* calc based on small RA line */
-	pos1.dec = proj->centre_dec + 1.0;
-	pos2.dec = proj->centre_dec -1.0;
-	
-	pos1.ra = step;
-	pos2.ra = step + 180.0;
-	
-	robject->coord[0].posn = &pos1;
-	robject->coord[1].posn = &pos2;
-	
-	proj->trans->sky_to_proj_equ(proj, &robject->coord[0]);
-	proj->trans->sky_to_proj_equ(proj, &robject->coord[1]);
-	
-	/* calculate line gradient */
-	my = (robject->coord[1].x - robject->coord[0].x) / 
-		(robject->coord[1].y - robject->coord[0].y);	
-	
-	do_ra_line(robject, proj, 
-		robject->coord[0].x, robject->coord[0].y, my);
-}
-
-static inline void do_dec_line(struct render_object *robject, 
-	struct projection *proj, gdouble x, gdouble y, gdouble mx)
-{
-	gdouble x1, y1, x2, y2;
-	
-	x1 = 0;
-	y1 = y -mx * y;
-	x2 = proj->sky_width;
-	y2 = mx * (proj->sky_width - x) + y;
-	
-	cairo_move_to(robject->cr, x1, y1);
-	cairo_line_to(robject->cr, x2, y2);
-}
-
-/* draw a straight DEC grid line */
-static inline void draw_dec_line(struct render_object *robject, 
-	struct projection *proj, gdouble step)
-{
-	struct ln_equ_posn pos1, pos2;
-	gdouble mx;
-	
-	/* calc based on small DEC line */
-	pos1.ra = proj->centre_ra + 1.0;
-	pos2.ra = proj->centre_ra -1.0;
-	
-	pos1.dec = step;
-	pos2.dec = step;
-	
-	robject->coord[0].posn = &pos1;
-	robject->coord[1].posn = &pos2;
-	
-	proj->trans->sky_to_proj_equ(proj, &robject->coord[0]);
-	proj->trans->sky_to_proj_equ(proj, &robject->coord[1]);
-	
-	/* calculate line gradient */
-	mx = (robject->coord[1].y - robject->coord[0].y) / 
-		(robject->coord[1].x - robject->coord[0].x);
-	
-	do_dec_line(robject, proj, 
-		robject->coord[0].x, robject->coord[0].y, mx);
-}
-
-#if 0
-/* render all visible RA grid lines */
-static void equ_render_ra(struct render_object *robject, 
-	struct projection *proj, gint labels)
-{
-	gdouble centre_x, centre_y, radius, x, y, step, 
-		step_delta, ra_start, ra_end;
-	struct ln_equ_posn pos1, pos2;
-	
-	pos1.dec = -proj->centre_dec;
-	pos2.dec = -proj->centre_dec;
-
-	step_delta = get_ra_step_delta(proj);
-	clip_ra_equ_grid(proj, step_delta, &ra_start, &ra_end);
-
-	for (step = ra_start; step <= ra_end; step += step_delta) { 
-	
-		pos1.ra = step;
-		pos2.ra = step + 180.0;
-	
-		robject->coord[0].posn = &pos1;
-		robject->coord[1].posn = &pos2;
-	
-		proj->trans->sky_to_proj_equ(proj, &robject->coord[0]);
-		proj->trans->sky_to_proj_equ(proj, &robject->coord[1]);
 	
-		centre_x = robject->coord[0].x + 
-			((robject->coord[1].x - robject->coord[0].x) / 2.0);
-		centre_y = robject->coord[0].y + 
-			((robject->coord[1].y - robject->coord[0].y) / 2.0);
-		x = centre_x - robject->coord[0].x;
-		y = centre_y - robject->coord[0].y;
-		radius = sqrt(x * x + y * y);
-
-		if (!is_arc_visible(proj, centre_x, centre_y, radius) && 
-			step != proj->centre_ra)
-			continue;
-
-/* need cairo_arc_to() */
-#if 0
-		if (step == 0.0 || step == 90.0 || 
-			step == 180.0 || step == 270.0) {
-			struct ln_equ_posn pos1, pos2;
-	
-			pos1.dec = 80.0;
-			pos2.dec = -80.0;
-			pos1.ra = step;
-			pos2.ra = step;
-			robject->num_coords = 2;
-	
-			robject->coord[0].posn = &pos1;
-			robject->coord[1].posn = &pos2;
-			proj->trans->sky_to_proj_equ(proj, robject);
-	
-			cairo_new_sub_path(robject->cr);                                                           
-			cairo_arc_to(robject->cr, 
-				robject->coord[0].x, robject->coord[0].y, 
-				robject->coord[1].x, robject->coord[1].y,
-				radius);
-		} else {
-			if (is_arc_line(proj, centre_x))
-				draw_ra_line(robject, proj, step);
-			else {
-				cairo_new_sub_path(robject->cr);
-				cairo_arc(robject->cr, centre_x, centre_y, 
-					radius, circle_start, circle_end);
+	for (ra = 0; ra < GRID_RA_TILES; ra++) {
+		for (dec = 0; dec < GRID_DEC_TILES; dec++) {
+			 
+			if (is_tile_visible(proj, ra, dec)) {
+				proj->grid_tile[ra][dec] = 1;
+				mark_neighbour_tiles(proj, ra, dec);
 			}
 		}
-#else
-		if (is_arc_line(proj, centre_x))
-			draw_ra_line(robject, proj, step);
-		else {
-			cairo_new_sub_path(robject->cr);
-			cairo_arc(robject->cr, centre_x, centre_y, 
-					radius, 0, 2 * M_PI);
-		}
-#endif
-	}
-}
-#endif
-
-#if 0
-/* render all visible DEC grid lines */
-static void equ_render_dec(struct render_object *robject, 
-	struct projection *proj, gint labels)
-{
-	gdouble centre_x, centre_y, radius, x, y, step, 
-		step_delta, dec_start, dec_end;
-	struct ln_equ_posn pos1, pos2;
-	
-	pos1.ra = proj->centre_ra;
-	pos2.ra = proj->centre_ra + 180.0;
-	
-	step_delta = get_dec_step_delta(proj);
-	clip_dec_equ_grid(proj, step_delta, &dec_start, &dec_end);
-	
-	for (step = dec_start; step <= dec_end; step += step_delta) { 
-	
-		pos1.dec = step;
-		pos2.dec = step;
-	
-		robject->coord[0].posn = &pos1;
-		robject->coord[1].posn = &pos2;
-	
-		proj->trans->sky_to_proj_equ(proj, &robject->coord[0]);
-		proj->trans->sky_to_proj_equ(proj, &robject->coord[1]);
-	
-		centre_x = robject->coord[0].x + 
-			((robject->coord[1].x - robject->coord[0].x) / 2.0);
-		centre_y = robject->coord[0].y + 
-			((robject->coord[1].y - robject->coord[0].y) / 2.0);
-		x = centre_x - robject->coord[0].x;
-		y = centre_y - robject->coord[0].y;
-		radius = sqrt(x * x + y * y);
-
-		if (!is_arc_visible(proj, centre_x, centre_y, radius) &&
-			step != proj->centre_dec)
-			continue;
-		
-		cairo_new_sub_path(robject->cr);
-
-		if (is_arc_line(proj, centre_x))
-			draw_dec_line(robject, proj, step);
-		else
-			cairo_arc(robject->cr, centre_x, centre_y, 
-					radius, 0, 2 * M_PI);
 	}
 }
-#endif
 
-/* render all visible RA grid lines */
-static void hrz_render_ra(struct render_object *robject, 
-	struct projection *proj, gint labels)
+/* get grid RA step size for projection in arcsecs */
+static gdouble get_ra_step_delta(struct projection *proj)
 {
-	gdouble centre_x, centre_y, radius, x, y, step, 
-		step_delta, ra_start, ra_end;
-	struct ln_equ_posn pos1, pos2;
-	
-	pos1.dec = -proj->centre_dec;
-	pos2.dec = -proj->centre_dec;
-
-	step_delta = get_ra_step_delta(proj);
-	clip_ra_equ_grid(proj, step_delta, &ra_start, &ra_end);
-
-	for (step = ra_start; step <= ra_end; step += step_delta) { 
-	
-		pos1.ra = step;
-		pos2.ra = step + 180.0;
-	
-		robject->coord[0].posn = &pos1;
-		robject->coord[1].posn = &pos2;
+	gint i;
 	
-		proj->trans->sky_to_proj_hrz(proj, &robject->coord[0]);
-		proj->trans->sky_to_proj_hrz(proj, &robject->coord[1]);
-	
-		centre_x = robject->coord[0].x + 
-			((robject->coord[1].x - robject->coord[0].x) / 2.0);
-		centre_y = robject->coord[0].y + 
-			((robject->coord[1].y - robject->coord[0].y) / 2.0);
-		x = centre_x - robject->coord[0].x;
-		y = centre_y - robject->coord[0].y;
-		radius = sqrt(x * x + y * y);
-
-		if (!is_arc_visible(proj, centre_x, centre_y, radius) && 
-			step != proj->centre_ra)
-			continue;
-
-/* need cairo_arc_to() */
-#if 0
-		if (step == 0.0 || step == 90.0 || 
-			step == 180.0 || step == 270.0) {
-			struct ln_equ_posn pos1, pos2;
-	
-			pos1.dec = 80.0;
-			pos2.dec = -80.0;
-			pos1.ra = step;
-			pos2.ra = step;
-			robject->num_coords = 2;
-	
-			robject->coord[0].posn = &pos1;
-			robject->coord[1].posn = &pos2;
-			proj->trans->sky_to_proj_hrz(proj, robject);
-	
-			cairo_new_sub_path(robject->cr);                                                           
-			cairo_arc_to(robject->cr, 
-				robject->coord[0].x, robject->coord[0].y, 
-				robject->coord[1].x, robject->coord[1].y,
-				radius);
-		} else {
-			if (is_arc_line(proj, centre_x))
-				draw_ra_line(robject, proj, step);
-			else {
-				cairo_new_sub_path(robject->cr);
-				cairo_arc(robject->cr, centre_x, centre_y, 
-					radius, circle_start, circle_end);
-			}
-		}
-#else
-		if (is_arc_line(proj, centre_x))
-			draw_ra_line(robject, proj, step);
-		else {
-			cairo_new_sub_path(robject->cr);
-			cairo_arc(robject->cr, centre_x, centre_y, 
-					radius, 0, 2 * M_PI);
-		}
-#endif
+	for (i = 0; i < nsize(grid_hms_ra); i++) {
+		if (proj->fov / 1.1 > grid_hms_ra[i] / 3600.0)
+			return grid_hms_ra[i] / 3600.0;
 	}
+	return grid_hms_ra[i] / 3600.0;
 }
 
-/* render all visible DEC grid lines */
-static void hrz_render_dec(struct render_object *robject, 
-	struct projection *proj, gint labels)
+/* get grid DEC step size for projection in arcsecs */
+static gdouble get_dec_step_delta(struct projection *proj)
 {
-	gdouble centre_x, centre_y, radius, x, y, step, 
-		step_delta, dec_start, dec_end;
-	struct ln_equ_posn pos1, pos2;
-	
-	pos1.ra = proj->centre_ra;
-	pos2.ra = proj->centre_ra + 180.0;
-	
-	step_delta = get_dec_step_delta(proj);
-	clip_dec_equ_grid(proj, step_delta, &dec_start, &dec_end);
-	
-	for (step = dec_start; step <= dec_end; step += step_delta) { 
-	
-		pos1.dec = step;
-		pos2.dec = step;
-	
-		robject->coord[0].posn = &pos1;
-		robject->coord[1].posn = &pos2;
+	gint i;
 	
-		proj->trans->sky_to_proj_hrz(proj, &robject->coord[0]);
-		proj->trans->sky_to_proj_hrz(proj, &robject->coord[1]);
-	
-		centre_x = robject->coord[0].x + 
-			((robject->coord[1].x - robject->coord[0].x) / 2.0);
-		centre_y = robject->coord[0].y + 
-			((robject->coord[1].y - robject->coord[0].y) / 2.0);
-		x = centre_x - robject->coord[0].x;
-		y = centre_y - robject->coord[0].y;
-		radius = sqrt(x * x + y * y);
-
-		if (!is_arc_visible(proj, centre_x, centre_y, radius) &&
-			step != proj->centre_dec)
-			continue;
-		
-		cairo_new_sub_path(robject->cr);
-
-		if (is_arc_line(proj, centre_x))
-			draw_dec_line(robject, proj, step);
-		else
-			cairo_arc(robject->cr, centre_x, centre_y, 
-					radius, 0, 2 * M_PI);
+	for (i = 0; i < nsize(grid_dms_dec); i++) {
+		if (proj->fov / 1.1 > grid_dms_dec[i] / 3600.0)
+			return grid_dms_dec[i] / 3600.0;
 	}
+	return grid_dms_dec[i] / 3600.0;
 }
 
 static void render_dec_labels_at(struct projection *proj, 
@@ -727,7 +311,7 @@ void equ_render_dec_labels(struct render_object *robject, struct projection *pro
 	pos1.ra = proj->centre_ra;
 	
 	step_delta = get_dec_step_delta(proj);
-	clip_dec_equ_grid(proj, step_delta, &dec_start, &dec_end);
+	//clip_dec_equ_grid(proj, step_delta, &dec_start, &dec_end);
 	robject->coord[0].posn = &pos1;
 	
 	for (step = dec_start; step <= dec_end; step += step_delta) { 
@@ -745,7 +329,7 @@ void equ_render_ra_labels(struct render_object *robject, struct projection *proj
 	pos1.ra = proj->centre_dec;
 	
 	step_delta = get_ra_step_delta(proj);
-	clip_ra_equ_grid(proj, step_delta, &ra_start, &ra_end);
+	//clip_ra_equ_grid(proj, step_delta, &ra_start, &ra_end);
 	robject->coord[0].posn = &pos1;
 	
 	for (step = ra_start; step <= ra_end; step += step_delta) { 
@@ -763,7 +347,7 @@ void hrz_render_dec_labels(struct render_object *robject, struct projection *pro
 	pos1.ra = proj->centre_ra;
 	
 	step_delta = get_dec_step_delta(proj);
-	clip_dec_equ_grid(proj, step_delta, &dec_start, &dec_end);
+	//clip_dec_equ_grid(proj, step_delta, &dec_start, &dec_end);
 	robject->coord[0].posn = &pos1;
 	
 	for (step = dec_start; step <= dec_end; step += step_delta) { 
@@ -781,7 +365,7 @@ void hrz_render_ra_labels(struct render_object *robject, struct projection *proj
 	pos1.ra = proj->centre_dec;
 	
 	step_delta = get_ra_step_delta(proj);
-	clip_ra_equ_grid(proj, step_delta, &ra_start, &ra_end);
+	//clip_ra_equ_grid(proj, step_delta, &ra_start, &ra_end);
 	robject->coord[0].posn = &pos1;
 	
 	for (step = ra_start; step <= ra_end; step += step_delta) { 
@@ -791,77 +375,92 @@ void hrz_render_ra_labels(struct render_object *robject, struct projection *proj
 	}
 }
 
-static void equ_render_dec(struct render_object *robject, 
-	struct projection *proj, gint labels)
+static inline void ra_line(struct render_object *robject, 
+	struct projection *proj, struct ln_equ_posn *pos, 
+	struct ln_equ_posn *end)
 {
-	gdouble step, dec_start = -90, dec_end = 90, step_delta;
-	struct ln_equ_posn pos1;
-	int start_visible, end_visible;
-	
-	step_delta = get_dec_step_delta(proj);
-	//clip_dec_equ_grid(proj, step_delta, &dec_start, &dec_end);
-	robject->coord[0].posn = &pos1;
-	
-	for (pos1.dec = dec_start; pos1.dec <= dec_end; pos1.dec += step_delta) { 
-	
-		pos1.ra = 0;
+	gdouble divs = 5.0;//proj->pixels_per_degree
+	gdouble step = (end->dec - pos->dec) / divs;
+//printf("step %3.2f\n", step);	
+	/* draw to RA end */
+	for (pos->dec = pos->dec + step; 
+		pos->dec <= end->dec; pos->dec += step) {
+//printf("ra %3.2f dec %3.2f\n", pos->ra, pos->dec);
 		proj->trans->sky_to_proj_equ(proj, &robject->coord[0]);
-		start_visible = projection_is_visible0(proj, robject);
-		cairo_move_to(robject->cr, 
-				robject->coord[0].x, 
-				robject->coord[0].y);
-	
-		for (step = 5; step <= 360; step += 5) { 
-			pos1.ra = step;
-			proj->trans->sky_to_proj_equ(proj, &robject->coord[0]);
-			end_visible = projection_is_visible0(proj, robject);
-			if (start_visible || end_visible)
-				cairo_line_to(robject->cr, 
-					robject->coord[0].x, 
-					robject->coord[0].y);
-			else
-				cairo_move_to(robject->cr, 
-					robject->coord[0].x, 
-					robject->coord[0].y);
-			start_visible = end_visible;
-		}
+		cairo_line_to(robject->cr, 
+			robject->coord[0].x, robject->coord[0].y);
 	}
 }
 
-static void equ_render_ra(struct render_object *robject, 
-	struct projection *proj, gint labels)
+static inline void dec_line(struct render_object *robject, 
+	struct projection *proj, struct ln_equ_posn *pos, 
+	struct ln_equ_posn *end)
 {
-	gdouble step, ra_start =0, ra_end = 360, step_delta;
-	struct ln_equ_posn pos1;
-	int start_visible, end_visible;
+	gdouble divs = 5.0;//proj->pixels_per_degree
+	gdouble step = (end->ra - pos->ra) / divs;
+//printf("step %3.2f\n", step);	
+	/* draw to DEC end */
+	for (pos->ra = pos->ra + step; 
+		pos->ra <= end->ra; pos->ra += step) {
+//printf("ra %3.2f dec %3.2f\n", pos->ra, pos->dec);
+		proj->trans->sky_to_proj_equ(proj, &robject->coord[0]);
+		cairo_line_to(robject->cr, 
+			robject->coord[0].x, robject->coord[0].y);
+	}
+}
+
+static inline void render_square(struct render_object *robject, 
+	struct projection *proj, gint ra, gint dec)
+{
+	gdouble ra_step_delta, dec_step_delta;
+	struct ln_equ_posn pos, start_pos, end_pos;
 	
-	step_delta = get_ra_step_delta(proj);
-	//clip_ra_equ_grid(proj, step_delta, &ra_start, &ra_end);
-	robject->coord[0].posn = &pos1;
+	ra_step_delta = get_ra_step_delta(proj);
+	dec_step_delta = get_dec_step_delta(proj);
+	robject->coord[0].posn = &pos;
+	
+	/* start corner */
+	start_pos.ra = pos.ra = ra * 15.0;
+	start_pos.dec = pos.dec = -90.0 + dec * 10.0;
 	
-	for (pos1.ra = ra_start; pos1.ra <= ra_end; pos1.ra += step_delta) { 
+	/* end corner */
+	end_pos.ra = start_pos.ra + 15.0;
+	end_pos.dec = start_pos.dec + 10.0;
 	
-		pos1.dec = -80;
+	/* RA lines */
+	for (; pos.ra <= end_pos.ra; pos.ra += ra_step_delta) {
+		
+		/* move to RA start */
+		pos.dec = start_pos.dec;
 		proj->trans->sky_to_proj_equ(proj, &robject->coord[0]);
-		start_visible = projection_is_visible0(proj, robject);
 		cairo_move_to(robject->cr, 
-				robject->coord[0].x, 
-				robject->coord[0].y);
+			robject->coord[0].x, robject->coord[0].y);
 	
-		for (step = -75; step <= 80; step += 5) { 
-			pos1.dec = step;
-			proj->trans->sky_to_proj_equ(proj, &robject->coord[0]);
-			end_visible = projection_is_visible0(proj, robject);
-			if (start_visible || end_visible)
-				cairo_line_to(robject->cr, 
-					robject->coord[0].x, 
-					robject->coord[0].y);
-			else
-				cairo_move_to(robject->cr, 
-					robject->coord[0].x, 
-					robject->coord[0].y);
-			start_visible = end_visible;
-		}
+		ra_line(robject, proj, &pos, &end_pos);
+	}
+	
+	/* DEC lines */
+	for (pos.dec = start_pos.dec; pos.dec <= end_pos.dec; 
+		pos.dec += dec_step_delta) {
+		
+		/* move to DEC start */
+		pos.ra = start_pos.ra;
+		proj->trans->sky_to_proj_equ(proj, &robject->coord[0]);
+		cairo_move_to(robject->cr, 
+			robject->coord[0].x, robject->coord[0].y);
+	
+		dec_line(robject, proj, &pos, &end_pos);
+	}	
+}
+
+void equ_render_grid(struct render_object *robject, struct projection *proj)
+{
+	gint ra, dec;
+	
+	for (ra = 0; ra < GRID_RA_TILES; ra++) {
+		for (dec = 1; dec < GRID_DEC_TILES - 2; dec++)
+			if (proj->grid_tile[ra][dec])
+				render_square(robject, proj, ra, dec);
 	}
 }
 
@@ -993,16 +592,19 @@ void grid_render(Sky *sky)
 	if (robject->type == RT_FAST) //TODO make step size * 2.0 when fast
 		cairo_set_tolerance (robject->cr, 1.0);
 	
+	get_visible_tiles(proj);
+	
 	switch (proj->grid_coords) {
 	case PC_RA_DEC:
-		equ_render_ra(robject, proj, labels);
-		equ_render_dec(robject, proj, labels);
+		//equ_render_ra(robject, proj, labels);
+		//equ_render_dec(robject, proj, labels);
+		equ_render_grid(robject, proj);
 		equ_render_dec_labels(robject, proj);
 		equ_render_ra_labels(robject, proj);
 		break;
 	case PC_ALT_AZ:
-		hrz_render_ra(robject, proj, labels);
-		hrz_render_dec(robject, proj, labels);
+		//hrz_render_ra(robject, proj, labels);
+		//hrz_render_dec(robject, proj, labels);
 		hrz_render_dec_labels(robject, proj);
 		hrz_render_ra_labels(robject, proj);
 		break;
diff --git a/src/sky/projection.c b/src/sky/projection.c
index b4b4ab3..15ec8ab 100644
--- a/src/sky/projection.c
+++ b/src/sky/projection.c
@@ -230,8 +230,8 @@ static void move_rel_pixels_hrz(struct projection *projection,
 			dec_offset / projection->pixels_per_degree;
 		break;
 	}
-	printf("hrz ra %3.2f dec %3.2f\n",projection->centre_ra, 
-		projection->centre_dec);
+	//printf("hrz ra %3.2f dec %3.2f\n",projection->centre_ra, 
+	//	projection->centre_dec);
 	projection_check_bounds(projection);
 }
 
diff --git a/src/sky/projection.h b/src/sky/projection.h
index 25c9626..f26644b 100644
--- a/src/sky/projection.h
+++ b/src/sky/projection.h
@@ -26,6 +26,9 @@
 #include "render.h"
 #include "settings.h"
 
+#define GRID_DEC_TILES	19
+#define GRID_RA_TILES	24
+
 enum projection_flip {
 	PF_NONE,
 	PF_TB,
@@ -95,6 +98,9 @@ struct projection {
 	gdouble observer_lat_sin;
 	gdouble observer_lat_cos;
 	gdouble hour_angle;
+	
+	/* grid */
+	int grid_tile[GRID_RA_TILES][GRID_DEC_TILES];	/*!< Visible grid subtiles */
 };
 
 extern struct transform transform_flip_none;
-- 
2.11.4.GIT