short edge e update

1 files changed, 72 insertions, 19 deletions

diff --git a/poly2.c b/poly2.c
index 0d8632b..cc8e41c 100644
--- a/poly2.c
+++ b/poly2.c
@@ -121,7 +121,6 @@ step_y (sample_t yi)
 	return yi + 1;
 }
 
-
 typedef struct polygon_t polygon_t;
 typedef struct point_t point_t;
 typedef struct seg_t seg_t;
@@ -154,7 +153,8 @@ typedef struct uninitialized_edge_t uninitialized_edge_t;
 typedef enum
 {
     VERTICAL,
-    SHORT,
+    SHORT_W,
+    SHORT_E,
     LONG,
     UNINITIALIZED
 } edge_type_t;
@@ -162,36 +162,39 @@ typedef enum
 struct edge_common_t
 {
     edge_type_t	type;
-    sample_t	bottom;
     int		dir;
+    sample_t	xi;
+    sample_t	bottom;
 };
 
 struct short_edge_t
 {
-    sample_t	xi;
-    uint32_t	e;
-    uint32_t	delta_e_big_x;
-    uint32_t	delta_e_small_x;
-    uint32_t	delta_e_big_y;
-    uint32_t	delta_e_small_y;
+    edge_common_t	common;
+    uint32_t		e;
+    uint32_t		delta_e_big_x;
+    uint32_t		delta_e_small_x;
+    uint32_t		delta_e_big_y;
+    uint32_t		delta_e_small_y;
 };
 
 struct vertical_edge_t
 {
-    sample_t	xi;
+    edge_common_t	common;
 };
 
 struct long_edge_t
 {
+    edge_common_t	common;
     /* stuff here, pointer */
 };
 
 struct uninitialized_edge_t
 {
-    sample_t	   yi;
-    const seg_t   *seg;
-    const point_t *top;
-    const point_t *bottom;
+    edge_common_t	common;
+    sample_t		yi;
+    const seg_t *	seg;
+    const point_t *	top;
+    const point_t *	bottom;
 };
 
 union edge_t
@@ -205,6 +208,48 @@ union edge_t
 };
 
 static void
+short_e_edge_update_error (short_edge_t *edge)
+{
+    while (edge->e <= 0)
+    {
+	if (fixed_frac (edge->common.xi) == N_GRID_X - 1)
+	{
+	    edge->e += edge->delta_e_big_x;
+	    edge->common.xi = fixed_floor (edge->common.xi + fixed_1);
+	}
+	else
+	{
+	    edge->e += edge->delta_e_small_x;
+	    edge->common.xi++;
+	}
+    }
+}
+
+static void
+short_w_edge_update_error (short_edge_t *edge)
+{
+again:
+    if (fixed_frac (edge->common.xi) == 0)
+    {
+	if (edge->e > edge->delta_e_big_x)
+	{
+	    edge->e -= edge->delta_e_big_x;
+	    edge->common.xi = (edge->common.xi - fixed_1) | (N_GRID_X - 1);
+	    goto again;
+	}
+    }
+    else
+    {
+	if (edge->e > edge->delta_e_small_x)
+	{
+	    edge->e -= edge->delta_e_small_x;
+	    edge->common.xi--;
+	    goto again;
+	}
+    }
+}
+
+static void
 edge_init (edge_t *edge, sample_t first_yi)
 {
     const point_t *top = edge->uninitialized.top;
@@ -213,12 +258,12 @@ edge_init (edge_t *edge, sample_t first_yi)
 
     edge->common.dir = 2 * (top == &seg->p1) - 1;
     edge->common.bottom = next_sample_y (bottom->y);
+    edge->common.xi = next_sample_x (top->x);
 
     if (top->x == bottom->x)
     {
 	/* vertical */
 	edge->common.type = VERTICAL;
-	edge->vertical.xi = next_sample_x (top->x);
     }
     else
     {
@@ -234,16 +279,24 @@ edge_init (edge_t *edge, sample_t first_yi)
 	    dx < 8 * dy)
 	{
 	    /* short */
-	    sample_t xi = next_sample_x (top->x);
-
-	    edge->short_.xi = xi;
 	    edge->short_.e =
-		(sample_to_pos_x (xi) - top->x) * dy -
+		(sample_to_pos_x (edge->common.xi) - top->x) * dy -
 		(sample_to_pos_y (first_yi) - top->y) * dx;
 	    edge->short_.delta_e_big_x = BIG_STEP_X * dy;
 	    edge->short_.delta_e_small_x = SMALL_STEP_X * dy;
 	    edge->short_.delta_e_big_y = BIG_STEP_Y * dx;
 	    edge->short_.delta_e_small_y = SMALL_STEP_Y * dx;
+
+	    if (dx >= 0)
+	    {
+		edge->common.type = SHORT_E;
+		short_e_edge_update_error (&edge->short_);
+	    }
+	    else
+	    {
+		edge->common.type = SHORT_W;
+		short_w_edge_update_error (&edge->short_);
+	    }
 	}
 	else
 	{