Move most state to an edge struct

1 files changed, 61 insertions, 40 deletions

diff --git a/dda.c b/dda.c
index 033be52..8446293 100644
--- a/dda.c
+++ b/dda.c
@@ -69,6 +69,38 @@ sample_step_x_backward (double x)
 	return 0.25;
 }
 
+typedef struct
+{
+    int xi;
+    int yi;
+    int bottom;
+    int dx_positive;
+    double e;
+    double delta_e_big_x;
+    double delta_e_small_x;
+    double delta_e_big_y;
+    double delta_e_small_y;
+} edge_t;
+
+static void
+edge_init (edge_t *edge, double x0, double y0, double x1, double y1)
+{
+    double dx = (x1 - x0);
+    double dy = (y1 - y0);
+
+    edge->xi = next_sample_x (x0);
+    edge->yi = next_sample_y (y0);
+    edge->bottom = next_sample_y (y1);
+    edge->e =
+	(sample_to_pos (edge->xi) - x0) * dy -
+	(sample_to_pos (edge->yi) - y0) * dx;
+    edge->delta_e_big_x = BIG_STEP_X * dy;
+    edge->delta_e_small_x = SMALL_STEP_X * dy;
+    edge->delta_e_big_y = BIG_STEP_Y * dx;
+    edge->delta_e_small_y = SMALL_STEP_Y * dx;
+    edge->dx_positive = (dx >= 0);
+}
+
 static void
 dda (test_data_t *testdata)
 {
@@ -81,83 +113,72 @@ dda (test_data_t *testdata)
 #if 0
     printf ("= = = = %f %f %f %f = = = = \n", x0, y0, x1, y1);
 #endif
+    edge_t edge;
 
-    double dx = (x1 - x0);
-    double dy = (y1 - y0);
-    int yi = next_sample_y (y0);
-    int xi = next_sample_x (x0);
-    int bottom = next_sample_y (y1);
-    double e = (sample_to_pos (xi) - x0) * dy - (sample_to_pos (yi) - y0) * dx;
-    double delta_e_big_x, delta_e_big_y;
-    double delta_e_small_x, delta_e_small_y;
-
-    delta_e_big_x = BIG_STEP_X * dy;
-    delta_e_small_x = SMALL_STEP_X * dy;
-    delta_e_big_y = BIG_STEP_Y * dx;
-    delta_e_small_y = SMALL_STEP_Y * dx;
-
-    while (yi < bottom)
+    edge_init (&edge, x0, y0, x1, y1);
+
+    while (edge.yi < edge.bottom)
     {
-	if (dx >= 0)
+	if (edge.dx_positive)
 	{
-	    while (e <= 0)
+	    while (edge.e <= 0)
 	    {
-		if ((xi & 0xff) == N_GRID_X - 1)
+		if ((edge.xi & 0xff) == N_GRID_X - 1)
 		{
-		    e += delta_e_big_x;
-		    xi += (1 << 8);
-		    xi &= 0xffffff00;
+		    edge.e += edge.delta_e_big_x;
+		    edge.xi += (1 << 8);
+		    edge.xi &= 0xffffff00;
 		}
 		else
 		{
-		    e += delta_e_small_x;
-		    xi++;
+		    edge.e += edge.delta_e_small_x;
+		    edge.xi++;
 		}
 	    }
 	}
 	else
 	{
 	begin:
-	    if ((xi & 0xff) == 0)
+	    if ((edge.xi & 0xff) == 0)
 	    {
-		if (e > delta_e_big_x)
+		if (edge.e > edge.delta_e_big_x)
 		{
-		    e -= delta_e_big_x;
-		    xi -= (1 << 8);
-		    xi |= (N_GRID_X - 1);
+		    edge.e -= edge.delta_e_big_x;
+		    edge.xi -= (1 << 8);
+		    edge.xi |= (N_GRID_X - 1);
 		    goto small;
 		}
 	    }
 	    else
 	    {
 	    small:
-		if (e > delta_e_small_x)
+		if (edge.e > edge.delta_e_small_x)
 		{
-		    e -= delta_e_small_x;
-		    xi--;
+		    edge.e -= edge.delta_e_small_x;
+		    edge.xi--;
 		    goto begin;
 		}
 	    }
 	}
 
-	if (testdata->points[i++] != sample_to_pos (xi)		||
-	    testdata->points[i++] != sample_to_pos (yi))
+	if (testdata->points[i++] != sample_to_pos (edge.xi)		||
+	    testdata->points[i++] != sample_to_pos (edge.yi))
 	{
 	    printf ("%d error %f %f\n", i, testdata->points[i - 1],
-		    sample_to_pos (xi));
+		    sample_to_pos (edge.xi));
 	    exit (-1);
 	}
 
-	if ((yi & 0xff) == (N_GRID_Y - 1))
+	if ((edge.yi & 0xff) == (N_GRID_Y - 1))
 	{
-	    e -= delta_e_big_y;
-	    yi += (1 << 8);
-	    yi &= 0xffffff00;
+	    edge.e -= edge.delta_e_big_y;
+	    edge.yi += (1 << 8);
+	    edge.yi &= 0xffffff00;
 	}
 	else
 	{
-	    e -= delta_e_small_y;
-	    yi++;
+	    edge.e -= edge.delta_e_small_y;
+	    edge.yi++;
 	}
     }
 }