Make xi a sample number

1 files changed, 50 insertions, 38 deletions

diff --git a/dda.c b/dda.c
index dcc3dca..d0ba4b7 100644
--- a/dda.c
+++ b/dda.c
@@ -14,31 +14,14 @@
 #define SMALL_STEP_Y           0.25
 #define FIRST_STEP_Y           0.125
 
-static double
-next_sample_x (double x)
-{
-    double i = floor (x);
-    double f = x - i;
-    double s =  (floor ((f - STEP/2.0) / STEP) + 1) * (STEP) + STEP/2.0;
-
-    if (s == 0.875)
-    {
-	s += STEP;
-    }
-
-    if (s > 1.0)
-    {
-	s -= 1.0;
-	i += 1;
-    }
-
-    return s + i;
-}
+#define BIG_STEP_X             0.5
+#define SMALL_STEP_X           0.25
+#define FIRST_STEP_X           0.125
 
 static double
 sample_to_pos (int y)
 {
-    return (((unsigned)y) >> 8) + (y & 0xff) * SMALL_STEP_Y + FIRST_STEP_Y;
+    return (y >> 8) + (y & 0xff) * SMALL_STEP_Y + FIRST_STEP_Y;
 }
 
 static int
@@ -62,6 +45,12 @@ next_sample_y (double y)
     return r;
 }
 
+static int
+next_sample_x (double x)
+{
+    return next_sample_y (x);
+}
+
 static double
 sample_step_x_forward (double x)
 {
@@ -89,43 +78,66 @@ dda (test_data_t *testdata)
     double y1 = testdata->segment.y1;
     int i = 0;
 
-    double dx = (x1 - x0);
-    double dy = (y1 - y0);
-    int yi = next_sample_y (y0);
-    double xi = next_sample_x (x0);
-    double e = (xi - x0) * dy - (sample_to_pos (yi) - y0) * dx;
-
 #if 0
     printf ("= = = = %f %f %f %f = = = = \n", x0, y0, x1, y1);
 #endif
 
+    double dx = (x1 - x0);
+    double dy = (y1 - y0);
+    int yi = next_sample_y (y0);
+    int xi = next_sample_x (x0);
+    double e = (sample_to_pos (xi) - x0) * dy - (sample_to_pos (yi) - y0) * dx;
+
     while (yi < next_sample_y (y1))
     {
 	if (dx >= 0)
 	{
 	    while (e <= 0)
 	    {
-		double s = sample_step_x_forward (xi);
-
-		e += s * dy;
-		xi += s;
+		if ((xi & 0xff) == N_GRID_X - 1)
+		{
+		    e += BIG_STEP_X * dy;
+		    xi += (1 << 8);
+		    xi &= 0xffffff00;
+		}
+		else
+		{
+		    e += SMALL_STEP_X * dy;
+		    xi++;
+		}
 	    }
 	}
 	else
 	{
-	    double s;
-
-	    while (s = sample_step_x_backward (xi), e > s * dy)
+	begin:
+	    if ((xi & 0xff) == 0)
 	    {
-		e -= s * dy;
-		xi -= s;
+		if (e > BIG_STEP_X * dy)
+		{
+		    e -= BIG_STEP_X * dy;
+		    xi -= (1 << 8);
+		    xi |= (N_GRID_X - 1);
+
+		    goto begin;
+		}
+	    }
+	    else
+	    {
+		if (e > SMALL_STEP_X * dy)
+		{
+		    e -= SMALL_STEP_X * dy;
+		    xi--;
+
+		    goto begin;
+		}
 	    }
 	}
 
-	if (testdata->points[i++] != xi		||
+	if (testdata->points[i++] != sample_to_pos (xi)		||
 	    testdata->points[i++] != sample_to_pos (yi))
 	{
-	    printf ("%d error %f %f\n", i, testdata->points[i - 1], sample_to_pos (yi));
+	    printf ("%d error %f %f\n", i, testdata->points[i - 1],
+		    sample_to_pos (xi));
 	    exit (-1);
 	}