Eliminate some code duplication in the tick adjustment phase.

[acre] / acre.c

diff --git a/acre.c b/acre.c
index 6a4728ba99313b8798fdd793000e4c03e601ccc4..6149cd38515b849786643811547351970393bb5a 100644 (file)
--- a/acre.c
+++ b/acre.c
@@ -17,6 +17,9 @@
  * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
  */
 
+#define _ISOC99_SOURCE /* for round() */
+#define _XOPEN_SOURCE 500
+
 #include "acre.h"
 #include "xmalloc.h"
 
@@ -290,18 +293,41 @@ _step_for_range (double range)
  * amount for the major ticks (see _step_for_range). To get
  * nice-looking pixel-snapped ticks we want to expand the range
  * slightly. */
-static double
-_expand_range (double data_range, int pixel_size)
+static void
+_expand_range_for_width (double *axis_min, double *axis_max, int pixel_size)
 {
-    double step, pixel_step;
+    double range, new_range, step, pixel_step;
 
-    step = _step_for_range (data_range);
-    pixel_step = step * pixel_size / data_range;
+    range = *axis_max - *axis_min;
+
+    step = _step_for_range (range);
+    pixel_step = step * pixel_size / range;
 
     /* We expand the range by the ratio of the pixel step to the floor
      * of the pixel_step.
      */
-    return data_range * pixel_step / floor (pixel_step);
+    new_range = range * pixel_step / floor (pixel_step);
+
+    /* And spread the increase out on either side of the range. */
+    *axis_min -= (new_range - range) / 2.0;
+    *axis_max += (new_range - range) / 2.0;
+}
+
+/* Setup a transformation in acre->cr such that data values plotted
+ * will appear where they should within the chart.
+ */
+static void
+_set_transform_to_data_space (acre_t *acre)
+{
+    cairo_t *cr = acre->cr;
+
+    cairo_translate (cr,
+                    acre->chart.x,
+                    acre->chart.y + acre->chart.height);
+    cairo_scale (cr,
+                acre->chart.width / (acre->x_axis.max - acre->x_axis.min),
+                - acre->chart.height /(acre->y_axis.max - acre->y_axis.min));
+    cairo_translate (cr, -acre->x_axis.min, -acre->y_axis.min);
 }
 
 static void
@@ -309,8 +335,8 @@ _compute_axis_ranges (acre_t *acre)
 {
     unsigned int d, i;
     acre_data_t *data;
-    double x_range, new_x_range;
-    double y_range, new_y_range;
+    double x_adjust, y_adjust;
+    cairo_t *cr = acre->cr;
 
     /* First, simply find the extrema of the data. */
     for (d = 0; d < acre->num_data; d++) {
@@ -331,35 +357,35 @@ _compute_axis_ranges (acre_t *acre)
     /* Next, increase the axis ranges just enough so that the step
      * sizes for the ticks will be integers.
      */
-    x_range = acre->x_axis.max - acre->x_axis.min;
-    new_x_range = _expand_range (x_range, acre->chart.width);
+    _expand_range_for_width (&acre->x_axis.min,
+                            &acre->x_axis.max,
+                            acre->chart.width);
 
-    y_range = acre->y_axis.max - acre->y_axis.min;
-    new_y_range = _expand_range (y_range, acre->chart.height);
+    _expand_range_for_width (&acre->y_axis.min,
+                            &acre->y_axis.max,
+                            acre->chart.height);
 
-    /* And spread the increase out on either side of the range. */
-    acre->x_axis.min -= (new_x_range - x_range) / 2.0;
-    acre->x_axis.max += (new_x_range - x_range) / 2.0;
+    /* Finally, we also translate the axis ranges slightly so that the
+     * ticks land on half-integer device-pixel positions.
+     */
+    cairo_save (cr);
+    {
+       _set_transform_to_data_space (acre);
 
-    acre->y_axis.min -= (new_y_range - y_range) / 2.0;
-    acre->y_axis.max += (new_y_range - y_range) / 2.0;
-}
+       x_adjust = 0.0;
+       y_adjust = 0.0;
+       cairo_user_to_device (cr, &x_adjust, &y_adjust);
+       x_adjust = (round (x_adjust + 0.5) - 0.5) - x_adjust;
+       y_adjust = (round (y_adjust + 0.5) - 0.5) - y_adjust;
+       cairo_device_to_user_distance (cr, &x_adjust, &y_adjust);
 
-/* Setup a transformation in acre->cr such that data values plotted
- * will appear where they should within the chart.
- */
-static void
-_set_transform_to_data_space (acre_t *acre)
-{
-    cairo_t *cr = acre->cr;
+       acre->x_axis.min -= x_adjust;
+       acre->x_axis.max -= x_adjust;
 
-    cairo_translate (cr,
-                    acre->chart.x,
-                    acre->chart.y + acre->chart.height);
-    cairo_scale (cr,
-                acre->chart.width / (acre->x_axis.max - acre->x_axis.min),
-                - acre->chart.height /(acre->y_axis.max - acre->y_axis.min));
-    cairo_translate (cr, -acre->x_axis.min, -acre->y_axis.min);
+       acre->y_axis.min -= y_adjust;
+       acre->y_axis.max -= y_adjust;
+    }
+    cairo_restore (cr);
 }
 
 static void
@@ -418,7 +444,7 @@ _draw_frame_and_ticks (acre_t *acre)
            {
                cairo_identity_matrix (cr);
                cairo_rel_line_to (cr, 0, 0.5);
-               cairo_rel_line_to (cr, 0, -ACRE_TICK_SIZE);
+               cairo_rel_line_to (cr, 0, -ACRE_TICK_SIZE-0.5);
                cairo_set_line_width (cr, 1.0);
                cairo_stroke (cr);
            }
@@ -434,7 +460,7 @@ _draw_frame_and_ticks (acre_t *acre)
            {
                cairo_identity_matrix (cr);
                cairo_rel_line_to (cr, -0.5, 0);
-               cairo_rel_line_to (cr, ACRE_TICK_SIZE, 0);
+               cairo_rel_line_to (cr, ACRE_TICK_SIZE+0.5, 0);
                cairo_set_line_width (cr, 1.0);
                cairo_stroke (cr);
            }