Finish adjustment of tick positions for pixel-snapping.

[acre] / acre.c

diff --git a/acre.c b/acre.c
index 6a4728ba99313b8798fdd793000e4c03e601ccc4..6d1262abe0af95f72864255d0781c688d3bf65fd 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"
 
@@ -304,13 +307,31 @@ _expand_range (double data_range, int pixel_size)
     return data_range * pixel_step / floor (pixel_step);
 }
 
+/* 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
 _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_range, new_x_range, x_adjust;
+    double y_range, new_y_range, y_adjust;
+    cairo_t *cr = acre->cr;
 
     /* First, simply find the extrema of the data. */
     for (d = 0; d < acre->num_data; d++) {
@@ -343,23 +364,28 @@ _compute_axis_ranges (acre_t *acre)
 
     acre->y_axis.min -= (new_y_range - y_range) / 2.0;
     acre->y_axis.max += (new_y_range - y_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;
+    /* 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);
 
-    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);
+       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);
+
+       acre->x_axis.min -= x_adjust;
+       acre->x_axis.max -= x_adjust;
+
+       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);
            }