Fix rounding when deciding between major and minor tick

[acre] / acre.c

diff --git a/acre.c b/acre.c
index 8ba639ebf24e5c86321a482c6b9e2482ce3aa6d6..3ddf14382a880a7db7edebff34512040e34fb1e3 100644 (file)
--- a/acre.c
+++ b/acre.c
@@ -164,7 +164,6 @@ acre_add_data (acre_t *acre, acre_data_t *data)
 #define ACRE_PAD (ACRE_FONT_SIZE)
 #define ACRE_TICK_MAJOR_SIZE 6
 #define ACRE_TICK_MINOR_SIZE 3
-#define ACRE_TICK_MINOR_DIVISIONS 5
 #define ACRE_X_TICK_VALUE_PAD 2
 #define ACRE_Y_TICK_VALUE_PAD 4
 
@@ -335,7 +334,7 @@ _draw_title_and_labels (acre_t *acre)
 /* For a given axis range, compute a step size (in data space) to
  * generate a suitable number of ticks (5 or so). */
 static double
-_step_for_range (double range)
+_step_for_range (double range, int *minor_divisions)
 {
     double step, scale_factor;
 
@@ -351,15 +350,21 @@ _step_for_range (double range)
      * 10). The threshold values between these are computed
      * logarithmically. */
     if (step < 3.535533905932738) {
-       if (step < 1.58113883008419)
+       if (step < 1.58113883008419) {
            step = 1.0;
-       else
+           *minor_divisions = 4;
+       } else {
            step = 2.5;
+           *minor_divisions = 5;
+       }
     } else {
-       if (step < 7.071067811865475)
+       if (step < 7.071067811865475) {
            step = 5.0;
-       else
+           *minor_divisions = 5;
+       } else {
            step = 10.0;
+           *minor_divisions = 4;
+       }
     }
 
     /* Un-normalize and we now have the data value that we want to
@@ -372,14 +377,17 @@ _step_for_range (double range)
  * nice-looking pixel-snapped ticks we want to expand the range
  * slightly. */
 static void
-_expand_range_for_width (double *axis_min, double *axis_max, int pixel_size)
+_expand_range_for_width (double *axis_min, double *axis_max, int pixel_range)
 {
-    double range, new_range, step, pixel_step;
+    double range, new_range, step, step_minor, pixel_step;
+    int minor_divisions;
 
     range = *axis_max - *axis_min;
 
-    step = _step_for_range (range);
-    pixel_step = step * pixel_size / range / ACRE_TICK_MINOR_DIVISIONS;
+    step = _step_for_range (range, &minor_divisions);
+    step_minor = step / minor_divisions;
+
+    pixel_step = step_minor * (pixel_range / range);
 
     /* We expand the range by the ratio of the pixel step to the floor
      * of the pixel_step.
@@ -437,7 +445,24 @@ _compute_axis_ranges (acre_t *acre)
        }
     }
 
-    /* Next, increase the axis ranges just enough so that the step
+    /* Next, we want to ensure that the data never collides with the
+     * ticks. So we expand each axis on its minimum side as needed. */
+    cairo_save (cr);
+    {
+       double x, y;
+
+       _set_transform_to_data_space (acre);
+
+       x = ACRE_TICK_MAJOR_SIZE + 2.0;
+       y = ACRE_TICK_MAJOR_SIZE + 2.0;
+       cairo_device_to_user_distance (cr, &x, &y);
+
+       acre->x_axis.min -= x;
+       acre->y_axis.min += y;
+    }
+    cairo_restore (cr);
+
+    /* Then, increase the axis ranges just enough so that the step
      * sizes for the ticks will be integers.
      */
     _expand_range_for_width (&acre->x_axis.min,
@@ -513,20 +538,21 @@ _draw_ticks (acre_t *acre,
 {
     cairo_t *cr = acre->cr;
     double t, step, sub_step;
+    int minor_divisions;
 
     cairo_save (cr);
 
     _set_transform_to_data_space (acre);
 
-    step = _step_for_range (axis_max - axis_min);
-    sub_step = step / ACRE_TICK_MINOR_DIVISIONS;
+    step = _step_for_range (axis_max - axis_min, &minor_divisions);
+    sub_step = step / minor_divisions;
 
     for (t = (floor (axis_min / sub_step) + 1) * sub_step;
         t <= axis_max;
         t += sub_step)
     {
        int tick_size;
-       if (fabs((t / step) - (int) (t / step)) < 0.5 * (sub_step / step))
+       if (fabs((t / step) - round (t / step)) < 0.5 * (sub_step / step))
            tick_size = ACRE_TICK_MAJOR_SIZE;
        else
            tick_size = ACRE_TICK_MINOR_SIZE;