X-Git-Url: https://git.cworth.org/git?a=blobdiff_plain;f=acre.c;h=6d1262abe0af95f72864255d0781c688d3bf65fd;hb=bdcec99e706ccb2af0600bce67b7ade6e0abf348;hp=5949a96a1a38ccc37fe48397b0cb3ea3d755e046;hpb=256fd062ba200c24faab99c2e773744f33770c1c;p=acre diff --git a/acre.c b/acre.c index 5949a96..6d1262a 100644 --- 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" @@ -251,12 +254,86 @@ _draw_title_and_labels (acre_t *acre) cairo_restore (cr); } +/* 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) +{ + double step, scale_factor; + + /* We want roughly 5 major ticks for the chart. */ + step = range / 5; + + /* Normalize the step so we can easily snap it to a desirable + * value. */ + scale_factor = pow (10.0, floor (log10 (step))); + step /= scale_factor; + + /* We want increments of 1, 2.5, 5, or 10 (times some power of + * 10). The threshold values between these are computed + * logarithmically. */ + if (step < 3.535533905932738) { + if (step < 1.58113883008419) + step = 1.0; + else + step = 2.5; + } else { + if (step < 7.071067811865475) + step = 5.0; + else + step = 10.0; + } + + /* Un-normalize and we now have the data value that we want to + * step at. */ + return step * scale_factor; +} + +/* Given an axis range, we can compute a desired data-space step + * 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) +{ + double step, pixel_step; + + step = _step_for_range (data_range); + pixel_step = step * pixel_size / data_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); +} + +/* 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, 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++) { data = acre->data[d]; for (i = 0; i < data->num_points; i++) { @@ -271,23 +348,44 @@ _compute_axis_ranges (acre_t *acre) acre->y_axis.max = data->points[i].y; } } -} -/* 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; + /* 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); - cairo_translate (cr, - acre->chart.x + 0.5, - acre->chart.y + acre->chart.height - 0.5); - 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); + y_range = acre->y_axis.max - acre->y_axis.min; + new_y_range = _expand_range (y_range, 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; + + acre->y_axis.min -= (new_y_range - y_range) / 2.0; + acre->y_axis.max += (new_y_range - y_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); + + 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 @@ -323,39 +421,6 @@ _draw_data (acre_t *acre) cairo_restore (cr); } -static double -_step_for_range (double range) -{ - double step, scale_factor; - - /* We want roughly 5 major ticks for the chart. */ - step = range / 5; - - /* Normalize the step so we can easily snap it to a desirable - * value. */ - scale_factor = pow (10.0, floor (log10 (step))); - step /= scale_factor; - - /* We want increments of 1, 2.5, 5, or 10 (times some power of - * 10). The threshold values between these are computed - * logarithmically. */ - if (step < 3.535533905932738) { - if (step < 1.58113883008419) - step = 1.0; - else - step = 2.5; - } else { - if (step < 7.071067811865475) - step = 5.0; - else - step = 10.0; - } - - /* Un-normalize and we now have the data value that we want to - * step at. */ - return step * scale_factor; -} - static void _draw_frame_and_ticks (acre_t *acre) { @@ -379,7 +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); } @@ -395,7 +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); }