+void
+apply_gridfit(image_desc_t *im)
+{
+ if (isnan(im->minval) || isnan(im->maxval))
+ return;
+ ytr(im,DNAN);
+ if (im->logarithmic) {
+ double ya, yb, ypix, ypixfrac;
+ double log10_range = log10(im->maxval) - log10(im->minval);
+ ya = pow((double)10, floor(log10(im->minval)));
+ while (ya < im->minval)
+ ya *= 10;
+ if (ya > im->maxval)
+ return; /* don't have y=10^x gridline */
+ yb = ya * 10;
+ if (yb <= im->maxval) {
+ /* we have at least 2 y=10^x gridlines.
+ Make sure distance between them in pixels
+ are an integer by expanding im->maxval */
+ double y_pixel_delta = ytr(im, ya) - ytr(im, yb);
+ double factor = y_pixel_delta / floor(y_pixel_delta);
+ double new_log10_range = factor * log10_range;
+ double new_ymax_log10 = log10(im->minval) + new_log10_range;
+ im->maxval = pow(10, new_ymax_log10);
+ ytr(im, DNAN); /* reset precalc */
+ log10_range = log10(im->maxval) - log10(im->minval);
+ }
+ /* make sure first y=10^x gridline is located on
+ integer pixel position by moving scale slightly
+ downwards (sub-pixel movement) */
+ ypix = ytr(im, ya) + im->ysize; /* add im->ysize so it always is positive */
+ ypixfrac = ypix - floor(ypix);
+ if (ypixfrac > 0 && ypixfrac < 1) {
+ double yfrac = ypixfrac / im->ysize;
+ im->minval = pow(10, log10(im->minval) - yfrac * log10_range);
+ im->maxval = pow(10, log10(im->maxval) - yfrac * log10_range);
+ ytr(im, DNAN); /* reset precalc */
+ }
+ } else {
+ /* Make sure we have an integer pixel distance between
+ each minor gridline */
+ double ypos1 = ytr(im, im->minval);
+ double ypos2 = ytr(im, im->minval + im->ygrid_scale.gridstep);
+ double y_pixel_delta = ypos1 - ypos2;
+ double factor = y_pixel_delta / floor(y_pixel_delta);
+ double new_range = factor * (im->maxval - im->minval);
+ double gridstep = im->ygrid_scale.gridstep;
+ double minor_y, minor_y_px, minor_y_px_frac;
+ im->maxval = im->minval + new_range;
+ ytr(im, DNAN); /* reset precalc */
+ /* make sure first minor gridline is on integer pixel y coord */
+ minor_y = gridstep * floor(im->minval / gridstep);
+ while (minor_y < im->minval)
+ minor_y += gridstep;
+ minor_y_px = ytr(im, minor_y) + im->ysize; /* ensure > 0 by adding ysize */
+ minor_y_px_frac = minor_y_px - floor(minor_y_px);
+ if (minor_y_px_frac > 0 && minor_y_px_frac < 1) {
+ double yfrac = minor_y_px_frac / im->ysize;
+ double range = im->maxval - im->minval;
+ im->minval = im->minval - yfrac * range;
+ im->maxval = im->maxval - yfrac * range;
+ ytr(im, DNAN); /* reset precalc */
+ }
+ calc_horizontal_grid(im); /* recalc with changed im->maxval */
+ }
+}
+