levels.c

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/*
    This file is part of darktable,
    Copyright (C) 2009-2013, 2016, 2018 johannes hanika.
    Copyright (C) 2010 Alexandre Prokoudine.
    Copyright (C) 2010-2011 Bruce Guenter.
    Copyright (C) 2010-2012 Henrik Andersson.
    Copyright (C) 2010, 2012-2016, 2018-2019 Tobias Ellinghaus.
    Copyright (C) 2011 Jochen Schroeder.
    Copyright (C) 2011 Olivier Tribout.
    Copyright (C) 2011 Robert Bieber.
    Copyright (C) 2011 Rostyslav Pidgornyi.
    Copyright (C) 2011-2014, 2016-2017 Ulrich Pegelow.
    Copyright (C) 2012 Christian Tellefsen.
    Copyright (C) 2012 José Carlos García Sogo.
    Copyright (C) 2012, 2014 parafin.
    Copyright (C) 2012 Richard Wonka.
    Copyright (C) 2013 Dennis Gnad.
    Copyright (C) 2013-2016 Roman Lebedev.
    Copyright (C) 2014, 2018-2022 Pascal Obry.
    Copyright (C) 2015 Pedro Côrte-Real.
    Copyright (C) 2017-2018, 2020-2021 Dan Torop.
    Copyright (C) 2017 Heiko Bauke.
    Copyright (C) 2018-2019, 2022-2026 Aurélien PIERRE.
    Copyright (C) 2018-2019 Edgardo Hoszowski.
    Copyright (C) 2018 Maurizio Paglia.
    Copyright (C) 2018 rawfiner.
    Copyright (C) 2019 Andreas Schneider.
    Copyright (C) 2019-2020, 2022 Diederik Ter Rahe.
    Copyright (C) 2019 Diederik ter Rahe.
    Copyright (C) 2019 emeikei.
    Copyright (C) 2020 Aldric Renaudin.
    Copyright (C) 2020-2021 Chris Elston.
    Copyright (C) 2020-2021 Ralf Brown.
    Copyright (C) 2021 Hubert Kowalski.
    Copyright (C) 2021 lhietal.
    Copyright (C) 2022 Hanno Schwalm.
    Copyright (C) 2022 Martin Bařinka.
    Copyright (C) 2022 Philipp Lutz.
    
    darktable is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.
    
    darktable is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
    
    You should have received a copy of the GNU General Public License
    along with darktable.  If not, see <http://www.gnu.org/licenses/>.
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <assert.h>
#include <math.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
 
#include "bauhaus/bauhaus.h"
#include "common/colorspaces.h"
#include "common/opencl.h"
#include "control/control.h"
#include "develop/develop.h"
#include "develop/imageop.h"
#include "develop/imageop_math.h"
#include "develop/imageop_gui.h"
#include "develop/openmp_maths.h"
#include "dtgtk/drawingarea.h"
#include "gui/draw.h"
#include "gui/gtk.h"
 
#include "gui/presets.h"
#include "iop/iop_api.h"
#include "libs/colorpicker.h"
 
#define DT_GUI_CURVE_EDITOR_INSET DT_PIXEL_APPLY_DPI(5)
#define DT_GUI_CURVE_INFL .3f
 
DT_MODULE_INTROSPECTION(2, dt_iop_levels_params_t)
 
static gboolean dt_iop_levels_area_draw(GtkWidget *widget, cairo_t *crf, gpointer user_data);
static gboolean dt_iop_levels_motion_notify(GtkWidget *widget, GdkEventMotion *event, gpointer user_data);
static gboolean dt_iop_levels_button_press(GtkWidget *widget, GdkEventButton *event, gpointer user_data);
static gboolean dt_iop_levels_button_release(GtkWidget *widget, GdkEventButton *event, gpointer user_data);
static gboolean dt_iop_levels_leave_notify(GtkWidget *widget, GdkEventCrossing *event, gpointer user_data);
static gboolean dt_iop_levels_scroll(GtkWidget *widget, GdkEventScroll *event, gpointer user_data);
static void dt_iop_levels_autoadjust_callback(GtkRange *range, dt_iop_module_t *self);
//static void dt_iop_levels_mode_callback(GtkWidget *combo, gpointer user_data);
//static void dt_iop_levels_percentiles_callback(GtkWidget *slider, gpointer user_data);
 
typedef enum dt_iop_levels_mode_t
{
  LEVELS_MODE_MANUAL,   // $DESCRIPTION: "manual"
  LEVELS_MODE_AUTOMATIC // $DESCRIPTION: "automatic"
} dt_iop_levels_mode_t;
 
typedef struct dt_iop_levels_params_t
{
  dt_iop_levels_mode_t mode; // $DEFAULT: LEVELS_MODE_MANUAL
  float black; // $MIN: 0.0 $MAX: 100.0 $DEFAULT: 0.0
  float gray;  // $MIN: 0.0 $MAX: 100.0 $DEFAULT: 50.0
  float white; // $MIN: 0.0 $MAX: 100.0 $DEFAULT: 100.0
  float levels[3];
} dt_iop_levels_params_t;
 
typedef struct dt_iop_levels_gui_data_t
{
  GList *modes;
  GtkWidget *mode;
  GtkWidget *mode_stack;
  GtkDrawingArea *area;
  double mouse_x, mouse_y;
  int dragging, handle_move;
  float drag_start_percentage;
  GtkToggleButton *activeToggleButton;
  float last_picked_color;
  GtkWidget *percentile_black;
  GtkWidget *percentile_grey;
  GtkWidget *percentile_white;
  float auto_levels[3];
  uint64_t hash;
  GtkWidget *blackpick, *greypick, *whitepick;
} dt_iop_levels_gui_data_t;
 
typedef struct dt_iop_levels_data_t
{
  dt_iop_levels_mode_t mode;
  float percentiles[3];
  float levels[3];
  float in_inv_gamma;
  float lut[0x10000];
} dt_iop_levels_data_t;
 
const char *name()
{
  return _("levels (legacy)");
}
 
int default_group()
{
  return IOP_GROUP_TONES;
}
 
int flags()
{
  return IOP_FLAGS_SUPPORTS_BLENDING | IOP_FLAGS_DEPRECATED;
}
 
int default_colorspace(dt_iop_module_t *self, dt_dev_pixelpipe_t *pipe, const dt_dev_pixelpipe_iop_t *piece)
{
  return IOP_CS_LAB;
}
 
void input_format(dt_iop_module_t *self, dt_dev_pixelpipe_t *pipe, dt_dev_pixelpipe_iop_t *piece,
                  dt_iop_buffer_dsc_t *dsc)
{
  default_input_format(self, pipe, piece, dsc);
  dsc->channels = 4;
  dsc->datatype = TYPE_FLOAT;
}
 
const char **description(struct dt_iop_module_t *self)
{
  return dt_iop_set_description(self, _("adjust black, white and mid-gray points"),
                                      _("creative"),
                                      _("linear or non-linear, Lab, display-referred"),
                                      _("non-linear, Lab"),
                                      _("non-linear, Lab, display-referred"));
}
 
int legacy_params(dt_iop_module_t *self, const void *const old_params, const int old_version,
                  void *new_params, const int new_version)
{
  if(old_version == 1 && new_version == 2)
  {
    typedef struct dt_iop_levels_params_v1_t
    {
      float levels[3];
      int levels_preset;
    } dt_iop_levels_params_v1_t;
 
    dt_iop_levels_params_v1_t *o = (dt_iop_levels_params_v1_t *)old_params;
    dt_iop_levels_params_t *n = (dt_iop_levels_params_t *)new_params;
    dt_iop_levels_params_t *d = (dt_iop_levels_params_t *)self->default_params;
 
    *n = *d; // start with a fresh copy of default parameters
 
    n->levels[0] = o->levels[0];
    n->levels[1] = o->levels[1];
    n->levels[2] = o->levels[2];
    return 0;
  }
  return 1;
}
 
static void dt_iop_levels_compute_levels_manual(const uint32_t *histogram, float *levels)
{
  if(IS_NULL_PTR(histogram)) return;
 
  // search histogram for min (search from bottom)
  for(int k = 0; k <= 4 * 255; k += 4)
  {
    if(histogram[k] > 1)
    {
      levels[0] = ((float)(k) / (4 * 256));
      break;
    }
  }
  // then for max (search from top)
  for(int k = 4 * 255; k >= 0; k -= 4)
  {
    if(histogram[k] > 1)
    {
      levels[2] = ((float)(k) / (4 * 256));
      break;
    }
  }
  levels[1] = levels[0] / 2 + levels[2] / 2;
}
 
__DT_CLONE_TARGETS__
static void dt_iop_levels_compute_levels_automatic(dt_iop_module_t *self,
                                                   const dt_dev_pixelpipe_iop_t *piece)
{
  dt_iop_levels_data_t *d = (dt_iop_levels_data_t *)piece->data;
  dt_dev_histogram_stats_t histogram_stats = { 0 };
  uint32_t *histogram = NULL;
 
  dt_iop_gui_enter_critical_section(self);
  histogram_stats = self->histogram_stats;
  if(self->histogram && histogram_stats.bins_count > 0)
  {
    const size_t histogram_size = 4 * histogram_stats.bins_count * sizeof(uint32_t);
    histogram = dt_alloc_align(histogram_size);
    if(!IS_NULL_PTR(histogram)) memcpy(histogram, self->histogram, histogram_size);
  }
  dt_iop_gui_leave_critical_section(self);
 
  uint32_t total = histogram_stats.pixels;
 
  dt_aligned_pixel_t thr;
  for(int k = 0; k < 3; k++)
  {
    thr[k] = (float)total * d->percentiles[k] / 100.0f;
    d->levels[k] = NAN;
  }
 
  if(IS_NULL_PTR(histogram)) return;
 
  // find min and max levels
  size_t n = 0;
  for(uint32_t i = 0; i < histogram_stats.bins_count; i++)
  {
    n += histogram[4 * i];
 
    for(int k = 0; k < 3; k++)
    {
      if(isnan(d->levels[k]) && (n >= thr[k]))
      {
        d->levels[k] = (float)i / (float)(histogram_stats.bins_count - 1);
      }
    }
  }
 
  dt_free_align(histogram);
 
  // for numerical reasons sometimes the threshold is sharp but in float and n is size_t.
  // in this case we want to make sure we don't keep nan:
  if(isnan(d->levels[2])) d->levels[2] = 1.0f;
 
  // compute middle level from min and max levels
  float center = d->percentiles[1] / 100.0f;
  if(!isnan(d->levels[0]) && !isnan(d->levels[2]))
    d->levels[1] = (1.0f - center) * d->levels[0] + center * d->levels[2];
}
 
__DT_CLONE_TARGETS__
static void compute_lut(const dt_dev_pixelpipe_iop_t *piece)
{
  dt_iop_levels_data_t *d = (dt_iop_levels_data_t *)piece->data;
 
  // Building the lut for values in the [0,1] range
  float delta = (d->levels[2] - d->levels[0]) / 2.0f;
  float mid = d->levels[0] + delta;
  float tmp = (d->levels[1] - mid) / delta;
  d->in_inv_gamma = pow(10, tmp);
 
  for(unsigned int i = 0; i < 0x10000; i++)
  {
    float percentage = (float)i / (float)0x10000ul;
    d->lut[i] = 100.0f * powf(percentage, d->in_inv_gamma);
  }
}
 
void color_picker_apply(dt_iop_module_t *self, GtkWidget *picker, dt_dev_pixelpipe_t *pipe, dt_dev_pixelpipe_iop_t *piece)
{
  (void)pipe;
  (void)piece;
  dt_iop_levels_gui_data_t *c = (dt_iop_levels_gui_data_t *)self->gui_data;
  dt_iop_levels_params_t *p = (dt_iop_levels_params_t *)self->params;
 
  /* we need to save the last picked color to prevent flickering when
   * changing from one picker to another, as the picked_color value does not
   * update as rapidly */
 
  float mean_picked_color = *self->picked_color / 100.0;
 
  if(mean_picked_color != c->last_picked_color)
  {
    dt_aligned_pixel_t previous_color;
    previous_color[0] = p->levels[0];
    previous_color[1] = p->levels[1];
    previous_color[2] = p->levels[2];
 
    c->last_picked_color = mean_picked_color;
 
    if(picker == c->blackpick)
    {
      if(mean_picked_color > p->levels[1])
      {
        p->levels[0] = p->levels[1] - FLT_EPSILON;
      }
      else
      {
        p->levels[0] = mean_picked_color;
      }
    }
    else if(picker == c->greypick)
    {
      if(mean_picked_color < p->levels[0] || mean_picked_color > p->levels[2])
      {
        p->levels[1] = p->levels[1];
      }
      else
      {
        p->levels[1] = mean_picked_color;
      }
    }
    else if(picker == c->whitepick)
    {
      if(mean_picked_color < p->levels[1])
      {
        p->levels[2] = p->levels[1] + FLT_EPSILON;
      }
      else
      {
        p->levels[2] = mean_picked_color;
      }
    }
 
    if(previous_color[0] != p->levels[0]
       || previous_color[1] != p->levels[1]
       || previous_color[2] != p->levels[2])
    {
      dt_dev_add_history_item(darktable.develop, self, TRUE, TRUE);
    }
  }
}
 
/*
 * WARNING: unlike commit_params, which is thread safe wrt gui thread and
 * pipes, this function lives in the pipeline thread, and NOT thread safe!
 */
static inline __attribute__((always_inline)) void commit_params_late(dt_iop_module_t *self, const dt_dev_pixelpipe_t *pipe,
                               const dt_dev_pixelpipe_iop_t *piece)
{
  dt_iop_levels_data_t *d = (dt_iop_levels_data_t *)piece->data;
  dt_iop_levels_gui_data_t *g = (dt_iop_levels_gui_data_t *)self->gui_data;
 
  if(d->mode == LEVELS_MODE_AUTOMATIC)
  {
    if(!IS_NULL_PTR(g) && !dt_dev_pixelpipe_has_preview_output(self->dev, pipe, &piece->roi_out))
    {
      dt_iop_gui_enter_critical_section(self);
      const uint64_t hash = g->hash;
      dt_iop_gui_leave_critical_section(self);
 
      // note that the case 'hash == 0' on first invocation in a session implies that d->levels[]
      // contains NANs which initiates special handling below to avoid inconsistent results. in all
      // other cases we make sure that the preview pipe has left us with proper readings for
      // g->auto_levels[]. if data are not yet there we need to wait (with timeout).
      if(hash != piece->global_hash)
        dt_control_log(_("inconsistent output"));
 
      dt_iop_gui_enter_critical_section(self);
      d->levels[0] = g->auto_levels[0];
      d->levels[1] = g->auto_levels[1];
      d->levels[2] = g->auto_levels[2];
      dt_iop_gui_leave_critical_section(self);
 
      compute_lut(piece);
    }
 
    if(dt_dev_pixelpipe_has_preview_output(self->dev, pipe, &piece->roi_out)
       || isnan(d->levels[0]) || isnan(d->levels[1])
       || isnan(d->levels[2]))
    {
      dt_iop_levels_compute_levels_automatic(self, piece);
      compute_lut(piece);
    }
 
    if(!IS_NULL_PTR(g) && dt_dev_pixelpipe_has_preview_output(self->dev, pipe, &piece->roi_out)
       && d->mode == LEVELS_MODE_AUTOMATIC)
    {
      uint64_t hash = piece->global_hash;
      dt_iop_gui_enter_critical_section(self);
      g->auto_levels[0] = d->levels[0];
      g->auto_levels[1] = d->levels[1];
      g->auto_levels[2] = d->levels[2];
      g->hash = hash;
      dt_iop_gui_leave_critical_section(self);
    }
  }
}
 
__DT_CLONE_TARGETS__
int process(dt_iop_module_t *self, const dt_dev_pixelpipe_t *pipe, const dt_dev_pixelpipe_iop_t *piece,
            const void *const ivoid, void *const ovoid)
{
  const dt_iop_roi_t *const roi_out = &piece->roi_out;
  const int ch = 4;
  const dt_iop_levels_data_t *const d = (dt_iop_levels_data_t *)piece->data;
  (void)pipe;
 
  if(d->mode == LEVELS_MODE_AUTOMATIC)
  {
    commit_params_late(self, pipe, piece);
  }
 
  const float *const restrict in = (float*)ivoid;
  float *const restrict out = (float*)ovoid;
  const size_t npixels = (size_t)roi_out->width * roi_out->height;
  __OMP_PARALLEL_FOR__()
  for(int i = 0; i < ch * npixels; i += ch)
  {
    const float L_in = in[i] / 100.0f;
    float L_out;
    if(L_in <= d->levels[0])
    {
      // Anything below the lower threshold just clips to zero
      L_out = 0.0f;
    }
    else
    {
      const float percentage = (L_in - d->levels[0]) / (d->levels[2] - d->levels[0]);
      // Within the expected input range we can use the lookup table, else we need to compute from scratch
      L_out = percentage < 1.0f ? d->lut[(int)(percentage * 0x10000ul)] : 100.0f * powf(percentage, d->in_inv_gamma);
    }
 
    // Preserving contrast
    const float denom = (in[i] > 0.01f) ? in[i] : 0.01f;
    out[i] = L_out;
    out[i+1] = in[i+1] * L_out / denom;
    out[i+2] = in[i+2] * L_out / denom;
  }
 
  if(pipe->mask_display & DT_DEV_PIXELPIPE_DISPLAY_MASK)
    dt_iop_alpha_copy(ivoid, ovoid, roi_out->width, roi_out->height);
  return 0;
}
 
// void init_presets (dt_iop_module_so_t *self)
//{
//  dt_iop_levels_params_t p;
//  p.levels_preset = 0;
//
//  p.levels[0] = 0;
//  p.levels[1] = 0.5;
//  p.levels[2] = 1;
//  dt_gui_presets_add_generic(_("unmodified"), self->op, self->version(), &p, sizeof(p), 1);
//}
 
void commit_params(dt_iop_module_t *self, dt_iop_params_t *p1, dt_dev_pixelpipe_t *pipe,
                   dt_dev_pixelpipe_iop_t *piece)
{
  dt_iop_levels_data_t *d = (dt_iop_levels_data_t *)piece->data;
  dt_iop_levels_params_t *p = (dt_iop_levels_params_t *)p1;
 
  if(dt_dev_pixelpipe_has_preview_output(self->dev, pipe, NULL))
    piece->request_histogram |= (DT_REQUEST_ON);
  else
    piece->request_histogram &= ~(DT_REQUEST_ON);
 
  piece->request_histogram |= (DT_REQUEST_ONLY_IN_GUI);
 
  piece->histogram_params.bins_count = 256;
 
  if(p->mode == LEVELS_MODE_AUTOMATIC)
  {
    d->mode = LEVELS_MODE_AUTOMATIC;
 
    piece->request_histogram |= (DT_REQUEST_ON);
    self->request_histogram &= ~(DT_REQUEST_ON);
 
    if(!self->dev->gui_attached) piece->request_histogram &= ~(DT_REQUEST_ONLY_IN_GUI);
 
    piece->histogram_params.bins_count = 16384;
 
    /*
     * in principle, we do not need/want histogram in FULL pipe
     * because we will use histogram from preview pipe there,
     * but it might happen that for some reasons we do not have
     * histogram of preview pipe yet - e.g. on first pipe run
     * (just after setting mode to automatic)
     */
 
    d->percentiles[0] = p->black;
    d->percentiles[1] = p->gray;
    d->percentiles[2] = p->white;
 
    d->levels[0] = NAN;
    d->levels[1] = NAN;
    d->levels[2] = NAN;
 
    // commit_params_late() will compute LUT later
  }
  else
  {
    d->mode = LEVELS_MODE_MANUAL;
 
    self->request_histogram |= (DT_REQUEST_ON);
 
    d->levels[0] = p->levels[0];
    d->levels[1] = p->levels[1];
    d->levels[2] = p->levels[2];
    compute_lut(piece);
  }
}
 
void init_pipe(dt_iop_module_t *self, dt_dev_pixelpipe_t *pipe, dt_dev_pixelpipe_iop_t *piece)
{
  piece->data = dt_calloc_align(sizeof(dt_iop_levels_data_t));
  piece->data_size = sizeof(dt_iop_levels_data_t);
}
 
void cleanup_pipe(dt_iop_module_t *self, dt_dev_pixelpipe_t *pipe, dt_dev_pixelpipe_iop_t *piece)
{
  // clean up everything again.
  dt_free_align(piece->data);
  piece->data = NULL;
}
 
void gui_changed(dt_iop_module_t *self, GtkWidget *w, void *previous)
{
  dt_iop_levels_gui_data_t *g = (dt_iop_levels_gui_data_t *)self->gui_data;
  dt_iop_levels_params_t *p = (dt_iop_levels_params_t *)self->params;
 
  if(w == g->mode)
  {
    /* blackpick/greypick/whitepick live on the "manual" stack page. Switching mode
       can hide that page while a picker stays active, sampling/drawing on the image
       for a control the user can no longer see or turn off from this widget. */
    dt_iop_color_picker_reset(self, FALSE);
 
    if(p->mode == LEVELS_MODE_AUTOMATIC)
      gtk_stack_set_visible_child_name(GTK_STACK(g->mode_stack), "automatic");
    else
      gtk_stack_set_visible_child_name(GTK_STACK(g->mode_stack), "manual");
  }
}
 
void gui_update(dt_iop_module_t *self)
{
  dt_iop_levels_gui_data_t *g = (dt_iop_levels_gui_data_t *)self->gui_data;
  dt_iop_levels_params_t *p = (dt_iop_levels_params_t *)self->params;
 
  dt_bauhaus_combobox_set(g->mode, p->mode);
 
  gui_changed(self, g->mode, 0);
 
  dt_iop_gui_enter_critical_section(self);
  g->auto_levels[0] = NAN;
  g->auto_levels[1] = NAN;
  g->auto_levels[2] = NAN;
  g->hash = 0;
  dt_iop_gui_leave_critical_section(self);
 
  gtk_widget_queue_draw(self->widget);
}
 
void init(dt_iop_module_t *module)
{
  dt_iop_default_init(module);
 
  module->request_histogram |= (DT_REQUEST_ON);
 
  dt_iop_levels_params_t *d = module->default_params;
 
  d->levels[0] = 0.0f;
  d->levels[1] = 0.5f;
  d->levels[2] = 1.0f;
}
 
void gui_init(dt_iop_module_t *self)
{
  dt_iop_levels_gui_data_t *c = IOP_GUI_ALLOC(levels);
 
  dt_iop_gui_enter_critical_section(self);
  c->auto_levels[0] = NAN;
  c->auto_levels[1] = NAN;
  c->auto_levels[2] = NAN;
  c->hash = 0;
  dt_iop_gui_leave_critical_section(self);
 
  c->modes = NULL;
 
  c->mouse_x = c->mouse_y = -1.0;
  c->dragging = 0;
  c->activeToggleButton = NULL;
  c->last_picked_color = -1;
 
  c->mode_stack = gtk_stack_new();
  gtk_stack_set_homogeneous(GTK_STACK(c->mode_stack),FALSE);
 
  c->area = GTK_DRAWING_AREA(gtk_drawing_area_new());
  gtk_widget_set_hexpand(GTK_WIDGET(c->area), TRUE);
  GtkWidget *vbox_manual = GTK_WIDGET(gtk_box_new(GTK_ORIENTATION_VERTICAL, DT_GUI_BOX_SPACING));
  gtk_box_pack_start(GTK_BOX(vbox_manual),
                     dt_ui_resizable_drawing_area(GTK_WIDGET(c->area),
                                                  "plugins/darkroom/levels/graphheight", 280, 100),
                     FALSE, FALSE, 0);
 
  gtk_widget_set_tooltip_text(GTK_WIDGET(c->area),_("drag handles to set black, gray, and white points. "
                                                    "operates on L channel."));
 
  gtk_widget_add_events(GTK_WIDGET(c->area), GDK_POINTER_MOTION_MASK
                                             | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK
                                             | GDK_LEAVE_NOTIFY_MASK | darktable.gui->scroll_mask);
  g_signal_connect(G_OBJECT(c->area), "draw", G_CALLBACK(dt_iop_levels_area_draw), self);
  g_signal_connect(G_OBJECT(c->area), "button-press-event", G_CALLBACK(dt_iop_levels_button_press), self);
  g_signal_connect(G_OBJECT(c->area), "button-release-event", G_CALLBACK(dt_iop_levels_button_release), self);
  g_signal_connect(G_OBJECT(c->area), "motion-notify-event", G_CALLBACK(dt_iop_levels_motion_notify), self);
  g_signal_connect(G_OBJECT(c->area), "leave-notify-event", G_CALLBACK(dt_iop_levels_leave_notify), self);
  g_signal_connect(G_OBJECT(c->area), "scroll-event", G_CALLBACK(dt_iop_levels_scroll), self);
 
  GtkWidget *box = gtk_box_new(GTK_ORIENTATION_HORIZONTAL, DT_GUI_BOX_SPACING);
 
  GtkWidget *autobutton = gtk_button_new_with_label(_("auto"));
  gtk_widget_set_tooltip_text(autobutton, _("apply auto levels"));
  g_signal_connect(G_OBJECT(autobutton), "clicked", G_CALLBACK(dt_iop_levels_autoadjust_callback), self);
 
  c->blackpick = dt_color_picker_new(self, DT_COLOR_PICKER_POINT, NULL);
  gtk_widget_set_tooltip_text(c->blackpick, _("pick black point from image"));
  gtk_widget_set_name(GTK_WIDGET(c->blackpick), "picker-black");
 
  c->greypick = dt_color_picker_new(self, DT_COLOR_PICKER_POINT, NULL);
  gtk_widget_set_tooltip_text(c->greypick, _("pick medium gray point from image"));
  gtk_widget_set_name(GTK_WIDGET(c->greypick), "picker-grey");
 
  c->whitepick = dt_color_picker_new(self, DT_COLOR_PICKER_POINT, NULL);
  gtk_widget_set_tooltip_text(c->whitepick, _("pick white point from image"));
  gtk_widget_set_name(GTK_WIDGET(c->whitepick), "picker-white");
 
  gtk_box_pack_start(GTK_BOX(box), GTK_WIDGET(autobutton  ), TRUE, TRUE, 0);
  gtk_box_pack_start(GTK_BOX(box), GTK_WIDGET(c->blackpick), TRUE, TRUE, 0);
  gtk_box_pack_start(GTK_BOX(box), GTK_WIDGET(c->greypick ), TRUE, TRUE, 0);
  gtk_box_pack_start(GTK_BOX(box), GTK_WIDGET(c->whitepick), TRUE, TRUE, 0);
  gtk_box_pack_start(GTK_BOX(vbox_manual), box, TRUE, TRUE, 0);
 
  gtk_stack_add_named(GTK_STACK(c->mode_stack), vbox_manual, "manual");
 
  GtkWidget *vbox_automatic = self->widget = GTK_WIDGET(gtk_box_new(GTK_ORIENTATION_VERTICAL, DT_GUI_BOX_SPACING));
 
  c->percentile_black = dt_bauhaus_slider_from_params(self, N_("black"));
  gtk_widget_set_tooltip_text(c->percentile_black, _("black percentile"));
  dt_bauhaus_slider_set_format(c->percentile_black, "%");
 
  c->percentile_grey = dt_bauhaus_slider_from_params(self, N_("gray"));
  gtk_widget_set_tooltip_text(c->percentile_grey, _("gray percentile"));
  dt_bauhaus_slider_set_format(c->percentile_grey, "%");
 
  c->percentile_white = dt_bauhaus_slider_from_params(self, N_("white"));
  gtk_widget_set_tooltip_text(c->percentile_white, _("white percentile"));
  dt_bauhaus_slider_set_format(c->percentile_white, "%");
 
  gtk_stack_add_named(GTK_STACK(c->mode_stack), vbox_automatic, "automatic");
 
  // start building top level widget
  self->widget = GTK_WIDGET(gtk_box_new(GTK_ORIENTATION_VERTICAL, DT_GUI_BOX_SPACING));
 
  c->mode = dt_bauhaus_combobox_from_params(self, N_("mode"));
 
  gtk_box_pack_start(GTK_BOX(self->widget), c->mode_stack, TRUE, TRUE, 0);
}
 
void gui_cleanup(dt_iop_module_t *self)
{
  dt_iop_levels_gui_data_t *g = (dt_iop_levels_gui_data_t *)self->gui_data;
  g_list_free(g->modes);
  g->modes = NULL;
 
  IOP_GUI_FREE;
}
 
static gboolean dt_iop_levels_leave_notify(GtkWidget *widget, GdkEventCrossing *event, gpointer user_data)
{
  dt_iop_module_t *self = (dt_iop_module_t *)user_data;
  dt_iop_levels_gui_data_t *c = (dt_iop_levels_gui_data_t *)self->gui_data;
  c->mouse_x = c->mouse_y = -1.0;
  gtk_widget_queue_draw(widget);
  return TRUE;
}
 
static gboolean dt_iop_levels_area_draw(GtkWidget *widget, cairo_t *crf, gpointer user_data)
{
  dt_iop_module_t *self = (dt_iop_module_t *)user_data;
  dt_iop_levels_gui_data_t *c = (dt_iop_levels_gui_data_t *)self->gui_data;
  dt_iop_levels_params_t *p = (dt_iop_levels_params_t *)self->params;
 
  const int inset = DT_GUI_CURVE_EDITOR_INSET;
  GtkAllocation allocation;
  gtk_widget_get_allocation(GTK_WIDGET(c->area), &allocation);
  int width = allocation.width, height = allocation.height;
  cairo_surface_t *cst = dt_cairo_image_surface_create(CAIRO_FORMAT_ARGB32, width, height);
  cairo_t *cr = cairo_create(cst);
 
  // clear bg
  cairo_set_source_rgb(cr, .2, .2, .2);
  cairo_paint(cr);
 
  cairo_translate(cr, inset, inset);
  width -= 2 * inset;
  height -= 2 * inset;
 
  cairo_set_line_width(cr, DT_PIXEL_APPLY_DPI(1.0));
  cairo_set_source_rgb(cr, .1, .1, .1);
  cairo_rectangle(cr, 0, 0, width, height);
  cairo_stroke(cr);
 
  cairo_set_source_rgb(cr, .3, .3, .3);
  cairo_rectangle(cr, 0, 0, width, height);
  cairo_fill(cr);
 
  // draw grid
  cairo_set_line_width(cr, DT_PIXEL_APPLY_DPI(.4));
  cairo_set_source_rgb(cr, .1, .1, .1);
  dt_draw_vertical_lines(cr, 4, 0, 0, width, height);
 
  // Drawing the vertical line indicators
  cairo_set_line_width(cr, DT_PIXEL_APPLY_DPI(2.));
 
  for(int k = 0; k < 3; k++)
  {
    if(k == c->handle_move && c->mouse_x > 0)
      cairo_set_source_rgb(cr, 1, 1, 1);
    else
      cairo_set_source_rgb(cr, .7, .7, .7);
 
    cairo_move_to(cr, width * p->levels[k], height);
    cairo_rel_line_to(cr, 0, -height);
    cairo_stroke(cr);
  }
 
  // draw x positions
  cairo_set_line_width(cr, DT_PIXEL_APPLY_DPI(1.));
  const float arrw = DT_PIXEL_APPLY_DPI(7.0f);
  for(int k = 0; k < 3; k++)
  {
    switch(k)
    {
      case 0:
        cairo_set_source_rgb(cr, 0, 0, 0);
        break;
 
      case 1:
        cairo_set_source_rgb(cr, 0.5, 0.5, 0.5);
        break;
 
      default:
        cairo_set_source_rgb(cr, 1, 1, 1);
        break;
    }
 
    cairo_move_to(cr, width * p->levels[k], height + inset - 1);
    cairo_rel_line_to(cr, -arrw * .5f, 0);
    cairo_rel_line_to(cr, arrw * .5f, -arrw);
    cairo_rel_line_to(cr, arrw * .5f, arrw);
    cairo_close_path(cr);
    if(c->handle_move == k && c->mouse_x > 0)
      cairo_fill(cr);
    else
      cairo_stroke(cr);
  }
 
  cairo_translate(cr, 0, height);
 
  // draw lum histogram in background
  // only if the module is enabled
  if(self->enabled)
  {
    uint32_t *hist = self->histogram;
    const gboolean is_linear = FALSE;
    float hist_max = is_linear ? self->histogram_max[0] : logf(1.0 + self->histogram_max[0]);
    if(!IS_NULL_PTR(hist) && hist_max > 0.0f)
    {
      cairo_save(cr);
      cairo_scale(cr, width / 255.0, -(height - DT_PIXEL_APPLY_DPI(5)) / hist_max);
      cairo_set_source_rgba(cr, .2, .2, .2, 0.5);
      dt_draw_histogram_8(cr, hist, 4, 0, is_linear);
      cairo_restore(cr);
    }
  }
 
  // Cleaning up
  cairo_destroy(cr);
  cairo_set_source_surface(crf, cst, 0, 0);
  cairo_paint(crf);
  cairo_surface_destroy(cst);
  return TRUE;
}
 
static void dt_iop_levels_move_handle(dt_iop_module_t *self, int handle_move, float new_pos, float *levels,
                                      float drag_start_percentage)
{
  dt_iop_levels_gui_data_t *c = (dt_iop_levels_gui_data_t *)self->gui_data;
  float min_x = 0;
  float max_x = 1;
 
  if((handle_move < 0) || handle_move > 2) return;
 
  if(IS_NULL_PTR(levels)) return;
 
  // Determining the minimum and maximum bounds for the drag handles
  switch(handle_move)
  {
    case 0:
      max_x = fminf(levels[2] - (0.05 / drag_start_percentage), 1);
      max_x = fminf((levels[2] * (1 - drag_start_percentage) - 0.05) / (1 - drag_start_percentage), max_x);
      break;
 
    case 1:
      min_x = levels[0] + 0.05;
      max_x = levels[2] - 0.05;
      break;
 
    case 2:
      min_x = fmaxf((0.05 / drag_start_percentage) + levels[0], 0);
      min_x = fmaxf((levels[0] * (1 - drag_start_percentage) + 0.05) / (1 - drag_start_percentage), min_x);
      break;
  }
 
  levels[handle_move] = fminf(max_x, fmaxf(min_x, new_pos));
 
  if(handle_move != 1) levels[1] = levels[0] + (drag_start_percentage * (levels[2] - levels[0]));
 
  if(!IS_NULL_PTR(c->activeToggleButton)) gtk_toggle_button_set_active(c->activeToggleButton, FALSE);
  c->last_picked_color = -1;
}
 
static gboolean dt_iop_levels_motion_notify(GtkWidget *widget, GdkEventMotion *event, gpointer user_data)
{
  dt_iop_module_t *self = (dt_iop_module_t *)user_data;
  dt_iop_levels_gui_data_t *c = (dt_iop_levels_gui_data_t *)self->gui_data;
  dt_iop_levels_params_t *p = (dt_iop_levels_params_t *)self->params;
  const int inset = DT_GUI_CURVE_EDITOR_INSET;
  GtkAllocation allocation;
  gtk_widget_get_allocation(widget, &allocation);
  int height = allocation.height - 2 * inset, width = allocation.width - 2 * inset;
  if(!c->dragging)
  {
    c->mouse_x = CLAMP(event->x - inset, 0, width);
    c->drag_start_percentage = (p->levels[1] - p->levels[0]) / (p->levels[2] - p->levels[0]);
  }
  c->mouse_y = CLAMP(event->y - inset, 0, height);
 
  if(c->dragging)
  {
    if(c->handle_move >= 0 && c->handle_move < 3)
    {
      const float mx = (CLAMP(event->x - inset, 0, width)) / (float)width;
 
      dt_iop_levels_move_handle(self, c->handle_move, mx, p->levels, c->drag_start_percentage);
    }
    dt_dev_add_history_item(darktable.develop, self, TRUE, TRUE);
  }
  else
  {
    c->handle_move = 0;
    const float mx = CLAMP(event->x - inset, 0, width) / (float)width;
    float dist = fabsf(p->levels[0] - mx);
    for(int k = 1; k < 3; k++)
    {
      float d2 = fabsf(p->levels[k] - mx);
      if(d2 < dist)
      {
        c->handle_move = k;
        dist = d2;
      }
    }
  }
  gtk_widget_queue_draw(widget);
 
  return TRUE;
}
 
static gboolean dt_iop_levels_button_press(GtkWidget *widget, GdkEventButton *event, gpointer user_data)
{
  // set active point
  if(event->button == 1)
  {
    dt_iop_module_t *self = (dt_iop_module_t *)user_data;
 
    if(self->dev->gui_module != self) dt_iop_request_focus(self);
 
    if(event->type == GDK_2BUTTON_PRESS)
    {
      // Reset
      dt_iop_levels_gui_data_t *c = (dt_iop_levels_gui_data_t *)self->gui_data;
      memcpy(self->params, self->default_params, self->params_size);
 
      // Needed in case the user scrolls or drags immediately after a reset,
      // as drag_start_percentage is only updated when the mouse is moved.
      c->drag_start_percentage = 0.5;
      dt_dev_add_history_item(darktable.develop, self, TRUE, TRUE);
      gtk_widget_queue_draw(self->widget);
    }
    else
    {
      dt_iop_levels_gui_data_t *c = (dt_iop_levels_gui_data_t *)self->gui_data;
      c->dragging = 1;
    }
    return TRUE;
  }
  return FALSE;
}
 
static gboolean dt_iop_levels_button_release(GtkWidget *widget, GdkEventButton *event, gpointer user_data)
{
  if(event->button == 1)
  {
    dt_iop_module_t *self = (dt_iop_module_t *)user_data;
    dt_iop_levels_gui_data_t *c = (dt_iop_levels_gui_data_t *)self->gui_data;
    c->dragging = 0;
    return TRUE;
  }
  return FALSE;
}
 
static gboolean dt_iop_levels_scroll(GtkWidget *widget, GdkEventScroll *event, gpointer user_data)
{
  dt_iop_module_t *self = (dt_iop_module_t *)user_data;
  dt_iop_levels_gui_data_t *c = (dt_iop_levels_gui_data_t *)self->gui_data;
  dt_iop_levels_params_t *p = (dt_iop_levels_params_t *)self->params;
 
  int delta_y;
 
  dt_iop_color_picker_reset(self, TRUE);
 
  if(c->dragging)
  {
    return FALSE;
  }
 
  if(self->dev->gui_module != self) dt_iop_request_focus(self);
 
  const float interval = 0.002; // Distance moved for each scroll event
  if(dt_gui_get_scroll_unit_deltas(event, NULL, &delta_y))
  {
    float new_position = p->levels[c->handle_move] - interval * delta_y;
    dt_iop_levels_move_handle(self, c->handle_move, new_position, p->levels, c->drag_start_percentage);
    dt_dev_add_history_item(darktable.develop, self, TRUE, TRUE);
    return TRUE;
  }
 
  return TRUE; // Ensure that scrolling the widget cannot move side panel
}
 
static void dt_iop_levels_autoadjust_callback(GtkRange *range, dt_iop_module_t *self)
{
  if(dt_gui_widgets_suppressed()) return;
  dt_iop_levels_params_t *p = (dt_iop_levels_params_t *)self->params;
  dt_iop_levels_gui_data_t *c = (dt_iop_levels_gui_data_t *)self->gui_data;
 
  dt_iop_color_picker_reset(self, TRUE);
 
  dt_iop_levels_compute_levels_manual(self->histogram, p->levels);
 
  if(!IS_NULL_PTR(c->activeToggleButton)) gtk_toggle_button_set_active(c->activeToggleButton, FALSE);
  c->last_picked_color = -1;
 
  dt_dev_add_history_item(darktable.develop, self, TRUE, TRUE);
}
 
// clang-format off
// modelines: These editor modelines have been set for all relevant files by tools/update_modelines.py
// vim: shiftwidth=2 expandtab tabstop=2 cindent
// kate: tab-indents: off; indent-width 2; replace-tabs on; indent-mode cstyle; remove-trailing-spaces modified;
// clang-format on