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Fl_Progress

The Fl_Progress widget displays a progress bar to show the completion status of an operation. It’s ideal for providing visual feedback during long-running tasks.

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Header File

#include <FL/Fl_Progress.H>

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Class Overview

Fl_Progress is a simple widget for displaying progress as a filled bar. Features include:
  • Configurable minimum and maximum values
  • Current value displayed as a filled portion
  • Customizable colors for bar and background
  • Optional text label showing percentage or custom text
  • Horizontal orientation

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Inheritance

Fl_Widget
  └── Fl_Progress
Inherits from: Fl_Widget

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Constructor

Fl_Progress(int x, int y, int w, int h, const char *l = 0)
Creates a new progress bar widget.
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x
int
The X coordinate of the widget relative to the enclosing window
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y
int
The Y coordinate of the widget relative to the enclosing window
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w
int
Width of the progress bar in pixels
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h
int
Height of the progress bar in pixels
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l
const char*
default:"nullptr"
Optional label text (often used to display percentage)

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Public Methods

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maximum()

float maximum() const
void maximum(float v)
Gets or sets the maximum value for the progress bar.
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v
float
Maximum value (typically 1.0 for 0-100% or 100 for percentage values)
Returns: For getter, the current maximum value

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minimum()

float minimum() const
void minimum(float v)
Gets or sets the minimum value for the progress bar.
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v
float
Minimum value (typically 0.0)
Returns: For getter, the current minimum value

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value()

float value() const
void value(float v)
Gets or sets the current value of the progress bar.
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v
float
Current progress value (between minimum and maximum)
Returns: For getter, the current value
Setting the value automatically calls redraw() to update the display.

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Protected Methods

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draw()

void draw() override
Draws the progress bar with current value. Called automatically by FLTK.

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Inherited Methods

From Fl_Widget, commonly used methods include:
  • color() / color(Fl_Color) - Background color
  • selection_color() / selection_color(Fl_Color) - Progress bar fill color
  • labelcolor() / labelcolor(Fl_Color) - Text color for percentage label
  • box() / box(Fl_Boxtype) - Border/box style
  • label() / label(const char*) - Text displayed on the bar

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Usage Example

From examples/progress-simple.cxx: 
#include <stdio.h>
#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Button.H>
#include <FL/Fl_Progress.H>

#ifdef _WIN32
#include <windows.h>
#define usleep(v) Sleep(v/1000)
#else
#include <unistd.h>
#endif

void butt_cb(Fl_Widget *butt, void *data) {
  // Deactivate the button
  butt->deactivate();
  Fl::check();
  
  // Create progress bar
  Fl_Window *w = (Fl_Window*)data;
  w->begin();
  Fl_Progress *progress = new Fl_Progress(10, 50, 200, 30);
  progress->minimum(0);
  progress->maximum(1);
  progress->color(0x88888800);            // Background color
  progress->selection_color(0x4444ff00);  // Progress bar color
  progress->labelcolor(FL_WHITE);         // Percent text color
  w->end();
  
  // Computation loop
  for (int t = 1; t <= 500; t++) {
    progress->value(float(t / 500.0));
    
    // Update label with percentage
    char percent[10];
    sprintf(percent, "%d%%", int((t / 500.0) * 100.0));
    progress->label(percent);
    
    Fl::check();  // Update screen
    usleep(1000); // Simulate work
  }
  
  // Cleanup
  w->remove(progress);
  delete progress;
  butt->activate();
  w->redraw();
}

int main() {
  Fl_Window win(220, 90);
  Fl_Button butt(10, 10, 100, 25, "Press");
  butt.callback(butt_cb, &win);
  win.resizable(win);
  win.show();
  return Fl::run();
}

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File Download Progress Example

#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Progress.H>
#include <FL/Fl_Box.H>
#include <stdio.h>

Fl_Progress *progress;
Fl_Box *status_label;
float downloaded = 0;
float total_size = 100.0;  // MB

void download_timeout(void *) {
  downloaded += 2.5;  // Simulate downloading 2.5 MB
  
  if (downloaded >= total_size) {
    downloaded = total_size;
    progress->value(downloaded);
    progress->label("Complete!");
    status_label->label("Download finished");
    return;  // Stop timer
  }
  
  progress->value(downloaded);
  
  char percent[32];
  sprintf(percent, "%.0f%%", (downloaded / total_size) * 100.0);
  progress->copy_label(percent);
  
  char status[64];
  sprintf(status, "%.1f / %.1f MB", downloaded, total_size);
  status_label->copy_label(status);
  
  // Schedule next update
  Fl::repeat_timeout(0.1, download_timeout);
}

int main(int argc, char **argv) {
  Fl_Window *window = new Fl_Window(400, 150);
  
  Fl_Box *title = new Fl_Box(50, 20, 300, 25, "Downloading file...");
  title->labelsize(16);
  
  progress = new Fl_Progress(50, 60, 300, 30);
  progress->minimum(0);
  progress->maximum(total_size);
  progress->color(FL_BACKGROUND2_COLOR);
  progress->selection_color(FL_BLUE);
  progress->labelcolor(FL_WHITE);
  progress->label("0%");
  
  status_label = new Fl_Box(50, 100, 300, 25, "0.0 / 100.0 MB");
  
  window->end();
  window->show(argc, argv);
  
  // Start the download simulation
  Fl::add_timeout(0.1, download_timeout);
  
  return Fl::run();
}

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Processing Tasks Example

#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Progress.H>
#include <FL/Fl_Button.H>
#include <stdio.h>

Fl_Progress *progress;
int current_task = 0;
const int total_tasks = 50;

void process_cb(void *) {
  current_task++;
  
  float progress_value = float(current_task) / float(total_tasks);
  progress->value(progress_value);
  
  char label[32];
  sprintf(label, "Task %d/%d", current_task, total_tasks);
  progress->copy_label(label);
  
  if (current_task < total_tasks) {
    Fl::repeat_timeout(0.05, process_cb);
  } else {
    progress->selection_color(FL_GREEN);
    progress->label("All tasks complete!");
    progress->redraw();
  }
}

void start_cb(Fl_Widget *w, void *) {
  current_task = 0;
  progress->value(0);
  progress->selection_color(FL_BLUE);
  progress->label("");
  w->deactivate();
  
  Fl::add_timeout(0.05, process_cb);
  
  // Re-enable button after completion
  Fl::add_timeout(2.6, [](void *btn) { 
    ((Fl_Widget*)btn)->activate(); 
  }, w);
}

int main(int argc, char **argv) {
  Fl_Window *window = new Fl_Window(350, 120);
  
  Fl_Button *btn = new Fl_Button(100, 20, 150, 30, "Start Processing");
  btn->callback(start_cb);
  
  progress = new Fl_Progress(25, 70, 300, 30);
  progress->minimum(0.0);
  progress->maximum(1.0);
  progress->color(0xDDDDDD00);
  progress->selection_color(FL_BLUE);
  
  window->end();
  window->show(argc, argv);
  return Fl::run();
}

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Color Customization

Fl_Progress *progress = new Fl_Progress(10, 10, 300, 40);

// Set background color
progress->color(FL_DARK_BLUE);

// Set progress bar fill color
progress->selection_color(FL_GREEN);

// Set text color
progress->labelcolor(FL_WHITE);

// Set border style
progress->box(FL_PLASTIC_DOWN_BOX);

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Common Use Cases

  • File operations - Upload/download progress
  • Installation - Software installation progress
  • Processing - Batch operation progress (image processing, data conversion)
  • Loading - Application startup or resource loading
  • Rendering - 3D rendering or video encoding progress
  • Computation - Long calculations or simulations

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Tips

  • Use Fl::check() or Fl::wait() in loops to keep the UI responsive
  • Update the label to show percentage, current/total, or status messages
  • Consider using selection_color() to change bar color based on status (blue for normal, green for complete, red for error)
  • For indeterminate progress, consider using Fl_Hor_Fill_Slider or animating a custom widget

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See Also