Add progress information

[swissspidy]

On the command line --vips-progress runs a progress indicator during computation. It can be useful to see where libvips is looping and how often.

I wonder if it's possible to expose progress in a similar way in wasm-vips, for example by adding an option to provide a callback function that gets called with the current progress. That way, if an operation takes a bit longer, one can display a progress bar to users as well.

[kleisauke]

Good idea! I just implemented this with commit c004099, allowing you to do this:

// Load a huge image
const im = vips.Image.black(100000, 100000);

// Attach progress feedback
let lastPercent = 0;
im.onProgress = (percent) => {
  // This callback is triggered once per work unit (typically a 128 x
  // 128 area of pixels) during image computation. Therefore, we only
  // need to print when there's a change in the percentage.
  if (percent !== lastPercent) {
    console.log(`${percent}% complete`);
    lastPercent = percent;
  }

  // To stop long-running computations, we could block evaluation after a
  // certain amount of time. To avoid complexity in this example, issue the
  // kill signal after 25% completion.
  if (percent >= 25) {
    im.kill = true;
  }
};

// Save
im.writeToFile('x.png');

I also made it possible to stop long-running computations with commit 20f8414, as shown in the example above.

This will be in v0.0.8.

[swissspidy]

This is fantastic, thanks a lot for this fast response & implementation!

Looking forward to implementing both in my project.

[kleisauke]

v0.0.8 is now available with these improvements.