Progressive quality digression to meet max_size requirements.

[s2young]

Ok, this one may be off the rails. But I'm encountering size issues with some of my splash screens, so I thought it would be nice to have some flexibility in setting the 'quality' property during the render process.

This change adds the following properties:

max_size - this value, in bytes, tells web2splash the max file size goal. It does NOT prevent the output of a splash image if the size cannot be attained, but a warning message is attached to the image output in the onRenderImage function.

min_quality - this allows you to specify that you don't want your PNG to drop below a certain quality, even if the max_size cannot be attained.

quality_increment - this integer is used in decrementing the quality setting on a retry. Default is 5.

In short, web2splash would first attempt a render at 100% quality. If the file size is below max_size, great. If not, the quality would be decremented by the quality_increment amount (default 5) and the render would retry. Once the max_size value is reached, it moves on. If it can't be reached, then a 'warn' value is added to the image hash the is sent to the onRenderImage function. Something like this:

{
 name: 'ios-ipad-2x-portrait.png',
  width: 1536,
  height: 2008,
  pixelRatio: 2,
  size: 9646890,
  quality: 50,
  warn: 'Could not render image under the max_size setting (2048000) without going under the min_quality setting (50).' 
}

[s2young]

Anyone have comments on this?

[mwbrooks]

Should be function() {

[mwbrooks]

Hi @s2young,

The feature is a little off the rails, but if you have a use for it then I imagine others do as well!

Here are a few points for feedback:

Naming conventions:

Let's keep the camelCase convention going. So we should change the various setting variables from max_size to maxSize.

Exposing the options:

Let's encapsulate the options under an options object. This will keep the programmatic API more aligned with other node projects that use a similar API design.

web2splash.options = {
    maxSize: 9646890,
    minQuality: 50
}
web2splash.render(input, output, function(e) {
    // ...
}

quality-exports

Maybe a dumb question, but I'm confused where the variable quality-exports comes from.

CLI

If we offer this sort of feature, it needs to be exposed from the CLI as well.

Documentation

We need to update the following documentation:

• README.md for the CLI
• README.md for the Node Interface
• CLI help output should explain the options available

Formatting

I've left a few note within the commit diff on matching the code formatting.

Cheers!
Michael