LibGDX: Blending in html gwt web

If you use OpenGl blending functions, you probably are doing something with the alpha buffer (or not). By default the alpha buffer is disabled on the html / gwt / web config.

So you need to go to the HtmlLauncher and set the alpha boolean to true:

public GwtApplicationConfiguration getConfig() {
	final GwtApplicationConfiguration config = new ...;
	config.alpha = true;
	return config;
}

A side effect by enabling the alpha buffer is the actual background will become pseudo transparent. At the end of the drawing the alpha buffer will be handled as the alpha channel of the whole canvas. So if there is no need for some transparency, at the end of drawing the whole alpha buffer should be filled with 1s. 

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Html: Enter handler on input text field

Every single time you have a input text field and submit-like button next to it, at some point, you would like to bind the same action of the submit button to the press of the enter key.

It's trivial, but also it's simply better to just copy-paste it. So here its is:

function onenter(ele, f) {
	ele.addEventListener('keydown', function (e) {
		if (e.keyCode === 13) { f(e); e.preventDefault(); }
	})
}

And also while we are here, instead of using the-not-be-named lib, just use these:

function q(x) { return document.querySelector(x); }
function qa(x) { return [...document.querySelectorAll(x)]; }
function range(x) { return Array.from({length: x}, (v, i) => i); }

For more just go here.

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Html: Unwanted cached resources

So as you write a simple a html file with one or two resources, lets say one css and one js file, and you then deploy it (= copy paste) to a sever, and then you make some changes (= fix a bug), and then you redeploy (= copy paste, overwrite popup, press yes), and then nothing changes.

The browser, like always, remembers the old 'main.js' from before and then you pres Ctrl+F5. But your tester in the other side, has no clue what a Ctrl is. So you have to do something.

The first thing is to add a simple '?1' at the end of 'main.js' and every other resource, the browser thinks it may be a different file and deletes the cached version.

So now lets make a script to automate the replacement of the '?1' with '?2':

sed 's/"\(.*\)?.*"/"\1?2"||/' -i index.html

But we may want the browser to actually keep some cached files, the files that have not changed. Only if, instead of '?2', we could generate a number that only changes if the actual file changes and also does not repeat it self.

Hash functions? Checksums? Yes.

Lets use 'md5sum' to freak out the people who don't know. A single sed will not make it, lets write a sed to generate multiple seds and pipe it into a sh.

First we find checksums:

find -regex '.*\(js\|css\)$' -exec md5sum {} \+

Then we pipe that to our first sed:

sed 's/\(.*\)  \(.*\)/ ... \2 ... \1 ... /'

where in the place '...' we reconstruct version of our original sed (gets very unreadable). And finally we pipe it to a sh to actually do the substitution.

The whole thing if placed in Makefile would look like this:

index.html: *.css *.js
    find *.css *.js -exec md5sum {} \+ | \
        sed 's/\(.*\)  \(.*\)/sed \"s|\\"\2?[^\\"]*|\\"\2?\1|\" -i index.html/' | sh

_done