add support for transparant png

[ryanhc]

Modified to use libpng to read .png files. We use stb_image to read all other image files.
This requires updated submodule: servo/rust-png#13

This patch is for:
#1279

[larsbergstrom]

You will need to add the update to the submodule (which I merged) by doing:

cd src/support/png/rust-png
git pull origin master
cd ../../../..
git add src/support/png/rust-png

[larsbergstrom]

These changes look good otherwise. And we all appreciate the cleanup of stray whitespace :-)

[ryanhc]

I've just executed the above commands.
Just one quick question: The changes to the submodule's already merged.
In that case, why do I need to run the last git add command? That only indicates
that I have local changes. Correct me if I'm wrong :)

[larsbergstrom]

After running those commands, your git status doesn't show:

# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#       modified:   ../src/support/png/rust-png

? I'm a bit confused, as I believe the rust-png submodule has not been updated. I've merged the PR (which means it is now at the tip of master in the rust-png repository). But submodules in git are not like svn:external in subversion - they are pinned to a particular change, as identified by the hash associated with that commit. The commands I put in my first comment update the servo repo's pointer to that submodule to pull in the head of the rust-png repo.

[ryanhc]

cd src/support/png/rust-png
git log

shows that the submodule's updated.

What messages do I need to look for?

[larsbergstrom]

if you do 'git log' in that directory, you should see:

commit bd3b394e35dee36989e3c80abd9bcc1f99affa27
Merge: a06ce5a b422b09
Author: Jack Moffitt <jack@metajack.im>
Date:   Wed Oct 30 14:56:58 2013 -0700

    Merge pull request #11 from kmcallister/rust-upgrade

    Upgrade Rust

After you do git pull origin master in that directory, you should see:

commit 519c291139813bf6cda192a45745013d543c99fe
Merge: bd3b394 a7d6ec6
Author: Lars Bergstrom <lbergstrom@mozilla.com>
Date:   Tue Nov 19 13:15:28 2013 -0800

    Merge pull request #13 from ryanhc/transparent_png

    add support for transparent png

If you do git status in there, you will see no edits because you haven't made any in that submodule:

[lbergstrom@lbergstrom rust-png]$ git status
# HEAD detached from bd3b394

But if you go up a few dirs, you should see an edit of the submodule in the servo repo:

[lbergstrom@lbergstrom src]$ git status
# On branch master
# Changes not staged for commit:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
#       modified:   support/png/rust-png (new commits)

And then you should need to git add and it should all work.

Or is your git log already showing commit 519c291 as the head? I just tested this on a clean servo directory I pulled down, but maybe you're seeing something different?

[ryanhc]

Thanks for your kind instruction :)
I've updated this pr to refer to the updated submodule.

[larsbergstrom]

r+

[larsbergstrom]

@bors: retry

[bors-servo]

saw approval from larsbergstrom
at ryanhc@589530c

[bors-servo]

merging ryanhc/servo/transparent_png = 589530c into auto

[bors-servo]

ryanhc/servo/transparent_png = 589530c merged ok, testing candidate = d049978

[bors-servo]

some tests failed:
failure: http://servo-buildbot.pub.build.mozilla.org/builders/mac/builds/604

[bors-servo]

saw approval from larsbergstrom
at ryanhc@589530c

[bors-servo]

merging ryanhc/servo/transparent_png = 589530c into auto

[bors-servo]

ryanhc/servo/transparent_png = 589530c merged ok, testing candidate = 052a543

[bors-servo]

all tests pass:
success: http://servo-buildbot.pub.build.mozilla.org/builders/linux/builds/650
success: http://servo-buildbot.pub.build.mozilla.org/builders/mac/builds/605

[bors-servo]

fast-forwarding master to auto = 052a543