Development Notes

# The Mesa 3D Graphics Library

# Development Notes

## Adding Extensions

To add a new GL extension to Mesa you have to do at least the following.

- If glext.h doesn't define the extension, edit include/GL/gl.h and add code like this:

           #ifndef GL_EXT_the_extension_name
           #define GL_EXT_the_extension_name 1
           /* declare the new enum tokens */
           /* prototype the new functions */
           /* TYPEDEFS for the new functions */
           #endif

- In the src/mapi/glapi/gen/ directory, add the new extension functions and enums to the gl_API.xml file. Then, a bunch of source files must be regenerated by executing the corresponding Python scripts.
- Add a new entry to the `gl_extensions` struct in mtypes.h
- Update the `extensions.c` file.
- From this point, the best way to proceed is to find another extension, similar to the new one, that's already implemented in Mesa and use it as an example.
- If the new extension adds new GL state, the functions in get.c, enable.c and attrib.c will most likely require new code.
- The dispatch tests check_table.cpp and dispatch_sanity.cpp should be updated with details about the new extensions functions. These tests are run using 'make check'

## Coding Style

Mesa's code style has changed over the years. Here's the latest.

Comment your code! It's extremely important that open-source code be well documented. Also, strive to write clean, easily understandable code.

3-space indentation

If you use tabs, set them to 8 columns

Line width: the preferred width to fill comments and code in Mesa is 78 columns. Exceptions are sometimes made for clarity (e.g. tabular data is sometimes filled to a much larger width so that extraneous carriage returns don't obscure the table).

Brace example:

    	if (condition) {
    	   foo;
    	}
    	else {
    	   bar;
    	}

    	switch (condition) {
    	case 0:
    	   foo();
    	   break;

    	case 1: {
    	   ...
    	   break;
    	}

    	default:
    	   ...
    	   break;
    	}

Here's the GNU indent command which will best approximate my preferred style: (Note that it won't format switch statements in the preferred way)

    	indent -br -i3 -npcs --no-tabs infile.c -o outfile.c

Local variable name example: localVarName (no underscores)

Constants and macros are ALL_UPPERCASE, with _ between words

Global variables are not allowed.

Function name examples:

    	glFooBar()       - a public GL entry point (in glapi_dispatch.c)
    	_mesa_FooBar()   - the internal immediate mode function
    	save_FooBar()    - retained mode (display list) function in dlist.c
    	foo_bar()        - a static (private) function
    	_mesa_foo_bar()  - an internal non-static Mesa function

Places that are not directly visible to the GL API should prefer the use of `bool`, `true`, and `false` over `GLboolean`, `GL_TRUE`, and `GL_FALSE`. In C code, this may mean that `#include <stdbool.h>` needs to be added. The `try_emit_`* methods in src/mesa/program/ir_to_mesa.cpp and src/mesa/state_tracker/st_glsl_to_tgsi.cpp can serve as examples.

## Submitting patches

You should always run the Mesa Testsuite before submitting patches. The Testsuite can be run using the 'make check' command. All tests must pass before patches will be accepted, this may mean you have to update the tests themselves.

Patches should be sent to the Mesa mailing list for review. When submitting a patch make sure to use git send-email rather than attaching patches to emails. Sending patches as attachments prevents people from being able to provide in-line review comments.

When submitting follow-up patches you can use --in-reply-to to make v2, v3, etc patches show up as replies to the originals. This usually works well when you're sending out updates to individual patches (as opposed to re-sending the whole series). Using --in-reply-to makes it harder for reviewers to accidentally review old patches.

## Marking a commit as a candidate for a stable branch

If you want a commit to be applied to a stable branch, you should add an appropriate note to the commit message.

Here are some examples of such a note:

- CC: <mesa-stable@lists.freedesktop.org>
- CC: "9.2 10.0" <mesa-stable@lists.freedesktop.org>
- CC: "10.0" <mesa-stable@lists.freedesktop.org>

Simply adding the CC to the mesa-stable list address is adequate to nominate the commit for the most-recently-created stable branch. It is only necessary to specify a specific branch name, (such as "9.2 10.0" or "10.0" in the examples above), if you want to nominate the commit for an older stable branch. And, as in these examples, you can nominate the commit for the older branch in addition to the more recent branch, or nominate the commit exclusively for the older branch. This "CC" syntax for patch nomination will cause patches to automatically be copied to the mesa-stable@ mailing list when you use "git send-email" to send patches to the mesa-dev@ mailing list. Also, if you realize that a commit should be nominated for the stable branch after it has already been committed, you can send a note directly to the mesa-stable@lists.freedesktop.org where the Mesa stable-branch maintainers will receive it. Be sure to mention the commit ID of the commit of interest (as it appears in the mesa master branch). The latest set of patches that have been nominated, accepted, or rejected for the upcoming stable release can always be seen on the Mesa Stable Queue page.

## Criteria for accepting patches to the stable branch

Mesa has a designated release manager for each stable branch, and the release manager is the only developer that should be pushing changes to these branches. Everyone else should simply nominate patches using the mechanism described above. The stable-release manager will work with the list of nominated patches, and for each patch that meets the crtieria below will cherry-pick the patch with: `git cherry-pick -x <commit>`. The `-x` option is important so that the picked patch references the comit ID of the original patch. The stable-release manager may at times need to force-push changes to the stable branches, for example, to drop a previously-picked patch that was later identified as causing a regression). These force-pushes may cause changes to be lost from the stable branch if developers push things directly. Consider yourself warned. The stable-release manager is also given broad discretion in rejecting patches that have been nominated for the stable branch. The most basic rule is that the stable branch is for bug fixes only, (no new features, no regressions). Here is a non-exhaustive list of some reasons that a patch may be rejected:

- Patch introduces a regression. Any reported build breakage or other regression caused by a particular patch, (game no longer work, piglit test changes from PASS to FAIL), is justification for rejecting a patch.
- Patch is too large, (say, larger than 100 lines)
- Patch is not a fix. For example, a commit that moves code around with no functional change should be rejected.
- Patch fix is not clearly described. For example, a commit message of only a single line, no description of the bug, no mention of bugzilla, etc.
- Patch has not obviously been reviewed, For example, the commit message has no Reviewed-by, Signed-off-by, nor Tested-by tags from anyone but the author.
- Patch has not already been merged to the master branch. As a rule, bug fixes should never be applied first to a stable branch. Patches should land first on the master branch and then be cherry-picked to a stable branch. (This is to avoid future releases causing regressions if the patch is not also applied to master.) The only things that might look like exceptions would be backports of patches from master that happen to look significantly different.
- Patch depends on too many other patches. Ideally, all stable-branch patches should be self-contained. It sometimes occurs that a single, logical bug-fix occurs as two separate patches on master, (such as an original patch, then a subsequent fix-up to that patch). In such a case, these two patches should be squashed into a single, self-contained patch for the stable branch. (Of course, if the squashing makes the patch too large, then that could be a reason to reject the patch.)
- Patch includes new feature development, not bug fixes. New OpenGL features, extensions, etc. should be applied to Mesa master and included in the next major release. Stable releases are intended only for bug fixes. Note: As an exception to this rule, the stable-release manager may accept hardware-enabling "features". For example, backports of new code to support a newly-developed hardware product can be accepted if they can be reasonably determined to not have effects on other hardware.
- Patch is a performance optimization. As a rule, performance patches are not candidates for the stable branch. The only exception might be a case where an application's performance was recently severely impacted so as to become unusable. The fix for this performance regression could then be considered for a stable branch. The optimization must also be non-controversial and the patches still need to meet the other criteria of being simple and self-contained
- Patch introduces a new failure mode (such as an assert). While the new assert might technically be correct, for example to make Mesa more conformant, this is not the kind of "bug fix" we want in a stable release. The potential problem here is that an OpenGL program that was previously working, (even if technically non-compliant with the specification), could stop working after this patch. So that would be a regression that is unaacceptable for the stable branch.

## Making a New Mesa Release

These are the instructions for making a new Mesa release.

### Get latest source files

Use git to get the latest Mesa files from the git repository, from whatever branch is relevant. This document uses the convention X.Y.Z for the release being created, which should be created from a branch named X.Y.

### Perform basic testing

The release manager should, at the very least, test the code by compiling it, installing it, and running the latest piglit to ensure that no piglit tests have regressed since the previous release.

The release manager should do this testing with at least one hardware driver, (say, whatever is contained in the local development machine), as well as on both Gallium and non-Gallium software drivers. The software testing can be performed by running piglit with the following environment-variable set:

    LIBGL_ALWAYS_SOFTWARE=1

And Gallium vs. non-Gallium software drivers can be obtained by using the following configure flags on separate builds:

    --with-dri-drivers=swrast
    --with-gallium-drivers=swrast

Note: If both options are given in one build, both swrast_dri.so drivers will be compiled, but only one will be installed. The following command can be used to ensure the correct driver is being tested:

    LIBGL_ALWAYS_SOFTWARE=1 glxinfo | grep "renderer string"

If any regressions are found in this testing with piglit, stop here, and do not perform a release until regressions are fixed.

### Update version in file VERSION

Increment the version contained in the file VERSION at Mesa's top-level, then commit this change.

### Create release notes for the new release

Create a new file docs/relnotes/X.Y.Z.html, (follow the style of the previous release notes). Note that the sha256sums section of the release notes should be empty at this point.

Two scripts are available to help generate portions of the release notes:

    	./bin/bugzilla_mesa.sh
    	./bin/shortlog_mesa.sh

The first script identifies commits that reference bugzilla bugs and obtains the descriptions of those bugs from bugzilla. The second script generates a log of all commits. In both cases, HTML-formatted lists are printed to stdout to be included in the release notes.

Commit these changes

### Make the release archives, signatures, and the release tag

From inside the Mesa directory:

    	./autogen.sh
    	make -j1 tarballs

After the tarballs are created, the sha256 checksums for the files will be computed and printed. These will be used in a step below.

It's important at this point to also verify that the constructed tar file actually builds:

    	tar xjf MesaLib-X.Y.Z.tar.bz2
    	cd Mesa-X.Y.Z
    	./configure --enable-gallium-llvm
    	make -j6
    	make install

Some touch testing should also be performed at this point, (run glxgears or more involved OpenGL programs against the installed Mesa).

Create detached GPG signatures for each of the archive files created above:

    	gpg --sign --detach MesaLib-X.Y.Z.tar.gz
    	gpg --sign --detach MesaLib-X.Y.Z.tar.bz2
    	gpg --sign --detach MesaLib-X.Y.Z.zip

Tag the commit used for the build:

    	git tag -s mesa-X.Y.X -m "Mesa X.Y.Z release"

Note: It would be nice to investigate and fix the issue that causes the tarballs target to fail with multiple build process, such as with "-j4". It would also be nice to incorporate all of the above commands into a single makefile target. And instead of a custom "tarballs" target, we should incorporate things into the standard "make dist" and "make distcheck" targets.

### Add the sha256sums to the release notes

Edit docs/relnotes/X.Y.Z.html to add the sha256sums printed as part of "make tarballs" in the previous step. Commit this change.

### Push all commits and the tag creates above

This is the first step that cannot easily be undone. The release is going forward from this point:

    	git push origin X.Y --tags

### Install the release files and signatures on the distribution server

The following commands can be used to copy the release archive files and signatures to the freedesktop.org server:

    	scp MesaLib-X.Y.Z* people.freedesktop.org:
    	ssh people.freedesktop.org
    	cd /srv/ftp.freedesktop.org/pub/mesa
    	mkdir X.Y.Z
    	cd X.Y.Z
    	mv ~/MesaLib-X.Y.Z* .

### Back on mesa master, andd the new release notes into the tree

Something like the following steps will do the trick:

    	cp docs/relnotes/X.Y.Z.html /tmp
            git checkout master
            cp /tmp/X.Y.Z.html docs/relnotes
            git add docs/relnotes/X.Y.Z.html

Also, edit docs/relnotes.html to add a link to the new release notes, and edit docs/index.html to add a news entry. Then commit and push:

    	git commit -a -m "docs: Import X.Y.Z release notes, add news item."
            git push origin

### Update the mesa3d.org website

NOTE: The recent release managers have not been performing this step themselves, but leaving this to Brian Paul, (who has access to the sourceforge.net hosting for mesa3d.org). Brian is more than willing to grant the permission necessary to future release managers to do this step on their own.

Update the web site by copying the docs/ directory's files to /home/users/b/br/brianp/mesa-www/htdocs/ with:
`sftp USERNAME,mesa3d@web.sourceforge.net`

### Announce the release

Make an announcement on the mailing lists: mesa-dev@lists.freedesktop.org, and mesa-announce@lists.freedesktop.org Follow the template of previously-sent release announcements. The following command can be used to generate the log of changes to be included in the release announcement:

    	git shortlog mesa-X.Y.Z-1..mesa-X.Y.Z