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e3d6bc36d3
This re-designs the matrix stack so we now keep track of each separate
operation such as rotating, scaling, translating and multiplying as
immutable, ref-counted nodes in a graph.
Being a "graph" here means that different transformations composed of
a sequence of linked operation nodes may share nodes.
The first node in a matrix-stack is always a LOAD_IDENTITY operation.
As an example consider if an application where to draw three rectangles
A, B and C something like this:
cogl_framebuffer_scale (fb, 2, 2, 2);
cogl_framebuffer_push_matrix(fb);
cogl_framebuffer_translate (fb, 10, 0, 0);
cogl_framebuffer_push_matrix(fb);
cogl_framebuffer_rotate (fb, 45, 0, 0, 1);
cogl_framebuffer_draw_rectangle (...); /* A */
cogl_framebuffer_pop_matrix(fb);
cogl_framebuffer_draw_rectangle (...); /* B */
cogl_framebuffer_pop_matrix(fb);
cogl_framebuffer_push_matrix(fb);
cogl_framebuffer_set_modelview_matrix (fb, &mv);
cogl_framebuffer_draw_rectangle (...); /* C */
cogl_framebuffer_pop_matrix(fb);
That would result in a graph of nodes like this:
LOAD_IDENTITY
|
SCALE
/ \
SAVE LOAD
| |
TRANSLATE RECTANGLE(C)
| \
SAVE RECTANGLE(B)
|
ROTATE
|
RECTANGLE(A)
Each push adds a SAVE operation which serves as a marker to rewind too
when a corresponding pop is issued and also each SAVE node may also
store a cached matrix representing the composition of all its ancestor
nodes. This means if we repeatedly need to resolve a real CoglMatrix
for a given node then we don't need to repeat the composition.
Some advantages of this design are:
- A single pointer to any node in the graph can now represent a
complete, immutable transformation that can be logged for example
into a journal. Previously we were storing a full CoglMatrix in
each journal entry which is 16 floats for the matrix itself as well
as space for flags and another 16 floats for possibly storing a
cache of the inverse. This means that we significantly reduce
the size of the journal when drawing lots of primitives and we also
avoid copying over 128 bytes per entry.
- It becomes much cheaper to check for equality. In cases where some
(unlikely) false negatives are allowed simply comparing the pointers
of two matrix stack graph entries is enough. Previously we would use
memcmp() to compare matrices.
- It becomes easier to do comparisons of transformations. By looking
for the common ancestry between nodes we can determine the operations
that differentiate the transforms and use those to gain a high level
understanding of the differences. For example we use this in the
journal to be able to efficiently determine when two rectangle
transforms only differ by some translation so that we can perform
software clipping.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
(cherry picked from commit f75aee93f6b293ca7a7babbd8fcc326ee6bf7aef)
|
||
|---|---|---|
| build | ||
| cogl | ||
| cogl-pango | ||
| doc | ||
| examples | ||
| po | ||
| tests | ||
| .gitignore | ||
| .vimrc | ||
| autogen.sh | ||
| ChangeLog | ||
| cogl.doap | ||
| config-custom.h | ||
| config.h.win32.in | ||
| configure.ac | ||
| COPYING | ||
| Makefile.am | ||
| NEWS | ||
| README.in | ||
README for Cogl @COGL_1_VERSION@
===============================================================================
Note: This file is delimited with -- markers so it is possible to split
sections out for other purposes, such as for release notes.
--
DESCRIPTION
-------------------------------------------------------------------------------
Cogl is a small open source library for using 3D graphics hardware for
rendering. The API departs from the flat state machine style of OpenGL and is
designed to make it easy to write orthogonal components that can render without
stepping on each others toes.
As well as aiming for a nice API, we think having a single library as opposed
to an API specification like OpenGL has a few advantages too; like being
able to paper over the inconsistencies/bugs of different OpenGL
implementations in a centralized place, not to mention the myriad of OpenGL
extensions. It also means we are in a better position to provide utility
APIs that help software developers since they only need to be implemented
once and there is no risk of inconsistency between implementations.
Having other backends, besides OpenGL, such as drm, Gallium or D3D are
options we are interested in for the future.
--
REQUIREMENTS
-------------------------------------------------------------------------------
Cogl currently only requires:
• GLib ≥ @GLIB_REQ_VERSION@
• OpenGL ≥ 1.3 (or 1.2 + multitexturing), or OpenGL ES 2.0 (or 1.1)
• GLX, AGL, WGL or an EGL implementation
Cogl also has optional dependencies:
• GDK-Pixbuf ≥ @GDK_PIXBUF_REQ_VERSION@
- for image loading
• Cairo ≥ @CAIRO_REQ_VERSION@
- for debugging texture atlasing (debug builds only)
The optional Cogl Pango library requires:
• Cairo ≥ @CAIRO_REQ_VERSION@
• PangoCairo ≥ @PANGOCAIRO_REQ_VERSION@
On X11, Cogl depends on the following extensions
• XComposite ≥ @XCOMPOSITE_REQ_VERSION@
• XDamage
• XExt
• XFixes ≥ @XFIXES_REQ_VERSION@
When running with OpenGL, Cogl requires at least version 1.3
or 1.2 with the multitexturing extension. However to build Cogl
you will need the latest GL headers which can be obtained from:
http://www.khronos.org
If you are building the API reference you will also need:
• GTK-Doc ≥ @GTK_DOC_REQ_VERSION@
If you are building the additional documentation you will also need:
• xsltproc
• jw (optional, for generating PDFs)
If you are building the Introspection data you will also need:
• GObject-Introspection ≥ @GI_REQ_VERSION@
GObject-Introspection is available from:
git://git.gnome.org/gobject-introspection
If you want support for profiling Cogl you will also need:
• UProf ≥ @UPROF_REQ_VERSION@
UProf is available from:
git://github.com/rib/UProf.git
--
DOCUMENTATION
-------------------------------------------------------------------------------
The API references for the latest stable release are available at:
http://docs.clutter-project.org/docs/cogl/stable/
The experimental 2.0 API can be found here:
http://docs.clutter-project.org/docs/cogl-2.0-experimental/stable/
Note: The confusing "stable" at the end refers to the overall Cogl release
status, not the documentation specifically.
--
LICENSE
-------------------------------------------------------------------------------
Most of Cogl is licensed under the terms of the GNU Lesser General Public
License, version 2.1 or (at your option) later. Some files are licensed under
more permissive licenses MIT or BSD style licenses though so please see
individual files for details.
--
BUILDING AND INSTALLATION
-------------------------------------------------------------------------------
Please refer to the INSTALL document.
--
BUGS
-------------------------------------------------------------------------------
Please report bugs here:
http://bugzilla.gnome.org/enter_bug.cgi?product=cogl
You will need a Bugzilla account.
Please include the following in bug reports:
• what system you're running Cogl on;
• which version of Cogl you are using;
• which version of GLib and OpenGL (or OpenGL ES) you are using;
• which video card and which drivers you are using, including output of
glxinfo and xdpyinfo (if applicable);
• how to reproduce the bug.
If you cannot reproduce the bug with one of the tests that come with
Cogl's source code, it can help a lot to include a small test case
displaying the bad behaviour.
If the bug exposes a crash, the exact text printed out and a stack trace
obtained using gdb are greatly appreciated.
--
CONTRIBUTING
-------------------------------------------------------------------------------
The CODING_STYLE file describes the coding style we use throughout Cogl,
please try your best to conform to this style because the consistency
really helps keep the code maintainable.
We can accept contributions in several ways:
• Either as patches attached to bugs on bugzilla
- For this you may be interested in using git-bz.
See http://git.fishsoup.net/man/git-bz.html for details
• You can email us patches
- For this we recommend using git-send-email
• You can create a remote branch and ask us to pull from that for more
substantial changes.
- For this we recommend using github.
Ideally standalone patches should be created using git format-patch since
that makes it easiest to import the patch with a commit message into a
git repository.