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James Park
ba21fb947e
There are cases where alpha is multiplied unnecessarily. This change attempts to use premultiplied alpha blending for composition. To keep this change simple, The filter chain will continue to use straight alpha. Otherwise, every source would need to modified to output premultiplied, and every filter modified for premultiplied input. "DrawAlphaDivide" shader techniques have been added to convert from premultiplied alpha to straight alpha for final output. "DrawMatrix" techniques ignore alpha, so they do not appear to need changing. One remaining issue is that scale effects are set up here to use the same shader logic for both scale filters (straight alpha - incorrectly), and output composition (premultiplied alpha - correctly). A fix could be made to add additional shaders for straight alpha, but the "real" fix may be to eliminate the straight alpha path at some point. For graphics, SrcBlendAlpha and DestBlendAlpha were both ONE, and could combine together to form alpha values greater than one. This is not as noticeable of a problem for UNORM targets because the channels are clamped, but it will likely become a problem in more situations if FLOAT targets are used. This change switches DestBlendAlpha to INVSRCALPHA. The blending behavior of stacked transparents is preserved without overflowing the alpha channel. obs-transitions: Use premultiplied alpha blend, and simplify shaders because both inputs and outputs use premultiplied alpha now. Fixes https://obsproject.com/mantis/view.php?id=1108
OBS Studio <https://obsproject.com> =================================== .. image:: https://travis-ci.org/obsproject/obs-studio.svg?branch=master :alt: OBS Studio Build Status - Travis CI :target: https://travis-ci.org/obsproject/obs-studio .. image:: https://ci.appveyor.com/api/projects/status/github/obsproject/obs-studio?branch=master&svg=true :alt: OBS Studio Build Status - AppVeyor CI :target: https://ci.appveyor.com/project/jp9000/obs-studio/branch/master .. image:: https://dev.azure.com/obsjim/obsjim/_apis/build/status/obsproject.obs-studio?branchName=master :alt: OBS Studio Build Status - Azure Pipelines :target: https://dev.azure.com/obsjim/obsjim/_build/latest?definitionId=1&branchName=master .. image:: https://discordapp.com/api/guilds/348973006581923840/widget.png?style=shield :alt: OBS Studio Discord Server :target: https://obsproject.com/discord What is OBS Studio? ------------------- OBS Studio is software designed for capturing, compositing, encoding, recording, and streaming video content, efficiently. It's distributed under the GNU General Public License v2 (or any later version) - see the accompanying COPYING file for more details. Quick Links ----------- - Website: https://obsproject.com - Help/Documentation/Guides: https://github.com/obsproject/obs-studio/wiki - Forums: https://obsproject.com/forum/ - Build Instructions: https://github.com/obsproject/obs-studio/wiki/Install-Instructions - Developer/API Documentation: https://obsproject.com/docs - Bug Tracker: https://obsproject.com/mantis/ (Note: The bug tracker is linked to forum accounts. To use the bug tracker, log in to a forum account) Contributing ------------ - If you wish to contribute code to the project, please make sure to read the coding and commit guidelines: https://github.com/obsproject/obs-studio/blob/master/CONTRIBUTING.rst - Developer/API documentation can be found here: https://obsproject.com/docs - If you wish to contribute translations, do not submit pull requests. Instead, please use Crowdin. For more information read this thread: https://obsproject.com/forum/threads/how-to-contribute-translations-for-obs.16327/ - Other ways to contribute are by helping people out with support on our forums or in our community chat. Please limit support to topics you fully understand -- bad advice is worse than no advice. When it comes to something that you don't fully know or understand, please defer to the official help or official channels.