- save texture paths in relative format as well
- always write portable relative paths on Windows using '/' instead of '\'
- remove an ancient piece of code that could sometimes fail loading relative paths
- fix absolute path handling between different drives for Windows
- integrate video_shader_resolve_relative() into video_shader_parse_* functions
- move shader flags from the video drivers to the context drivers
- rework config_load_shader_preset() from configuration.c into retroarch_load_shader_preset() in retroarch.c with proper compatibility check
- implicitly call retroarch_load_shader_preset() in retroarch_get_shader_preset() once per core/content life cycle
- use video_shader_is_supported() instead of video_driver_test_all_flags() where appropriate
- remove GFX_CTX_FLAGS_NONE because it is meaningless
- gl.c: refactor backend fallback into more general gl2_get_fallback_shader_type
- d3d9-12, gl_core, gx2_gfx, gl, vulkan: more consistent shader init and `set_shader` behavior
- configuration.c: remove check_shader_compatibility
- shader_glsl.c, shader_gl_cg.c: use `video_shader_get_type_from_ext`
- shader_gl_cg.c: add shader type check with fallback to stock like in shader_glsl.c
- menu_shader.c: use `enum rarch_shader_type` instead of `unsigned`
- video_shader_parse.c: add `video_shader_to_str` for easier logging
- remove `type` from `struct video_shader`, which was always set to CG and wrongly used in lang_process.cpp's `slang_process()` (has no further consequences because the code is unused)
- video_shader_parse_type()'s fallback only worked for NULL paths and was wrongly used, now returns RARCH_SHADER_NONE like video_shader_get_type_from_ext().
- video_shader_get_type_from_ext() should not be checking video driver flags, this is instead done by video_shader_is_supported()
- video_driver_get_all_flags() did not actually 'get' flags, changed to video_driver_test_all_flags()
workaround for crash due to glcore not always using at least OpenGL 3.2
This driver should sunset the old gl2 driver, but that driver will
likely live on to support really ancient and terrible GL stacks.
All the worst legacy cruft has been ripped out, and it's almost a decent
backend now.
Requirements for slang are GL 3.2+ or GLES3.
Some shaders require features which are not directly compatible with
GLES2 or legacy GL.
This driver shares a lot of concepts from the Vulkan driver.
The slang shader stack and SPIRV-Cross are used to implement the shader
spec, and the menu shaders are also shared with Vulkan.
