ec5738c651
I have disabled building SDL with headless EGL, because SDL_config_minimal.h doesn't work with EGL, and I don't know how to implement a an SDL config that would work with EGL. I have verified that this works in a separate project, and that it compiles in this project. ``` $ ./build.sh -e release $ find ./out/ -name "*EGL*" ./out/cmake-release/filament/backend/CMakeFiles/backend.dir/src/opengl/platforms/PlatformEGL.cpp.o ./out/cmake-release/filament/backend/CMakeFiles/backend.dir/src/opengl/platforms/PlatformEGLHeadless.cpp.o ./out/cmake-release/libs/bluegl/CMakeFiles/bluegl.dir/src/BlueGLLinuxEGL.cpp.o ```
BlueGL Mechanics
So you want to call glClear()?
Step 0: Run bluegl-gen.py
This step is only required if updating or modifying BlueGL. These artifacts should already be checked into the Filament repository.
From the libs/bluegl folder, run:
./bluegl-gen.py
The bluegl-gen.py script generates a set of files:
- assembly (proxy) files:
BlueGLCore*.S - header files:
include/BlueGLDefines.handinclude/bluegl/BlueGL.h - a private header:
include/private_BlueGL.h
Step 1: Include the BlueGL defines header:
#include <bluegl/BlueGLDefines.h>
This headers adds a bunch of defines:
...
#define glClear bluegl_glClear
...
Step 2: Include the BlueGL header after the defines header:
#include <bluegl/BlueGLDefines.h>
#include <bluegl/BlueGL.h>
This also includes the GL headers, like <GL/glcorearb.h> for you.
Step 3: Call bluegl::bind()
Internally, the BlueGL library maintains a list of function pointers:
void* __blue_glCore_glClear;
During bluegl::bind(), each function gets assigned to the appropriate symbol loaded from the OS-specific GL shared library via dlopen, dlsym, and equivalents.
Step 4: Call glClear()
Because of the prior #define, you'll actually be calling bluegl_glClear(). This is a trampoline function, defined in the BlueGLCore*.S assembly file (the exact implementation varies slightly on each platform):
.private_extern _bluegl_glClear
_bluegl_glClear:
mov ___blue_glCore_glClear@GOTPCREL(%rip), %r11
jmp *(%r11)
The invokes the __blue_glCore_glClear function, which was previously assigned to the actual GL function.