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Design of the GLES Tracing Library
Code Runtime Behavior:
Initialization:
egl_display_t::initialize() calls initEglTraceLevel() to figure out whether tracing should be
enabled. Currently, the shell properties "debug.egl.trace" and "debug.egl.debug_proc" together
control whether tracing should be enabled for a certain process. If tracing is enabled, this
calls GLTrace_start() to start the trace server.
Note that initEglTraceLevel() is also called from early_egl_init(), but that happens in the
context of the zygote, so that invocation has no effect.
egl_display_t::initialize() then calls setGLHooksThreadSpecific() where we set the thread
specific gl_hooks structure to point to the trace implementation. From this point on, every
GLES call is redirected to the trace implementation.
Application runtime:
While the application is running, all its GLES calls are directly routed to their corresponding
trace implementation.
For EGL calls, the trace library provides a bunch of functions that must be explicitly called
from the EGL library. These functions are declared in glestrace.h
Application shutdown:
Currently, the application is killed when the user stops tracing from the frontend GUI. We need
to explore if a more graceful method of stopping the application, or detaching tracing from the
application is required.
Code Structure:
glestrace.h declares all the hooks exposed by libglestrace. These are used by EGL/egl.cpp and
EGL/eglApi.cpp to initialize the trace library, and to inform the library of EGL calls.
All GL calls are present in GLES_Trace/src/gltrace_api.cpp. This file is generated by the
GLES_Trace/src/genapi.py script. The structure of all the functions looks like this:
void GLTrace_glFunction(args) {
// declare a protobuf
// copy arguments into the protobuf
// call the original GLES function
// if there is a return value, save it into the protobuf
// fixup the protobuf if necessary
// transport the protobuf to the host
}
The fixupGLMessage() call does any custom processing of the protobuf based on the GLES call.
This typically amounts to copying the data corresponding to input or output pointers.
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