mesa: if MESA_DEBUG=context, create a debug context

A number of drivers report useful debug/perf information accessible
through GL_ARB_debug_output and with debug contexts (i.e. setting the
GLX_CONTEXT_DEBUG_BIT_ARB flag).  But few applications actually use
the GL_ARB_debug_output extension.

This change lets one set the MESA_DEBUG env var to "context" to force-set
a debug context and report debug/perf messages to stderr (or whatever
file MESA_LOG_FILE is set to).  This is a useful debugging tool.

The small change in st_api_create_context() is needed so that
st_update_debug_callback() gets called to hook up the driver debug
callbacks when ST_CONTEXT_FLAG_DEBUG was not set, but MESA_DEBUG=context.

v2: use %.*s format string instead of allocating temporary buffer.

Reviewed-by: Nicolai Hähnle <[email protected]>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/mesa/state_tracker/st_manager.c b/src/mesa/state_tracker/st_manager.c
index 0f71e6311b1..c3d8286b5a7 100644
--- a/src/mesa/state_tracker/st_manager.c
+++ b/src/mesa/state_tracker/st_manager.c
@@ -680,7 +680,9 @@ st_api_create_context(struct st_api *stapi, struct st_manager *smapi,
       }
 
       st->ctx->Const.ContextFlags |= GL_CONTEXT_FLAG_DEBUG_BIT;
+   }
 
+   if (st->ctx->Const.ContextFlags & GL_CONTEXT_FLAG_DEBUG_BIT) {
       st_update_debug_callback(st);
    }