Added support for the DEBUG_INVOCATION environment variable

Fixes https://github.com/libsdl-org/SDL/issues/12275

include/SDL3/SDL_hints.h

@@ -2410,6 +2410,10 @@ extern "C" {
  *
  * `app=info,assert=warn,test=verbose,*=error`
  *
+ * If the `DEBUG_INVOCATION` environment variable is set to "1", the default log levels are equivalent to:
+ *
+ * `assert=warn,test=verbose,*=debug`
+ *
  * This hint can be set anytime.
  *
  * \since This hint is available since SDL 3.2.0.

src/SDL_log.c

@@ -375,6 +375,9 @@ void SDL_ResetLogPriorities(void)
 
     SDL_LockMutex(SDL_log_lock);
     {
+        const char *env = SDL_getenv("DEBUG_INVOCATION");
+        bool debug = (env && *env && *env != '0');
+
         CleanupLogPriorities();
 
         SDL_log_default_priority = SDL_LOG_PRIORITY_INVALID;
@@ -397,7 +400,11 @@ void SDL_ResetLogPriorities(void)
 
             switch (i) {
             case SDL_LOG_CATEGORY_APPLICATION:
-                SDL_log_priorities[i] = SDL_LOG_PRIORITY_INFO;
+                if (debug) {
+                    SDL_log_priorities[i] = SDL_LOG_PRIORITY_DEBUG;
+                } else {
+                    SDL_log_priorities[i] = SDL_LOG_PRIORITY_INFO;
+                }
                 break;
             case SDL_LOG_CATEGORY_ASSERT:
                 SDL_log_priorities[i] = SDL_LOG_PRIORITY_WARN;
@@ -406,7 +413,11 @@ void SDL_ResetLogPriorities(void)
                 SDL_log_priorities[i] = SDL_LOG_PRIORITY_VERBOSE;
                 break;
             default:
-                SDL_log_priorities[i] = SDL_LOG_PRIORITY_ERROR;
+                if (debug) {
+                    SDL_log_priorities[i] = SDL_LOG_PRIORITY_DEBUG;
+                } else {
+                    SDL_log_priorities[i] = SDL_LOG_PRIORITY_ERROR;
+                }
                 break;
             }
         }