egl: Improve driver matching.

Make drv->Probe return a score so that the matching can be done by
finding the driver with the highest score.

src/egl/main/egldisplay.h

@@ -26,7 +26,6 @@ struct _egl_display
 
    EGLNativeDisplayType NativeDisplay;
 
-   const char *DriverName;
    _EGLDriver *Driver;
    void *DriverData; /* private to driver */
 

src/egl/main/egldriver.c

@@ -218,32 +218,35 @@ _eglLoadDriver(const char *path, const char *args)
 
 /**
  * Match a display to a preloaded driver.
+ *
+ * The matching is done by finding the driver with the highest score.
  */
 static _EGLDriver *
 _eglMatchDriver(_EGLDisplay *dpy)
 {
-   _EGLDriver *defaultDriver = NULL;
-   EGLint i;
+   _EGLDriver *best_drv = NULL;
+   EGLint best_score = -1, i;
 
    for (i = 0; i < _eglGlobal.NumDrivers; i++) {
       _EGLDriver *drv = _eglGlobal.Drivers[i];
+      EGLint score;
 
-      /* display specifies a driver */
-      if (dpy->DriverName) {
-         if (strcmp(dpy->DriverName, drv->Name) == 0)
-            return drv;
+      score = (drv->Probe) ? drv->Probe(drv, dpy) : 0;
+      if (score > best_score) {
+         if (best_drv) {
+            _eglLog(_EGL_DEBUG, "driver %s has higher score than %s",
+                  drv->Name, best_drv->Name);
          }
-      else if (drv->Probe) {
-         if (drv->Probe(drv, dpy))
-            return drv;
-      }
-      else {
-         if (!defaultDriver)
-            defaultDriver = drv;
+
+         best_drv = drv;
+         best_score = score;
+         /* perfect match */
+         if (score >= 100)
+            break;
       }
    }
 
-   return defaultDriver;
+   return best_drv;
 }
 
 

src/egl/main/egldriver.h

@@ -16,9 +16,22 @@ struct _egl_driver
    const char *Args;  /**< args to load this driver */
 
    const char *Name;  /**< name of this driver */
-   /**< probe a display to see if it is supported */
-   EGLBoolean (*Probe)(_EGLDriver *drv, _EGLDisplay *dpy);
-   /**< called before dlclose to release this driver */
+
+   /**
+    * Probe a display and return a score.
+    *
+    * Roughly,
+    *  50 means the driver supports the display;
+    *  90 means the driver can accelerate the display;
+    * 100 means a perfect match.
+    */
+   EGLint (*Probe)(_EGLDriver *drv, _EGLDisplay *dpy);
+
+   /**
+    * Release the driver resource.
+    *
+    * It is called before dlclose().
+    */
    void (*Unload)(_EGLDriver *drv);
 
    _EGLAPI API;  /**< EGL API dispatch table */