Find the best EGL config available between those returned by eglChoos…

…eConfig

This existed in the old Android Java code, it got lost in the migration to the
commong EGL code.

src/video/SDL_egl.c

@@ -218,7 +218,9 @@ SDL_EGL_ChooseConfig(_THIS)
     /* 64 seems nice. */
     EGLint attribs[64];
     EGLint found_configs = 0;
-    int i;
+    /* 128 seems even nicer here */
+    EGLConfig configs[128];
+    int i, j, best_bitdiff = -1, bitdiff, value;
 
     if (!_this->egl_data) {
         /* The EGL library wasn't loaded, SDL_GetError() should have info */
@@ -273,12 +275,44 @@ SDL_EGL_ChooseConfig(_THIS)
 
     if (_this->egl_data->eglChooseConfig(_this->egl_data->egl_display,
         attribs,
-        &_this->egl_data->egl_config, 1,
+        configs, SDL_arraysize(configs),
         &found_configs) == EGL_FALSE ||
         found_configs == 0) {
         return SDL_SetError("Couldn't find matching EGL config");
     }
 
+    /* eglChooseConfig returns a number of configurations that match or exceed the requested attribs. */
+    /* From those, we select the one that matches our requirements more closely via a makeshift algorithm */
+
+    for ( i=0; i<found_configs; i++ ) {
+        bitdiff = 0;
+        for (j = 0; ; j += 2) {
+            if (attribs[j] == EGL_NONE) {
+               break;
+            }
+
+            if ( attribs[j+1] != EGL_DONT_CARE && (
+                attribs[j] == EGL_RED_SIZE ||
+                attribs[j] == EGL_GREEN_SIZE ||
+                attribs[j] == EGL_BLUE_SIZE ||
+                attribs[j] == EGL_ALPHA_SIZE ||
+                attribs[j] == EGL_DEPTH_SIZE ||
+                attribs[j] == EGL_STENCIL_SIZE)) {
+
+                _this->egl_data->eglGetConfigAttrib(_this->egl_data->egl_display, configs[i], attribs[j], &value);
+                bitdiff += value - attribs[j + 1]; /* value is always >= attrib */
+            }
+        }
+
+        if (bitdiff < best_bitdiff || best_bitdiff == -1) {
+            _this->egl_data->egl_config = configs[i];
+
+            best_bitdiff = bitdiff;
+        }
+
+        if (bitdiff == 0) break; /* we found an exact match! */
+    }
+
     return 0;
 }