Allow falling back to GLES2

This allows running the TPS demo on a greater range of devices
and platforms, while also allowing its use for GLES2 renderer testing.

Several automatic adjustments are made to ensure it looks as good
as possible (within the limitations of GLES2 and the lack of baked
lightmaps).

level/geometry/environment.tres

@@ -1,7 +1,15 @@
-[gd_resource type="Environment" format=2]
+[gd_resource type="Environment" load_steps=2 format=2]
+
+[sub_resource type="ProceduralSky" id=1]
+sky_top_color = Color( 0.65098, 0.498039, 0.356863, 1 )
+sky_horizon_color = Color( 0.101961, 0.0784314, 0.054902, 1 )
+ground_bottom_color = Color( 0.101961, 0.0784314, 0.054902, 1 )
+ground_horizon_color = Color( 0.101961, 0.0784314, 0.054902, 1 )
+sun_energy = 0.0
 
 [resource]
 background_mode = 1
+background_sky = SubResource( 1 )
 ambient_light_color = Color( 0.258824, 0.203922, 0.152941, 1 )
 ambient_light_sky_contribution = 0.0
 fog_enabled = true

level/level.gd

@@ -8,13 +8,25 @@ signal replace_main_scene # Useless, but needed as there is no clean way to chec
 onready var world_environment = $WorldEnvironment
 
 func _ready():
-	if Settings.gi_quality == Settings.GIQuality.HIGH:
+	if OS.get_current_video_driver() == OS.VIDEO_DRIVER_GLES3 and Settings.gi_quality == Settings.GIQuality.HIGH:
 		ProjectSettings["rendering/quality/voxel_cone_tracing/high_quality"] = true
-	elif Settings.gi_quality == Settings.GIQuality.LOW:
+	elif OS.get_current_video_driver() == OS.VIDEO_DRIVER_GLES3 and Settings.gi_quality == Settings.GIQuality.LOW:
 		ProjectSettings["rendering/quality/voxel_cone_tracing/high_quality"] = false
 	else:
+		# GLES2 fallback only supports ReflectionProbe, not GIProbe.
+		# However, ReflectionProbes don't blend well with environment lighting in GLES2,
+		# so it looks better (and performs better) when ReflectionProbes are also hidden.
 		$GIProbe.hide()
-		$ReflectionProbes.show()
+		if OS.get_current_video_driver() == OS.VIDEO_DRIVER_GLES3:
+			$ReflectionProbes.show()
+		else:
+			$ReflectionProbes.hide()
+			# Brighten level if falling back to GLES2, as it looks very dark otherwise.
+			# A procedural sky is used to provide ambient and reflected lighting as a fallback.
+			world_environment.environment.background_mode = Environment.BG_SKY
+			world_environment.environment.ambient_light_sky_contribution = 1.0
+			# Adjust glow strength for GLES2 (since there is no HDR).
+			world_environment.environment.glow_strength = 1.5
 
 	if Settings.aa_quality == Settings.AAQuality.AA_8X:
 		get_viewport().msaa = Viewport.MSAA_8X

menu/menu.gd

@@ -8,6 +8,7 @@ signal replace_main_scene
 signal quit # Useless, but needed as there is no clean way to check if a node exposes a signal
 
 onready var ui = $UI
+onready var gles2_fallback = ui.get_node(@"GLES2Fallback")
 onready var main = ui.get_node(@"Main")
 onready var play_button = main.get_node(@"Play")
 onready var settings_button = main.get_node(@"Settings")
@@ -54,6 +55,12 @@ onready var loading_progress = loading.get_node(@"Progress")
 onready var loading_done_timer = loading.get_node(@"DoneTimer")
 
 func _ready():
+	if OS.get_current_video_driver() == OS.VIDEO_DRIVER_GLES2:
+		gles2_fallback.visible = true
+		# GI and SSAO are not supported in GLES2.
+		gi_menu.visible = false
+		ssao_menu.visible = false
+
 	get_tree().set_screen_stretch(SceneTree.STRETCH_MODE_2D, SceneTree.STRETCH_ASPECT_KEEP, Vector2(1920, 1080))
 	play_button.grab_focus()
 	var sound_effects = $BackgroundCache/RedRobot/SoundEffects

menu/menu.tscn

@@ -200,6 +200,18 @@ __meta__ = {
 "_edit_use_anchors_": false
 }
 
+[node name="GLES2Fallback" type="Label" parent="UI"]
+visible = false
+margin_left = 97.9495
+margin_top = 200.0
+margin_right = 837.949
+margin_bottom = 253.0
+custom_colors/font_color = Color( 1, 0.870588, 0.356863, 1 )
+text = "GLES2 fallback (degraded graphics quality)"
+__meta__ = {
+"_edit_use_anchors_": false
+}
+
 [node name="Main" type="Control" parent="UI"]
 anchor_left = -0.000673103
 anchor_top = -0.00189865

project.godot

@@ -217,6 +217,7 @@ toggle_debug={
 
 [rendering]
 
+quality/driver/fallback_to_gles2=true
 vram_compression/import_etc2=false
 quality/shadow_atlas/size=2048
 quality/filters/msaa=2