game: add shader to indicate low hp

assets/shaders/screen_low_hp.gdshader

@@ -0,0 +1,39 @@
+shader_type canvas_item;
+
+uniform sampler2D screen_texture : hint_screen_texture;
+uniform float damage_amount : hint_range(0.0, 1.0) = 0.0;
+uniform float noise_strength : hint_range(0.0, 1.0) = 0.3;
+uniform float pulse_strength : hint_range(0.0, 1.0) = 0.2;
+uniform float time;
+
+// TODO: uniform vec2 player_uv; // use this to calculate player offset to camera
+
+float random(vec2 uv) {
+    return fract(sin(dot(uv.xy ,vec2(12.9898,78.233))) * 43758.5453);
+}
+
+void fragment() {
+    // Distance from screen center
+    vec2 center = vec2(0.5, 0.5);
+    float dist = distance(SCREEN_UV, center);
+    float edge_factor = smoothstep(0.4, 0.7, dist); // stronger at edges
+	float edge_factor_gray = smoothstep(0.0, 1.0-damage_amount, dist);
+
+    // Noise flicker
+    float n = random(SCREEN_UV * 200.0 + time * 2.0); 
+    float noise = (n - 0.5) * noise_strength;
+
+    // Pulsing intensity
+    float pulse = sin(time * 5.0) * pulse_strength;
+
+    // Final intensity
+    float final_amount = damage_amount * edge_factor + noise + pulse;
+    final_amount = clamp(final_amount, 0.0, 1.0);
+	
+	vec4 base = texture(screen_texture, SCREEN_UV);
+	float gray = dot(base.rgb, vec3(0.299, 0.587, 0.114));
+	base.rgb = mix(base.rgb, vec3(gray), edge_factor_gray * damage_amount);
+	
+    vec4 red_tint = vec4(1.0, 0.0, 0.0, 1.0);
+    COLOR = mix(base, red_tint, final_amount);
+}

assets/shaders/screen_low_hp.gdshader.uid

@@ -0,0 +1 @@
+uid://dnwiwj1ak1bu5

global_const.gd

@@ -12,6 +12,10 @@ signal sig_debug_stats_set(key: String, value: String)
 signal sig_stop_spawning(value: bool)
 @warning_ignore("unused_signal")
 signal sig_set_spawn_rate(value: float)
+@warning_ignore("unused_signal")
+signal sig_on_player_hp_change(hp: float, max_hp: float)
+@warning_ignore("unused_signal")
+signal sig_toggle_low_hp_shader(toggled_on: float)
 
 const GROUP_ENEMY = "enemy"
 const GROUP_DAMAGEABLE = "damagable"

scenes/enemies/enemy_base.gd

@@ -56,6 +56,10 @@ func do_movement(delta: float) -> void:
 		_do_simple_movement()
 	else:
 		_do_nav_agent_movement()
+	if velocity.x < 0:
+		sprite_2d.flip_h = true
+	else:
+		sprite_2d.flip_h = false
 
 
 func _has_direct_path():

scenes/managers/ui/main_ui.gd

@@ -5,9 +5,35 @@ extends Control
 @onready var player_ui: PlayerUI = $CanvasLayer/PlayerUI
 @onready var debug_ui: DebugUI = $CanvasLayer/DebugUI
 @onready var level_up_ui: LevelUpUI = $CanvasLayer/LevelUpUI
+@onready var low_hp_indicator: ColorRect = $CanvasLayer/LowHPIndicator
+
+var elapsed_time: float
 
 
 func _ready() -> void:
 	pause_ui.visible = false
 	player_ui.visible = true
 	level_up_ui.visible = false
+	low_hp_indicator.visible = false
+	GlobalConst.sig_on_player_hp_change.connect(_on_player_hp_change)
+	GlobalConst.sig_toggle_low_hp_shader.connect(_on_toggle_low_hp_shader)
+
+
+func _process(delta: float) -> void:
+	elapsed_time += delta
+	if low_hp_indicator.visible:
+		low_hp_indicator.material.set_shader_parameter("time", elapsed_time)
+
+
+func _on_player_hp_change(hp: float, max_hp: float):
+	print_debug("got sig")
+	var percent_hp = hp / max_hp * 100
+	if percent_hp < 40:
+		low_hp_indicator.visible = true
+		low_hp_indicator.material.set_shader_parameter("damage_amount", 1 - (percent_hp / 100))
+	else:
+		low_hp_indicator.visible = false
+
+
+func _on_toggle_low_hp_shader(toggled_on: bool):
+	low_hp_indicator.visible = !low_hp_indicator.visible

scenes/managers/ui/main_ui.tscn

@@ -1,11 +1,19 @@
-[gd_scene load_steps=6 format=3 uid="uid://b18uib08hvdpq"]
+[gd_scene load_steps=8 format=3 uid="uid://b18uib08hvdpq"]
 
 [ext_resource type="Script" uid="uid://dcxc70fvu7kl2" path="res://scenes/managers/ui/main_ui.gd" id="1_3a826"]
 [ext_resource type="Script" uid="uid://sjnxf0hj3egp" path="res://scenes/managers/ui/pause_ui.gd" id="1_lke1m"]
+[ext_resource type="Shader" uid="uid://dnwiwj1ak1bu5" path="res://assets/shaders/screen_low_hp.gdshader" id="2_lcbsd"]
 [ext_resource type="Script" uid="uid://dbq74tvxtpfjc" path="res://scenes/managers/ui/player_ui.gd" id="3_gaipe"]
 [ext_resource type="Script" uid="uid://d2o6tqnqg2o25" path="res://scenes/managers/ui/debug_ui.gd" id="4_217l8"]
 [ext_resource type="PackedScene" uid="uid://isg7vt4l7eem" path="res://scenes/managers/ui/level_up_ui.tscn" id="5_cfhdr"]
 
+[sub_resource type="ShaderMaterial" id="ShaderMaterial_cg7ol"]
+shader = ExtResource("2_lcbsd")
+shader_parameter/damage_amount = 0.5
+shader_parameter/noise_strength = 0.2
+shader_parameter/pulse_strength = 0.05
+shader_parameter/time = 0.0
+
 [node name="MainUI" type="Control"]
 layout_mode = 3
 anchors_preset = 15
@@ -17,6 +25,14 @@ script = ExtResource("1_3a826")
 
 [node name="CanvasLayer" type="CanvasLayer" parent="."]
 
+[node name="LowHPIndicator" type="ColorRect" parent="CanvasLayer"]
+material = SubResource("ShaderMaterial_cg7ol")
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+
 [node name="PauseUI" type="Control" parent="CanvasLayer"]
 layout_mode = 3
 anchors_preset = 15

scenes/player.gd

@@ -51,6 +51,7 @@ func take_damage(value: float) -> void:
 	dm.damage_taken = value
 	dm.player_damage = false
 	add_child(dm)
+	GlobalConst.sig_on_player_hp_change.emit(current_hp, max_hp)
 	main_ui.player_ui.update_hp()
 	if player_stats.current_health <= 0:
 		die()