Restructured screen shaders in node tree

core/shaders/outline/outline_canvas_layer.tscn

@@ -0,0 +1,19 @@
+[gd_scene load_steps=3 format=3 uid="uid://dxp3dru2lrv6h"]
+
+[ext_resource type="Shader" path="res://core/shaders/outline/outline_shader.gdshader" id="1_27aro"]
+
+[sub_resource type="ShaderMaterial" id="ShaderMaterial_myg35"]
+shader = ExtResource("1_27aro")
+
+[node name="OutlineShader" type="CanvasLayer"]
+editor_description = "Outline & glow"
+
+[node name="ColorRect" type="ColorRect" parent="."]
+material = SubResource("ShaderMaterial_myg35")
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+color = Color(0, 0, 0, 1)
+metadata/_edit_use_anchors_ = true

core/shaders/outline/outline_shader.gdshader

@@ -0,0 +1,54 @@
+shader_type canvas_item;
+render_mode unshaded;
+
+// uniforms
+
+uniform sampler2D screen_texture : hint_screen_texture, repeat_disable, filter_linear_mipmap;
+
+// constants
+
+const vec3 BLACK = vec3(0);
+const float glow_strength = 0.5;
+const float glow_size_lod = 3.0;
+const int outline_radius = 1;
+
+// simple edge detection based on black
+
+bool is_edge(int radius, vec2 screen_uv, vec2 screen_pixel_size) {
+	bool ed_found_bg = false;
+	bool ed_found_color = false;
+	// check neighbor pixels
+	for (int x = -radius; x <= radius; x++) {
+		for (int y = -radius; y <= radius; y++) {
+			vec4 p = texture(screen_texture, screen_uv + (vec2(float(x), float(y)) * screen_pixel_size));
+			if (p.rgb == BLACK) {
+				ed_found_bg = true;
+			} else {
+				ed_found_color = true;
+			}
+		}
+	}
+	return ed_found_bg && ed_found_color;
+}
+
+//
+
+void fragment() {
+	// get screen texture
+	vec4 screen = texture(screen_texture, SCREEN_UV);
+	// apply edge detection
+	if (is_edge(outline_radius, SCREEN_UV, SCREEN_PIXEL_SIZE)) {
+		if (screen.rgb != BLACK) { // would be incompatible with target backgrounds != black
+			COLOR = screen;
+		}
+	}
+	// apply glow
+	// blur a relative radius -> x * log(1.0/SCREEN_PIXEL_SIZE.y)
+	// using log, because the LOD value seems to affect the blur radius exponentially
+	vec4 glow = textureLod(screen_texture, SCREEN_UV, glow_size_lod);
+	if (screen.rgb == BLACK) {
+		COLOR += glow * glow_strength;
+	}
+	// set alpha to 1
+	COLOR.a = 1.0;
+}