Added effects manager and two effects to test attached to the player

scene.

shaders/flash.gdshader

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+shader_type canvas_item;
+
+// Color of the flash overlay
+uniform vec4 flash_color : source_color = vec4(1.0, 1.0, 1.0, 1.0);
+
+// Overall intensity of the flash (0.0 = none, 1.0 = full)
+// Set dynamically by FlashEffect.gd each frame
+uniform float flash_intensity : hint_range(0.0, 1.0) = 0.0;
+
+// How the flash blends with the original sprite
+uniform int blend_mode : hint_enum("Mix", "Additive", "Screen") = 0;
+
+// Additional brightness added to the flash color (0.0 = none, 1.0 = double)
+uniform float brightness_boost : hint_range(0.0, 1.0) = 0.0;
+
+void fragment() {
+    vec4 original = texture(TEXTURE, UV);
+
+    vec3 flash_rgb = flash_color.rgb * (1.0 + brightness_boost);
+
+    vec3 result;
+    float alpha = original.a;
+
+    if (original.a == 0.0) {
+        // Skip processing for fully transparent pixels
+        COLOR = original;
+    } else if (blend_mode == 0) {
+        // Mix: Linear interpolation between original and flash color
+        result = mix(original.rgb, flash_rgb, flash_intensity);
+        // Modulate alpha by flash intensity for a flickering transparency effect
+        alpha = mix(original.a, flash_color.a, flash_intensity);
+    } else if (blend_mode == 1) {
+        // Additive: Flash adds light to the original, clamped to avoid HDR blowout
+        result = clamp(original.rgb + flash_rgb * flash_intensity, 0.0, 1.0);
+        // Additive naturally brightens, so boost alpha when flashing
+        alpha = clamp(original.a + flash_color.a * flash_intensity, 0.0, 1.0);
+    } else {
+        // Screen: Brightens without washing out highlights
+        result = original.rgb + (1.0 - original.rgb) * flash_rgb * flash_intensity;
+        alpha = clamp(original.a + (1.0 - original.a) * flash_color.a * flash_intensity, 0.0, 1.0);
+    }
+
+    COLOR = vec4(result, alpha);
+}

shaders/flash.gdshader.uid

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+uid://dp4svqyxg1dum