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);
}