shader_type canvas_item;
// Full-screen nausea desaturation.
// Samples the screen, converts to luminance, and blends back toward grayscale
// based on the `desaturation` uniform (0 = full color, 1 = full grayscale).

uniform sampler2D screen_tex : hint_screen_texture, filter_linear_mipmap;
uniform float desaturation : hint_range(0.0, 1.0) = 0.0;

// Rec. 709 luma weights.
const vec3 LUMA = vec3(0.2126, 0.7152, 0.0722);

void fragment() {
	vec3 col = texture(screen_tex, SCREEN_UV).rgb;
	float gray = dot(col, LUMA);
	vec3 result = mix(col, vec3(gray), clamp(desaturation, 0.0, 1.0));
	COLOR = vec4(result, 1.0);
}