shader_type canvas_item;
render_mode unshaded;

uniform sampler2D screen_texture : hint_screen_texture, filter_linear_mipmap;
uniform float motion_blur_amount : hint_range(0.0, 0.03) = 0.0;
uniform float chromatic_aberration : hint_range(0.0, 0.02) = 0.0;
uniform float vignette_strength : hint_range(0.0, 1.0) = 0.22;


vec4 motion_sample(vec2 uv) {
	// A restrained centre-directed velocity smear. The camera script scales it
	// with ship speed/turbo; mipmapped screen reads soften the outer samples.
	if (motion_blur_amount < 0.0001) {
		return textureLod(screen_texture, uv, 0.0);
	}
	vec2 step_uv = (uv - vec2(0.5)) * motion_blur_amount;
	vec4 color = textureLod(screen_texture, uv, 0.0) * 0.36;
	color += textureLod(screen_texture, uv - step_uv * 0.35, 0.5) * 0.25;
	color += textureLod(screen_texture, uv - step_uv * 0.7, 1.0) * 0.21;
	color += textureLod(screen_texture, uv - step_uv, 1.5) * 0.18;
	return color;
}


void fragment() {
	vec2 radial = UV - vec2(0.5);
	vec2 chroma = radial * chromatic_aberration;
	vec4 center = motion_sample(UV);
	vec3 color = center.rgb;
	// The branch is driven by one uniform for the whole draw, so non-turbo
	// frames avoid eight redundant screen taps without causing warp divergence.
	if (chromatic_aberration > 0.0001) {
		color.r = motion_sample(UV + chroma).r;
		color.b = motion_sample(UV - chroma).b;
	}

	// Aspect-correct vignette, always subtle and tightened slightly on turbo.
	vec2 aspect_radial = radial;
	aspect_radial.x *= SCREEN_PIXEL_SIZE.y / SCREEN_PIXEL_SIZE.x;
	float vignette = smoothstep(0.38, 0.78, length(aspect_radial));
	color *= 1.0 - vignette * vignette_strength;
	COLOR = vec4(color, 1.0);
}