feat(rendering): add cinematic post processing

Game/shaders/post_process.gdshader

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+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);
+}

Game/shaders/post_process.gdshader.uid

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+uid://cx1lpjodunjhx