Add “Cinematic Bloom” — star-shaped and anisotropic lens flare effect to Environment settings

[Eagle6393]

Currently, Godot’s Bloom/Glow system uses a simple Gaussian blur for bright pixels.
While efficient, it lacks the cinematic lens flare and star-shaped bloom effects seen in modern AAA games like Forza Horizon, Gran Turismo, and Unreal Engine 5.

Proposal:

Add a new mode in Environment → Glow (or Bloom):

New Mode: “Cinematic Bloom”

Parameters:

Cinematic Bloom: bool — enables advanced bloom mode;

Aperture Shape: Texture2D — defines the shape of the lens (star, cross, streaks, etc.);

Streak Intensity: float — anisotropic light stretch;

Star Sharpness: float — controls shape precision;

Color Aberration: float — subtle chromatic effect for realism.

Implementation idea:

In post-processing (Vulkan):

1. After the regular bloom pass, perform an additional convolution pass using the user-provided shape mask (kernel_shape).

2. Combine results via additive blending with the scene.

3. Optional: integrate with existing glow buffers for better performance.

Example GLSL concept:

uniform sampler2D source_tex;
uniform sampler2D kernel_shape;
uniform float intensity = 1.0;

void fragment() {
    vec2 uv = SCREEN_UV;
    vec3 base = texture(source_tex, uv).rgb;
    vec3 bloom = vec3(0.0);

    for (int x = -4; x <= 4; x++) {
        for (int y = -4; y <= 4; y++) {
            vec2 offset = vec2(x, y) / vec2(512.0);
            float mask = texture(kernel_shape, vec2((x + 4.0) / 8.0, (y + 4.0) / 8.0)).r;
            vec3 col = texture(source_tex, uv + offset * mask).rgb;
            bloom += col * mask;
        }
    }

    COLOR.rgb = base + bloom * intensity;
}

Why it matters:

Produces realistic sunlight, reflections, and headlight glares;

Adds a cinematic feel to the camera;

Lightweight compared to full lens simulation;

Ideal for racing, cinematic, and sci-fi scenes;

Could be implemented as an optional shader pass without breaking existing Glow code.

[Calinou]

Thanks for the proposal! Consolidating in #9695 and #6194.