drifty_fog.gdshader

shader_type canvas_item;
//render_mode unshaded;  <-- to remove lighting

// The seamless noise texture that will create the cloudy pattern
uniform sampler2D noise_texture : repeat_enable;

// Your custom black & white mask (White = Fog, Black = Transparent)
uniform sampler2D mask_texture;

// Fog color settings
uniform vec4 fog_default_color : source_color = vec4(0.5, 0.5, 0.5, 0.5); // Grey
uniform vec4 fog_heaven_color : source_color = vec4(0.8, 0.8, 0.0, 0.5); // Dark Yellow
uniform vec4 fog_hell_color : source_color = vec4(0.5, 0.0, 0.0, 0.5); // Dark Red

// Sin level: -1.0 (Hell) to 1.0 (Heaven)
uniform float sin_level : hint_range(-1.0, 1.0) = 0.0;

// Direction and speed of the drifting wind over time
uniform vec2 scroll_speed = vec2(0.05, 0.02);

// Sharpness / thickness of the clouds
uniform float fog_density : hint_range(0.0, 2.0) = 1.0;

void fragment() {
    // 1. Scroll our UV coordinates over time to push the clouds
    vec2 scrolled_uv = UV + scroll_speed * TIME;
    
    // 2. Read the noise value at the moving coordinate (Red channel)
    float noise_val = texture(noise_texture, scrolled_uv).r;
    noise_val = clamp(noise_val * fog_density, 0.0, 1.0);
    
    // 3. Read the exact static Mask pixel where we currently are
    vec4 mask_val = texture(mask_texture, UV);
    // Support either Alpha-transparent PNGs or flat B&W JPEGs for the mask
    float mask_alpha = mask_val.a * mask_val.r;
    
    // Lerp fog color based on sin_level
    vec4 current_fog_color = fog_default_color;
    if (sin_level > 0.0) {
        current_fog_color = mix(fog_default_color, fog_heaven_color, sin_level);
    } else if (sin_level < 0.0) {
        current_fog_color = mix(fog_default_color, fog_hell_color, -sin_level);
    }

    // 4. Output the fog colour, multiplied by the noise clouds AND the hard mask edge!
    COLOR.rgb = current_fog_color.rgb;
    COLOR.a = noise_val * mask_alpha * current_fog_color.a;
}