// ---Фрагментный шейдер (Fragment Shader)

varying vec2 TexCoord;
varying float viewZ; 
varying vec3 pos;

uniform sampler2D Texture;
uniform float uDistanceToPlanetSurface;          

const vec4 FOG_COLOR = vec4(0.0, 0.5, 1.0, 1.0); // Синий туман

varying vec3 worldPosition;

uniform vec3 uViewPos;

void main()
{
    
    vec4 textureColor = texture2D(Texture, TexCoord); 
    vec3 finalColor = textureColor.rgb; 
	
	float realDist = distance(worldPosition, uViewPos);
	
	float alphaFactor = clamp((2000 - realDist) / 500.0, 0.0, 1.0);

	float fogFactor;
	if (uDistanceToPlanetSurface > 1000)
	{
		gl_FragColor = vec4(finalColor.rgb, 1.0);
	}
	else if (uDistanceToPlanetSurface > 100)
	{
		float t = clamp((uDistanceToPlanetSurface - 100) / 900.0, 0.0, 1.0); // 1 upstairs, 0 downstairs
		
		fogFactor = clamp((realDist - 2400) / (300.0*(1 + 10*t)), 0.0, 1.0);
		
		gl_FragColor = mix(vec4(finalColor.rgb, alphaFactor), FOG_COLOR, fogFactor*(1.0 - t));
	}
	else if (uDistanceToPlanetSurface > 40)
	{
		//From 100 to 40:
		//(1000 < realDist < 1800)
		
		float t = clamp((uDistanceToPlanetSurface - 40) / 60.0, 0.0, 1.0); // 1 upstairs, 0 downstairs
		
		fogFactor = clamp((realDist - 2400) / 300.0, 0.0, 1.0); // old fog factor
		
		float fogFactor2 = clamp((realDist - 1000) / 800.0, 0.0, 1.0);
		
		gl_FragColor = mix(vec4(finalColor.rgb, alphaFactor), FOG_COLOR, max(fogFactor, fogFactor2*(1.0 - t)));
	}
	else 
	{
		fogFactor = clamp((realDist - 1000) / (800.0), 0.0, 1.0);
		
		gl_FragColor = mix(vec4(finalColor.rgb, alphaFactor), FOG_COLOR, fogFactor);
	}
    
}