//===========================================================================
//
// Vanilla Doom wall colormap equation
//
//===========================================================================
float R_WallColormap(float lightnum, float z, vec3 normal)
{
	// R_ScaleFromGlobalAngle calculation
	float projection = 160.0; // projection depends on SCREENBLOCKS!! 160 is the fullscreen value
	vec2 line_v1 = pixelpos.xz; // in vanilla this is the first curline vertex
	vec2 line_normal = normal.xz;
	float texscale = projection * clamp(dot(normalize(uCameraPos.xz - line_v1), line_normal), 0.0, 1.0) / z;

	float lightz = clamp(16.0 * texscale, 0.0, 47.0);

	// scalelight[lightnum][lightz] lookup
	float startmap = (15.0 - lightnum) * 4.0;
	return startmap - lightz * 0.5;
}

//===========================================================================
//
// Vanilla Doom plane colormap equation
//
//===========================================================================
float R_PlaneColormap(float lightnum, float z)
{
	float lightz = clamp(z / 16.0f, 0.0, 127.0);

	// zlight[lightnum][lightz] lookup
	float startmap = (15.0 - lightnum) * 4.0;
	float scale = 160.0 / (lightz + 1.0);
	return startmap - scale * 0.5;
}

//===========================================================================
//
// zdoom colormap equation
//
//===========================================================================
float R_ZDoomColormap(float light, float z)
{
	float L = light * 255.0;
	float vis = min(uGlobVis / z, 24.0 / 32.0);
	float shade = 2.0 - (L + 12.0) / 128.0;
	float lightscale = shade - vis;
	return lightscale * 31.0;
}

float R_DoomColormap(float light, float z)
{
	if ((uPalLightLevels >> 16) == 16) // gl_lightmode 16
	{
		float lightnum = clamp(light * 15.0, 0.0, 15.0);

		if (dot(vWorldNormal.xyz, vWorldNormal.xyz) > 0.5)
		{
			vec3 normal = normalize(vWorldNormal.xyz);
			return mix(R_WallColormap(lightnum, z, normal), R_PlaneColormap(lightnum, z), abs(normal.y));
		}
		else // vWorldNormal is not set on sprites
		{
			return R_PlaneColormap(lightnum, z);
		}
	}
	else
	{
		return R_ZDoomColormap(light, z);
	}
}

//===========================================================================
//
// Doom software lighting equation
//
//===========================================================================
float R_DoomLightingEquation(float light)
{
	// z is the depth in view space, positive going into the screen
	float z;
	if (((uPalLightLevels >> 8)  & 0xff) == 2)
	{
		z = distance(pixelpos.xyz, uCameraPos.xyz);
	}
	else 
	{
		z = pixelpos.w;
	}

	if ((uPalLightLevels >> 16) == 5) // gl_lightmode 5: Build software lighting emulation.
	{
		// This is a lot more primitive than Doom's lighting...
		float numShades = float(uPalLightLevels & 255);
		float curshade = (1.0 - light) * (numShades - 1.0);
		float visibility = max(uGlobVis * uLightFactor * z, 0.0);
		float shade = clamp((curshade + visibility), 0.0, numShades - 1.0);
		return clamp(shade * uLightDist, 0.0, 1.0);
	}

	float colormap = R_DoomColormap(light, z);

	if ((uPalLightLevels & 0xff) != 0)
		colormap = floor(colormap) + 0.5;

	// Result is the normalized colormap index (0 bright .. 1 dark)
	return clamp(colormap, 0.0, 31.0) / 32.0;
}