shader_type spatial;

// Texture Inputs
uniform sampler2D flat_albedo : source_color, filter_linear_mipmap_anisotropic; // e.g., Grass
uniform sampler2D flat_normal : hint_normal, filter_linear_mipmap_anisotropic;
uniform sampler2D steep_albedo : source_color, filter_linear_mipmap_anisotropic; // e.g., Cliff/Rock
uniform sampler2D steep_normal : hint_normal, filter_linear_mipmap_anisotropic;

// Shader Control Knobs
uniform float texture_scale = 0.05;
uniform float slope_threshold : hint_range(0.0, 1.0) = 0.7;
uniform float slope_blend : hint_range(0.01, 0.5) = 0.1;

// Triplanar helper function to prevent stretching on procedural cliffs
vec4 triplanar_sample(sampler2D tex, vec3 world_pos, vec3 normal) {
	vec3 blending = abs(normal);
	blending = normalize(max(blending, 0.00001)); // Avoid division by zero
	blending /= (blending.x + blending.y + blending.z);

	vec4 x_tex = texture(tex, world_pos.zy * texture_scale);
	vec4 y_tex = texture(tex, world_pos.xz * texture_scale);
	vec4 z_tex = texture(tex, world_pos.xy * texture_scale);

	return x_tex * blending.x + y_tex * blending.y + z_tex * blending.z;
}

varying vec3 world_position;
varying vec3 world_normal;

void vertex() {
	// Grab real-world coordinates from Terrainy's procedural vertices
	world_position = (MODEL_MATRIX * vec4(VERTEX, 1.0)).xyz;
	world_normal = MODEL_NORMAL_MATRIX * NORMAL;
}

void fragment() {
	// Normalize vectors for accurate angle calculations
	vec3 normal = normalize(world_normal);
	
	// Sample textures using triplanar projection mapping
	vec4 grass_c = triplanar_sample(flat_albedo, world_position, normal);
	vec4 grass_n = triplanar_sample(flat_normal, world_position, normal);
	vec4 rock_c = triplanar_sample(steep_albedo, world_position, normal);
	vec4 rock_n = triplanar_sample(steep_normal, world_position, normal);

	// Calculate slope: dot product against the world UP vector (0, 1, 0)
	float slope = dot(normal, vec3(0.0, 1.0, 0.0));
	
	// Create a smooth mask transitioning between flat areas and cliffs
	float weight = smoothstep(slope_threshold - slope_blend, slope_threshold + slope_blend, slope);

	// Blend the textures together based on the procedural terrain angles
	ALBEDO = mix(rock_c.rgb, grass_c.rgb, weight);
	NORMAL_MAP = mix(rock_n.rgb, grass_n.rgb, weight);
	ROUGHNESS = 0.8; // Uniform roughness default
}