// This shader is used to bake the global albedo map.
// It exposes a subset of the main shader API, so uniform names were not modified.

shader_type spatial;

// I had to remove source_color` from colormap in Godot 3 because it makes sRGB conversion kick in,
// which snowballs to black when doing GPU painting on that texture...
uniform sampler2D u_terrain_colormap;
uniform sampler2D u_terrain_splat_index_map;
uniform sampler2D u_terrain_splat_weight_map;

uniform sampler2DArray u_ground_albedo_bump_array : source_color;

// TODO Have UV scales for each texture in an array?
uniform float u_ground_uv_scale;
// Keep depth blending because it has a high effect on the final result
uniform bool u_depth_blending = true;


vec3 get_depth_blended_weights(vec3 splat, vec3 bumps) {
	float dh = 0.2;

	vec3 h = bumps + splat;

	// TODO Keep improving multilayer blending, there are still some edge cases...
	// Mitigation: nullify layers with near-zero splat
	h *= smoothstep(0, 0.05, splat);

	vec3 d = h + dh;
	d.r -= max(h.g, h.b);
	d.g -= max(h.r, h.b);
	d.b -= max(h.g, h.r);

	vec3 w = clamp(d, 0, 1);
	// Had to normalize, since this approach does not preserve components summing to 1
	return w / (w.x + w.y + w.z);
}

void vertex() {
	vec4 wpos = MODEL_MATRIX * vec4(VERTEX, 1);
	vec2 cell_coords = wpos.xz;
	// Must add a half-offset so that we sample the center of pixels,
	// otherwise bilinear filtering of the textures will give us mixed results (#183)
	cell_coords += vec2(0.5);

	// Normalized UV
	UV = (cell_coords / vec2(textureSize(u_terrain_splat_index_map, 0)));
}

void fragment() {
	vec4 tint = texture(u_terrain_colormap, UV);
	vec4 tex_splat_indexes = texture(u_terrain_splat_index_map, UV);
	vec4 tex_splat_weights = texture(u_terrain_splat_weight_map, UV);
	// TODO Can't use texelFetch!
	// https://github.com/godotengine/godot/issues/31732
	
	vec3 splat_indexes = tex_splat_indexes.rgb * 255.0;

	// Get bump at normal resolution so depth blending is accurate
	vec2 ground_uv = UV / u_ground_uv_scale;
	float b0 = texture(u_ground_albedo_bump_array, vec3(ground_uv, splat_indexes.x)).a;
	float b1 = texture(u_ground_albedo_bump_array, vec3(ground_uv, splat_indexes.y)).a;
	float b2 = texture(u_ground_albedo_bump_array, vec3(ground_uv, splat_indexes.z)).a;

	// Take the center of the highest mip as color, because we can't see details from far away.
	vec2 ndc_center = vec2(0.5, 0.5);
	vec3 a0 = textureLod(u_ground_albedo_bump_array, vec3(ndc_center, splat_indexes.x), 10.0).rgb;
	vec3 a1 = textureLod(u_ground_albedo_bump_array, vec3(ndc_center, splat_indexes.y), 10.0).rgb;
	vec3 a2 = textureLod(u_ground_albedo_bump_array, vec3(ndc_center, splat_indexes.z), 10.0).rgb;

	vec3 splat_weights = vec3(
		tex_splat_weights.r, 
		tex_splat_weights.g,
		1.0 - tex_splat_weights.r - tex_splat_weights.g
	);
	
	// TODO An #ifdef macro would be nice! Or copy/paste everything in a different shader...
	if (u_depth_blending) {
		splat_weights = get_depth_blended_weights(splat_weights, vec3(b0, b1, b2));
	}

	ALBEDO = tint.rgb * (
		  a0 * splat_weights.x 
		+ a1 * splat_weights.y
		+ a2 * splat_weights.z
	);
}