bgfx/examples/41-tess/fs_terrain_render_normal.sc

$input v_texcoord0

#include "terrain_common.sh"

void main()
{
	vec2 s = texture2D(u_SmapSampler, v_texcoord0).rg * u_DmapFactor;
	vec3 n = normalize(vec3(-s, 1));
	gl_FragColor = vec4(abs(n), 1);
}