first commit

addons/zylann.hterrain/tools/texture_editor/display_normal.gdshader

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+shader_type canvas_item;
+
+uniform float u_strength = 1.0;
+uniform bool u_flip_y = false;
+
+vec3 unpack_normal(vec4 rgba) {
+	vec3 n = rgba.xzy * 2.0 - vec3(1.0);
+	// Had to negate Z because it comes from Y in the normal map,
+	// and OpenGL-style normal maps are Y-up.
+	n.z *= -1.0;
+	return n;
+}
+
+vec3 pack_normal(vec3 n) {
+	n.z *= -1.0;
+	return 0.5 * (n.xzy + vec3(1.0));
+}
+
+void fragment() {
+	vec4 col = texture(TEXTURE, UV);
+	vec3 n = unpack_normal(col);
+	n = normalize(mix(n, vec3(-n.x, n.y, -n.z), 0.5 - 0.5 * u_strength));
+	if (u_flip_y) {
+		n.z = -n.z;
+	}
+	col.rgb = pack_normal(n);
+	COLOR = vec4(col.rgb, 1.0);
+}