Add depth pass for picking a location

resources/shaders/camera_distance.shader

@@ -0,0 +1,83 @@
+[shaders]
+vertex =
+    uniform highp mat4 u_modelMatrix;
+    uniform highp mat4 u_viewProjectionMatrix;
+
+    attribute highp vec4 a_vertex;
+
+    varying highp vec3 v_vertex;
+
+    void main()
+    {
+        vec4 world_space_vert = u_modelMatrix * a_vertex;
+        gl_Position = u_viewProjectionMatrix * world_space_vert;
+
+        v_vertex = world_space_vert.xyz;
+    }
+
+fragment =
+    uniform highp vec3 u_viewPosition;
+
+    varying highp vec3 v_vertex;
+
+    void main()
+    {
+        highp float distance_to_camera = distance(v_vertex, u_viewPosition) * 1000.; // distance in micron
+
+        vec3 encoded; // encode float into 3 8-bit channels; this gives a precision of a micron at a range of up to ~16 meter
+        encoded.b = floor(distance_to_camera / 65536.0);
+        encoded.g = floor((distance_to_camera - encoded.b * 65536.0) / 256.0);
+        encoded.r = floor(distance_to_camera - encoded.b * 65536.0 - encoded.g * 256.0);
+
+        gl_FragColor.rgb = encoded / 255.;
+        gl_FragColor.a = 1.0;
+    }
+
+vertex41core =
+    #version 410
+    uniform highp mat4 u_modelMatrix;
+    uniform highp mat4 u_viewProjectionMatrix;
+
+    in highp vec4 a_vertex;
+
+    out highp vec3 v_vertex;
+
+    void main()
+    {
+        vec4 world_space_vert = u_modelMatrix * a_vertex;
+        gl_Position = u_viewProjectionMatrix * world_space_vert;
+
+        v_vertex = world_space_vert.xyz;
+    }
+
+fragment41core =
+    #version 410
+    uniform highp vec3 u_viewPosition;
+
+    in highp vec3 v_vertex;
+
+    out vec4 frag_color;
+
+    void main()
+    {
+        highp float distance_to_camera = distance(v_vertex, u_viewPosition) * 1000.; // distance in micron
+
+        vec3 encoded; // encode float into 3 8-bit channels; this gives a precision of a micron at a range of up to ~16 meter
+        encoded.b = floor(distance_to_camera / 65536.0);
+        encoded.g = floor((distance_to_camera - encoded.b * 65536.0) / 256.0);
+        encoded.r = floor(distance_to_camera - encoded.b * 65536.0 - encoded.g * 256.0);
+
+        frag_color.rgb = encoded / 255.;
+        frag_color.a = 1.0;
+    }
+
+[defaults]
+
+[bindings]
+u_modelMatrix = model_matrix
+u_viewProjectionMatrix = view_projection_matrix
+u_normalMatrix = normal_matrix
+u_viewPosition = view_position
+
+[attributes]
+a_vertex = vertex