Add X-Ray view mode to 3D viewport (#15770)

resources/shaders/140/xray.vs

@@ -0,0 +1,31 @@
+#version 140
+
+uniform mat4 view_model_matrix;
+uniform mat4 projection_matrix;
+uniform mat3 view_normal_matrix;
+uniform mat4 volume_world_matrix;
+
+// Clipping, as in gouraud.vs: the preview's top / bottom plane and the SLA gizmo's free one.
+uniform vec2 z_range;
+uniform vec4 clipping_plane;
+
+in vec3 v_position;
+in vec3 v_normal;
+
+out vec3 eye_normal;
+out vec3 eye_position;
+out vec3 clipping_planes_dots;
+
+void main()
+{
+    eye_normal = view_normal_matrix * v_normal;
+
+    vec4 position = view_model_matrix * vec4(v_position, 1.0);
+    eye_position = position.xyz;
+
+    // A component below zero means the fragment is clipped away.
+    vec4 world_pos = volume_world_matrix * vec4(v_position, 1.0);
+    clipping_planes_dots = vec3(dot(world_pos, clipping_plane), world_pos.z - z_range.x, z_range.y - world_pos.z);
+
+    gl_Position = projection_matrix * position;
+}