Fix external outline Thickness (#14741)

* Fix external outline

* Format and values

* frag_color -> gl_FragColor

* Remove Transform3d& view_matrix

* Clarify rendering comments in 3DScene.cpp

Updated comments to clarify rendering process using stencil buffer.

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Co-authored-by: Ian Bassi <ian.bassi@outlook.com>
Co-authored-by: Noisyfox <timemanager.rick@gmail.com>

resources/shaders/110/ssao.fs

@@ -11,6 +11,7 @@ uniform sampler2D normal_texture;
 uniform vec2 inv_tex_size;
 uniform float z_near;
 uniform float z_far;
+uniform bool is_outline;
 
 varying vec2 tex_coord;
 
@@ -22,6 +23,10 @@ float linearize_depth(float depth)
 
 void main()
 {
+    if (is_outline) {
+        gl_FragColor = vec4(texture2D(color_texture, tex_coord).rgb, 1.0);
+        return;
+    }
     vec3 base = texture2D(color_texture, tex_coord).rgb;
     float depth_center = linearize_depth(texture2D(depth_texture, tex_coord).r);