Removed assignment to gl_FragDepth into gouraud.fs shader. Replaced with small offset of triangles along their normal.

resources/shaders/110/gouraud.fs

@@ -26,8 +26,6 @@ struct SlopeDetection
 uniform vec4 uniform_color;
 uniform SlopeDetection slope;
 
-uniform bool offset_depth_buffer;
-
 #ifdef ENABLE_ENVIRONMENT_MAP
     uniform sampler2D environment_tex;
     uniform bool use_environment_tex;
@@ -78,9 +76,4 @@ void main()
     else
 #endif
         gl_FragColor = vec4(vec3(intensity.y) + color * intensity.x, alpha);
-		
-    // In the support painting gizmo and the seam painting gizmo are painted triangles rendered over the already
-    // rendered object. To resolved z-fighting between previously rendered object and painted triangles, values
-    // inside the depth buffer are offset by small epsilon for painted triangles inside those gizmos.
-    gl_FragDepth = gl_FragCoord.z - (offset_depth_buffer ? EPSILON : 0.0);
 }

resources/shaders/140/gouraud.fs

@@ -26,8 +26,6 @@ struct SlopeDetection
 uniform vec4 uniform_color;
 uniform SlopeDetection slope;
 
-uniform bool offset_depth_buffer;
-
 #ifdef ENABLE_ENVIRONMENT_MAP
     uniform sampler2D environment_tex;
     uniform bool use_environment_tex;
@@ -78,9 +76,4 @@ void main()
     else
 #endif
         gl_FragColor = vec4(vec3(intensity.y) + color * intensity.x, alpha);
-		
-    // In the support painting gizmo and the seam painting gizmo are painted triangles rendered over the already
-    // rendered object. To resolved z-fighting between previously rendered object and painted triangles, values
-    // inside the depth buffer are offset by small epsilon for painted triangles inside those gizmos.
-    gl_FragDepth = gl_FragCoord.z - (offset_depth_buffer ? EPSILON : 0.0);
 }

resources/shaders/gouraud.fs

@@ -26,8 +26,6 @@ struct SlopeDetection
 uniform vec4 uniform_color;
 uniform SlopeDetection slope;
 
-uniform bool offset_depth_buffer;
-
 #ifdef ENABLE_ENVIRONMENT_MAP
     uniform sampler2D environment_tex;
     uniform bool use_environment_tex;
@@ -78,9 +76,4 @@ void main()
     else
 #endif
         gl_FragColor = vec4(vec3(intensity.y) + color * intensity.x, alpha);
-		
-    // In the support painting gizmo and the seam painting gizmo are painted triangles rendered over the already
-    // rendered object. To resolved z-fighting between previously rendered object and painted triangles, values
-    // inside the depth buffer are offset by small epsilon for painted triangles inside those gizmos.
-    gl_FragDepth = gl_FragCoord.z - (offset_depth_buffer ? EPSILON : 0.0);
 }

src/slic3r/GUI/Gizmos/GLGizmoPainterBase.cpp

@@ -918,8 +918,6 @@ void TriangleSelectorGUI::render(ImGuiWrapper* imgui)
 
     assert(shader->get_name() == "gouraud");
 
-    ScopeGuard guard([shader]() { if (shader) shader->set_uniform("offset_depth_buffer", false);});
-    shader->set_uniform("offset_depth_buffer", true);
     for (auto iva : {std::make_pair(&m_iva_enforcers, enforcers_color),
                      std::make_pair(&m_iva_blockers, blockers_color)}) {
 #if ENABLE_LEGACY_OPENGL_REMOVAL
@@ -1014,6 +1012,9 @@ void TriangleSelectorGUI::update_render_data()
         iva.release_geometry();
 #endif // ENABLE_LEGACY_OPENGL_REMOVAL
 
+    // small value used to offset triangles along their normal to avoid z-fighting
+    static const float offset = 0.001f;
+
     for (const Triangle &tr : m_triangles) {
         if (!tr.valid() || tr.is_split() || (tr.get_state() == EnforcerBlockerType::NONE && !tr.is_selected_by_seed_fill()))
             continue;
@@ -1037,15 +1038,17 @@ void TriangleSelectorGUI::update_render_data()
         //FIXME the normal may likely be pulled from m_triangle_selectors, but it may not be worth the effort
         // or the current implementation may be more cache friendly.
         const Vec3f           n   = (v1 - v0).cross(v2 - v1).normalized();
+        // small value used to offset triangles along their normal to avoid z-fighting
+        const Vec3f    offset_n   = offset * n;
 #if ENABLE_LEGACY_OPENGL_REMOVAL
-        iva.add_vertex(v0, n);
+        iva.add_vertex(v0 + offset_n, n);
-        iva.add_vertex(v1, n);
+        iva.add_vertex(v1 + offset_n, n);
-        iva.add_vertex(v2, n);
+        iva.add_vertex(v2 + offset_n, n);
         iva.add_triangle((unsigned int)cnt, (unsigned int)cnt + 1, (unsigned int)cnt + 2);
 #else
-        iva.push_geometry(v0, n);
+        iva.push_geometry(v0 + offset_n, n);
-        iva.push_geometry(v1, n);
+        iva.push_geometry(v1 + offset_n, n);
-        iva.push_geometry(v2, n);
+        iva.push_geometry(v2 + offset_n, n);
         iva.push_triangle(cnt, cnt + 1, cnt + 2);
 #endif // ENABLE_LEGACY_OPENGL_REMOVAL
         cnt += 3;