Fixed z-fighting between contour around the area selected by smart fill and painted triangles inside the FDM support painting gizmo.

resources/shaders/gouraud.fs

@@ -32,6 +32,8 @@ 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;
@@ -69,4 +71,9 @@ 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/GLGizmoMmuSegmentation.cpp

@@ -143,7 +143,7 @@ void GLGizmoMmuSegmentation::render_painter_gizmo() const
     glsafe(::glEnable(GL_BLEND));
     glsafe(::glEnable(GL_DEPTH_TEST));
 
-    render_triangles(selection, false);
+    render_triangles(selection);
 
     m_c->object_clipper()->render_cut();
     m_c->instances_hider()->render_cut();
@@ -174,7 +174,7 @@ void GLGizmoMmuSegmentation::set_painter_gizmo_data(const Selection &selection)
     }
 }
 
-void GLGizmoMmuSegmentation::render_triangles(const Selection &selection, const bool use_polygon_offset_fill) const
+void GLGizmoMmuSegmentation::render_triangles(const Selection &selection) const
 {
     ClippingPlaneDataWrapper clp_data = this->get_clipping_plane_data();
     auto                    *shader   = wxGetApp().get_shader("mm_gouraud");

src/slic3r/GUI/Gizmos/GLGizmoMmuSegmentation.hpp

@@ -89,7 +89,7 @@ public:
 
     void set_painter_gizmo_data(const Selection& selection) override;
 
-    void render_triangles(const Selection& selection, bool use_polygon_offset_fill) const override;
+    void render_triangles(const Selection& selection) const override;
 
     // TriangleSelector::serialization/deserialization has a limit to store 19 different states.
     // EXTRUDER_LIMIT + 1 states are used to storing the painting because also uncolored triangles are stored.

src/slic3r/GUI/Gizmos/GLGizmoPainterBase.cpp

@@ -64,17 +64,8 @@ GLGizmoPainterBase::ClippingPlaneDataWrapper GLGizmoPainterBase::get_clipping_pl
     return clp_data_out;
 }
 
-void GLGizmoPainterBase::render_triangles(const Selection& selection, const bool use_polygon_offset_fill) const
+void GLGizmoPainterBase::render_triangles(const Selection& selection) const
 {
-    ScopeGuard offset_fill_guard([&use_polygon_offset_fill]() {
-        if (use_polygon_offset_fill)
-            glsafe(::glDisable(GL_POLYGON_OFFSET_FILL));
-    });
-    if (use_polygon_offset_fill) {
-        glsafe(::glEnable(GL_POLYGON_OFFSET_FILL));
-        glsafe(::glPolygonOffset(-5.0, -5.0));
-    }
-
     auto *shader = wxGetApp().get_shader("gouraud");
     if (! shader)
         return;
@@ -585,7 +576,8 @@ void TriangleSelectorGUI::render(ImGuiWrapper* imgui)
     if (! shader)
         return;
     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 (iva.first->has_VBOs()) {
@@ -611,7 +603,7 @@ void TriangleSelectorGUI::render(ImGuiWrapper* imgui)
         auto *contour_shader = wxGetApp().get_shader("mm_contour");
         contour_shader->start_using();
 
-        glsafe(::glDepthFunc(GL_GEQUAL));
+        glsafe(::glDepthFunc(GL_LEQUAL));
         m_paint_contour.render();
         glsafe(::glDepthFunc(GL_LESS));
 

src/slic3r/GUI/Gizmos/GLGizmoPainterBase.hpp

@@ -126,7 +126,7 @@ public:
     virtual bool gizmo_event(SLAGizmoEventType action, const Vec2d& mouse_position, bool shift_down, bool alt_down, bool control_down);
 
 protected:
-    virtual void render_triangles(const Selection& selection, bool use_polygon_offset_fill = true) const;
+    virtual void render_triangles(const Selection& selection) const;
     void render_cursor() const;
     void render_cursor_circle() const;
     void render_cursor_sphere(const Transform3d& trafo) const;