Highlighting edges in mesh

Gamero

Im trying to edit the texture of a mesh, adding different color around sharp edges. To do this, I figure that I have to check the edges and if the angle between the faces attached to an edge is above some threshold value, I color the texture along that edge.
So far im just coloring all edges to see how this works, but I got some strange results.
The cube works, but apparently the outer edges only have one face attached to them, so I have to find the pairs somehow and check the angle.
However, when I run the code on a cylinder, it goes haywire.

MeshInstance3D meshInstance = GetNode<MeshInstance3D>("../barrel");
		Mesh droneMesh = meshInstance.Mesh;
		MeshDataTool meshDataTool = new MeshDataTool();
		var arrMesh = new ArrayMesh();
		arrMesh.AddSurfaceFromArrays(Mesh.PrimitiveType.Triangles, droneMesh.SurfaceGetArrays(0));
		meshDataTool.CreateFromSurface(arrMesh, 0);
		Image image = Image.Create(500, 500, false, Image.Format.Rgb8);
		for(int edgeCounter = 0; edgeCounter < meshDataTool.GetEdgeCount(); edgeCounter++){
			for (int y = 0; y < image.GetHeight(); y++) {
				for (int x = 0; x < image.GetWidth(); x++) {
					int[] faceIds = meshDataTool.GetEdgeFaces(edgeCounter);
					if(faceIds.Length == 1 && x%3==0){
						//calculate distance from edge to point x,y
						Vector2 uv = meshDataTool.GetVertexUV(meshDataTool.GetEdgeVertex(edgeCounter, 0));
						Vector2 uv2 = meshDataTool.GetVertexUV(meshDataTool.GetEdgeVertex(edgeCounter, 1));
						float a = (uv-uv2).Length();
						float b = (uv - new Vector2((float)x/500f,(float)y/500f)).Length();
						float c = (uv2 - new Vector2((float)x/500f,(float)y/500f)).Length();
						float s = (a + b + c)/2;
						float distance = 2 * (float) Math.Sqrt(s * (s-a) * (s-b) * (s-c)) / a;
						if(distance < lineWidth){
							image.SetPixel(x, y, new Color(1.0f, 1.0f, 1.0f));
						}	
					}
					if(faceIds.Length == 2 && x%3==1 && meshDataTool.GetFaceNormal(faceIds[0]) != meshDataTool.GetFaceNormal(faceIds[1])){
						//calculate distance from edge to point x,y
						Vector2 uv = meshDataTool.GetVertexUV(meshDataTool.GetEdgeVertex(edgeCounter, 0));
						Vector2 uv2 = meshDataTool.GetVertexUV(meshDataTool.GetEdgeVertex(edgeCounter, 1));
						float a = (uv-uv2).Length();
						float b = (uv - new Vector2((float)x/500f,(float)y/500f)).Length();
						float c = (uv2 - new Vector2((float)x/500f,(float)y/500f)).Length();
						float s = (a + b + c)/2;
						float distance = 2 * (float) Math.Sqrt(s * (s-a) * (s-b) * (s-c)) / a;
						if(distance < lineWidth){
							image.SetPixel(x, y, new Color(1.0f, 0.0f, 0.0f));
						}	
					}	
					if(faceIds.Length == 2 && x%3==2 && meshDataTool.GetFaceNormal(faceIds[0]) == meshDataTool.GetFaceNormal(faceIds[1])){
						//calculate distance from edge to point x,y
						Vector2 uv = meshDataTool.GetVertexUV(meshDataTool.GetEdgeVertex(edgeCounter, 0));
						Vector2 uv2 = meshDataTool.GetVertexUV(meshDataTool.GetEdgeVertex(edgeCounter, 1));
						float a = (uv-uv2).Length();
						float b = (uv - new Vector2((float)x/500f,(float)y/500f)).Length();
						float c = (uv2 - new Vector2((float)x/500f,(float)y/500f)).Length();
						float s = (a + b + c)/2;
						float distance = 2 * (float) Math.Sqrt(s * (s-a) * (s-b) * (s-c)) / a;
						if(distance < lineWidth){
							image.SetPixel(x, y, new Color(0.0f, 1.0f, 0.0f));
						}	
					}			
				}
			}
		}

xyz

Gamero Format the code properly using ``` tags.

xyz

Gamero Is that Godot's cylinder?

Gamero

It took some fiddling with the editor to get the format right.
Yes, that is the godot cylinder, and the godot boxmesh.

xyz

Gamero Try making a simpler version first, the one that renders all edges without discrimination, to see if your edge distance calculations are correct. I'd also use Geometry2D::GetClosestPointToSegment() to calculate the distance instead of this complicated way via Heron's formula.