added sphere generator

opengl_beginnings/src/custom/sphere_generator.rs

@@ -0,0 +1,154 @@
+use crate::engine::mesh::Mesh;
+use nalgebra::Vector3;
+
+pub struct OctaSphere {
+    mesh: Option<Mesh>,
+    resolution: i32,
+    generator: OctaSphereGenerator,
+}
+
+impl OctaSphere {
+    pub fn new(resolution: i32) -> Result<Self, String> {
+        match resolution {
+            r if r >= 0 => Ok(Self
+            {
+                resolution,
+                generator: OctaSphereGenerator::new(resolution),
+                mesh: None,
+            }),
+            _ => Err(String::from("Resolution of an octa sphere must be positive"))
+        }
+    }
+
+    pub fn generate_sphere(&mut self) {
+        let (vertices, indices) = self.generator.generate_sphere();
+        self.mesh = Some(Mesh::new(vertices, indices))
+    }
+}
+
+struct OctaSphereGenerator {
+    resolution: i32,
+}
+
+impl OctaSphereGenerator {
+    fn new(resolution: i32) -> Self {
+        Self {
+            resolution,
+        }
+    }
+
+    // Thanks Sebastian Lague
+    fn generate_sphere(&self) -> (Vec<Vector3<f32>>, Vec<u32>) {
+        // Indices of the vertex pairs that make up each of the initial 12 edges
+        let vertex_pairs = [0, 1, 0, 2, 0, 3, 0, 4, 1, 2, 2, 3, 3, 4, 4, 1, 5, 1, 5, 2, 5, 3, 5, 4];
+        // Indices of the edge triplets that make up the initial 8 faces
+        let edge_triplets = [0, 1, 4, 1, 2, 5, 2, 3, 6, 3, 0, 7, 8, 9, 4, 9, 10, 5, 10, 11, 6, 11, 8, 7];
+        // The six initial vertices        up                               left                             back                            right                           forward                          down
+        let base_vertices = [Vector3::y_axis().into_inner(), -Vector3::x_axis().into_inner(), -Vector3::z_axis().into_inner(), Vector3::x_axis().into_inner(), Vector3::z_axis().into_inner(), -Vector3::y_axis().into_inner()];
+
+        let num_divisions = self.resolution;
+        let num_vertices_per_face = ((num_divisions + 3) * (num_divisions + 3) - (num_divisions + 3)) / 2;
+        let num_vertices = num_vertices_per_face * 8 - (num_divisions + 2) * 12 + 6;
+        let num_tris_per_face = (num_divisions + 1) * (num_divisions + 1);
+
+        let mut vertices = Vec::<Vector3<f32>>::with_capacity(num_vertices as usize);
+        let mut indicies = Vec::<u32>::with_capacity((num_tris_per_face * 8 * 3) as usize);
+        vertices.copy_from_slice(&base_vertices);
+
+        // Create 12 edges, with n vertices added along them (n = numDivisions)
+        let mut edges = Vec::<Edge>::with_capacity(12);
+        for i in (0..vertex_pairs.len()).step_by(2) {
+            let start_vertex = vertices[vertex_pairs[i]];
+            let end_vertex = vertices[vertex_pairs[i + 1]];
+
+            let mut edge_vertex_indices = Vec::<u32>::with_capacity((num_divisions + 2) as usize);
+            edge_vertex_indices[0] = vertex_pairs[i] as u32;
+
+            // Add vertices along edge
+            for division_index in 0..num_divisions {
+                let t = (division_index as f32 + 1.0) / (num_divisions as f32 + 1.0);
+                edge_vertex_indices[(division_index + 1) as usize] = vertices.len() as u32;
+                vertices.push(start_vertex.slerp(&end_vertex, t));
+            }
+
+            edge_vertex_indices[(num_divisions + 1) as usize] = vertex_pairs[i + 1] as u32;
+            let edge_index = i / 2;
+            edges[edge_index] = Edge::new(edge_vertex_indices)
+        }
+
+        // Create faces
+        for i in (0..edge_triplets.len()).step_by(3) {
+            let face_index = i / 3;
+            let reverse = face_index >= 4;
+            self.create_face(&edges[edge_triplets[i]], &edges[edge_triplets[i + 1]], &edges[edge_triplets[i + 2]], reverse, num_vertices_per_face, &mut vertices, &mut indicies);
+        }
+
+
+        (vertices, indicies)
+    }
+
+    fn create_face(&self, side_a: &Edge, side_b: &Edge, bottom: &Edge, reverse: bool, num_vertices_per_face: i32, vertices: &mut Vec<Vector3<f32>>, indices: &mut Vec<u32>) {
+        let num_points_in_edge = side_a.vertex_indices.len();
+        let mut vertex_map = Vec::<u32>::with_capacity(num_vertices_per_face as usize);
+        vertex_map.push(side_a.vertex_indices[0]); // top of triangle
+
+        for i in 1..num_points_in_edge-1 {
+            // Side A vertex
+            vertex_map.push(side_a.vertex_indices[i]);
+
+            //add vertices between side a and b
+            let side_a_vertex = vertices[(side_a.vertex_indices[i]) as usize];
+            let side_b_vertex = vertices[(side_b.vertex_indices[i]) as usize];
+            let num_inner_points = i - 1;
+            for j in 0..num_inner_points {
+                let t = (j as f32 + 1.0) / (num_inner_points as f32 + 1.0);
+                vertex_map.push(vertices.len() as u32);
+                vertices.push(side_a_vertex.slerp(&side_b_vertex, t));
+            }
+
+            // Side B vertex
+            vertex_map.push(side_b.vertex_indices[i]);
+        }
+
+        // add bottom edge vertices
+        for i in 0..num_points_in_edge {
+            vertex_map.push(bottom.vertex_indices[i]);
+        }
+
+        // Triangulate
+        let num_rows = self.resolution + 1;
+        for row in 0..num_rows {
+            // vertices down left edge follow quadratic sequence: 0, 1, 3, 6, 10, 15...
+            // the nth term can be calculated with: (n^2 - n)/2
+            let top_vertex = (((row + 1) * (row + 1) - row - 1) / 2) as usize;
+            let bottom_vertex = (((row + 2) * (row + 2) + row - 2) / 2) as usize;
+
+            let num_triangles_in_row = 1 + 2 * row;
+            for column in 0..num_triangles_in_row {
+                let v0;
+                let v1;
+                let v2;
+
+                if column % 2 == 0 {
+                    v0 = top_vertex;
+                    v1 = bottom_vertex + 1;
+                    v2 = bottom_vertex;
+                } else {
+                    v0 = top_vertex;
+                    v1 = bottom_vertex;
+                    v2 = top_vertex + 1;
+                }
+
+                indices.push(vertex_map[v0]);
+                indices.push(vertex_map[if reverse {v2} else {v1}]);
+                indices.push(vertex_map[if reverse {v1} else {v2}]);
+            }
+        }
+    }
+}
+
+struct Edge {
+    vertex_indices: Vec<u32>,
+}
+
+impl Edge {fn new(vertex_indices: Vec<u32>) -> Self {Self{vertex_indices}}}