feat: draw tilted circle

feat: generate orbit points at an angle

CMakeLists.txt

@@ -29,6 +29,7 @@ add_executable(${PROJECT_NAME}
     src/io.cpp
     src/icosphere.cpp
     src/gfx.cpp
+    src/orbit.cpp
 )
 
 if(WIN32)

src/hello.cpp

@@ -45,6 +45,7 @@
 
 #include "gfx.hpp"
 #include "icosphere.hpp"
+#include "orbit.hpp"
 
 #include <cmath>
 #include "astro/twoBodyMethods.hpp"
@@ -149,7 +150,8 @@ int main()
         return -1;
 
     GLuint shaderProgram = compileShaderProgram();
-    Icosphere sphere(2);
+    //Icosphere sphere(0.5, 2);
+    Orbit orbit(30, glm::vec3(.5, .5, 0));
 
     glEnable(GL_DEPTH_TEST);
 
@@ -166,7 +168,8 @@ int main()
         updateModelViewProjectionMatrix(shaderProgram, glfwGetTime());
 
         // Render objects
-        sphere.render();
+        //sphere.render();
+        orbit.render();
 
         glfwSwapBuffers(window);
         glfwPollEvents();

src/orbit.cpp

@@ -0,0 +1,57 @@
+#include "orbit.hpp"
+
+#include "glm/gtx/quaternion.hpp"
+
+Orbit::Orbit(int vertexCount, glm::vec3 up)
+{
+    const float pi = 3.14159265359;
+    const glm::vec3 worldUp = glm::vec3(0.0, 1.0, 0.0);
+
+    // Compute the rotation between world 'up' and our defined up
+    glm::quat rot = glm::rotation(worldUp, normalize(up));
+
+    for (int i = 0; i < vertexCount; i++)
+    {
+        float a = (float)i / (float)vertexCount;
+        a *= 2.0 * pi;
+
+        glm::vec3 v = glm::vec3(cos(a), 0.0, sin(a));
+
+        // Rotate generated point to align with new up vector
+        v = rot * v;
+
+        _vertices.push_back(v.x);
+        _vertices.push_back(v.y);
+        _vertices.push_back(v.z);
+    }
+
+    glGenVertexArrays(1, &_vao);
+    glGenBuffers(1, &_vbo);
+
+    glBindVertexArray(_vao);
+
+    glBindBuffer(GL_ARRAY_BUFFER, _vbo);
+    size_t vboBufferSize = _vertices.size() * sizeof(float);
+    glBufferData(GL_ARRAY_BUFFER, vboBufferSize, &_vertices[0], GL_STATIC_DRAW);
+
+    glEnableVertexAttribArray(0);
+    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
+
+    glBindBuffer(GL_ARRAY_BUFFER, 0);
+    glBindVertexArray(0);
+}
+
+void Orbit::render()
+{
+    glBindVertexArray(_vao);
+    glBindBuffer(GL_ARRAY_BUFFER, _vbo);
+
+    glDrawArrays(GL_LINE_LOOP, 0, _vertices.size() / 3);
+}
+
+Orbit::~Orbit()
+{
+    glDeleteVertexArrays(1, &_vao);
+    glDeleteBuffers(1, &_vbo);
+}
+

src/orbit.hpp

@@ -0,0 +1,19 @@
+#pragma once
+
+#include <GL/glew.h>
+#include <vector>
+
+#include "glm/glm.hpp"
+
+class Orbit
+{
+public:
+    Orbit(int vertexCount, glm::vec3 up);
+    void render();
+    ~Orbit(); 
+private:
+    GLuint _vbo;
+    GLuint _vao;
+
+    std::vector<float> _vertices;
+};