refactor: extract sphere model matrix calc

src/gfx.cpp

@@ -116,18 +116,22 @@ void updateProjectionMatrix(GLuint shaderProgram)
     glUniformMatrix4fv(projectionLocation, 1, GL_FALSE, &projection[0][0]);
 }
 
-void updateModelMatrix(GLuint shaderProgram, float time)
+void updateModelMatrix(GLuint shaderProgram)
 {
-    constexpr float angle = glm::radians(10.0);
-    glm::vec3 axis = glm::vec3(0.0, 1.0, 0.0);
-    glm::mat4 model = glm::rotate(glm::mat4(1.0), angle * time, axis);
+    glm::mat4 model = glm::mat4(1.0);
     GLint modelLocation = getShaderUniformLocation(shaderProgram, "_Model");
     glUniformMatrix4fv(modelLocation, 1, GL_FALSE, &model[0][0]);
 }
 
-void updateViewMatrix(GLuint shaderProgram)
+void updateViewMatrix(GLuint shaderProgram, float time)
 {
     glm::mat4 view = glm::mat4(1.0);
+
+    // Rotation
+    constexpr float angle = glm::radians(10.0);
+    glm::vec3 axis = glm::vec3(0.0, 1.0, 0.0);
+    view = glm::rotate(view, angle * time, axis);
+
     GLint viewLocation = getShaderUniformLocation(shaderProgram, "_View");
     glUniformMatrix4fv(viewLocation, 1, GL_FALSE, &view[0][0]);
 }
@@ -136,8 +140,8 @@ void updateModelViewProjectionMatrix(GLuint shaderProgram, float time)
 {
     // Calculate matrices
     updateProjectionMatrix(shaderProgram);
-    updateModelMatrix(shaderProgram, time);
-    updateViewMatrix(shaderProgram);
+    updateModelMatrix(shaderProgram);
+    updateViewMatrix(shaderProgram, time);
 }
 
 GLint getShaderUniformLocation(GLuint shaderProgram, const std::string& uniformName)

src/gfx.hpp

@@ -13,6 +13,6 @@ GLuint compileShader(const std::string& shaderPath, GLenum shaderType);
 GLint getShaderUniformLocation(GLuint shaderProgram, const std::string& uniformName);
 
 void updateProjectionMatrix(GLuint shaderProgram);
-void updateModelMatrix(GLuint shaderProgram, float time);
-void updateViewMatrix(GLuint shaderProgram);
+void updateModelMatrix(GLuint shaderProgram);
+void updateViewMatrix(GLuint shaderProgram, float time);
 void updateModelViewProjectionMatrix(GLuint shaderProgram, float time);

src/icosphere.cpp

@@ -3,7 +3,13 @@
 #include <iostream>
 #include <array>
 
-Icosphere::Icosphere(float radius, int subdivisions)
+#include "glm/gtc/matrix_transform.hpp"
+
+#include "gfx.hpp"
+
+Icosphere::Icosphere(float radius, int subdivisions, GLuint shaderProgram, glm::vec3 position) :
+    _shaderProgram(shaderProgram),
+    _position(position)
 {
     VertexList vertices = _isocahedronVertices;
     TriangleList triangles = _isocahedronTriangles;
@@ -125,8 +131,20 @@ Icosphere::TriangleList Icosphere::subdivide(VertexList& vertices, TriangleList
     return result;
 }
 
+void Icosphere::updateModelMatrix()
+{
+    // To be able to define a position for a particular instance of a sphere we will
+    // need to calculate a model projection matrix per-instance
+    glm::mat4 model = glm::translate(glm::mat4(1.0), _position);
+
+    GLint modelLocation = getShaderUniformLocation(_shaderProgram, "_Model");
+    glUniformMatrix4fv(modelLocation, 1, GL_FALSE, &model[0][0]);
+}
+
 void Icosphere::render()
 {
+    updateModelMatrix();
+
 	glBindVertexArray(_vao);
 	glBindBuffer(GL_ARRAY_BUFFER, _vbo);
 	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _ebo);

src/icosphere.hpp

@@ -10,7 +10,7 @@
 class Icosphere
 {
 public:
-	Icosphere(float radius, int subdivisions);
+    Icosphere(float radius, int subdivisions, GLuint shaderProgram, glm::vec3 position);
 	void render();
 
 	~Icosphere();
@@ -19,10 +19,13 @@ private:
 	GLuint _vbo;
 	GLuint _vao;
 	GLuint _ebo;
+    GLuint _shaderProgram;
 
 	std::vector<float> _vertices;
 	std::vector<unsigned int> _indices;
 
+    glm::vec3 _position;
+
     // Generating an isosphere
     // https://schneide.blog/2016/07/15/generating-an-icosphere-in-c/
 	struct Triangle
@@ -56,4 +59,6 @@ private:
 
     int vertexForEdge(Lookup& lookup, VertexList& vertices, int first, int second);
     TriangleList subdivide(VertexList& vertices, TriangleList triangles);
+
+    void updateModelMatrix();
 };

src/main.cpp

@@ -51,7 +51,7 @@ int main()
     GLuint litProgram = compileShaderProgram("./frag_lit.glsl");
     GLuint unlitProgram = compileShaderProgram("./frag_unlit.glsl");
 
-    Icosphere sphere(0.5, 2);
+    Icosphere sphere(0.5, 2, litProgram, glm::vec3(0.0, 0.0, 0.0));
     Orbit orbit(100);
 
     // Main loop