Scene & Objects

Before starting to draw things, I want to define a couple more structures that will make the code a bit more organized. I want to define a container for any type of object that will be drawn into the screen. Additionally, I want to also define a “Scene” where all the objects will be positioned.

The Entity

The entity will be any type of object that I would like to draw. Here I define 3 different variants of entity, a Triangle, a Rectangle (a.k.a Quad), and a Cube. They all have a 3d position, scale, rotation, and color.

#ifndef ENTITY_H_
#define ENTITY_H_

#include <glm/glm.hpp>

enum class entity_type {
    Triangle,
    Quad,
    Cube,
};

struct entity {
    entity_type Type;
    glm::vec3 Position;
    glm::vec3 Scale;
    glm::vec4 Rotation;
    glm::vec4 Color;
};
#endif

The Scene

All the entities will be contained in this scene struct. What I want to achieve with this at the end is to perform 1 draw call with the scene and the renderer will know how to draw the different objects that belong to the Scene.

#ifndef SCENE_H_
#define SCENE_H_

#include <vector>
#include "entity.h"

struct scene {
    std::vector<entity> Entities;
};

scene Scene_Create();
void Scene_Destroy(scene &Scene);
void Scene_AddEntity(scene &Scene, entity &Entity);

#endif

Drawing the Scene

I will add a new method to the renderer to draw the scene. For now it will be empty but I will implement it as I progress in this series.

In renderer.h:

void Renderer_DrawScene(const renderer &Renderer, const scene &Scene);

And in renderer.cpp:

void Renderer_DrawScene(const renderer &Renderer, const scene &Scene) {
    // TODO: Implement
}

Creating the Scene

Now, in main.cpp I can create a scene and add entities to it.

int main() {
    ...
    scene Scene = Scene_Create();

    entity Triangle = {
        .Type = entity_type::Triangle,
        .Position = glm::vec3(0.0f, 0.0f, 0.0f),
        .Scale = glm::vec3(0.0f),
        .Rotation = glm::vec4(0.0f, 1.0f, 0.3f, 0.5f),
        .Color = glm::vec4(1.0f, 0.5f, 0.31f, 1.0f),
    };

    Scene_AddEntity(Scene, Triangle);

    ...

    while (!glfwWindowShouldClose(Context.Window)) {
        ...
        Renderer_ClearBackground(0.1f, 0.1f, 0.1f, 1.0f);
        Renderer_DrawScene(Renderer, Scene);
    }
}

I’m ready to start drawing things on the screen!