mobile-game-core/main.cpp

// #define SDL_MAIN_USE_CALLBACKS 1  /* use the callbacks instead of main() */
#include <SDL3/SDL.h>
#include <stdio.h>
#include <math.h>
#include <GLES3/gl3.h>

#if defined(__ANDROID__)
    #define APP_MAIN SDL_main
    #define SDL_WINDOW_FLAG SDL_WINDOW_FULLSCREEN
#else
    #define APP_MAIN main
    #define SDL_WINDOW_FLAG 0
#endif

#define SCREEN_WIDTH 1600
#define SCREEN_HEIGHT 720

#define BOX_WIDTH 250
#define BOX_HEIGHT 250

static SDL_Window *window = NULL;

static bool running = true;

static Uint8 color = 0x18;

static Uint64 elapsed = 0;
static float boxX = 0.f;
static float boxY = 0.f;
static float boxVelX = 1.f;
static float boxVelY = 1.f;

static float boxSpeed = 250.f;

const char* vShader = "#version 300 es\n"
"layout (location = 0) in vec2 aPos;\n"
"uniform mat4 uTransform;\n"
"void main()\n"
"{\n"
"    gl_Position = uTransform * vec4(aPos, 0.0, 1.0);\n"
"}";

const char* fShader = "#version 300 es\n"
"precision mediump float;\n"
"out vec4 FragColor;\n"
"void main()\n"
"{\n"
"    FragColor = vec4(1.0, 0.2, 0.3, 1.0); // red-ish\n"
"}";

void makeRotationZ(float angle, float* m)
{
    float c = cosf(angle);
    float s = sinf(angle);

    // column-major (OpenGL style)
    m[0] =  c; m[4] = -s; m[8]  = 0; m[12] = 0;
    m[1] =  s; m[5] =  c; m[9]  = 0; m[13] = 0;
    m[2] =  0; m[6] =  0; m[10] = 1; m[14] = 0;
    m[3] =  0; m[7] =  0; m[11] = 0; m[15] = 1;
}

extern "C" int APP_MAIN(int argc, char **argv) {
    SDL_SetAppMetadata("Example Renderer Primitives", "1.0", "com.example.renderer-primitives");
    SDL_SetHint(SDL_HINT_ORIENTATIONS, "LandscapeLeft LandscapeRight");

    if (!SDL_Init(SDL_INIT_VIDEO)) {
        SDL_Log("Couldn't initialize SDL: %s", SDL_GetError());
        return SDL_APP_FAILURE;
    }

    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);

    window = SDL_CreateWindow("examples/renderer/primitives", SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_FLAG | SDL_WINDOW_OPENGL);
    if (!window) {
        SDL_Log("Couldn't create window/renderer: %s", SDL_GetError());
        return SDL_APP_FAILURE;
    }

    SDL_GLContext glContext = SDL_GL_CreateContext(window);

    int success;
    char infoLog[512];

    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vShader, NULL);
    glCompileShader(vertexShader);
    // print compile errors if any
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        printf("ERROR::SHADER::VERTEX::COMPILATION_FAILED\n%s\n", infoLog);
    };

    GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fShader, NULL);
    glCompileShader(fragmentShader);
    // print compile errors if any
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        printf("ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n%s\n", infoLog);
    };

    GLuint program = glCreateProgram();
    glAttachShader(program, vertexShader);
    glAttachShader(program, fragmentShader);
    glLinkProgram(program);
    // print linking errors if any
    glGetProgramiv(program, GL_LINK_STATUS, &success);
    if (!success)
    {
        glGetProgramInfoLog(program, 512, NULL, infoLog);
        printf("ERROR::SHADER::PROGRAM::LINKING_FAILED\n%s\n", infoLog);
    }

    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    float vertices[] = {
        // positions (x, y)
        -0.5f, -0.5f,
        0.5f, -0.5f,
        0.5f, 0.5f,

        -0.5f, -0.5f,
        0.5f, 0.5f,
        -0.5f, 0.5f};

    GLuint vao, vbo;
    glGenVertexArrays(1, &vao);
    glGenBuffers(1, &vbo);

    glBindVertexArray(vao);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float), (void *)0);
    glEnableVertexAttribArray(0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);

    glViewport(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);
    glEnable(GL_DEPTH_TEST);

    float transform[16];

    while (running) {
        SDL_Event event;
        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_EVENT_QUIT) {
                running = false;
            }
        }

        auto now = SDL_GetTicks();
        float dt = now - elapsed;
        elapsed = now;
        // SDL_Log("dt: %f\n", dt);
        dt /= 1000.f;

        boxX += boxSpeed * boxVelX * dt;
        boxY += boxSpeed * boxVelY * dt;
        boxSpeed += 50.f * dt;

        if (boxX + BOX_WIDTH >= SCREEN_WIDTH || boxX <= 0) boxVelX *= -1.f;
        if (boxY + BOX_HEIGHT >= SCREEN_HEIGHT || boxY <= 0) boxVelY *= -1.f;

        glClearColor(0x18/255.f, 0x18/255.f, 0x18/255.f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        // Draw your 3D stuff here

        float angle = SDL_GetTicks() / 1000.0f; // rotates over time

        float transform[16];
        makeRotationZ(angle, transform);

        GLuint loc = glGetUniformLocation(program, "uTransform");
        glUseProgram(program);
        glUniformMatrix4fv(loc, 1, GL_FALSE, transform);

        glBindVertexArray(vao);

        glDrawArrays(GL_TRIANGLES, 0, 6);

        SDL_GL_SwapWindow(window);
    }

    return 0;
}