In this section, we will examine a program that moves balls of different speeds, at least one and at most three, continuously in the main window.
When the program runs, in addition to the basic operations, the following operations occur:
struct objects {
float x;
float y;
float width;
float height;
float vel_x;
float vel_y;
} ball1, ball2, ball3;
main.c file content will be as follows:
#include <stdio.h>
#include <SDL3/SDL.h>
#include <SDL3_image/SDL_image.h>
// Window width and height
#define WINDOW_WIDTH 640
#define WINDOW_HEIGHT 480
// Global variables
int is_running = false; // Variable that controls the execution of the main loop of the program
SDL_Window *window = NULL; // Main window variable
SDL_Texture *texture = NULL; // Texture variable
SDL_Renderer *renderer = NULL; // Renderer variable
unsigned int last_frame_time; // Last frame time
int balls_no; // Number of visible balls
// Struct declaration
struct objects {
float x;
float y;
float width;
float height;
float vel_x;
float vel_y;
} ball1, ball2, ball3;
// Function prototypes
int init_window(void); // Create window and renderer
void init_vars(void); // Initialize variables
void load_img(void); // Load image to texture
void process_event(void); // Process events
void update_screen(); // Update values
void set_ball_vals(struct objects *ball, float time_delta); // Set ball values
void draw_screen(void); // Draw screen
void destroy_window(void); // Destroy window
int main(int argc, char* argv[])
{
// Create window and renderer
is_running = init_window();
// Initialize variables
init_vars();
// Load .png file to texture
load_img();
// Main loop
while (is_running) {
process_event(); // Processing SDL events (Here keyboard inputs)
update_screen(); // Updating variables
draw_screen(); // Drawing objects on the window (Rendering)
}
// Destroy renderer and SDL window
destroy_window();
return 0;
}
// Create window and renderer
int init_window(void)
{
// Initialize the SDL library.
if(SDL_Init(SDL_INIT_VIDEO) == false) {
SDL_Log("SDL init error: %s\n", SDL_GetError());
return false;
}
// Create a window and a 2D rendering context for the window.
if(!SDL_CreateWindowAndRenderer("SDL3 window", WINDOW_WIDTH, WINDOW_HEIGHT, 0, &window, &renderer)) {
return false;
}
return true;
}
// Initialization function that runs only once at the beginning of the program
void init_vars(void)
{
balls_no = 3;
last_frame_time = 0;
ball1.x = 0;
ball1.y = 0;
ball1.width = 20;
ball1.height = 20;
ball1.vel_x = 100;
ball1.vel_y = 100;
ball2.x = 600;
ball2.y = 100;
ball2.width = 20;
ball2.height = 20;
ball2.vel_x = 50;
ball2.vel_y = 50;
ball3.x = 100;
ball3.y = 400;
ball3.width = 20;
ball3.height = 20;
ball3.vel_x = 200;
ball3.vel_y = 200;
}
// Load image to texture
void load_img(void)
{
// Loading image to texture
texture = IMG_LoadTexture(renderer, "balls.png");
if(texture == NULL) {
SDL_Log("IMG_LoadTexture error: %s\n", SDL_GetError());
}
}
// Function to control SDL events and process keyboard inputs
void process_event(void)
{
SDL_Event event;
// Creating a loop to process user inputs
while (SDL_PollEvent(&event)) {
switch (event.type) {
case SDL_EVENT_QUIT: // Logout action by the user (x button at the top right of the window)
is_running = false; // Terminates the execution of the program main loop.
break;
case SDL_EVENT_KEY_DOWN: // Key pressed.
switch(event.key.key) {
case SDLK_1: balls_no = 1; break;
case SDLK_2: balls_no = 2; break;
case SDLK_3: balls_no = 3; break;
case SDLK_ESCAPE: is_running = false; break;
}
break;
}
}
}
// Updates objects in the main window
void update_screen(void)
{
// Get the difference between the active time and the previous time of loop in seconds
float time_delta = (SDL_GetTicks() - last_frame_time) / 1000.0;
// Assign the active time to use in the next iteration of the loop
last_frame_time = SDL_GetTicks();
set_ball_vals(&ball1, time_delta);
set_ball_vals(&ball2, time_delta);
set_ball_vals(&ball3, time_delta);
}
void set_ball_vals(struct objects *ball, float time_delta)
{
// Calculate moving size
// Multiplication of ball.vel_x and the loop repeat time (delta time)
float move_x = ball->vel_x * time_delta;
// Ball x coordinate increased by move_x
ball->x += move_x;
// If ball.x is lower than 0 or, sum of ball.x and ball.width is greater than windows width
// ball.x gets its previous value and reverse velocity direction
if((ball->x<0) || (ball->x + ball->width > WINDOW_WIDTH)) {
ball->x -= move_x;
ball->vel_x = -ball->vel_x;
}
// Multiplication of ball.vel_y and the loop repeat time (delta time)
float move_y = ball->vel_y * time_delta;
// Ball y coordinate increased by move_y
ball->y += move_y;
// If ball.yx is lower than 0 or, sum of ball.y and ball.height is greater than windows height
// ball.y gets its previous value and reverse velocity direction
if((ball->y<0) || (ball->y + ball->height > WINDOW_HEIGHT)) {
ball->y -= move_y;
ball->vel_y = -ball->vel_y;
}
}
// Render function used to draw game objects in the main window
void draw_screen(void)
{
SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255); // Set the color used for drawing operations.
SDL_RenderClear(renderer); // Clear the current rendering target with the drawing color.
SDL_FRect frect_src = { 0, 0, 20, 20 };
SDL_FRect frect_dst = { ball1.x, ball1.y, 20, 20 };
SDL_RenderTexture(renderer, texture, &frect_src, &frect_dst);
if(balls_no>1) {
frect_src.y = 20;
frect_dst.x = ball2.x;
frect_dst.y = ball2.y;
SDL_RenderTexture(renderer, texture, &frect_src, &frect_dst);
}
if(balls_no>2) {
frect_src.y = 40;
frect_dst.x = ball3.x;
frect_dst.y = ball3.y;
SDL_RenderTexture(renderer, texture, &frect_src, &frect_dst);
}
// Loading all objects drawn one by one to the back buffer to the front buffer at once and loading them onto the screen
// This process prevents each drawn object from being displayed on the screen one by one.
SDL_RenderPresent(renderer); // Update on screen all operations performed since the previous call
char cdizi[200];
sprintf(cdizi, "Number of balls: %d", balls_no);
SDL_SetWindowTitle(window, cdizi);
}
// Destroy Renderer and SDL window, exit from SDL3
void destroy_window(void)
{
SDL_DestroyTexture(texture);
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
}