In this section, we will examine the program that automatically moves a 20-pixel ball up, down, left, right, left up, right up, left down and right down by accepting the edges of the main window, the edges of a rectangle with a width of 200 pixels and a height of 300 pixels located in the middle of the main window and four circles with a width of 20 pixels located at different coordinates of the main window as the borders, reverses the movement by detecting collisions in the border areas, changes the obstacle status of the rectangle with the R key, changes the obstacle status of the circles with the 1-4 keys, enables or disables the speed change in the horizontal and vertical directions with the X and Y keys, and changes the speed with the up and down arrow keys.
When the program runs, the following operations are performed in addition to the basic operations:
struct objects { float x; float y; float width; float height; float vel_x; float vel_y; bool enabled; } ball, ball2, ball3, ball4, ball5;
struct { int x, y; int r; } circle_check;
main.c file content will be as follows:
#include <stdio.h>
#include <stdlib.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
SDL_FRect frect_col; // Rectangle variable
bool rect_enabled; // Rectangle state variable
int width_ball = 20; // Ball width
int height_ball = 20; // Ball height
bool x_vel, y_vel; // Velocity change enabled variables
// Struct declaration
struct objects {
float x;
float y;
float width;
float height;
float vel_x;
float vel_y;
bool enabled;
} ball, ball2, ball3, ball4, ball5;
struct {
int x, y;
int r;
} circle_check;
// 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 draw_screen(void); // Draw screen
void destroy_window(void); // Destroy window
bool ball_in_rect(void);
bool ball_in_circle(void);
double distance_piksel(int x1, int y1, int x2, int y2);
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)
{
last_frame_time = 0;
rect_enabled = true;
x_vel = true;
y_vel = true;
frect_col.x = 220.00;
frect_col.y = 90.00;
frect_col.w = 200.00;
frect_col.h = 300.00;
ball.x = width_ball/2;
ball.y = height_ball/2;
ball.width = width_ball;
ball.height = height_ball;
ball.vel_x = 200;
ball.vel_y = 200;
ball2.x = 100;
ball2.y = 150;
ball2.width = width_ball;
ball2.height = height_ball;
ball2.vel_x = 0;
ball2.vel_y = 0;
ball2.enabled = true;
ball3.x = 540;
ball3.y = 150;
ball3.width = width_ball;
ball3.height = height_ball;
ball3.vel_x = 0;
ball3.vel_y = 0;
ball3.enabled = true;
ball4.x = 100;
ball4.y = 330;
ball4.width = width_ball;
ball4.height = height_ball;
ball4.vel_x = 0;
ball4.vel_y = 0;
ball4.enabled = true;
ball5.x = 540;
ball5.y = 330;
ball5.width = width_ball;
ball5.height = height_ball;
ball5.vel_x = 0;
ball5.vel_y = 0;
ball5.enabled = true;
circle_check.x = ball.x;
circle_check.y = ball.y;
circle_check.r = width_ball/2;
}
// Load image to texture
void load_img(void)
{
// Loading image to texture
texture = IMG_LoadTexture(renderer, "ball_group.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_UP:
if(abs(ball.vel_x)<1000.00 && x_vel) {
ball.vel_x += (ball.vel_x>0) ? 10.00 : -10.00;
}
if(abs(ball.vel_y)<1000.00 && y_vel) {
ball.vel_y += (ball.vel_y>0) ? 10.00 : -10.00;
}
break;
case SDLK_DOWN:
if(abs(ball.vel_x)>0.00 && x_vel) {
ball.vel_x += (ball.vel_x>0) ? -10.00 : 10.00;
}
if(abs(ball.vel_y)>0.00 && y_vel) {
ball.vel_y += (ball.vel_y>0) ? -10.00 : 10.00;
}
break;
case SDLK_X: x_vel = !x_vel; break;
case SDLK_Y: y_vel = !y_vel; break;
case SDLK_1: ball2.enabled = !ball2.enabled; break;
case SDLK_2: ball3.enabled = !ball3.enabled; break;
case SDLK_3: ball4.enabled = !ball4.enabled; break;
case SDLK_4: ball5.enabled = !ball5.enabled; break;
case SDLK_R: rect_enabled = !rect_enabled; 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();
// Calculate moving size
// Multiplication of ball.vel_x and the loop repeat time (delta time) assigned to move_x variable.
float move_x = ball.vel_x * time_delta;
// Ball x coordinate increased by move_x
ball.x += move_x;
circle_check.x = ball.x;
circle_check.y = ball.y;
// 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.
if((ball.x-circle_check.r<0) || (ball.x + circle_check.r> WINDOW_WIDTH) || ball_in_rect() || ball_in_circle()) {
ball.x -= move_x;
circle_check.x = ball.x;
circle_check.y = ball.y;
ball.vel_x = -ball.vel_x;
}
// Multiplication of ball.vel_y and the loop repeat time (delta time), assigned to move_y variable.
float move_y = ball.vel_y * time_delta;
// Ball y coordinate increased by move_y
ball.y += move_y;
circle_check.x = ball.x;
circle_check.y = ball.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.
if((ball.y-circle_check.r<0) || (ball.y + circle_check.r > WINDOW_HEIGHT) || ball_in_rect() || ball_in_circle()) {
ball.y -= move_y;
circle_check.x = ball.x;
circle_check.y = ball.y;
ball.vel_y = -ball.vel_y;
}
char cdizi[150];
sprintf(cdizi, "x: %.2f y: %.2f vel_x: %.2f vel_y: %.2f - Rect: %s - Circles: %s %s %s %s",
ball.x, ball.y, ball.vel_x, ball.vel_y, rect_enabled ? "On" : "Off",
ball2.enabled ? "On" : "Off", ball3.enabled ? "On" : "Off",
ball4.enabled ? "On" : "Off", ball5.enabled ? "On" : "Off");
SDL_SetWindowTitle(window, cdizi);
}
bool ball_in_rect(void)
{
// Closest point in collision rectangle
int x_close, y_close;
// Finding the nearest x-coordinate
if(circle_check.x < frect_col.x) {
x_close = frect_col.x;
}
else if(circle_check.x > frect_col.x + frect_col.w) {
x_close = frect_col.x + frect_col.w;
}
else {
x_close = circle_check.x;
}
// Finding the nearest y-coordinate
if(circle_check.y < frect_col.y) {
y_close = frect_col.y;
}
else if(circle_check.y > frect_col.y + frect_col.h) {
y_close = frect_col.y + frect_col.h;
}
else {
y_close = circle_check.y;
}
// If the closest point is inside the circle
if(rect_enabled && (distance_piksel(circle_check.x, circle_check.y, x_close, y_close ) < circle_check.r * circle_check.r)) {
return true;
}
return false;
}
bool ball_in_circle()
{
// Total number of pixels of the ball
int pixel_no = circle_check.r + circle_check.r;
pixel_no = pixel_no * pixel_no;
// If the distance between the centers of the circles is less than the sum of their radii
if((ball2.enabled && (distance_piksel(circle_check.x, circle_check.y, ball2.x, ball2.y) < pixel_no)) ||
(ball3.enabled && (distance_piksel(circle_check.x, circle_check.y, ball3.x, ball3.y) < pixel_no)) ||
(ball4.enabled && (distance_piksel(circle_check.x, circle_check.y, ball4.x, ball4.y) < pixel_no)) ||
(ball5.enabled && (distance_piksel(circle_check.x, circle_check.y, ball5.x, ball5.y) < pixel_no))
) {
return true;
}
return false;
}
double distance_piksel(int x1, int y1, int x2, int y2)
{
int dist_x = x2 - x1;
int dist_y = y2 - y1;
return (dist_x*dist_x) + (dist_y*dist_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.
// Collision rectangle
SDL_SetRenderDrawColor(renderer, rect_enabled ? 255 : 0, !rect_enabled ? 255 : 0, 0, 255);
SDL_RenderRect(renderer, &frect_col);
SDL_FRect rect_src = { 0, 0, 20, 20 };
SDL_FRect rect_dst = { ball.x-circle_check.r, ball.y-circle_check.r, 20, 20 };
SDL_RenderTexture(renderer, texture, &rect_src, &rect_dst);
// Collision circles
rect_src.y = (ball2.enabled) ? 20 : 40;
rect_dst.x = ball2.x-circle_check.r;
rect_dst.y = ball2.y-circle_check.r;
SDL_RenderTexture(renderer, texture, &rect_src, &rect_dst);
rect_src.y = (ball3.enabled) ? 20 : 40;
rect_dst.x = ball3.x-circle_check.r;
rect_dst.y = ball3.y-circle_check.r;
SDL_RenderTexture(renderer, texture, &rect_src, &rect_dst);
rect_src.y = (ball4.enabled) ? 20 : 40;
rect_dst.x = ball4.x-circle_check.r;
rect_dst.y = ball4.y-circle_check.r;
SDL_RenderTexture(renderer, texture, &rect_src, &rect_dst);
rect_src.y = (ball5.enabled) ? 20 : 40;
rect_dst.x = ball5.x-circle_check.r;
rect_dst.y = ball5.y-circle_check.r;
SDL_RenderTexture(renderer, texture, &rect_src, &rect_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
}
// Destroy Renderer and SDL window, exit from SDL3
void destroy_window(void)
{
SDL_DestroyTexture(texture);
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
}