Animasyon

In this section, we will examine a program that creates a walking animation by loading and moving 16 different images of a human drawing in different stages of walking in a texture created from a .png image file, in order, when the left and right arrow keys are pressed.

Animation is showing images one after another to create the impression of movement.

When the program runs, the following operations are performed in addition to the basic operations:

1. At the beginning of the program, the following global variables are first defined:
   • SDL_Texture *texture_back: Background texture
   • SDL_Texture *texture_front: Player texture
   • int move_size: Motion size
   • unsigned int last_frame_time: Last frame time
   • A variable named player is defined with the following structure data type:

     struct players {
       float x;
       float y;
       float width;
       float height;
       float vel_x;
       float vel_y;
       int frame;
     } player;
     

2. The init_vars() function assigns initial values ​​to global variables.
3. In the load_img() function, a background image and an image for the player animation images are loaded into the texture variables with the IMG_LoadTexture() function.
4. In the process_event() function,
   • When the arrow keys are pressed, the move_size variable value in the direction the arrow points to is added to the player.vel_x or player.vel_y variable, which has a value of 0. Thus, movement is achieved.
   • When the arrow keys are released, the move_size variable value in the direction the arrow points to is subtracted from the player.vel_x or player.vel_y variable, and the values ​​of these variables are set to 0. This ends the movement.
   • The move_size variable value is increased or decreased by 10 with the PageUp and PageDown keys.
5. Inside update_screen(),
   • The difference between the active time and the previous time of the loop is taken in seconds and assigned to the time_delta variable.
   • The active time is taken with the SDL_GetTicks() function and assigned to the last_frame_time variable to be used in the next iteration of the loop.
   • The product of player.vel_x and the loop iteration time (time_delta) is assigned to the move_x variable.
   • The player.x value is increased by the move_x value.
   • If player.x is less than 0 or the sum of player.x and player.width is greater than the width of the window, player.x takes its previous value.
   • If there is movement and the player x coordinate value is a multiple of 12,
     • If the left arrow key is pressed, if the player.frame value is equal to or less than 15, it is 8, otherwise it is increased by itself.
     • If the right arrow key is pressed, if the player.frame value is equal to or less than 7, it is 0, otherwise it is increased by itself.
   • The product of player.vel_y and the loop iteration time (time_delta) is assigned to the move_y variable.
   • The player.y value is incremented by the move_y value.
   • If player.y is less than 0 or the sum of player.y and player.height is greater than the height of the window, player.y returns to its previous value.
6. In the draw_screen() function,
   • The texture_back value is copied to the main window with the SDL_RenderTexture() function.
   • The image read from the texture_front value according to the player.frame variable value with the SDL_RenderTexture() function is copied to the main window according to the player.x and player.y variable coordinates.
   • The x and y coordinates of the player variable, the frame index value and the movement size are written to the main window title.

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_back = NULL;  // Background texture
SDL_Texture *texture_front = NULL; // Foreground texture
SDL_Renderer *renderer = NULL;     // Renderer variable
              
int move_size;                     // Move size
unsigned int last_frame_time;      // Last frame time

// Struct declaration
struct players {
    float x;
    float y;
    float width;
    float height;
    float vel_x;
    float vel_y;
    int frame;
} player;

// 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

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)
{
    move_size = 100;
	last_frame_time = 0;

    player.x = 0;
    player.y = 310;
    player.width = 88;
    player.height = 110;
    player.vel_x = 0;
    player.vel_y = 0;
    player.frame = 0;
}

// Load image to texture
void load_img(void)
{
    // Loading image to background texture
 	texture_back = IMG_LoadTexture(renderer, "background.png");

	if(texture_back == NULL) {
       SDL_Log("IMG_LoadTexture error: %s\n", SDL_GetError());
	}
    
	// Loading player images 
	texture_front = IMG_LoadTexture(renderer, "player.png");

	if(texture_front == 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.
               if(event.key.repeat == 0) {
                  switch(event.key.key) {
                     case SDLK_UP: player.vel_y -= move_size; break;
                     case SDLK_DOWN: player.vel_y += move_size; break;
                     case SDLK_LEFT: player.vel_x -= move_size; break;
                     case SDLK_RIGHT: player.vel_x += move_size; break;

                     case SDLK_PAGEUP: if(move_size<1000) move_size += 10; break;
                     case SDLK_PAGEDOWN: if(move_size>0) move_size -= 10; break;

                     case SDLK_ESCAPE: is_running = false; break;
                  }
                }
                break;

          case SDL_EVENT_KEY_UP: // Key released.
               if(event.key.repeat == 0) {
                  switch(event.key.key) {
                     case SDLK_UP: player.vel_y += move_size; break;
                     case SDLK_DOWN: player.vel_y -= move_size; break;
                     case SDLK_LEFT: player.vel_x += move_size; break;
                     case SDLK_RIGHT: player.vel_x -= move_size; 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
    // player.vel_x assigned to move_x variable.
    float move_x = player.vel_x * time_delta;

    // Ball x coordinate increased by move_x
    player.x += move_x;
    // If player.x is lower than 0 or, sum of player.x and player.width is greater than windows width
    // player.x gets its previous value.
    if((player.x<0) || (player.x + player.width > WINDOW_WIDTH)) {
	    player.x -= move_x;
    }

    const bool *kb_state = SDL_GetKeyboardState(NULL);

    // If player moves
    if(player.x>0 && ((int)player.x%12==0)) {
       if(kb_state[SDL_SCANCODE_LEFT]) {
          player.frame = (player.frame==15 || player.frame<8) ? 8 : player.frame+1;
       }
       if(kb_state[SDL_SCANCODE_RIGHT]) {
          player.frame = (player.frame==7 || player.frame>7) ? 0 : player.frame+1;
       }
    }

    // player.vel_y assigned to move_y variable.
    float move_y = player.vel_y * time_delta;

    // Ball y coordinate increased by move_y
    player.y += move_y;
    // If player.yx is lower than 0 or, sum of player.y and player.height is greater than windows height
    // player.y gets its previous value.
    if((player.y<0) || (player.y + player.height > WINDOW_HEIGHT-60)) {
       player.y -= move_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_RenderTexture(renderer, texture_back, NULL, NULL);

    SDL_FRect frect_src = { player.frame*player.width, 0, player.width, player.height };
    SDL_FRect frect_dst = { (int) player.x, (int) player.y, (int) player.width, (int) player.height };

    SDL_RenderTexture(renderer, texture_front, &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[100];
    sprintf(cdizi, "x: %d y: %d Frame: %d - Move size: %d", (int) player.x, (int) player.y, player.frame, move_size);
    SDL_SetWindowTitle(window, cdizi);
}

// Destroy Renderer and SDL window, exit from SDL3
void destroy_window(void)
{
    SDL_DestroyTexture(texture_back);
    SDL_DestroyTexture(texture_front);
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();
}