Loading image with texture

In this section, we will examine a program that loads an image file with the extension .png into the main window via texture.

Instead of the IMG_Load() function used in the previous section, the IMG_LoadTexture() function is used to assign the image file directly to the texture variable.

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

• When the load_img() function runs, the image file named horse.png is assigned directly to the texture variable with the IMG_LoadTexture() function.

Used texture functions

• IMG_LoadTexture() function loads an image file into a GPU texture. An SDL_Texture represents an image in GPU memory, usable by SDL's 2D Render API.

The main.c file content will be as follows:

#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 for image
SDL_Renderer *renderer = NULL;    // Renderer variable

// Function prototypes
int init_window(void);            // Create window and renderer
void init_vals(void);             // Initialize values
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 values
    init_vals();

    // 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 - Load png image with texture", 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_vals(void)
{

}

// Load image to texture
void load_img(void)
{
     // Load an image into a GPU texture.
     texture = IMG_LoadTexture(renderer, "horse.png");

	 if(texture == NULL)	{
	    SDL_Log("Load texture 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: // Indicate that a key was pressed.
                 if(event.key.key == SDLK_ESCAPE) { // Indicates that the pressed key is the Esc key.
                    is_running = false; // Terminates the execution of the program main loop.
                 }
                 break;
        }
     }
}

// Updates objects in the main window
void update_screen(void)
{

}

// 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.

     // Copy texture to main window
	 SDL_RenderTexture(renderer, texture, NULL, NULL);

     // 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();
}