Loading image with surface and texture

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

When the program runs,

1. In addition to the basic operations, the following operations occur:
2. At the beginning of the program, the global variables shown below are defined:
   • SDL_Surface *surface_scr: Surface variable for the main window
   • SDL_Texture *texture: Texture variable for the image file to be loaded
3. When the load_img() function runs,
   • A surface is created by loading the image file named horse.png with the IMG_Load() function and the created surface is assigned to the surface_img variable.
   • A texture is created from the surface value with the SDL_CreateTextureFromSurface() function and assigned to the texture variable.
4. When the draw_screen() function runs,
   • The texture content is copied to the main window with the SDL_RenderTexture() function and the image is displayed in the main window.

Used texture functions

• The SDL_CreateTextureFromSurface() function creates a texture from an existing surface.
• The SDL_RenderTexture() function copies a portion of the texture to the current render target with subpixel precision.

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_Surface *surface_img = NULL;  // Surface variable for image
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 surface
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 image surface
    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 surface and 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 surface
void load_img(void)
{
	 // Load image to surface
	 surface_img = IMG_Load("horse.png");

	 if(surface_img == NULL)	{
	    SDL_Log("Load image error: %s\n", SDL_GetError());
	 }

	 // Create a texture from a surface
	 texture = SDL_CreateTextureFromSurface(renderer, surface_img);
}

// 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_DestroySurface(surface_img);
     SDL_DestroyRenderer(renderer);
     SDL_DestroyWindow(window);
     SDL_Quit();
}