Texture rendering

In this section, we will examine a program that transfers a rectangle drawn on a texture to the main window.

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

1. In the init_window() function, a texture is created with the SDL_CreateTexture() function.
2. In the draw_screen() function,
   • The texture value is determined as the active rendering target with the SDL_SetRenderTarget() function.
   • The window background is painted with the SDL_RenderClear() function.
   • A filled rectangle is drawn with the SDL_RenderFillRect() function.
   • The renderer is refreshed with the SDL_RenderTarget() function.
   • The window background is painted again with the SDL_RenderClear() function.
   • The texture is transferred to the main window with the SDL_RenderTexture() function.
   • All drawings are displayed on the screen with the SDL_RenderPresent() function.

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;   // Background texture
SDL_Renderer *renderer = NULL; // Renderer variable

// 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;
    }

	texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA8888, SDL_TEXTUREACCESS_TARGET, WINDOW_WIDTH, WINDOW_HEIGHT);

	if(texture == NULL) {
	   SDL_Log("Can not create texture! SDL Error: %s\n", SDL_GetError());
	   return false;
	}

    return true;
}

// Initialization function that runs only once at the beginning of the program
void init_vars(void)
{

}

// Load image to texture
void load_img(void)
{

}

// 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_ESCAPE: is_running = false; break;
               }
               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)
{
    // Set texture as the current rendering target.
    SDL_SetRenderTarget(renderer, texture);

    // Clear screen
    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 = { (WINDOW_WIDTH/2)/2, (WINDOW_HEIGHT/2)/2, WINDOW_WIDTH/2, WINDOW_HEIGHT/2 };
    SDL_SetRenderDrawColor(renderer, 255, 100, 255, 255);
    SDL_RenderFillRect(renderer, &frect);

    // Reset render target
    SDL_SetRenderTarget(renderer, NULL);

    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 the current rendering target
    SDL_FRect frect_dst = { 0, 0, WINDOW_WIDTH, WINDOW_HEIGHT };
    SDL_RenderTexture(renderer, texture, NULL, &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
}

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