How to insert image in a part of the screen? - c++

Question

My board game is using a matrix. I created a board using rectangles. gimprimir() takes the matrix and translates it creating different types of rectangles.
I need to insert an image on a part of the screen. This tutorial teaches how to put an image on screen, but not how to load it in a part of the screen. Whenever I try to modify it, I get a segmentation fault. I want to keep it simple. The image format is .bmp.
My code:
bool loadMedia();
void close();
SDL_Texture* loadTexture( std::string path );
SDL_Window* gWindow = NULL;
SDL_Renderer* gRenderer = NULL;
const int SCREEN_WIDTH = 1200;
const int SCREEN_HEIGHT = 680;
int main(int argc, char* args[]){
nodo a;
if( !init() ){
cout << "Failed to initialize!\n" ;
}
else{
if(!loadMedia()){
cout << "Failed to load media!\n";
}
else{
bool quit = false; // flag ciclo principal
SDL_Event e; // variables manejo de eventos
SDL_Event t;
gimprimir(a);
}
}
}
Function gimprimir() prints a board using struct a:
struct nodo {
array<array<int,19>,19> tablero; // Estado tablero
array<int,2> p1,p2; // Posiciones
int d1,d2; // Distancias mínimas
int paredes1;
int paredes2;
} a;
gimprimir() uses empty and filled rectangles:
void gimprimir(nodo aa){
//Clear screen
SDL_SetRenderDrawColor( gRenderer, 0xFF, 0xFF, 0xFF, 0xFF );
SDL_RenderClear( gRenderer );
int i,j;
for (i=1; i<=17; i++){
if (i%2==1){
for (j=1; j<=17 ; j++){
if (j%2==1){
if (aa.p1[0]==i && aa.p1[1]==j){ // FICHA 1
SDL_Rect fillRect = {(50+SCREEN_WIDTH/11)+(SCREEN_WIDTH/11)*(j-1)/2+34, (SCREEN_HEIGHT/11)+(SCREEN_HEIGHT/11)*(i-1)/2+34, SCREEN_WIDTH/12, SCREEN_HEIGHT/12};
SDL_SetRenderDrawColor( gRenderer, 0xff, 0xcc, 0x66, 0xFF );
SDL_RenderFillRect( gRenderer, &fillRect );
}
else{
if (aa.p2[0]==i && aa.p2[1]==j){ // FICHA 2
SDL_Rect fillRect = {(50+SCREEN_WIDTH/11)+(SCREEN_WIDTH/11)*(j-1)/2+34, (SCREEN_HEIGHT/11)+(SCREEN_HEIGHT/11)*(i-1)/2+34, SCREEN_WIDTH/12, SCREEN_HEIGHT/12};
SDL_SetRenderDrawColor( gRenderer, 0x6E, 0x2C, 0x67, 0xFF );
SDL_RenderFillRect( gRenderer, &fillRect );
}
else{ // CASILLA VACÍA
SDL_Rect fillRect = {(50+SCREEN_WIDTH/11)+(SCREEN_WIDTH/11)*(j-1)/2+34, (SCREEN_HEIGHT/11)+(SCREEN_HEIGHT/11)*(i-1)/2+34, SCREEN_WIDTH/12, SCREEN_HEIGHT/12};
SDL_SetRenderDrawColor( gRenderer, 0x8B, 0x45, 0x13, 0xFF);
SDL_RenderFillRect( gRenderer, &fillRect );
}
}
}
}
}
}
SDL_RenderPresent( gRenderer );
}
loadMedia():
bool loadMedia()
{
//Loading success flag
bool success = true;
//Nothing to load
return success;
}
I want to have both on screen. To load the image to be left in a part of the screen forever and then update the rectangles generated with gimprimir().

Answer 1

SDL_BlitSurface is the SDL function used to blit (copy) from a surface to another, it takes two SDL_Rect arguments, srcrect for source and dstrect for destination.
SDL_BlitSurface isn't changed much from SDL1.2 to SDL2, so, old examples which use it should still work.
In the getting_an_image_on_the_screen example you propose a NULL pointer is used for both src and dst rect, a NULL rect mean copy the whole src surface into the destination at top, left = 0, 0 with a maximum size equal to the destination size (if the source is bigger should be cropped).
To blit a partial image just specify src and dst rect:
SDL_Rect srcrect = { 0, 0, 100, 100 };
SDL_Rect dstrect = { 50, 50, 100, 100 };
//Apply the image
SDL_BlitSurface( gHelloWorld, &srcrect, gScreenSurface, &dstrect );
In this case top, left = 0, 0 with width, height = 100, 100 from source surface (gHelloWorld) is blit to top, left = 50, 50 of dest surface (gScreenSurface).
how to load it with other types of objects
Sorry but is not clear to me what you mean by other types of objects

Answer 2

SDL_BlitSurface() will work, but since you're using SDL2 you're probably working mostly with SDL_Textures and not SDL_Surfaces. If this is the case the easiest way to copy one texture onto another texture or onto the screen is using SDL_RenderCopy() as keltar mentioned. The advantages of using SDL_Texture are explained here: http://wiki.libsdl.org/MigrationGuide#Video
As documented here, SDL_RenderCopy() takes four arguments: a pointer to the SDL_Renderer, a pointer to your source texture, a pointer to the source rectangle, and a pointer to the destination rectangle. By default the texture will be copied onto the screen but you can copy onto other textures by setting a target texture with SDL_SetRenderTarget().
Everything about source and destination rectangles carries over from SDL_BlitSurface.