Trying to create an SDL texture, just get blank screen

SDL Development
1

Hello I have got the book SDL game development from amazon and I am trying to learn SDL2 to write games. I have my first game engine up and running but when adding code to try and get a bmp on the screen on lines 8-15 in Game.cpp I just get a blank screen when I run. Have I got the texture creation code in the right place in the init function. Please can someone help me so I can progress further through the book. Thanks.

main.cpp

#include <SDL2/SDL.h>
#include “Game.h”
#include “Game.cpp”

int main(int argc, char * args[])
{
Game * g_game = new Game;

g_game->init(“Chapter 1”, 100,100,640,480,false);

while(g_game->running())
{
g_game->handleEvents();
g_game->update();
g_game->renderer();
}
g_game->clean();

return 0;

}

Game.cpp

#include “Game.h”
#include

bool Game::init(const char* title, int xpos, int ypos, int width,
int height, bool fullscreen)
{

SDL_Surface * pTempSurface = SDL_LoadBMP("assets/rider.bmp");	
m_pTexture = SDL_CreateTextureFromSurface(m_pRenderer,pTempSurface);
SDL_FreeSurface(pTempSurface);
SDL_QueryTexture(m_pTexture, NULL,NULL,&m_sourceRectangle.w,&m_sourceRectangle.h);
m_destinationRectangle.x = m_sourceRectangle.x =0;
m_destinationRectangle.y = m_sourceRectangle.y =0;
m_destinationRectangle.w = m_sourceRectangle.w;
m_destinationRectangle.h = m_sourceRectangle.h;	

int flags = 0;

if (fullscreen)
{
flags = SDL_WINDOW_FULLSCREEN;
}

// attempt to initialize SDL
if(SDL_Init(SDL_INIT_EVERYTHING) == 0)
{
std::cout<<"SDL Init Success\n";
// init the window
m_pWindow = SDL_CreateWindow(title, xpos, ypos, width, height, flags);

if(m_pWindow != 0) //window init success
{
std::cout<<"Window Creation Success\n";
m_pRenderer = SDL_CreateRenderer(m_pWindow, -1, 0);

	if(m_pRenderer !=0) // render init success
	{
	std::cout<<"Renderer Creation Success\n";
	SDL_SetRenderDrawColor(m_pRenderer, 0,0,0,0);
	}	
	else
	{
	std::cout<<"Renderer Init Fail\n";
	return false; // renderer init fail
	}

}

else
{
std::cout<<"Window Init Fail\n";
return false; //window init fail
}

}

else
{
std::cout<<“SDL Init Fail\n”;
return false; // SDL init fail
}

std::cout<<“Init success\n”;
m_bRunning = true; // everything inited successfully
// start the main loop

return true;

}

void Game::renderer()
{
SDL_RenderClear(m_pRenderer); // clears the renderer
// to the draw colour

SDL_RenderCopy(m_pRenderer, m_pTexture, &m_sourceRectangle,&m_destinationRectangle);

SDL_RenderPresent(m_pRenderer); // draw to the screen
}

void Game::update()
{
}

void Game::clean()
{
std::cout<<“Cleaning game\n”;
SDL_DestroyWindow(m_pWindow);
SDL_DestroyRenderer(m_pRenderer);
SDL_Quit();
}

void Game::handleEvents()
{
SDL_Event event;
if(SDL_PollEvent(&event))
{
switch (event.type)
{
case SDL_QUIT:
m_bRunning = false;
break;
}
}
}

Game.h

#ifndef Game
#define Game

class Game
{
public:
Game() {}
~Game() {}

bool init(const char* title, int xpos, int ypos, int width,
int height, bool fullscreen);
void renderer();
void update();
void handleEvents();
void clean();

// a function to access the private running variable
bool running() {return m_bRunning;}

private:

SDL_Window * m_pWindow;
SDL_Renderer * m_pRenderer;
SDL_Texture * m_pTexture; //the new SDL Texture variable
SDL_Rect m_sourceRectangle; // the first rectangle
SDL_Rect m_destinationRectangle;// another rectangle

bool m_bRunning;
};

#endif /* defined(Game_h) */
2

Set out breakpoints in your code to check if everything is created successfully. For example, after the creation of the SDL_Surface, after the creation of the SDL_Texture etc. The image file might not be found, which causes the surface to be invalid, which causes the texture to be invalid and so on.
If the SDL_Surface and SDL_Texture are successfully created, check that the source rectangle and the destination rectangle are containing correct data.

3

Thanks I will try this.

5

Btw, I now realize that you’re attempting to execute SDL-specific functions before SDL is initialized. You need to initialize SDL before doing any SDL-specific operations and before executing any SDL-specific functions.

So my recommendation is that, at the startup of the program, create everything in the following order:

  1. Initialize SDL by exeuting SDL_Init();
  2. Create the SDL window by executing SDL_CreateWindow();
  3. Create the SDL renderer by executing SDL_CreateRenderer();
  4. Create the texture(s) and other data.

Don’t forget to do error checking when creating stuff. SDL_GetError(); will help you a lot.

Note: when pasting code into a post here on the forum, you need to highlight all your code and then embed it into a code block by pressing the </> button. By doing this, the whole code is embedded into a code block and will be much easier to read.

6

Hi, thanks for your help managed to get it to work by putting the image creation code after SetRenderDrawColor.

Thanks for your help bro.