SDL2 Not Loading/Showing Images?

Jamie Edwards · 2014-06-06T15:14:58

Hi guys, so I've decided to start trying to making a simple game using SDL2. I'd found a ( what seems to be good ) Tutorial by Lazy Foo... Problem is.... Either I'm a complete noob, or something just isn't working (note: I've not used C++ in about a year, and came over from Java). This is what I have (also, this is my OOP approach to his tutorials, and I'll pick out the "problem" code): Gui.h: [spoiler] class Gui { private: ... SDL_Window* window; SDL_Surface* screenSurface; public: SDL_Surface* keyPressSurfaces[]; SDL_Surface* currentSurface; public: Gui(); void initGui(); bool loadMedia(); SDL_Surface* loadSurface ( std::string path ); ... }; [/spoiler] Gui.cpp: [spoiler] Gui::Gui() { window = NULL; screenSurface = NULL; currentSurface = NULL; keyPressSurface[Input::KEY_PRESS_SURFACE_TOTAL]; // There is a compiler warning here saying "statement has no effect"???? } void Gui::initGui() { window = SDL_CreateWindow ( .... ) // Creating the master window if ( window == NULL ) { } else { screenSurface = SDL_GetWindowSurface ( window ); // Get the window surface // set the default surface currentSurface = keyPressSurfaces[Input::KEY_PRESS_SURFACE_DEFAULT]; // Apply the current surface SDL_BlitSurface ( currentSurface, NULL, screenSurface, NULL ); // Update the surface SDL_UpdateWindowSurface ( window ); } } bool Gui::loadMedia() { Input input; bool success = true; // Load default surface keyPressSurfaces[input.KEY_PRESS_SURFACE_DEFAULT] = loadSurface ( "assets/surfaces/press.jpg" ); if ( keyPressSurfaces[input.KEY_PRESS_SURFACE_DEFAULT] == NULL ) { printf ( "Failed to load default image!\n" ); success = false; } // I'll omit the code for the up, down, left and right key presses as they are all identical to the "load default surface" one above ( except for // the path ) ... ... return success; } SDL_Surface* Gui::loadSurface ( std::string path ) { // Load image at specified path SDL_Surface* loadedSurface = SDL_LoadBMP ( path.c_str() ); return loadedSurface; } [/spoiler] Input.h: [spoiler] class Input { public: enum Key_Press_Surfaces { KEY_PRESS_SURFACE_DEFAULT, ... ... KEY_PRESS_SURFACE_RIGHT, KEY_PRESS_SURFACE_TOTAL }; public: Input(); }; [/spoiler] Event.cpp: [spoiler] void Initialize::event ( SDL_Event* event ) { Gui gui; Input input; // User presses a key else if ( Event -> type == SDL_KEYDOWN ) { // Select surface based on key press switch ( Event -> key.keysym.sym ) { case SDLK_w : gui.currentSurface = gui.keyPressSurfaces[input.KEY_PRESS_SURFACE_UP]; break; case SDLK_s : gui.currentSurface = gui.keyPressSurfaces[input.KEY_PRESS_SURFACE_DOWN]; break; case SDLK_a : gui.currentSurface = gui.keyPressSurfaces[input.KEY_PRESS_SURFACE_LEFT]; break; case SDLK_d : gui.currentSurface = gui.keyPressSurfaces[input.KEY_PRESS_SURFACE_RIGHT]; break; default: gui.currentSurface = gui.keyPressSurfaces[input.KEY_PRESS_SURFACE_DEFAULT]; break; } } [/spoiler] In my Initialize.cpp I've got the initGui function just before my event loop. Oh and my dev tree is as follows: [spoiler] Tutorial ( root ) assets/ surfaces/ press.bmp down.bmp left.bmp right.bmp up.bmp bin/ includes/ control/ Input.h gui/ Gui.h init/ Initialize.h includes.h obj/ src/ control/ Input.cpp gui/ Gui.cpp init/ Initialize.cpp main/ main.cpp term/ CleanUp.cpp [/spoiler] I don't understand what's going wrong, or I'm completely overlooking something, but that being said, when it's built and run, there are no error, except that one warning, and the surface goes black, so it's certainly doing something. Any help would be much appreciated. Thanks! Jamie.

For Beginners

Started by Jamie_Edwards June 05, 2014 03:58 PM

16 comments, last by yellowsputnik 9 years, 11 months ago

Jamie_Edwards

123

Author

June 05, 2014 09:28 PM

Why do you declare a Gui variable in Initialize::event()?

I declared it because I thought it would be easier to write "gui.keyPressSurfaces[]" rather than "Gui::keyPressSurfaces" as I have at least 5 points in my code where I have to write that. And same goes for Input too in the Event class ( if that makes sense ).

But changing the event calls to "Gui::" instead just makes the compiler vomit the following error:


error: invalid use of non-static data member 'Gui::keyPressSurfaces'

changing the "Gui::" back to "gui." and then changing "input." to "Input::" causes no errors.

Edit:

I changed everything to read:

Event.cpp ( with changes to KEY_PRESS_SURFACE_... to match what I wanted it to look like ):

Gui::currentSurface = Gui::keyPressSurfaces[Input::KEY_PRESS_SURFACE_DEFAULT];

Gui.h:

SDL_Surface* keyPressSurfaces[];
SDL_Surface* currentScreen;
 
// To:
static SDL_Surface* keyPressSurfaces[];
static SDL_Surface* currentScreen;

the compiler then gives:

undefined reference to 'Gui::currentSurface'

yellowsputnik

1,526

June 05, 2014 09:33 PM

You'll have to use the same Gui variable that you called initGui() on. Otherwise you're not using the window and surfaces that you created during initialization.

Jamie_Edwards

123

Author

June 05, 2014 10:09 PM

How do I go about doing that?

DejaimeNeto

4,221

June 05, 2014 10:24 PM

You are using a non-initialized Gui object on Event.cpp.

Every time you call the event( SDL_Event* ) function, you create a new Gui and use it without loading anything.

In the end of the function call, it is deleted.

So, as Yellowsputnik pointed out, you're not using the Gui object you think you are.

You could pass on the Gui object to the event function as in here:


void Initialize::event ( const Gui &gui, SDL_Event* event )

or even use a global variable for it.

What exactly is the Initialize class responsible for?

Build and Gun

Jamie_Edwards

123

Author

June 05, 2014 11:23 PM

You are using a non-initialized Gui object on Event.cpp.
Every time you call the event( SDL_Event* ) function, you create a new Gui and use it without loading anything.
In the end of the function call, it is deleted.
So, as Yellowsputnik pointed out, you're not using the Gui object you think you are.

Right ok.

You could pass on the Gui object to the event function as in here:
void Initialize::event ( const Gui &gui, SDL_Event* event )
or even use a global variable for it.

I tried doing as you said and I think I did it wrong as it threw errors at me. Could you show me how it should be implemented?

What exactly is the Initialize class responsible for?

It's responsible for pretty much everything, it initializes the event loop, gui, render and finally the cleanup when the app is closed.

DejaimeNeto

4,221

June 05, 2014 11:48 PM

Could you show me how it should be implemented?

Take a look at the following code snippet:

#include <iostream>

class MyClass {
	std::string myName;
	
public:
	MyClass(std::string name): myName(name){
            //myName = name;
        }

	void PrintMyName() {
		std::cout << myName << std::endl;
	}
};

void CallPrintMyName (MyClass& correct_object) {
	correct_object.PrintMyName();
}

int main (){
        // Creates two objects with their names.
        MyClass Dejaime("Dejaime Neto"), JohnSmith("John Smith");

        //Call the function passing the first object
	CallPrintMyName (Dejaime);
        //Call again with the second one
	CallPrintMyName (JohnSmith);
}

You see, I pass on the object I want to use inside the CallPrintMyName function.
It outputs the following:
>> Dejaime Neto
>> John Smith

If you want some advice, it just seems you are biting a bit more than you can chew at the moment. I'd advise you to take a step back and study a bit more variable scopes, functions and object orientation in general, be it with Java or C++. Give it a week or so and then get back to this problem, it can only do good!

Build and Gun

Jamie_Edwards

123

Author

June 06, 2014 03:08 PM

OK, I've decided to follow the tutorial a little closer to get the gist of how to make SDL work, but it's still not working properly. It builds and runs fine, but when I ask it to load a ".bmp" image, it just shows a white surface.

I've tried putting the image in with the "Initialize.cpp", "main.cpp", "Gui.cpp" and in the root directory, and even in the bin/debug folder and it still comes up with a just a white screen.

yellowsputnik

1,526

June 06, 2014 03:14 PM

Make sure to check return values of functions to see if they actually did what you think they should do.

When debugging, I always like to use breakpoints and step through the code to know exactly what's going on. You can try that here as well.

SDL2 Not Loading/Showing Images?

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