CODEWITHSUNDEEP
c++allegro
dagi12
dagi12

Reputation: 459

Allegro program displays a black screen then crash

I'm learning object-oriented programming and allegro library so I start to write a simple menu but code displays black screen and then crash.

I will be grateful for the suggestions about classes appearance, splitting code with headers, general syntax of the code and above all to find a problem for which the code does not work.

main.cpp

#include "Menu.h"

int main() {
    Menu m;
    return 0;
}
END_OF_MAIN()

Menu.h

#ifndef MENU_H_
#define MENU_H_
#include <allegro.h>

class Menu {
    static bool isWorking;
    static const int WIDTH = 800;
    static const int HEIGHT = 600;
public:
    Menu();
    virtual ~Menu();
};

#endif

menu.cpp

#include "MenuPointer.h"
#include "Menu.h"
#include <string>
using namespace std;

bool Menu::isWorking = true;

Menu::Menu() {
    allegro_init();
    install_keyboard();
    install_timer();
    set_color_depth(8);
    set_gfx_mode(GFX_AUTODETECT_WINDOWED, WIDTH, HEIGHT, 0, 0);
    string * menuOptions = new string[2];
    menuOptions[0] = "New Game";
    menuOptions[2] = "Exit";

    // menu pointer is an object highlighting menu options

    MenuPointer menuPointer(2, 0, WIDTH, HEIGHT/2, menuOptions);
    while (isWorking) {
        menuPointer.menuInit();
        blit(menuPointer.getBuffer(), screen, 0, 0, 0, 0, WIDTH, HEIGHT);
    }
}

Menu::~Menu() {
    allegro_exit();
    clear_keybuf();
}

MenuPointer.h

#ifndef MENUPOINTER_H_
#define MENUPOINTER_H_

#include <string>
#include <allegro.h>
using namespace std;

class MenuPointer {
    int pointerNumber;
    BITMAP * buffer;
    const int optionsNumber;
    const int pointerWidth;
    const int pointerHeight;
    BITMAP ** optionsImages;
    const string * optionsTexts;
    void paintPointer();
public:
    void menuInit();
    BITMAP * getBuffer();
    MenuPointer(int, int, int, int, BITMAP **);
    MenuPointer(int, int, int, int, const string *);
    virtual ~MenuPointer();
};

#endif

MenuPointer.cpp

#include "MenuPointer.h"
#include "Menu.h"
#include <string>
using namespace std;


// this constructor creates menu pointer when options are array of images
MenuPointer::MenuPointer(int i, int j, int k, int l, BITMAP ** optionsImages)
    :pointerNumber(j), optionsNumber(i), pointerWidth(k), pointerHeight(l) {
    buffer = create_bitmap(pointerWidth, pointerHeight);
    optionsTexts = NULL;
    this->optionsImages = optionsImages;
}

// this constructor creates menu pointer when options are array of text
MenuPointer::MenuPointer(int i, int j, int k, int l, const string * optionsTexts)
    :pointerNumber(j), optionsNumber(i), pointerWidth(k), pointerHeight(l) {
        buffer = create_bitmap(pointerWidth, pointerHeight);
        optionsImages = NULL;
        this->optionsTexts = optionsTexts;
}


// draws a rectangle in the range from the beginning to the next option which highlights
void MenuPointer::paintPointer() {
    rectfill(buffer, 0, pointerNumber*pointerHeight, pointerHeight, (pointerNumber+1)*pointerHeight, makecol( 128, 30, 30 ) );
}


void MenuPointer::menuInit() {
    clear_to_color(buffer, makecol( 128, 128, 128 ));
    paintPointer();
    if (optionsTexts != NULL) {
        // converts string to char array
        for (int i = 0; i < optionsNumber; ++i) {
            char *a = new char[optionsTexts[i].size()+1];
            a[optionsTexts[i].size()] = 0;
            memcpy(a, optionsTexts[i].c_str(), optionsTexts[i].size());
            textout_ex(screen, font, a, 0, i*pointerWidth, makecol(255,0,0), -1);
        }
    } else {
        // draws option image for images array
        for (int i = 0; i < optionsNumber; ++i) {
            masked_blit(optionsImages[i], screen, 0, 0, 0, i*pointerWidth, optionsImages[i]->w, optionsImages[i]->h);
        }
    }
}

BITMAP * MenuPointer::getBuffer() {
    return buffer;
}

MenuPointer::~MenuPointer() {
    destroy_bitmap(buffer);
}

Upvotes: 1

Views: 499

Answers (2)

Katastic Voyage
Katastic Voyage

Reputation: 1044

Always check return values! Especially when things start to crash.

You have asked Allegro to run in an 8-bit color depth. This can fail, Even asking for 24-bit on a 32-bit system can fail. You can use desktop_color_depth() to find out what the host is running in.

Ensure that set_gfx_mode() doesn't return an error before proceeding, and that all bitmaps are actually loaded. (not == null)

Upvotes: 1

Gerry
Gerry

Reputation: 66

Have you more debug-info about the crash?

First of all, one of the possible problem that can cause the crash is a bad access to the array menuoptions.

string * menuOptions = new string[2];
menuOptions[0] = "New Game";
menuOptions[2] = "Exit"; // THIS IS WRONG

You have leaks inside this loop:

    for (int i = 0; i < optionsNumber; ++i) {
        char *a = new char[optionsTexts[i].size()+1]; //this is never freed
        a[optionsTexts[i].size()] = 0;
        memcpy(a, optionsTexts[i].c_str(), optionsTexts[i].size());
        textout_ex(screen, font, a, 0, i*pointerWidth, makecol(255,0,0), -1);
    }

Various Hints:

  1. Use strncpy instead of memcpy to copy a string.
  2. Names for method/functions parameters must be more clear. ( never use i,j,k )
  3. I always prefer to put names on method/function declaration too.
  4. Put your loop method out of the constructor. ( a method called update could be ok )

Upvotes: 0

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