Question about libwiisprite transparency

void DrawableImage::SetAlpha(u32 i, u8 a){

   _pixels[i+3] = a;//This is the problem line

  }

#ifndef LIBWIISPRITE_DRAWABLEIMAGE
#define LIBWIISPRITE_DRAWABLEIMAGE
 
#include

 namespace wsp{ //The namespace used in libwiisprite

  class DrawableImage : public Image{

      public:

	DrawableImage(); //Constructor
	virtual ~DrawableImage(); //Destructor

     u8 GetRed(u32 i);//Retrieve the red value of a designated pixel on the DrawableImage
     u8 GetGreen(u32 i);//Retrieve the blue value of a designated pixel on the DrawableImage
     u8 GetBlue(u32 i);//Retrieve the green value of a designated pixel on the DrawableImage
     u8 GetAlpha(u32 i);//Retrieve the alpha value of a designated pixel on the DrawableImage

     void SetRed(u32 i, u8 r);//Sets the red value of a designated pixel on the DrawableImage
     void SetGreen(u32 i, u8 g);//Sets the blue value of a designated pixel on the DrawableImage
     void SetBlue(u32 i, u8 b);//Sets the green value of a designated pixel on the DrawableImage
     void SetAlpha(u32 i, u8 a);//Sets the alpha value of a designated pixel on the DrawableImage

     bool CheckPixel(u32 i, u8 r, u8 g, u8 b, u8 a);/*Compares the designated pixel on the DrawableImage with the values given to call the function*/

     void SetPixel(u32 i, u8 r, u8 g, u8 b, u8 a);//Sets the color values of the designated pixel on the DrawableImage

     void MakeTransparent(u8 r, u8 g, u8 b, u8 a);//Makes all pixels that match those values in the DrawableImage transparent

    private:

                u8* _pixels;
	u32 _width, _height;
	bool _initialized;
	GXTexObj _texObj;

  };
 };


 #endif

#include
#include "drawableimage.h"
#include 
#include 
#include 

 namespace wsp{ //Libwiisprite namespace

  DrawableImage::DrawableImage() : _pixels(NULL), _width(0), _height(0), _initialized(false){
  }

  DrawableImage::~DrawableImage(){

    DestroyImage();
  }

  u8 DrawableImage::GetRed(u32 i){
  
   u8 Red;
  
   Red = _pixels;
  
   return Red;
  }

  u8 DrawableImage::GetGreen(u32 i){
  
   u8 Green;

   Green = _pixels[i+1];
  
   return Green;
  }

  u8 DrawableImage::GetBlue(u32 i){
  
   u8 Blue;

   Blue = _pixels[i+2];
  
   return Blue;
  }

  u8 DrawableImage::GetAlpha(u32 i){
  
   u8 Alpha;

   Alpha = _pixels[i+3];
  
   return Alpha;
  }

  void DrawableImage::SetRed(u32 i, u8 r){

   //_pixels = r; Crash Line

  }

  void DrawableImage::SetGreen(u32 i, u8 g){

  //_pixels[i+1] = g; Crash Line

  }

  void DrawableImage::SetBlue(u32 i, u8 b){

   //_pixels[i+2] = b; Crash Line

  }

  void DrawableImage::SetAlpha(u32 i, u8 a){
  
  //_pixels[i+3] = a; Crash Line
   
  }

  bool DrawableImage::CheckPixel(u32 i, u8 r, u8 g, u8 b, u8 a){

   if(GetRed(i) == r && GetGreen(i) == g && GetBlue(i) == b && GetAlpha(i) == a)
     return true;

    else
     return false;

  }

  void DrawableImage::SetPixel(u32 i, u8 r, u8 g, u8 b, u8 a){

     SetRed(i, r);
     SetGreen(i, g);
     SetBlue(i, b);
     SetAlpha(i, a);

   }

   void DrawableImage::MakeTransparent(u8 r, u8 g, u8 b, u8 a){

    u32 height = GetHeight();
    u32 width = GetWidth();
	u32 total = width*height;
	
	_InitializeImage(width, height);

     for(u32 i = 0; i <= total; i++){

        if(CheckPixel(i, r, g, b, a))
         SetPixel(i, r, g, b, 0);

      }
     
    }

  }

#include 
#include 
#include 
#include 
#include 

#include  // The main libwiisprite header.
using namespace wsp; // To not make us type this again and again

#include "drawableimage.h"


// libwiisprite uses wsp as it's namespace
using namespace wsp;

int main(int argc, char **argv)
{

    int x = 320;
	int y = 240;
	int speed = 8;
	
	fatInitDefault();
	
	// Create the game window and initalise the VIDEO subsystem
	GameWindow gwd;
	gwd.InitVideo();
	
	

	// Initialise Wiimote
	WPAD_Init();
	
	Image *image1 = new Image();
    image1->LoadImage("data/background.png");
	
	DrawableImage *image2 = new DrawableImage();
    image2->LoadImage("data/pointer.png");
	image2->MakeTransparent(255, 0, 255, 0xFF);
	
	
	Sprite *background = new Sprite();
	background->SetImage(image1);
	background->Draw();
	
	Sprite *bat = new Sprite();
	bat->SetImage(image2, 48, 48);

	for(;;)
	{
		WPAD_ScanPads();
		
		background->Draw();
		
		bat->SetPosition(x, y);
		bat->Draw();
		bat->NextFrame();
		
		if(WPAD_ButtonsDown(WPAD_CHAN_0)&WPAD_BUTTON_UP)
		x -= speed;
		
		if(WPAD_ButtonsDown(WPAD_CHAN_0)&WPAD_BUTTON_DOWN)
		x += speed;
		
		if(WPAD_ButtonsDown(WPAD_CHAN_0)&WPAD_BUTTON_RIGHT)
		y -= speed;
		
		if(WPAD_ButtonsDown(WPAD_CHAN_0)&WPAD_BUTTON_LEFT)
		y += speed;
		
		if((WPAD_ButtonsDown(WPAD_CHAN_0)&WPAD_BUTTON_UP) && (WPAD_ButtonsDown(WPAD_CHAN_0)&WPAD_BUTTON_RIGHT)){
		x -= speed/2;
		y -= speed/2;
		}
		
		if((WPAD_ButtonsDown(WPAD_CHAN_0)&WPAD_BUTTON_UP) && (WPAD_ButtonsDown(WPAD_CHAN_0)&WPAD_BUTTON_LEFT)){
		x -= speed/2;
		y += speed/2;
		}
		
		if((WPAD_ButtonsDown(WPAD_CHAN_0)&WPAD_BUTTON_DOWN) && (WPAD_ButtonsDown(WPAD_CHAN_0)&WPAD_BUTTON_RIGHT)){
		x += speed/2;
		y -= speed/2;
		}
		
		if((WPAD_ButtonsDown(WPAD_CHAN_0)&WPAD_BUTTON_DOWN) && (WPAD_ButtonsDown(WPAD_CHAN_0)&WPAD_BUTTON_LEFT)){
		x += speed/2;
		y += speed/2;
		}
		
		if(WPAD_ButtonsDown(WPAD_CHAN_0)&WPAD_BUTTON_HOME)
			break;
		
		if(y < 0)
		y = 0;
		
		if(y > 480)
		y = 480;
		
		if(x < 0)
		x = 0;
		
		if(x > 640)
		x = 640;
		
		gwd.Flush();
	}
	return 0;
}

  bool DrawableImage::CheckPixel(u32 i, u8 r, u8 g, u8 b){

   if(GetRed(i) == r && GetGreen(i) == g && GetBlue(i) == b)
     return true;

    else
     return false;

  }


void DrawableImage::SetPixel(u32 i, u8 r, u8 g, u8 b, u8 a){

     SetRed(i, r);
     SetGreen(i, g);
     SetBlue(i, b);
     SetAlpha(i, a);

   }

   void DrawableImage::MakeTransparent(u8 r, u8 g, u8 b){

    u32 height = GetHeight();
    u32 width = GetWidth();
	u32 total = width*height;
	
	_InitializeImage(width, height);

     for(u32 i = 0; i <= total; i++){

        if(CheckPixel(i, r, g, b))
         SetPixel(i, r, g, b, 0);

      }
     
    }

Quote
chaosteil
_pixels is an array of u8. Or, as declared in the header file:

u8* _pixels; //!< Stores the pixeldata of this image. Use carefully.

So it shouldn't crash. At all. In fact, this is a wtf situation right here :/

struct GX_block1_pixel {
u8 A,R;
};

struct GX_block2_pixel {
u8 G,B
};

struct GX_block {
GX_block1_pixel block1[4*4];
GX_block2_pixel block2[4*4];
};

GX_block *_pixels;

u8 R = _pixel[((pixel - (pixel%16)) / 16) * 64 + (pixel%16) * 32]

Quote
henke37
That method is for the global alpha, but what you want is the real alpha channel in the png file. So get a better png file creator that allows you to specify the alpha channel.

void DrawableImage::SetAlpha(u32 i, u8 a){
  
  _pixels[i+3] = a; //This is the offending line of code
   
  }

_pixels[0+3] = 0;