ETIRER/RÉTRÉCIR UNE IMAGE BMP SANS STRETCHBLT

/*-----------------------------------------------------------------------------------------------*
//
//                                      ScaleImage
//
//Fait par         : MaegisInstinct (maegisinstinct@free.fr)
//
//le               : 29/07/2004 à 20:27:37
//
//Description      : Permet d'etirer/étrecir une image
					 Lire le .txt pour avoir des explications sur la méthode de Scale
//
/*----------------------------------------------------------------------------------------------*/

#include <windows.h>

#define PARTDEC(a) (a-(double)(int)a)		//retourne la partie décimale d'un double

struct PIXEL
{
	BYTE b;
	BYTE g;
	BYTE r;
};


/*--------------------------------*/
//Change la resolution d'une image
/*--------------------------------*/
void Scale(const PIXEL* src,DWORD srcwidth,DWORD srcheight,PIXEL* data,DWORD datawidth,DWORD dataheight,BOOL moyenne_etirement)
{
	DWORD	i,j,k,l;
	PIXEL*	save_data; 
	double	xratio,yratio;
	double	precx = 0.0,precy = 0.0;
	double	currentx,currenty;
	double	coeff;						//somme des coeffs pour la moyenne
	double	temp;
	double	somme_r,somme_g,somme_b;

	xratio = (double)srcwidth/(double)datawidth;
	yratio = (double)srcheight/(double)dataheight;
	save_data = data;
	currenty = 0.0;

	for(j=0;j<dataheight;j++)			//Pour chaque pixel du but
	{
		currentx = 0.0;
		currenty += yratio;
		for(i=0;i<datawidth;i++)
		{
			currentx += xratio;
			coeff = 0.0;
			somme_r = 0.0;
			somme_g = 0.0;
			somme_b = 0.0;
		
			//Calcul de la moyenne
			for(l=0;l<(unsigned int)yratio+1;l++)		//Pour chaque pixel de la source contenu dans le pixel du but
			{
				for(k=0;k<(unsigned int)xratio+1;k++)
				{
				//Coeff en x
					if (k==0)
						temp = 1.0-PARTDEC(precx);
					else if (k==(unsigned int)xratio)
						temp = xratio-(double)((int)xratio-1)-(1.0-PARTDEC(precx));
					else
						temp = 1;
				//Coeff en y
					if (l==0)
						temp = temp*(1.0-PARTDEC(precy));
					else if (l==(unsigned int)yratio)
						temp = temp*(yratio-(double)((int)yratio-1)-(1.0-PARTDEC(precy)));

					if ((int)precx+k<srcwidth && (int)precy+l<srcheight)		//si on est dans les limites
					{
						somme_r += src[(int)precx+k+((int)precy+l)*srcwidth].r*temp;
						somme_g += src[(int)precx+k+((int)precy+l)*srcwidth].g*temp;
						somme_b += src[(int)precx+k+((int)precy+l)*srcwidth].b*temp;
						coeff += temp;
					}

					if (moyenne_etirement)  //Moyenne lors de l'etirement si souhaité
					{
						if (xratio<1. && (int)currentx-(int)precx==1 && PARTDEC(currentx) != 0.)
						{
							temp = PARTDEC(currentx);
							somme_r += src[(int)precx+1 + (int)precy*srcwidth].r*temp;
							somme_g += src[(int)precx+1 + (int)precy*srcwidth].g*temp;
							somme_b += src[(int)precx+1 + (int)precy*srcwidth].b*temp;
							coeff += temp;
							temp = -1.0;
						}
						if (yratio<1. && (int)currenty-(int)precy==1 && PARTDEC(currenty) != 0.)
						{
							if (temp == -1.0)		//on compte le quatrieme carré
							{
								temp = PARTDEC(currenty)*PARTDEC(currentx);
								somme_r += src[(int)precx+1 + ((int)(precy)+1)*srcwidth].r*temp;
								somme_g += src[(int)precx+1 + ((int)(precy)+1)*srcwidth].g*temp;
								somme_b += src[(int)precx+1 + ((int)(precy)+1)*srcwidth].b*temp;
								coeff += temp;
							}
							temp = PARTDEC(currenty);
							somme_r += src[(int)precx + ((int)(precy)+1)*srcwidth].r*temp;
							somme_g += src[(int)precx + ((int)(precy)+1)*srcwidth].g*temp;
							somme_b += src[(int)precx + ((int)(precy)+1)*srcwidth].b*temp;
							coeff += temp;
						}
					}
				}
			}
			data->r = (BYTE)(somme_r/coeff);
			data->g = (BYTE)(somme_g/coeff);
			data->b = (BYTE)(somme_b/coeff);
			data++;
			precx = currentx;
		}
		precy = currenty;
		precx = 0.0;
	}
	data = save_data;
}

/*---------------------------------*/
//Enregistre un fichier bmp24 bits
/*---------------------------------*/
BOOL SaveBmp24(char *path,PIXEL *data,int width,int height)
{
	BITMAPFILEHEADER	fileheader;
	BITMAPINFOHEADER	infoheader;
	HANDLE				fichier;
	DWORD				dummy;
	int					size;
	int					bourrage = 0;
	int					i,j,k;
	char				*image = NULL;

	fichier = CreateFile(path,
						 GENERIC_WRITE,
						 FILE_SHARE_READ,
						 NULL,
						 CREATE_ALWAYS,
						 FILE_ATTRIBUTE_NORMAL,
						 NULL);
	if (fichier == INVALID_HANDLE_VALUE)
		return FALSE;

	fileheader.bfType = 0x4D42;	//"bm"
	fileheader.bfSize = 54 + width*height*3;
	fileheader.bfReserved2 = 0;
	fileheader.bfReserved1 = 0;
	fileheader.bfOffBits = 54;

	infoheader.biSize = sizeof(BITMAPINFOHEADER);
	infoheader.biWidth = width;
	infoheader.biHeight = height;
	infoheader.biPlanes = 1;
	infoheader.biBitCount = 24;
	infoheader.biCompression = 0;
	infoheader.biSizeImage = width*height;
	infoheader.biXPelsPerMeter = 0;
	infoheader.biYPelsPerMeter = 0;
	infoheader.biClrImportant = 0;
	infoheader.biClrUsed = 0;

	while ((3*width+bourrage) % 4 != 0)	//calcul du nb de bits de bourrage (3 car 24bits = 3octs)
		bourrage++;

	size = width*height;

	image = new char[size*3+bourrage*height];
	if (image == NULL)
	{
		CloseHandle(fichier);
		return FALSE;
	}
	
	for(i=0;i<height;i++)
	{
		for(j=0;j<width;j++)
		{
			image[i*(3*width+bourrage)+3*j]		= data[(height-i-1)*width+j].b;
			image[i*(3*width+bourrage)+3*j+1]	= data[(height-i-1)*width+j].g;
			image[i*(3*width+bourrage)+3*j+2]	= data[(height-i-1)*width+j].r;
		}
		for(k=1;k<bourrage;k++)
			image[i*(3*width+bourrage)+3*j+k] = 0;
	}

	WriteFile(fichier,&fileheader,14,&dummy,NULL);
	WriteFile(fichier,&infoheader,40,&dummy,NULL);
	WriteFile(fichier,image,size*3+bourrage*height,&dummy,NULL);

	CloseHandle(fichier);
	return TRUE;
}

/*---------------------*/
//Ouvre un bmp 24 bits
/*---------------------*/
BOOL GetBmp24(char* chemin,PIXEL **data,DWORD& width,DWORD& height)
{
	BITMAPFILEHEADER	fileheader;
	BITMAPINFOHEADER	infoheader;
	HANDLE				fichier;
	DWORD				dummy,i,j;
	DWORD				size;
	DWORD				bourrage	= 0;
	PIXEL				temp;
	BYTE				*buffer		= NULL;

	fichier = CreateFile(chemin,
						 GENERIC_READ,
						 FILE_SHARE_READ,
						 NULL,
						 OPEN_EXISTING,
						 FILE_ATTRIBUTE_NORMAL,
						 NULL);
	if (fichier == INVALID_HANDLE_VALUE)
		return FALSE;

	ReadFile(fichier,&fileheader,14,&dummy,NULL);
	ReadFile(fichier,&infoheader,40,&dummy,NULL);
	width = infoheader.biWidth;
	height = infoheader.biHeight;

	while ((3*width+bourrage) % 4 != 0)		//gestion du bourrage
		bourrage++;

	if (fileheader.bfType != 0x4D42 || infoheader.biBitCount != 24 
		|| infoheader.biCompression != 0)
	{
		CloseHandle(fichier);
		return FALSE;
	}
	size = width*height;

	buffer = new BYTE[size*3+bourrage*height];
	if (buffer == NULL)
		return FALSE;

	SetFilePointer(fichier,fileheader.bfOffBits,NULL,FILE_BEGIN);

	ReadFile(fichier,buffer,size*3+bourrage*height,&dummy,NULL);

	(*data) = new PIXEL[size];
	if ((*data) == NULL)
	{
		delete[] buffer;
		return FALSE;
	}

	for(i=0;i<height;i++)
	{
		memcpy((*data)+(i*width),buffer+i*(3*width+bourrage),width*3);
	}

	//remet dans le bon sens
	for(i=0;i<(height/2);i++)
	{
		for(j=0;j<width;j++)
		{
			temp  = (*data)[i*width+j];
			(*data)[i*width+j] = (*data)[(height-1-i)*width+j];
			(*data)[(height-1-i)*width+j] = temp;
		}
	}
	

	CloseHandle(fichier);
	delete[] buffer;
	return TRUE;
}

/*--------------*/
//Fonction Main
/*--------------*/
int APIENTRY WinMain(HINSTANCE hInstance,
					 HINSTANCE hPrevInstance,
					 LPSTR lpCmdLine,
					 int nShowCmd)
{
	PIXEL *data,*scaleddata;
	DWORD width,height;

	if (GetBmp24("image.bmp",&data,width,height))
	{
		scaleddata = new PIXEL[width*height*4];
		Scale(data,width,height,scaleddata,width/2,height/2,FALSE);
		SaveBmp24("Halfimage.bmp",scaleddata,width/2,height/2);
		Scale(data,width,height,scaleddata,width*2,height*2,FALSE);
		SaveBmp24("Doubleimage.bmp",scaleddata,width*2,height*2);
		Scale(data,width,height,scaleddata,width*2,height*2,TRUE);
		SaveBmp24("Doubleimagemoyenne.bmp",scaleddata,width*2,height*2);
		
		delete[] data;
		delete[] scaleddata;
		return 0;
	}
	return -1;
}