我想用我的代码加载并显示bmp 256色图像？ [英] I want to load and display a bmp 256-colors-image with my code ?

问题描述

我自己试着这样做。这里我的代码使用Dev-C ++：

I tried to do it myself. Here my code with Dev-C++ :

#include <iostream>
#include <fstream>
#include <glut.h>
using namespace std;
#pragma pack(push, 2 )
	struct BitmapHeader // 14 byte
	{
		short sigNature;			
		unsigned long fileSize;
		long reserved;
		long dataOffset;
	};
	struct BitmapInfoheader // 40 byte
	{
		unsigned long infoSize; 
		unsigned long width;    
		unsigned long heigh;	
		unsigned short planes;	
		unsigned short bitCount;	
		unsigned long compression; 
		unsigned long imageSize;	
		long xPixelsPerMeter;	
		long yPixelsPerMeter;	
		unsigned long clrUsed;  
		unsigned long clrImportant; 
	};
#pragma pack(pop)

//--------------------------------------

	struct	BitmapHeader bmheader;
	struct	BitmapInfoheader bmInfo;
	char* colorPlane;
	char* imgData;

int loadBmImg()
{
	char tt[20] ;
	ifstream sf;
	char word;
	cout<<"Input filename of image : ";
	cin.getline(tt,20);
	sf.open(tt,ios::in|ios::binary);

	if(sf.bad())
	{
		 cout<<"Can't open the image!";
		 return 0;
	}
		sf.read((char*)&bmheader,sizeof(bmheader));
		sf.read((char*)&bmInfo,sizeof(bmInfo));
		colorPlane = new char[4*256]; //it's simple bitCount=8
		imgData = new char[bmInfo.imageSize];
		sf.read(colorPlane,4*256);
		sf.read(imgData,bmInfo.imageSize);
	sf.close();
}

//---------------------------------

void init() 
{
    glClearColor (0.0, 0.0, 0.0, 0.0);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
    glOrtho(0, bmInfo.width, 0, bmInfo.heigh, -1.0, 1.0);

}

void drawBmImage(void)
{
	unsigned char r,g,b;
	GLint R,G,B;
	unsigned long int index;
	glBegin (GL_POINTS);
   for(int j=0; j<bmInfo.heigh; j++)
   		for(int i=0;i<bmInfo.width; i++)
   		{
   			index = (unsigned long)imgData[j*bmInfo.width+i];
   			r = colorPlane[4*index];
   			g = colorPlane[4*index+1];
   			b = colorPlane[4*index+2];
			R = (unsigned short)r;
   			G = (unsigned short)g;
   			B = (unsigned short)b;
   			glColor3ub(R,G,B);
   			glVertex3i(i,j,0);
   		}
   	glEnd();	
}

void display(void)
{
   glClear (GL_COLOR_BUFFER_BIT);
   drawBmImage();
   glFlush ();
}


int main(int argc, char** argv)
{
   loadBmImg();
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
   glutInitWindowSize (bmInfo.width, bmInfo.heigh); 
   glutInitWindowPosition (100, 100);
   glutCreateWindow ("OpenGL");
   init ();
   glutDisplayFunc(display); 
   glutMainLoop();
   return 0;
}

结果这里

看来我的颜色出错了。我该如何修复它们？

But the result here
It seems I get a mistake with the colors. How can I fix them ?

推荐答案

第一个已被建议：

The first was already suggested:

b = colorPlane[4*index];
g = colorPlane[4*index+1];
r = colorPlane[4*index+2];

这里有一些颜色和兼容性的改进：

Some more improvements for color and compatiblity are here:

sf.seekg(bmheader.dataOffset); // perform seek

imgData = new BYTE[bmInfo.imageSize];
sf.read((char*)imgData,bmInfo.imageSize);

并最终独立于宽度这很重要：

and finally to be independent from width this is important:

unsigned long stride = ((((bmInfo.width * bmInfo.bitCount) + 31) & ~31) >> 3);

for(int j=0; j<bmInfo.heigh; j++)
     for(int i=0;i<bmInfo.width; i++)
     {
         index = (unsigned long)imgData[stride*j + i];
         ... 

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