TGA格式图像是游戏中十分常见的一种图像格式，所以有必要了解其内部格式以及编程实现。

TGA图像一般有非压缩和压缩两种格式，下面分别进行介绍。

一、非压缩TGA图像

颜色表首的入口索引，整型（低位-高位）

下面的程序实现了绘制一个立方体，并进行纹理贴图。

需要注意的是：TGA图像中数据存放的顺序是BGR(A)，而在OpenGL中顺序是RGB(A)，所以在进行纹理生成的时候必须先进行格式的转化。

在OpenGL中只能加载24位或者32位的TGA图像生成纹理。

TGATexture.h定义了一些结构体以及函数声明：

#ifndef TGATEXTURE_H
#define TGATEXTURE_H#include <GL/glut.h>
#include <iostream>using namespace std;//纹理结构体定义
typedef struct
{GLubyte *imageData;//图像数据GLuint bpp;//像素深度GLuint width;//图像宽度GLuint height;//图像高度GLuint texID;//对应的纹理ID
}TextureImage;//加载TGA图像，生成纹理
bool LoadTGA(TextureImage *texture,char *fileName);#endif

TGATexture.cpp则包含加载TGA图像生成纹理的函数具体实现：

#include "TGATexture.h"//加载TGA图像（无压缩格式），生成纹理
bool LoadTGA(TextureImage *texture, char *filename)         // Loads A TGA File Into Memory
{    GLubyte        TGAheader[12]={0,0,2,0,0,0,0,0,0,0,0,0};   // Uncompressed TGA HeaderGLubyte       TGAcompare[12];                             // Used To Compare TGA HeaderGLubyte        header[6];                                  // First 6 Useful Bytes From The HeaderGLuint       bytesPerPixel;                              // Holds Number Of Bytes Per Pixel Used In The TGA FileGLuint       imageSize;                                  // Used To Store The Image Size When Setting Aside RamGLuint        temp;                                       // Temporary VariableGLuint     type=GL_RGBA;                              // Set The Default GL Mode To RBGA (32 BPP)FILE *file = fopen(filename, "rb");                       // Open The TGA Fileif( file==NULL ||                                     // Does File Even Exist?fread(TGAcompare,1,sizeof(TGAcompare),file)!=sizeof(TGAcompare) || // Are There 12 Bytes To Read?memcmp(TGAheader,TGAcompare,sizeof(TGAheader))!=0                ||  // Does The Header Match What We Want?fread(header,1,sizeof(header),file)!=sizeof(header))             // If So Read Next 6 Header Bytes{if (file == NULL)                                   // Did The File Even Exist? *Added Jim Strong*return false;                                 // Return Falseelse{fclose(file);                                   // If Anything Failed, Close The Filereturn false;                                  // Return False}}texture->width  = header[1] * 256 + header[0];            // Determine The TGA Width  (highbyte*256+lowbyte)texture->height = header[3] * 256 + header[2];          // Determine The TGA Height (highbyte*256+lowbyte)//OpenGL中纹理只能使用24位或者32位的TGA图像if( texture->width   <=0 ||                              // Is The Width Less Than Or Equal To Zerotexture->height    <=0 ||                              // Is The Height Less Than Or Equal To Zero(header[4]!=24 && header[4]!=32))                  // Is The TGA 24 or 32 Bit?{fclose(file);                                       // If Anything Failed, Close The Filereturn false;                                      // Return False}texture->bpp = header[4];                           // Grab The TGA's Bits Per Pixel (24 or 32)bytesPerPixel   = texture->bpp/8;                       // Divide By 8 To Get The Bytes Per PixelimageSize      = texture->width*texture->height*bytesPerPixel;  // Calculate The Memory Required For The TGA Datatexture->imageData=(GLubyte *)malloc(imageSize);       // Reserve Memory To Hold The TGA Dataif(   texture->imageData==NULL ||                            // Does The Storage Memory Exist?fread(texture->imageData, 1, imageSize, file)!=imageSize)  // Does The Image Size Match The Memory Reserved?{if(texture->imageData!=NULL)                      // Was Image Data Loadedfree(texture->imageData);                        // If So, Release The Image Datafclose(file);                                       // Close The Filereturn false;                                      // Return False}//RGB数据格式转换，便于在OpenGL中使用for(GLuint i=0; i<int(imageSize); i+=bytesPerPixel)        // Loop Through The Image Data{                                                     // Swaps The 1st And 3rd Bytes ('R'ed and 'B'lue)temp=texture->imageData[i];                            // Temporarily Store The Value At Image Data 'i'texture->imageData[i] = texture->imageData[i + 2];    // Set The 1st Byte To The Value Of The 3rd Bytetexture->imageData[i + 2] = temp;                  // Set The 3rd Byte To The Value In 'temp' (1st Byte Value)}fclose (file);                                            // Close The File// Build A Texture From The DataglGenTextures(1, &texture[0].texID);                   // Generate OpenGL texture IDsglBindTexture(GL_TEXTURE_2D, texture[0].texID);           // Bind Our TextureglTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);    // Linear FilteredglTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); // Linear Filteredif (texture[0].bpp==24)                                 // Was The TGA 24 Bits{type=GL_RGB;                                        // If So Set The 'type' To GL_RGB}glTexImage2D(GL_TEXTURE_2D, 0, type, texture[0].width, texture[0].height, 0, type, GL_UNSIGNED_BYTE, texture[0].imageData);return true;                                         // Texture Building Went Ok, Return True
}

main.cpp主程序：

#include "TGATexture.h"TextureImage texture[1];GLfloat xRot,yRot,zRot;//control cube's rotationint init()
{if(!LoadTGA(&texture[0],"GSK1.tga"))return GL_FALSE;glEnable(GL_TEXTURE_2D);glShadeModel(GL_SMOOTH);glClearColor(0.0f,0.0f,0.0f,0.5f);glClearDepth(1.0f);glEnable(GL_DEPTH_TEST);glDepthFunc(GL_LEQUAL);glHint(GL_PERSPECTIVE_CORRECTION_HINT,GL_NICEST);return GL_TRUE;
}void display()
{glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);glLoadIdentity();glTranslatef(0.0f,0.0f,-5.0f);glRotatef(xRot,1.0f,0.0f,0.0f);glRotatef(yRot,0.0f,1.0f,0.0f);glRotatef(zRot,0.0f,0.0f,1.0f);glBindTexture(GL_TEXTURE_2D,texture[0].texID);glBegin(GL_QUADS); // Front Face // Bottom Left Of The Texture and Quad glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f); // Bottom Right Of The Texture and Quad glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f); // Top Right Of The Texture and Quad glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f,  1.0f); // Top Left Of The Texture and Quad glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f,  1.0f); glEnd(); glBindTexture(GL_TEXTURE_2D,texture[0].texID);glBegin(GL_QUADS); // Back Face // Bottom Right Of The Texture and Quad glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f, -1.0f); // Top Right Of The Texture and Quad glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f,  1.0f, -1.0f); // Top Left Of The Texture and Quad glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f,  1.0f, -1.0f); // Bottom Left Of The Texture and Quad glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f, -1.0f); glEnd(); glBindTexture(GL_TEXTURE_2D,texture[0].texID);glBegin(GL_QUADS); // Top Face // Top Left Of The Texture and Quad glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f, -1.0f); // Bottom Left Of The Texture and Quad glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f,  1.0f,  1.0f); // Bottom Right Of The Texture and Quad glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f,  1.0f,  1.0f); // Top Right Of The Texture and Quad glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f, -1.0f); glEnd(); glBindTexture(GL_TEXTURE_2D,texture[0].texID);glBegin(GL_QUADS); // Bottom Face // Top Right Of The Texture and Quad glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, -1.0f, -1.0f); // Top Left Of The Texture and Quad glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, -1.0f, -1.0f); // Bottom Left Of The Texture and Quad glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f); // Bottom Right Of The Texture and Quad glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f); glEnd(); glBindTexture(GL_TEXTURE_2D,texture[0].texID);glBegin(GL_QUADS); // Right face // Bottom Right Of The Texture and Quad glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f, -1.0f); // Top Right Of The Texture and Quad glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f, -1.0f); // Top Left Of The Texture and Quad glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f,  1.0f,  1.0f); // Bottom Left Of The Texture and Quad glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f); glEnd(); glBindTexture(GL_TEXTURE_2D,texture[0].texID);glBegin(GL_QUADS); // Left Face // Bottom Left Of The Texture and Quad glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f, -1.0f); // Bottom Right Of The Texture and Quad glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f); // Top Right Of The Texture and Quad glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f,  1.0f,  1.0f); // Top Left Of The Texture and Quad glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f, -1.0f); glEnd(); glutSwapBuffers();
}void reshape(int w,int h)
{if (0 == h)h = 1;glViewport(0,0,(GLsizei)w,(GLsizei)h);glMatrixMode(GL_PROJECTION);glLoadIdentity();gluPerspective(60.0f,(GLfloat)w / (GLfloat)h,1,100);glMatrixMode(GL_MODELVIEW);glLoadIdentity();
}void keyboard(unsigned char key,int x,int y)
{switch(key){case 'x':xRot += 1.0f;glutPostRedisplay();break;case 'y':yRot += 1.0f;glutPostRedisplay();break;case 'z':zRot += 1.0f;glutPostRedisplay();break;default:break;}
}int main(int argc,char** argv)
{glutInit(&argc,argv);glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);glutInitWindowSize(400,400);glutInitWindowPosition(100,100);glutCreateWindow("Texture Map");init();glutDisplayFunc(display);glutReshapeFunc(reshape);glutKeyboardFunc(keyboard);glutMainLoop();return 0;
}

运行结果：

二、压缩TGA图像

其格式如下表：

颜色表首的入口索引，整型（低位-高位）

读取其像素数据部分需要注意一下，需要分情况讨论看是A类数据还是B类数据：

if(m_pImageData) delete []m_pImageData;
m_pImageData = new unsigned char[m_iImageDataSize];int iBytePerPixel = m_iBitsPerPixel/8;
int iPixelCnt = m_iImageWidth * m_iImageHeight;
int iCurPixel = 0;
unsigned char ucColorBuffer[4] = {'/0'};do{BYTE chunkheader = 0;is.read((char*)&chunkheader, sizeof(BYTE));//run length dataif(chunkheader & 0x80)//B类数据{int iCnt = (chunkheader & 0x7f) + 1;//计算连续的颜色值重复的像素数。注意：最高位的1是标记位，所以要特殊处理is.read((char*)ucColorBuffer, iBytePerPixel);for(int i = 0; i < iCnt; i++){m_pImageData[iCurPixel*iBytePerPixel + 0] = ucColorBuffer[0];m_pImageData[iCurPixel*iBytePerPixel + 1] = ucColorBuffer[1];m_pImageData[iCurPixel*iBytePerPixel + 2] = ucColorBuffer[2];if(m_iBitsPerPixel == 32){m_pImageData[iCurPixel*iBytePerPixel + 3] = ucColorBuffer[3];}iCurPixel++;if(iCurPixel > iPixelCnt)return false;}}//no processed dataelse//A类数据{int iCnt = chunkheader + 1;//颜色值不重复的像素数量，注意要加一for(int i = 0; i < iCnt; i++){                                             is.read((char*)ucColorBuffer, iBytePerPixel);m_pImageData[iCurPixel*iBytePerPixel + 0] = ucColorBuffer[0];m_pImageData[iCurPixel*iBytePerPixel + 1] = ucColorBuffer[1];m_pImageData[iCurPixel*iBytePerPixel + 2] = ucColorBuffer[2];if(m_iBitsPerPixel == 32){m_pImageData[iCurPixel*iBytePerPixel + 3] = ucColorBuffer[3];}iCurPixel++;if(iCurPixel > iPixelCnt)return false;}}}while(iCurPixel < iPixelCnt);

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