opengl中TGA图像加载技术-创新互联

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

注：前面的标记绿色的部分（共12字节）表示对于所有的非压缩TGA格式图像值都是相同的！所以通常用来在读取数据时鉴别是否为TGA图像。

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：

[cpp] view plain?

1. #ifndef TGATEXTURE_H

2. #define TGATEXTURE_H

4. #include 

5. #include 

7. using namespace std;

9. //纹理结构体定义

10. typedef struct

11. {

12.     GLubyte *p_w_picpathData;//图像数据

13.     GLuint bpp;//像素深度

14.     GLuint width;//图像宽度

15.     GLuint height;//图像高度

16.     GLuint texID;//对应的纹理ID

17. }TextureImage;

19. //加载TGA图像，生成纹理

20. bool LoadTGA(TextureImage *texture,char *fileName);

22. #endif

TGATexture.cpp则包含加载TGA图像生成纹理的函数具体实现：

[cpp] view plain?

1. #include "TGATexture.h"

3. //加载TGA图像（无压缩格式），生成纹理

4. bool LoadTGA(TextureImage *texture, char *filename)         // Loads A TGA File Into Memory

5. {

6.     GLubyte     TGAheader[12]={0,0,2,0,0,0,0,0,0,0,0,0};    // Uncompressed TGA Header

7.     GLubyte     TGAcompare[12];                             // Used To Compare TGA Header

8.     GLubyte     header[6];                                  // First 6 Useful Bytes From The Header

9.     GLuint      bytesPerPixel;                              // Holds Number Of Bytes Per Pixel Used In The TGA File

10.     GLuint      p_w_picpathSize;                                  // Used To Store The Image Size When Setting Aside Ram

11.     GLuint      temp;                                       // Temporary Variable

12.     GLuint      type=GL_RGBA;                               // Set The Default GL Mode To RBGA (32 BPP)

14.     FILE *file = fopen(filename, "rb");                     // Open The TGA File

16.     if( file==NULL ||                                       // Does File Even Exist?

17.         fread(TGAcompare,1,sizeof(TGAcompare),file)!=sizeof(TGAcompare) ||  // Are There 12 Bytes To Read?

18.         memcmp(TGAheader,TGAcompare,sizeof(TGAheader))!=0               ||  // Does The Header Match What We Want?

19.         fread(header,1,sizeof(header),file)!=sizeof(header))                // If So Read Next 6 Header Bytes

20.     {

21.         if (file == NULL)                                   // Did The File Even Exist? *Added Jim Strong*

22.             return false;                                   // Return False

23.         else

24.         {

25.             fclose(file);                                   // If Anything Failed, Close The File

26.             return false;                                   // Return False

27.         }

28.     }

30.     texture->width  = header[1] * 256 + header[0];           // Determine The TGA Width  (highbyte*256+lowbyte)

31.     texture->height = header[3] * 256 + header[2];           // Determine The TGA Height (highbyte*256+lowbyte)

33.     //OpenGL中纹理只能使用24位或者32位的TGA图像

34.     if( texture->width   <=0  ||                              // Is The Width Less Than Or Equal To Zero

35.         texture->height  <=0  ||                              // Is The Height Less Than Or Equal To Zero

36.         (header[4]!=24 && header[4]!=32))                   // Is The TGA 24 or 32 Bit?

37.     {

38.         fclose(file);                                       // If Anything Failed, Close The File

39.         return false;                                       // Return False

40.     }

42.     texture->bpp = header[4];                            // Grab The TGA's Bits Per Pixel (24 or 32)

43.     bytesPerPixel   = texture->bpp/8;                        // Divide By 8 To Get The Bytes Per Pixel

44.     p_w_picpathSize       = texture->width*texture->height*bytesPerPixel;   // Calculate The Memory Required For The TGA Data

46.     texture->p_w_picpathData=(GLubyte *)malloc(p_w_picpathSize);     // Reserve Memory To Hold The TGA Data

48.     if( texture->p_w_picpathData==NULL ||                          // Does The Storage Memory Exist?

49.         fread(texture->p_w_picpathData, 1, p_w_picpathSize, file)!=p_w_picpathSize)    // Does The Image Size Match The Memory Reserved?

50.     {

51.         if(texture->p_w_picpathData!=NULL)                     // Was Image Data Loaded

52.             free(texture->p_w_picpathData);                        // If So, Release The Image Data

54.         fclose(file);                                       // Close The File

55.         return false;                                       // Return False

56.     }

58.     //RGB数据格式转换，便于在OpenGL中使用

59.     for(GLuint i=0; i

60.     {                                                       // Swaps The 1st And 3rd Bytes ('R'ed and 'B'lue)

61.         temp=texture->p_w_picpathData[i];                          // Temporarily Store The Value At Image Data 'i'

62.         texture->p_w_picpathData[i] = texture->p_w_picpathData[i + 2];    // Set The 1st Byte To The Value Of The 3rd Byte

63.         texture->p_w_picpathData[i + 2] = temp;                    // Set The 3rd Byte To The Value In 'temp' (1st Byte Value)

64.     }

66.     fclose (file);                                          // Close The File

68.     // Build A Texture From The Data

69.     glGenTextures(1, &texture[0].texID);                    // Generate OpenGL texture IDs

71.     glBindTexture(GL_TEXTURE_2D, texture[0].texID);         // Bind Our Texture

72.     glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);   // Linear Filtered

73.     glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);   // Linear Filtered

75.     if (texture[0].bpp==24)                                 // Was The TGA 24 Bits

76.     {

77.         type=GL_RGB;                                        // If So Set The 'type' To GL_RGB

78.     }

80.     glTexImage2D(GL_TEXTURE_2D, 0, type, texture[0].width, texture[0].height, 0, type, GL_UNSIGNED_BYTE, texture[0].p_w_picpathData);

82.     return true;                                            // Texture Building Went Ok, Return True

83. }

main.cpp主程序：

[cpp] view plain?

1. #include "TGATexture.h"

3. TextureImage texture[1];

5. GLfloat xRot,yRot,zRot;//control cube's rotation

7. int init()

8. {

9.     if(!LoadTGA(&texture[0],"GSK1.tga"))

10.         return GL_FALSE;

11.     glEnable(GL_TEXTURE_2D);

12.     glShadeModel(GL_SMOOTH);

13.     glClearColor(0.0f,0.0f,0.0f,0.5f);

14.     glClearDepth(1.0f);

15.     glEnable(GL_DEPTH_TEST);

16.     glDepthFunc(GL_LEQUAL);

17.     glHint(GL_PERSPECTIVE_CORRECTION_HINT,GL_NICEST);

18.     return GL_TRUE;

19. }

21. void display()

22. {

23.     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

24.     glLoadIdentity();

25.     glTranslatef(0.0f,0.0f,-5.0f);

26.     glRotatef(xRot,1.0f,0.0f,0.0f);

27.     glRotatef(yRot,0.0f,1.0f,0.0f);

28.     glRotatef(zRot,0.0f,0.0f,1.0f);

30.     glBindTexture(GL_TEXTURE_2D,texture[0].texID);

32.     glBegin(GL_QUADS);

33.     // Front Face

34.     // Bottom Left Of The Texture and Quad

35.     glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f);

36.     // Bottom Right Of The Texture and Quad

37.     glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f);

38.     // Top Right Of The Texture and Quad

39.     glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f,  1.0f);

40.     // Top Left Of The Texture and Quad

41.     glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f,  1.0f);

42.     glEnd();

44.     glBindTexture(GL_TEXTURE_2D,texture[0].texID);

45.     glBegin(GL_QUADS);

46.     // Back Face

47.     // Bottom Right Of The Texture and Quad

48.     glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f, -1.0f);

49.     // Top Right Of The Texture and Quad

50.     glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f,  1.0f, -1.0f);

51.     // Top Left Of The Texture and Quad

52.     glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f,  1.0f, -1.0f);

53.     // Bottom Left Of The Texture and Quad

54.     glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f, -1.0f);

55.     glEnd();

57.     glBindTexture(GL_TEXTURE_2D,texture[0].texID);

58.     glBegin(GL_QUADS);

59.     // Top Face

60.     // Top Left Of The Texture and Quad

61.     glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f, -1.0f);

62.     // Bottom Left Of The Texture and Quad

63.     glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f,  1.0f,  1.0f);

64.     // Bottom Right Of The Texture and Quad

65.     glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f,  1.0f,  1.0f);

66.     // Top Right Of The Texture and Quad

67.     glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f, -1.0f);

68.     glEnd();

70.     glBindTexture(GL_TEXTURE_2D,texture[0].texID);

71.     glBegin(GL_QUADS);

72.     // Bottom Face

73.     // Top Right Of The Texture and Quad

74.     glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, -1.0f, -1.0f);

75.     // Top Left Of The Texture and Quad

76.     glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, -1.0f, -1.0f);

77.     // Bottom Left Of The Texture and Quad

78.     glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f);

79.     // Bottom Right Of The Texture and Quad

80.     glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f);

81.     glEnd();

83.     glBindTexture(GL_TEXTURE_2D,texture[0].texID);

84.     glBegin(GL_QUADS);

85.     // Right face

86.     // Bottom Right Of The Texture and Quad

87.     glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f, -1.0f);

88.     // Top Right Of The Texture and Quad

89.     glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f, -1.0f);

90.     // Top Left Of The Texture and Quad

91.     glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f,  1.0f,  1.0f);

92.     // Bottom Left Of The Texture and Quad

93.     glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f);

94.     glEnd();

96.     glBindTexture(GL_TEXTURE_2D,texture[0].texID);

97.     glBegin(GL_QUADS);

98.     // Left Face

99.     // Bottom Left Of The Texture and Quad

100.     glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f, -1.0f);

101.     // Bottom Right Of The Texture and Quad

102.     glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f);

103.     // Top Right Of The Texture and Quad

104.     glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f,  1.0f,  1.0f);

105.     // Top Left Of The Texture and Quad

106.     glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f, -1.0f);

107.     glEnd();

109.     glutSwapBuffers();

110. }

112. void reshape(int w,int h)

113. {

114.     if (0 == h)

115.         h = 1;

117.     glViewport(0,0,(GLsizei)w,(GLsizei)h);

118.     glMatrixMode(GL_PROJECTION);

119.     glLoadIdentity();

120.     gluPerspective(60.0f,(GLfloat)w / (GLfloat)h,1,100);

121.     glMatrixMode(GL_MODELVIEW);

122.     glLoadIdentity();

123. }

125. void keyboard(unsigned char key,int x,int y)

126. {

127.     switch(key){

128.         case 'x':

129.             xRot += 1.0f;

130.             glutPostRedisplay();

131.             break;

132.         case 'y':

133.             yRot += 1.0f;

134.             glutPostRedisplay();

135.             break;

136.         case 'z':

137.             zRot += 1.0f;

138.             glutPostRedisplay();

139.             break;

140.         default:

141.             break;

142.     }

143. }

145. int main(int argc,char** argv)

146. {

147.     glutInit(&argc,argv);

148.     glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);

149.     glutInitWindowSize(400,400);

150.     glutInitWindowPosition(100,100);

151.     glutCreateWindow("Texture Map");

152.     init();

153.     glutDisplayFunc(display);

154.     glutReshapeFunc(reshape);

155.     glutKeyboardFunc(keyboard);

156.     glutMainLoop();

157.     return 0;

158. }

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