- 理论基础
纹理贴图：通俗地讲就是可以把我们读取的纹理加载到图元表面的一种技术，这样大大的提高了图像的表现质量。
- 实例代码
//读取tga格式图片
/*tga图片头信息结构*/
#pragma pack(1)//结构体字节对齐
typedef struct
{
GLbyte identsize; // Size of ID field that follows header (0)
GLbyte colorMapType; // 0 = None, 1 = paletted
GLbyte imageType; // 0 = none, 1 = indexed, 2 = rgb, 3 = grey, +8=rle
unsigned short colorMapStart; // First colour map entry
unsigned short colorMapLength; // Number of colors
unsigned char colorMapBits; // bits per palette entry
unsigned short xstart; // image x origin
unsigned short ystart; // image y origin
unsigned short width; // width in pixels
unsigned short height; // height in pixels
GLbyte bits; // bits per pixel (8 16, 24, 32)
GLbyte descriptor; // image descriptor
} TGAHEADER;
#pragma pack(8)
/*tga图片读取*/
GLbyte *gltReadTGABits(const char *szFileName, GLint *iWidth, GLint *iHeight, GLint *iComponents, GLenum *eFormat)
{
FILE *pFile; // File pointer
TGAHEADER tgaHeader; // TGA file header
unsigned long lImageSize; // Size in bytes of image
short sDepth; // Pixel depth;
GLbyte *pBits = NULL; // Pointer to bits
// Default/Failed values
*iWidth = 0;
*iHeight = 0;
*eFormat = GL_RGB;
*iComponents = GL_RGB;
// Attempt to open the file
pFile = fopen(szFileName, "rb");
if(pFile == NULL)
return NULL;
// Read in header (binary)
fread(&tgaHeader, 18/* sizeof(TGAHEADER)*/, 1, pFile);
// Do byte swap for big vs little endian
#ifdef __APPLE__
LITTLE_ENDIAN_WORD(&tgaHeader.colorMapStart);
LITTLE_ENDIAN_WORD(&tgaHeader.colorMapLength);
LITTLE_ENDIAN_WORD(&tgaHeader.xstart);
LITTLE_ENDIAN_WORD(&tgaHeader.ystart);
LITTLE_ENDIAN_WORD(&tgaHeader.width);
LITTLE_ENDIAN_WORD(&tgaHeader.height);
#endif
// Get width, height, and depth of texture
*iWidth = tgaHeader.width;
*iHeight = tgaHeader.height;
sDepth = tgaHeader.bits / 8;
// Put some validity checks here. Very simply, I only understand
// or care about 8, 24, or 32 bit targa's.
if(tgaHeader.bits != 8 && tgaHeader.bits != 24 && tgaHeader.bits != 32)
return NULL;
// Calculate size of image buffer
lImageSize = tgaHeader.width * tgaHeader.height * sDepth;
// Allocate memory and check for success
pBits = (GLbyte*)malloc(lImageSize * sizeof(GLbyte));
if(pBits == NULL)
return NULL;
// Read in the bits
// Check for read error. This should catch RLE or other
// weird formats that I don't want to recognize
if(fread(pBits, lImageSize, 1, pFile) != 1)
{
free(pBits);
return NULL;
}
// Set OpenGL format expected
switch(sDepth)
{
#ifndef OPENGL_ES
case 3: // Most likely case
*eFormat = GL_BGR;
*iComponents = GL_RGB;
break;
#endif
case 4:
*eFormat = GL_BGRA;
*iComponents = GL_RGBA;
break;
case 1:
*eFormat = GL_LUMINANCE;
*iComponents = GL_LUMINANCE;
break;
default: // RGB
// If on the iPhone, TGA's are BGR, and the iPhone does not
// support BGR without alpha, but it does support RGB,
// so a simple swizzle of the red and blue bytes will suffice.
// For faster iPhone loads however, save your TGA's with an Alpha!
#ifdef OPENGL_ES
for(int i = 0; i < lImageSize; i+=3)
{
GLbyte temp = pBits[i];
pBits[i] = pBits[i+2];
pBits[i+2] = temp;
}
#endif
break;
}
// Done with File
fclose(pFile);
// Return pointer to image data
return pBits;
}//纹理贴图使用一般步骤：1，初始化：创建纹理对象，设置纹理过滤方式，为当前创建的纹理对象指定纹理 2，使用：激活，指定当前活动纹理并为顶点指定纹理坐标//
#include "GLTools.h"
#ifdef __APPLE__
#include <glut/glut.h>
#else
#define FREEGLUT_STATIC
#include <GL/glut.h>
#endif
GLuint texName;
GLbyte *pBits;
int nWidth, nHeight, nComponents;
GLenum eFormat;
void init(void)
{
glClearColor (0.0, 0.0, 0.0, 0.0);
glShadeModel(GL_FLAT);
glEnable(GL_DEPTH_TEST);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);//设置像素存储模式
//读取tga图像数据
pBits =
gltReadTGABits("/Users/app05/Desktop/opengl/stone.tga", &nWidth, &nHeight, &nComponents, &eFormat);
if(pBits == NULL)
printf("tga load failed");
glGenTextures(1, &texName);//生成1个未使用的纹理对象标志
glBindTexture(GL_TEXTURE_2D, texName);//创建纹理对象(存储纹理数据的容器)
/*设置纹理过滤方式*/
//指当纹理坐标的第一维坐标值大于1.0或小于0.0时，应该如何处理。
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
//指当纹理坐标的第二维坐标值大于1.0或小于0.0时，应该如何处理。
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
//纹理图象被使用到一个小于它的形状上，应该如何处理。
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
/*设置如果纹理图象被使用到一个大于它的形状上时，像素如何填充，可选择的设置有GL_NEAREST和GL_LINEAR，前者表示“使用纹理中坐标最接近的一个像素的颜色作为需要绘制的像素颜色”，后者表示“使用纹理中坐标最接近的若干个颜色，通过加权平均算法得到需要绘制的像素颜色",后者效果要比前者好。*/
glTexParameteri(GL_TEXTURE_2D,
GL_TEXTURE_MAG_FILTER, GL_LINEAR);
//指定二维纹理
glTexImage2D(GL_TEXTURE_2D, 0, nComponents, nWidth, nHeight, 0, eFormat, GL_UNSIGNED_BYTE, pBits);
free(pBits);
}
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable(GL_TEXTURE_2D);//激活二维纹理贴图
//设置纹理贴图方式(直接覆盖原来颜色或与原来颜色混合)
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);//直接使用纹理覆盖模式
glBindTexture(GL_TEXTURE_2D, texName);//指定当前使用的纹理(第一次使用和第二次使用含义不同)
//为每个顶点指定纹理坐标，类似指定法线一样glNormal()
glBegin(GL_QUADS);
glTexCoord2f(0.0, 0.0); glVertex3f(-2.0, -1.0, 0.0);
glTexCoord2f(0.0, 1.0); glVertex3f(-2.0, 1.0, 0.0);
glTexCoord2f(1.0, 1.0); glVertex3f(0.0, 1.0, 0.0);
glTexCoord2f(1.0, 0.0); glVertex3f(0.0, -1.0, 0.0);
glTexCoord2f(0.0, 0.0); glVertex3f(1.0, -1.0, 0.0);
glTexCoord2f(0.0, 1.0); glVertex3f(1.0, 1.0, 0.0);
glTexCoord2f(1.0, 1.0); glVertex3f(2.41421, 1.0, -1.41421);
glTexCoord2f(1.0, 0.0); glVertex3f(2.41421, -1.0, -1.41421);
glEnd();
glFlush();
glDisable(GL_TEXTURE_2D);//关闭二维纹理贴图
}
void reshape(int w, int h)
{
glViewport(0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60.0, (GLfloat) w/(GLfloat) h, 1.0, 30.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0, 0.0, -3.6);
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(250, 250);
glutInitWindowPosition(100, 100);
glutCreateWindow(argv[0]);
init();
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutMainLoop();
return 0;
}