OpenGL学习二十一：纹理坐标

在纹理贴图场景时，必须为每个顶点提供物体坐标和顶点坐标，经过变换之后，物体坐标决定了应该在屏幕上的那个地点渲染每个特定的顶点，纹理坐标决定了纹理图像中的那个纹理单元将分配给这个顶点
void glTexCoord{1,2,3,4}{sifd} (Type coords);

纹理的放大与缩小

1.原始大小
glTexCoord2f(0.0f, 0.0f); glVertex2f(-1.0f, -1.0f);
glTexCoord2f(1.0f, 0.0f); glVertex2f( 1.0f, -1.0f);
glTexCoord2f(1.0f, 1.0f); glVertex2f( 1.0f, 1.0f);
glTexCoord2f(0.0f, 1.0f); glVertex2f(-1.0f, 1.0f);

1.X轴重复（放大与缩小）
glTexCoord2f(0.0f, 0.0f); glVertex2f(-1.0f, -1.0f);
glTexCoord2f(n*1.0f, 0.0f); glVertex2f( 1.0f, -1.0f);
glTexCoord2f(n*1.0f, 1.0f); glVertex2f( 1.0f, 1.0f);
glTexCoord2f(0.0f, 1.0f); glVertex2f(-1.0f, 1.0f);

当n=2时 当n=0.5时

2.Y轴重复（放大与缩小）
glTexCoord2f(0.0f, 0.0f); glVertex2f(-1.0f, -1.0f);
glTexCoord2f(1.0f, 0.0f); glVertex2f( 1.0f, -1.0f);
glTexCoord2f(1.0f, n*1.0f); glVertex2f( 1.0f, 1.0f);
glTexCoord2f(0.0f, n*1.0f); glVertex2f(-1.0f, 1.0f);

当n=2时 当n=0.5时

3.纹理水平移动
glBegin(GL_QUADS);
glTexCoord2f(roll+0.0f, 0.0f); glVertex3f(-1.0f, -1.0f, 0.0f);
glTexCoord2f(roll+1.0f, 0.0f); glVertex3f( 1.0f, -1.0f, 0.0f);
glTexCoord2f(roll+1.0f,1.0f); glVertex3f( 1.0f, 1.0f, 0.0f);
glTexCoord2f(roll+0.0f,1.0f); glVertex3f(-1.0f, 1.0f, 0.0f);
glEnd()
其中roll决定纹理水平移动的幅度，roll应该在0.1之间

4.纹理上下移动
glBegin(GL_QUADS);
glTexCoord2f(0.0f, 0.0f+roll); glVertex3f(-1.0f, -1.0f, 0.0f);
glTexCoord2f(1.0f, 0.0f+roll); glVertex3f( 1.0f, -1.0f, 0.0f);
glTexCoord2f(1.0f,1.0f+roll); glVertex3f( 1.0f, 1.0f, 0.0f);
glTexCoord2f(0.0f,1.0f+roll); glVertex3f(-1.0f, 1.0f, 0.0f);
glEnd()
其中roll决定纹理上下移动的幅度，roll应该在0.1之间

纹理的重复与截取

当我们进行纹理放大时，纹理会以重复的形式进行平铺GL_REPEAT，但有时我们希望纹理坐标放大，可纹理并不进行重复的平铺，这就用到了截取GL_CLAMP

纹理重复：
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT)
下图左边为2*2纹理的重复，右边为1*1纹理

第一个矩形
glTexCoord2f(0.0, 0.0); glVertex3f(-2.0, -1.0, 0.0);
glTexCoord2f(0.0, 2.0); glVertex3f(-2.0, 1.0, 0.0);
glTexCoord2f(2.0, 2.0); glVertex3f(0.0, 1.0, 0.0);
glTexCoord2f(2.0, 0.0); glVertex3f(0.0, -1.0, 0.0);

第二个矩形

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(3, 1.0, -0);
glTexCoord2f(1.0, 0.0); glVertex3f(3, -1.0, -0);

纹理截取
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP)

第一个矩形

glTexCoord2f(0.0, 0.0); glVertex3f(-2.0, -1.0, 0.0);
glTexCoord2f(0.0, 2.0); glVertex3f(-2.0, 1.0, 0.0);
glTexCoord2f(2.0, 2.0); glVertex3f(0.0, 1.0, 0.0);
glTexCoord2f(2.0, 0.0); glVertex3f(0.0, -1.0, 0.0);

第二个矩形

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(3, 1.0, -0);
glTexCoord2f(1.0, 0.0); glVertex3f(3, -1.0, -0);

左边的图为2*2纹理放大，右边为1*1纹理放大（原始大小）

glTexParameter*（）函数的参数

参数(pname)			值(param)
GL_TEXTURE_WRAP_S 从左至右纹理环绕模式 GL_TEXTURE_WRAP_T 从下至上纹理环绕模式 GL_TEXTURE_WRAP_R 从里至外纹理环绕模式			GL_CLAMP：截取 GL_REPEAT：重复 GL_MIRRORED_REPEAT:镜像重复 GL_CLAMP_TO_EDGE:忽略边框截取 GL_CLAMP_TO_BORDER:代边框的截取
GL_TEXTURE_MAG_FILTER			GL_NEAREST或GL_LINEAR
GL_TEXTURE_MIN_FILTER			GL_NEAREST 速度快，效果差 GL_LINEAR  计算量大。效果好 GL_NEAREST_MIPMAP_NEAREST 速度快，效果差 GL_LINEAR_MIPMAP_NEAREST GL_NEAREST_MIPMAP_LINEAR GL_LINEAR_MIPMAP_LINEAR 计算量大。效果好
GL_TEXTURE_BORDER_COLOR
GL_TEXTURE_PRIORITY			(0，1)纹理优先级
GL_TEXTURE_BASE_LEVEL			浮点值
GL_TEXTURE_MAX_LEVEL			浮点值
GL_TEXTURE_MIN_LOD			浮点值
GL_TEXTURE_MAX_LEVEL			浮点值
GL_TEXTURE_LOD_BIAS
GL_TEXTURE_COMPARE_MODE 纹理比较模式			GL_COMPARE_R_TO_TEXTURE 深度比较
GL_DEPTH_TEXTURE_MODE			GL_RED:R GL_LUMINANCE:亮度 GL_INSENSITY GL_ALPHA:A
GL_TEXTURE_COMPARE_FUNC 纹理比较方式			GL_LEQUAL,GL_GEQUAL,GL_LESS,GL_GREATER,GL_EQUAL, GL_NOTEQUAL,GL_ALWAYS,GL_NEVER
GL_GENERATE_MIAMAP 自动生成多重细节层			GL_TRUE,GL_FALSE

纹理坐标DEMO

#include "header.h"


GLuint	texture[1];			
float rollx=0.0f;
float rolly=0.0f;
bool isX=false;
bool isY=false;
float xdouble=1.0f;
float ydouble=1.0f;


AUX_RGBImageRec *LoadBMP(char *Filename)				
{
	FILE *File=NULL;									

	if (!Filename)									
	{
		return NULL;								
	}

	File=fopen(Filename,"r");							

	if (File)										
	{
		fclose(File);									
		return auxDIBImageLoad(Filename);				
	}

	return NULL;										
}

int LoadGLTextures()									
{
	int Status=FALSE;									

	AUX_RGBImageRec *TextureImage[1];					

	memset(TextureImage,0,sizeof(void *)*1);           	

	
	if (TextureImage[0]=LoadBMP("Data/NeHe.bmp"))
	{
		Status=TRUE;									

		glGenTextures(1, &texture[0]);					

		// Typical Texture Generation Using Data From The Bitmap
		glBindTexture(GL_TEXTURE_2D, texture[0]);
		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, TextureImage[0]->sizeX, TextureImage[0]->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, TextureImage[0]->data);
	
	
		glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
		glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
	}

	if (TextureImage[0])									
	{
		if (TextureImage[0]->data)							
		{
			free(TextureImage[0]->data);					
		}

		free(TextureImage[0]);								
	}

	return Status;										
}

GLvoid ReSizeGLScene(GLsizei width, GLsizei height)		
{
	if (height==0)										
	{
		height=1;										
	}

	glViewport(0,0,width,height);						

	glMatrixMode(GL_PROJECTION);						
	glLoadIdentity();									

	// Calculate The Aspect Ratio Of The Window
	gluPerspective(45.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);

	glMatrixMode(GL_MODELVIEW);							
	glLoadIdentity();									
}

int InitGL(GLvoid)										
{
	if (!LoadGLTextures())						
	{
		return FALSE;									
	}

	glEnable(GL_TEXTURE_2D);							
	glShadeModel(GL_SMOOTH);							
	glClearColor(0.0f, 0.0f, 0.0f, 0.5f);
	glClearDepth(1.0f);									
	glEnable(GL_DEPTH_TEST);						
	
	glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);	
	return TRUE;										
}

void DrawGLScene(GLvoid)									
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);	
	glLoadIdentity();									
	glTranslatef(0.0f,0.0f,-5.0f);

	glBindTexture(GL_TEXTURE_2D, texture[0]);

	glBegin(GL_QUADS);
		// Front Face
		glTexCoord2f(0.0f+rollx, 0.0f+rolly); glVertex2f(-1.0f, -1.0f);
		glTexCoord2f(xdouble*1.0f+rollx, 0.0f+rolly); glVertex2f( 1.0f, -1.0f);
		glTexCoord2f(xdouble*1.0f+rollx,ydouble*1.0f+rolly); glVertex2f( 1.0f,  1.0f);
		glTexCoord2f(0.0f+rollx, ydouble*1.0f+rolly); glVertex2f(-1.0f,  1.0f);
	
	glEnd();

	glFlush();
}

void scroll()
{ 
	if(isX)
	{
		rollx+=0.002f;									
		if (rollx>1.0f)							
		{
			rollx-=1.0f;				
		}
	}
	if (isY)
	{
		rolly+=0.002f;									
		if (rolly>1.0f)							
		{
			rolly-=1.0f;				
		}
	}
	glutPostRedisplay();
}

void keyboard(unsigned char key,int x,int y)
{
	switch (key)
	{
	case 'x':
		isX=true;
		isY=false;
	glutIdleFunc(scroll);
		
		break;
	case 'y':
		isY=true;
		isX=false;

	glutIdleFunc(scroll);
		break;
	case 'X':
	 xdouble=xdouble+0.5f;

		break;
	case 'Y':
		isY=true;
	 ydouble=ydouble+0.5f;
		break;
	}


}
int main(int argc, char** argv)
{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
	glutInitWindowSize(640,480);
	glutCreateWindow("纹理坐标");
	glutReshapeFunc(ReSizeGLScene);
	glutDisplayFunc(DrawGLScene);
	glutKeyboardFunc(keyboard);
	InitGL();
	glutMainLoop();
	return 0;
}

纹理截取DEMO

#include "header.h"

#define	checkImageWidth 64
#define	checkImageHeight 64
static GLubyte checkImage[checkImageHeight][checkImageWidth][4];
static GLubyte otherImage[checkImageHeight][checkImageWidth][4];

static GLuint texName[2];

void makeCheckImages(void)
{
   int i, j, c;
    
   for (i = 0; i < checkImageHeight; i++) {
      for (j = 0; j < checkImageWidth; j++) {
         c = ((((i&0x8)==0)^((j&0x8))==0))*255;
         checkImage[i][j][0] = (GLubyte) c;
         checkImage[i][j][1] = (GLubyte) c;
         checkImage[i][j][2] = (GLubyte) c;
         checkImage[i][j][3] = (GLubyte) 255;
         c = ((((i&0x10)==0)^((j&0x10))==0))*255;
         otherImage[i][j][0] = (GLubyte) c;
         otherImage[i][j][1] = (GLubyte) 0;
         otherImage[i][j][2] = (GLubyte) 0;
         otherImage[i][j][3] = (GLubyte) 255;
      }
   }
}

void init(void)
{    
   glClearColor (0.0, 0.0, 0.0, 0.0);
   glShadeModel(GL_FLAT);
   glEnable(GL_DEPTH_TEST);

   makeCheckImages();
   glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

   glGenTextures(2, texName);
   glBindTexture(GL_TEXTURE_2D, texName[0]);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, 
                   GL_NEAREST);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, 
                   GL_NEAREST);
   glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, checkImageWidth,
                checkImageHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE,
                checkImage);

   glBindTexture(GL_TEXTURE_2D, texName[1]);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
   glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
   glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, checkImageWidth, 
                checkImageHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, 
                otherImage);
   glEnable(GL_TEXTURE_2D);
}

void display(void)
{
   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
   glBindTexture(GL_TEXTURE_2D, texName[0]);
   glBegin(GL_QUADS);
   glTexCoord2f(0.0, 0.0); glVertex3f(-2.0, -1.0, 0.0);
   glTexCoord2f(0.0, 4.0); glVertex3f(-2.0, 1.0, 0.0);
   glTexCoord2f(4.0, 4.0); glVertex3f(0.0, 1.0, 0.0);
   glTexCoord2f(4.0, 0.0); glVertex3f(0.0, -1.0, 0.0);
   glEnd();

   glBindTexture(GL_TEXTURE_2D, texName[1]);
   glBegin(GL_QUADS);
   glTexCoord2f(0.0, 0.0); glVertex3f(2.5, -1.0, 0.0);
   glTexCoord2f(0.0, 1.0); glVertex3f(2.5, 1.0, 0.0);
   glTexCoord2f(1.0, 1.0); glVertex3f(0.5, 1.0, -0);
   glTexCoord2f(1.0, 0.0); glVertex3f(0.5, -1.0, -0);
   glEnd();
   glFlush();
}

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, -5);
}

void keyboard(unsigned char key, int x, int y)
{
   switch (key) {
      case 27:
         exit(0);
         break;
   }
}

int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
   glutInitWindowSize(250, 250);
   glutInitWindowPosition(100, 100);
   glutCreateWindow("纹理截取");
   init();
   glutReshapeFunc(reshape);
   glutDisplayFunc(display);
   glutKeyboardFunc (keyboard);
   glutMainLoop();
   return 0; 
}