OpenGL学习二十：纹理函数

通过纹理函数（glTexEnv*()）可以把纹理图像的颜色与物体表面的原先的颜色进行混合

当我们指定纹理数据时，其第三个参数internalformat可以简化为6种格式

基本内部格式	所提取的源颜色（R,G,B,A）
GL_ALPHA	(0，0，0，A)
GL_LUMINANCE	(L,L,L,1)
GL_LUMINANCE_ALPHA	(L,L,L,A)
GL_INTENSITY	(I,I,I,I)
GL_RGB	(R,G,B,1)
GL_RGBA	(R,G,B,A)

void glTexEnvf (GLenum target, GLenum pname, GLfloat param);
如果target是GL_TEXTURE_FILTER_CONTROL pname必须是GL_TEXTURE_LOD_BIAS，param是个浮点数表示mipmap细节层的偏移量

target是GL_TEXTURE_ENV情况下

GL_TEXTURE_ENV_MODE	GL_DECAL,GL_REPLACE,GL_BLEND,GL_MODULATE,GL_ADD或GL_COMBINE
GL_TEXTURE_ENV_COLOR	包含4个浮点值的RGBA数组

GL_REPLACE，GL_MODULATE，GL_DECAL纹理函数

s表示纹理的源颜色 f表示新的片段值 c表示用GL_TEXURE_ENV_COLOR分配的颜色值 如果没有下标，表示最终计算所得的颜色

	GL_REPLACE	GL_MODULATE	GL_DECAL
GL_ALPHA	C=Cf A=As	C=Cf A=AsAf	未定义
GL_LUMINANCE	C=Cs A=Af	C=CfCs A=Af	未定义
GL_LUMINANCE_ALPHA	C=Cs A=As	C=CfCs A=AsAf	未定义
GL_INTENSITY	C=Cf A=Cs	C=CfCs A=AsAf	未定义
GL_RGB	C=Cs A=Af	C=CfCs A=Af	C=Cs A=Af
GL_RGBA	C=Cs A=As	C=CfCs A=AsAf	C=Cf(1-As)+CsAs A=Af

GL_BLEND,GL_ADD 纹理函数

	GL_BLEND	GL_ADD
GL_ALPHA	C=Cf A=AfAs	C=Cf A=AsAf
GL_LUMINANCE	C=Cf(1-Cs)+CcCs A=Af	C=Cf+Cs A=Af
GL_LUMINANCE_ALPHA	C=Cf(2-Cs)+CcCs A=AfAs	C=Cf+Cs A=AsAf
GL_INTENSITY	C=Cf(3-Cs)+CcCs A=Af(1-As)+AcAs	C=Cf+Cs A=Af+As
GL_RGB	C=Cf(4-Cs)+CcCs A=Af	C=Cf+Cs A=Af
GL_RGBA	C=Cf(5-Cs)+CcCs A=AfAs	C=Cf+Cs A=AfAs

#include "header.h"

#define	checkImageWidth 16
#define	checkImageHeight 16
GLubyte checkImage[checkImageWidth][checkImageHeight][4];
int texName;

enum InternalFormat
{
	alpha='a',
	luminance='b',
	luminance_alpha='c',
    intensity='d',
	rgb,
	rgba
};
enum Env
{
	ADD='A',
	BLEND='B',
	REPLACE='R',
	MODULATE='M',
	DECAL='D'
};
void makeImage()
{
	int i,j;
	for ( i=0;i<checkImageWidth;i++)
	{
		for (j = 0; j < checkImageHeight; j++)
		{
			if(j%2==0)
			{
				checkImage[i][j][0]=255;
				checkImage[i][j][1]=0;
				checkImage[i][j][2]=0;
				checkImage[i][j][3]=100;

			}else
			{
				checkImage[i][j][0]=0;
				checkImage[i][j][1]=255;
				checkImage[i][j][2]=0;
				checkImage[i][j][3]=200;
			}

		}
	}
}


void display(void)
{
	glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
	glLoadIdentity();
	
	glBlendFunc(GL_SRC_ALPHA,GL_ZERO);

	glBindTexture(GL_TEXTURE_2D,texName);
	glEnable(GL_BLEND);
	glBegin(GL_QUADS);

	glTexCoord2i(0,0); glVertex2i(-100,-100);
	glTexCoord2i(4,0); glVertex2i(100,-100);
	glTexCoord2i(4,4); glVertex2i(100,100);
	glTexCoord2i(0,4); glVertex2i(-100,100);

	glEnd();
	glFlush();
}


void init()
{
	
	GLfloat  white[] = { 1.0, 1.0, 1.0, 1.0 };
	glClearColor(0.5,0.5,0.5,1);
	glClearDepth(1.0);
	makeImage();

	glEnable(GL_DEPTH_TEST);					
	glDepthFunc(GL_LEQUAL);	
	glShadeModel(GL_SMOOTH);


	glGenTextures(1,&texName);                                                                                                                                                                                                                                                                                              
	glBindTexture(GL_TEXTURE_2D,texName);
	glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	//glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAP_S,GL_REPEAT);
	//glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAP_T,GL_REPEAT);
	glTexGeni(GL_S,GL_TEXTURE_GEN_MODE,GL_OBJECT_LINEAR);
	glTexGeni(GL_T,GL_TEXTURE_GEN_MODE,GL_OBJECT_LINEAR);


	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 16, 16, 
		0, GL_RGBA, GL_UNSIGNED_BYTE, checkImage);
		glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
	glEnable(GL_TEXTURE_2D);
}
void reshape(int w, int h)
{
	glViewport(0, 0, (GLsizei) w, (GLsizei) h);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();

	glOrtho(-200,600,-300,300,-100,100);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
}

void keyboard(unsigned char key,int x,int y)
{
	switch(key)
	{
	case alpha:
	
		glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, 16, 16, 
			0, GL_RGBA, GL_UNSIGNED_BYTE, checkImage);
		glBlendFunc(GL_SRC_ALPHA,GL_ZERO);
	
		glBindTexture(GL_TEXTURE_2D,texName);
		glEnable(GL_BLEND);
		glEnable(GL_TEXTURE_2D);
		break;
	
	case luminance:

		glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, 16, 16, 
			0, GL_RGBA, GL_UNSIGNED_BYTE, checkImage);
	
		glBindTexture(GL_TEXTURE_2D,texName);
		glEnable(GL_TEXTURE_2D);
		glDisable(GL_BLEND);
		break;
	case luminance_alpha:

		glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE_ALPHA, 16, 16, 
			0, GL_RGBA, GL_UNSIGNED_BYTE, checkImage);

		glBlendFunc(GL_SRC_ALPHA,GL_ZERO);

		glBindTexture(GL_TEXTURE_2D,texName);
		glEnable(GL_BLEND);
		glEnable(GL_TEXTURE_2D);
	
		break;
	case rgba:

		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 16, 16, 
			0, GL_RGBA, GL_UNSIGNED_BYTE, checkImage);

		glBlendFunc(GL_SRC_ALPHA,GL_ZERO);

		glBindTexture(GL_TEXTURE_2D,texName);
		glEnable(GL_BLEND);
		glEnable(GL_TEXTURE_2D);

		break;
	case rgb:

		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 16, 16, 
			0, GL_RGBA, GL_UNSIGNED_BYTE, checkImage);

		glBlendFunc(GL_SRC_ALPHA,GL_ZERO);

		glBindTexture(GL_TEXTURE_2D,texName);
		glEnable(GL_BLEND);
		glEnable(GL_TEXTURE_2D);

		break;

	case ADD:
	
	glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_ADD);


	break;
	case MODULATE:

		//glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_ADD);

		glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
		break;
	case DECAL:
		glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
		break;
	case BLEND:
		glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_BLEND);
		break;
	}	


	glutPostRedisplay();
}

void mouse(int button,int state,int x,int y)
{ 

}

int main(int argc,char **argv)
{
	glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_SINGLE|GLUT_RGBA|GLUT_DEPTH);
	glutInitWindowSize(800,600);
	glutInitWindowPosition(100,100);
	glutCreateWindow("纹理函数");
	glewInit();
	init();
	glutDisplayFunc(display);
	glutKeyboardFunc(keyboard);
	glutReshapeFunc(reshape);
	glutMouseFunc(mouse);
	glutMainLoop();
}