OpenGL学习二十八：蒙版

(本节对应分析NEHE教程第20课)

 

有时我们希望上层的图片的某些区域能投出下层的某些区域。当然我们可以通过关

键色进行处理，但是蒙版技术一样可以达到这样的效果，通过以下图片达到蒙版的效果

 

本节包含2个技术点
1.如何让纹理移动，放大（不是图像位置移动，是纹理移动）（前面以及介绍过了）
2.蒙版的设计
蒙版设计简单的说是通过控制Alpha来让白色的部分透，黑色的部分不透

 

蒙版的设计
1.第一张图与第二张图进行混合（1下2上），期望达到的效果是2图黑色部分不透，白色部分透到1图
分析：R新=Rs+Rd; G新=Gs+Gd; B新=Bs+Bd;其实S为图2，D为图1
期望效果：图2黑色区域：R新=Rd；G新=Gd; B新=Bd;
          图2白色区域：R新=Rs；G新=Gs; B新=Bs;
因此glBlendFunc(GL_DST_COLOR,GL_ZERO);方式进行混合的时候满足要求

2.第三张图与前两张混合，期望达到的效果是图3黑色区域透，非黑区域不透（S为图3，D为上一步混合图）
期望效果：图3黑色区域：R新=Rd；G新=Gd; B新=Bd;
         图3非黑色区域：R新=Rs；G新=Gs; B新=Bs;
因此 glBlendFunc(GL_ONE, GL_ONE) ;方式进行混合的时候满足要求
总结，蒙版技术看似2个图的混合，是指为3个图的混合而成，
我们期望达到的效果是图3黑色区域透出图1部分，非黑色部分不透。解决办法就是增加掩图（图2），掩图白色区域对于图3黑色区域，黑色其余对应图3非黑色区域

#include "header.h"

bool	masking=TRUE;		
bool	scene;				

GLuint	texture[5];			
GLuint	loop;				

GLfloat	roll;			


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[5];              
        memset(TextureImage,0,sizeof(void *)*5);        

        if ((TextureImage[0]=LoadBMP("Data/logo.bmp")) &&	
			(TextureImage[1]=LoadBMP("Data/mask1.bmp")) &&	
			(TextureImage[2]=LoadBMP("Data/image1.bmp")) &&	
			(TextureImage[3]=LoadBMP("Data/mask2.bmp")) &&	
			(TextureImage[4]=LoadBMP("Data/image2.bmp")))	
        {
                Status=TRUE;                            
                glGenTextures(5, &texture[0]);         

				for (loop=0; loop<5; loop++)			
				{
	                glBindTexture(GL_TEXTURE_2D, texture[loop]);
			        glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
				    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
					glTexImage2D(GL_TEXTURE_2D, 0, 3, TextureImage[loop]->sizeX, TextureImage[loop]->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, TextureImage[loop]->data);
				}
        }
		for (loop=0; loop<5; loop++)						
		{
	        if (TextureImage[loop])						
		    {
			        if (TextureImage[loop]->data)			
				    {
					        free(TextureImage[loop]->data);	
					}
					free(TextureImage[loop]);				
			}
		}
        return Status;                                
}

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

	glViewport(0,0,width,height);					
	glMatrixMode(GL_PROJECTION);						
	glLoadIdentity();								
	gluPerspective(45.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);	
	glMatrixMode(GL_MODELVIEW);							
	glLoadIdentity();								
}

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

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

void DrawGLScene(void)									
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	glLoadIdentity();									
	glTranslatef(0.0f,0.0f,-2.0f);						

	glBindTexture(GL_TEXTURE_2D, texture[0]);			
	glBegin(GL_QUADS);									
		glTexCoord2f(0.0f, -roll+0.0f); glVertex3f(-1.1f, -1.1f,  0.0f);	
		glTexCoord2f(3.0f, -roll+0.0f); glVertex3f( 1.1f, -1.1f,  0.0f);	
		glTexCoord2f(3.0f, -roll+3.0f); glVertex3f( 1.1f,  1.1f,  0.0f);	
		glTexCoord2f(0.0f, -roll+3.0f); glVertex3f(-1.1f,  1.1f,  0.0f);	
	glEnd();											

	glEnable(GL_BLEND);									
	glDisable(GL_DEPTH_TEST);						

	if (masking)									
	{
		glBlendFunc(GL_DST_COLOR,GL_ZERO);				
	}

	if (scene)									
	{
		glTranslatef(0.0f,0.0f,-1.0f);					
		glRotatef(roll*360,0.0f,0.0f,1.0f);				
		if (masking)									
		{
			glBindTexture(GL_TEXTURE_2D, texture[3]);	
			glBegin(GL_QUADS);							
				glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.1f, -1.1f,  0.0f);	
				glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.1f, -1.1f,  0.0f);	
				glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.1f,  1.1f,  0.0f);	
				glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.1f,  1.1f,  0.0f);	
			glEnd();									
		}

		glBlendFunc(GL_ONE, GL_ONE);					
		glBindTexture(GL_TEXTURE_2D, texture[4]);		
		glBegin(GL_QUADS);								
			glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.1f, -1.1f,  0.0f);	
			glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.1f, -1.1f,  0.0f);	
			glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.1f,  1.1f,  0.0f);	
			glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.1f,  1.1f,  0.0f);	
		glEnd();										
	}
	else												
	{
		if (masking)								
		{
			glBindTexture(GL_TEXTURE_2D, texture[1]);	
			glBegin(GL_QUADS);						
				glTexCoord2f(roll+0.0f, 0.0f); glVertex3f(-1.1f, -1.1f,  0.0f);	
				glTexCoord2f(roll+4.0f, 0.0f); glVertex3f( 1.1f, -1.1f,  0.0f);	
				glTexCoord2f(roll+4.0f, 4.0f); glVertex3f( 1.1f,  1.1f,  0.0f);	
				glTexCoord2f(roll+0.0f, 4.0f); glVertex3f(-1.1f,  1.1f,  0.0f);	
			glEnd();									
		}

		glBlendFunc(GL_ONE, GL_ONE);					
		glBindTexture(GL_TEXTURE_2D, texture[2]);		
		glBegin(GL_QUADS);								
			glTexCoord2f(roll+0.0f, 0.0f); glVertex3f(-1.1f, -1.1f,  0.0f);
			glTexCoord2f(roll+4.0f, 0.0f); glVertex3f( 1.1f, -1.1f,  0.0f);
			glTexCoord2f(roll+4.0f, 4.0f); glVertex3f( 1.1f,  1.1f,  0.0f);	
			glTexCoord2f(roll+0.0f, 4.0f); glVertex3f(-1.1f,  1.1f,  0.0f);	
		glEnd();										
	}

	glEnable(GL_DEPTH_TEST);							
	glDisable(GL_BLEND);						

	glFlush();										
}


void rotate()
{
	roll+=0.002f;									
	if (roll>1.0f)									
	{
		roll-=1.0f;										
	}
	glutPostRedisplay();
}
void mouse(int button,int state,int x,int y)
{ 
	switch(button)
	{
	case GLUT_LEFT_BUTTON:
		if(GLUT_DOWN==state)
		{
			glutIdleFunc(rotate);
		}
		break;
	case GLUT_RIGHT_BUTTON:
		if(GLUT_DOWN==state)
		{
			//glutIdleFunc(0);
		}
		break;
	}
}
void keyboard(unsigned char key,int x,int y)
{
	switch (key)
	{
	case 'M':
		masking=true;
		break;
	case 'm':
		masking=false;
		break;
	case 'S':
		scene=true;
		break;
	case 's':
		scene=false;	
		break;
	}
	glutPostRedisplay();

}


int main(int argc,char **argv)
{
	glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB|GLUT_DEPTH);
	glutInitWindowSize(800,600);
	glutInitWindowPosition(100,100);
	glutCreateWindow("蒙版");
	InitGL();
	glutDisplayFunc(DrawGLScene);
	glutKeyboardFunc(keyboard);
	glutMouseFunc(mouse);
	glutReshapeFunc(ReSizeGLScene);
	glutMainLoop();
}