OpenGL 反馈选择模式

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OpenGL对这些标记的定义

名称十六进制十进制

#define GL_PASS_THROUGH_TOKEN 0x0700 (1792)

#define GL_POINT_TOKEN 0x0701 (1793)

#define GL_LINE_TOKEN 0x0702 (1794)

#define GL_POLYGON_TOKEN 0x0703 (1795)

#define GL_BITMAP_TOKEN 0x0704 (1796)

#define GL_DRAW_PIXEL_TOKEN 0x0705 (1797)

#define GL_COPY_PIXEL_TOKEN 0x0706 (1798)

#define GL_LINE_RESET_TOKEN 0x0707 (1799)

绘制模型:

一个300X300的视口中,绘制一条"┌"线,以及在中间绘制一个点

代码:

#include <stdlib.h>

#include <stdio.h>

#include <GL/glut.h>

GLfloat feedBuffer[1024];

void init(void)

{

glEnable(GL_LIGHTING);

glEnable(GL_LIGHT0);

glClearColor (0.0, 0.0, 0.0, 0.0);

}

void drawGeometry (GLenum mode)

{

//绘制两条线段

glBegin (GL_LINE_STRIP);

glVertex3f (50.0, 50.0, 0.0);

glVertex3f (50.0, 250.0, 0.0);

glVertex3f (250.0, 250.0, 0.0);

glEnd ();

if (mode == GL_FEEDBACK)

{

glPassThrough (1.0);//在图元之间增加标记

}

// 绘制一个点此点在视野之外

glPointSize(5);

glBegin (GL_POINTS);

glVertex3f (-100.0, -100.0, -100.0);

glEnd ();

if (mode == GL_FEEDBACK)

{

glPassThrough (2.0);//在图元之间增加标记

}

// 绘制一个点

glBegin (GL_POINTS);

glNormal3f (0.0, 0.0, 1.0);

glVertex3f (150.0, 150.0, 0.0);

glEnd ();

}

void print3DcolorVertex (GLint size, GLint *count, GLfloat *buffer)

{

int i;

printf (" ");

for (i = 0; i < 7; i++)

{

printf ("*%4.2f* ", buffer[size-(*count)]);

*count = *count - 1;

}

printf ("\n");

}

void printBuffer(GLint size, GLfloat *buffer)

{

GLint count;

GLfloat token;

count = size;

while (count)

{

//获取反馈数据的第一个字节，是一个表示图元类型的代码

//可以是GL_POINT_TOKEN, GL_LINE_TOKEN等等

token = buffer[size-count];

count--;

if (token == GL_PASS_THROUGH_TOKEN)//如果图元是插入的标记

{

printf ("GL_PASS_THROUGH_TOKEN\n");

printf (" %4.2f\n", buffer[size-count]);

count--;

}

else if (token == GL_POINT_TOKEN)//如果图元是点

{

printf ("GL_POINT_TOKEN\n");

print3DcolorVertex (size, &count, buffer);

}

else if (token == GL_LINE_TOKEN)//如果图元是线

{

printf ("GL_LINE_TOKEN\n");

print3DcolorVertex (size, &count, buffer);

}

else if (token == GL_LINE_RESET_TOKEN)//如果图元是线，切对于点画模式进行了重置

{

printf ("GL_LINE_RESET_TOKEN\n");

print3DcolorVertex (size, &count, buffer);

}

void display(void)

{

glMatrixMode (GL_PROJECTION);

glLoadIdentity ();

glOrtho (0.0, 300.0, 0.0, 300.0, 0.0, 1.0);

glClear(GL_COLOR_BUFFER_BIT);

drawGeometry (GL_RENDER);

//指定保存反馈数据的数组，GL_3D_COLOR表示返回的顶点数据由坐标(x,y,z)和颜色(r,g,b,a)组成

//GLfloat feedBuffer[1024];

glFeedbackBuffer (1024, GL_3D_COLOR, feedBuffer);

glRenderMode (GL_FEEDBACK);//进入反馈模式

drawGeometry (GL_FEEDBACK);

GLint size = glRenderMode (GL_RENDER);//退出反馈模式，同时获得返回的图元的个数

printBuffer (size, feedBuffer);

}

int main(int argc, char** argv)

{

glutInit(&argc, argv);

glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);

glutInitWindowSize (300, 300);

glutInitWindowPosition (100, 100);

glutCreateWindow(argv[0]);

init();

glutDisplayFunc(display);

glutMainLoop();

return 0;

}

运行结果:

反馈后,在feedBuffer的数据如下:

数据格式排列有点乱......

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