15.OpenGL--图像

• 理论基础 
  图像：它与位图相似，都是二进制位来表示屏幕对应像素，只是图像的每个像素并不是由1个位来表示的，它的每个像素包含更多地信息。即位图1个位对应1个像素，图像多个位对应1个像素。OpenGL图像操作归根结底就是对像素进行操作。示例图如下： 
  

  注释：这些东西现在也基本是废弃机制了.

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• 代码示例(图像的缩放与复制操作)

#include "GLTools.h"#include "GLShaderManager.h"#ifdef __APPLE__#include <glut/glut.h>#else#define FREEGLUT_STATIC#include <GL/glut.h>#endif#define checkImageWidth 64#define checkImageHeight 64GLubyte checkImage[checkImageHeight][checkImageWidth][3];static GLdouble zoomFactor = 1.0;static GLint height;void makeCheckImage(void){    int i, j, c;    //棋盘图像数据    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;        }    }}void init(void){    glClearColor (0.0, 0.0, 0.0, 0.0);    glShadeModel(GL_FLAT);    makeCheckImage();    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);//设置像素存储模式}void display(void){    glClear(GL_COLOR_BUFFER_BIT);    glRasterPos2i(0, 0);//设置光栅化位置    glDrawPixels(checkImageWidth, checkImageHeight, GL_RGB, GL_UNSIGNED_BYTE, checkImage);//绘制图像    glFlush();}void reshape(int w, int h){    glViewport(0, 0, (GLsizei) w, (GLsizei) h);    height = (GLint) h;    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    gluOrtho2D(0.0, (GLdouble) w, 0.0, (GLdouble) h);    glMatrixMode(GL_MODELVIEW);    glLoadIdentity();}//鼠标拖动void motion(int x, int y){    static GLint screeny;    screeny = height - (GLint) y;    glRasterPos2i (x, screeny);    glPixelZoom (zoomFactor, zoomFactor);//x,y方向进行缩放    //复制颜色缓冲区指定的矩形区域到帧缓冲区    glCopyPixels (0, 0, checkImageWidth, checkImageHeight, GL_COLOR);    glPixelZoom (1.0, 1.0);    glFlush ();}void keyboard(unsigned char key, int x, int y){    switch (key) {        case 'r':        case 'R':            zoomFactor = 1.0;            glutPostRedisplay();            printf ("zoomFactor reset to 1.0\n");            break;        case 'z':            zoomFactor += 0.5;            if (zoomFactor >= 3.0)                zoomFactor = 3.0;            printf ("zoomFactor is now %4.1f\n", zoomFactor);            break;        case 'Z':            zoomFactor -= 0.5;            if (zoomFactor <= 0.5)                zoomFactor = 0.5;            printf ("zoomFactor is now %4.1f\n", zoomFactor);            break;        case 27:            exit(0);            break;        default:            break;    }}int main(int argc, char** argv){    glutInit(&argc, argv);    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);    glutInitWindowSize(250, 250);    glutInitWindowPosition(100, 100);    glutCreateWindow(argv[0]);    init();    glutDisplayFunc(display);    glutReshapeFunc(reshape);    glutKeyboardFunc(keyboard);    glutMotionFunc(motion);    glutMainLoop();    return 0; }
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