openCV打开摄像头，用openGL实现纹理贴图和视频预览

由于项目需要，在windows平台需要实现openGL预览摄像头。于是想到将openCV和openGL结合起来，而openCV恰好支持openGL。

首先感谢https://www.cnblogs.com/feifanrensheng/p/9201629.html链接中作者的无私奉献，本文在TA基础上加工而成，希望能够帮助到有需要的朋友。需要安装openGL库glew，以及openCV库。

  1 #include <iostream>
  2 #include <GL/glew.h>
  3 #include <opencv2/opencv.hpp>
  4 #include <windows.h>
  5 using namespace cv;
  6 using namespace std;
  7 
  8 
  9 cv::VideoCapture capture = cv::VideoCapture(0);
 10 GLuint m_backgroundTextureId;
 11 Mat m_backgroundImage;
 12 
 13 
 14 void drawCameraFrame()
 15 {
 16     glGenTextures(1, &m_backgroundTextureId);
 17     glBindTexture(GL_TEXTURE_2D, m_backgroundTextureId);
 18 
 19     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
 20     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
 21     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
 22     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
 23     glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
 24 
 25 
 26     int w = m_backgroundImage.cols;
 27     int h = m_backgroundImage.rows;
 28 
 29     glPixelStorei(GL_PACK_ALIGNMENT, 1);
 30     glBindTexture(GL_TEXTURE_2D, m_backgroundTextureId);
 31 
 32     // Upload new texture data:
 33     glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
 34     glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, w, h, 0, GL_BGR_EXT, GL_UNSIGNED_BYTE, m_backgroundImage.data);
 35 
 36     //glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, w, h, 0, GL_BGRA_EXT, GL_UNSIGNED_BYTE, m_backgroundImage.data);
 37 
 38     //glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, w, h, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, m_backgroundImage.data);
 39 
 40     const GLfloat bgTextureVertices[] = { 0, 0, w, 0, 0, h, w, h };
 41     const GLfloat bgTextureCoords[] = { 1, 0, 1, 1, 0, 0, 0, 1 };
 42     const GLfloat proj[] = { 0, -2.f / w, 0, 0, -2.f / h, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 1 };
 43 
 44     glMatrixMode(GL_PROJECTION);
 45     glLoadMatrixf(proj);
 46 
 47     glMatrixMode(GL_MODELVIEW);
 48     glLoadIdentity();
 49 
 50     glEnable(GL_TEXTURE_2D);
 51     glBindTexture(GL_TEXTURE_2D, m_backgroundTextureId);
 52 
 53     // Update attribute values.
 54     glEnableClientState(GL_VERTEX_ARRAY);
 55     glEnableClientState(GL_TEXTURE_COORD_ARRAY);
 56 
 57     glVertexPointer(2, GL_FLOAT, 0, bgTextureVertices);
 58     glTexCoordPointer(2, GL_FLOAT, 0, bgTextureCoords);
 59 
 60     glColor4f(1, 1, 1, 1);
 61     glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 62 
 63     glDisableClientState(GL_VERTEX_ARRAY);
 64     glDisableClientState(GL_TEXTURE_COORD_ARRAY);
 65     glDisable(GL_TEXTURE_2D);
 66 }
 67 void draw(void* param)
 68 {
 69     glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
 70     drawCameraFrame();
 71     glFlush();
 72 }
 73 
 74 const int g_nMaxAlphaValue = 100;
 75 double g_dAlphaValue;
 76 double g_dBetaValue;
 77 int initTrackVal = 0;//滑块的初始位置
 78 void onTracker(int nVal, void*pVal)
 79 {    
 80     g_dAlphaValue = (double)nVal/g_nMaxAlphaValue;
 81     g_dBetaValue = (1.0) - g_dAlphaValue;     
 82     updateWindow("windowName");
 83 
 84 }
 85 
 86 int main( int argc, char** argv)
 87 {
 88     if (!capture.isOpened())
 89     {
 90         printf("[%s][%d]could not load video data...
", __FUNCTION__, __LINE__);
 91         return -1;
 92     }
 93     
 94     while (capture.read(m_backgroundImage))
 95     {
 96         namedWindow("windowName", cv::WINDOW_OPENGL);
 97         resizeWindow("windowName", m_backgroundImage.cols, m_backgroundImage.rows);
 98         setOpenGlContext("windowName");
 99         setOpenGlDrawCallback("windowName", draw, NULL);
100         updateWindow("windowName");
101         char szTrackName[100];
102         sprintf(szTrackName, "参数 %d", g_nMaxAlphaValue);
103         //滑块
104         createTrackbar(szTrackName, "windowName", &initTrackVal, g_nMaxAlphaValue, onTracker);
105         onTracker(initTrackVal, 0);
106         char c = waitKey(10);
107         if (c == 27)//Esc键
108         {
109             break;
110         }
111     }
112     return 0;
113 }