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。

#include <iostream>
#include <GL/glew.h>
#include <opencv2/opencv.hpp>
#include <windows.h>
using namespace cv;
using namespace std;


cv::VideoCapture capture = cv::VideoCapture(0);
GLuint m_backgroundTextureId;
Mat m_backgroundImage;


void drawCameraFrame()
{
    glGenTextures(1, &m_backgroundTextureId);
    glBindTexture(GL_TEXTURE_2D, m_backgroundTextureId);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);


    int w = m_backgroundImage.cols;
    int h = m_backgroundImage.rows;

    glPixelStorei(GL_PACK_ALIGNMENT, 1);
    glBindTexture(GL_TEXTURE_2D, m_backgroundTextureId);

    // Upload new texture data:
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, w, h, 0, GL_BGR_EXT, GL_UNSIGNED_BYTE, m_backgroundImage.data);

    //glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, w, h, 0, GL_BGRA_EXT, GL_UNSIGNED_BYTE, m_backgroundImage.data);

    //glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, w, h, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, m_backgroundImage.data);

    const GLfloat bgTextureVertices[] = { 0, 0, w, 0, 0, h, w, h };
    const GLfloat bgTextureCoords[] = { 1, 0, 1, 1, 0, 0, 0, 1 };
    const GLfloat proj[] = { 0, -2.f / w, 0, 0, -2.f / h, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 1 };

    glMatrixMode(GL_PROJECTION);
    glLoadMatrixf(proj);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, m_backgroundTextureId);

    // Update attribute values.
    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);

    glVertexPointer(2, GL_FLOAT, 0, bgTextureVertices);
    glTexCoordPointer(2, GL_FLOAT, 0, bgTextureCoords);

    glColor4f(1, 1, 1, 1);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_TEXTURE_COORD_ARRAY);
    glDisable(GL_TEXTURE_2D);
}
void draw(void* param)
{
    glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
    drawCameraFrame();
    glFlush();
}

const int g_nMaxAlphaValue = 100;
double g_dAlphaValue;
double g_dBetaValue;
int initTrackVal = 0;//滑块的初始位置
void onTracker(int nVal, void*pVal)
{    
    g_dAlphaValue = (double)nVal/g_nMaxAlphaValue;
    g_dBetaValue = (1.0) - g_dAlphaValue;     
    updateWindow("windowName");

}

int main( int argc, char** argv)
{
    if (!capture.isOpened())
    {
        printf("[%s][%d]could not load video data...
", __FUNCTION__, __LINE__);
        return -1;
    }
    
    while (capture.read(m_backgroundImage))
    {
        namedWindow("windowName", cv::WINDOW_OPENGL);
        resizeWindow("windowName", m_backgroundImage.cols, m_backgroundImage.rows);
        setOpenGlContext("windowName");
        setOpenGlDrawCallback("windowName", draw, NULL);
        updateWindow("windowName");
        char szTrackName[100];
        sprintf(szTrackName, "参数 %d", g_nMaxAlphaValue);
        //滑块
        createTrackbar(szTrackName, "windowName", &initTrackVal, g_nMaxAlphaValue, onTracker);
        onTracker(initTrackVal, 0);
        char c = waitKey(10);
        if (c == 27)//Esc键
        {
            break;
        }
    }
    return 0;
}