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Editorial Team
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Asked: 2026-06-11T03:36:32+00:00

I am using this code from NEHE tutorial in my MFC based application on

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I am using this code from NEHE tutorial in my MFC based application on mouseclick 

void CRightOGL::OnLButtonDown(UINT nFlags, CPoint point)

{
// TODO: Add your message handler code here and/or call default

GLint viewport[4];
GLdouble modelview[16]={0};
GLdouble projection[16];
GLfloat winX, winY, winZ;
GLdouble posX, posY, posZ;
GLfloat mv[16];

glGetFloatv( GL_MODELVIEW_MATRIX, mv );
glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
glGetDoublev( GL_PROJECTION_MATRIX, projection );
glGetIntegerv( GL_VIEWPORT, viewport );

winX = (float)point.x;
winY = (float)viewport[3] - (float)point.y;
glReadPixels(point.x, int(winY), 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &winZ );

gluUnProject( winX, winY, winZ, modelview, projection, viewport, &posX, &posY, &posZ);


COpenGLControl::OnLButtonDown(nFlags, point);

    }

But the problem is that i am getting incorrect values every time posX, &posY, &posZ… and values always comes in -9.25555 , -9.255555 ,-9.255555. Not only this but also modelview matrix is returning same -9.555 value everytime.

If i initialize everything as 0 then posX,posY and PosZ returns me only 0 instead of correct coordinates. Mouse x and y values are perfectly fine so from mouse side there is no issue.

What i am doing wrong?

my opengl initialization code is as follow

void COpenGLControl::oglInitialize(void)
{
// Initial Setup:
//
static PIXELFORMATDESCRIPTOR pfd =
{
    sizeof(PIXELFORMATDESCRIPTOR),
    1,
    PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER,
    PFD_TYPE_RGBA,
    32, // bit depth
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    16, // z-buffer depth
    0, 0, 0, 0, 0, 0, 0,
};


// Get device context only once.
hdc = GetDC()->m_hDC;

// Pixel format.
m_nPixelFormat = ChoosePixelFormat(hdc, &pfd);
SetPixelFormat(hdc, m_nPixelFormat, &pfd);

// Create the OpenGL Rendering Context.
hrc = wglCreateContext(hdc);
wglMakeCurrent(hdc, hrc);

// Basic Setup:
//
// Set color to use when clearing the background.
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glClearDepth(1.0f);

// Turn on backface culling
glFrontFace(GL_CCW);
glCullFace(GL_BACK);

// Turn on depth testing
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LEQUAL);
glEnable(GL_DEPTH);


//glEnable(GL_TEXTURE_2D);  // Enable 2D textures
// Send draw request

GLenum a = glGetError();

OnDraw(NULL);
}
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1 Answer

  1. Editorial Team

    Okay i figured out the issue generating due to the below scenario

    i am using draw function between setting of two different hdc , because i have two different picture control window’s of mfc and both has different drawing. That is why inside the mouse down or mouse click event when i was using above gl code it always used to give me error 1282 by s = glGetError().

    So to make it work i just added the above code within the 

    wglMakeCurrent(hdc, hrc);

//my code

wglMakeCurrent(NULL, NULL);

    and it worked and all the x y and z values are now on the screen

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