Hi everyone,

I am trying to use OpenGl with C++ and am having problems with multiple
viewports. The problem happens when I try to display bitmaps in twp
different viewports.

I tried various combinations. The code seems to behave when I am
drawing triangles etc. However, when I try doing something with
bitmaps, it fails.

Here is the code in a nutshell:

glMatrixMode(GL_MODELVIEW);
glViewport(m_xPos, m_yPos, m_width,m_height);
glLoadIdentity();
glDrawPixels(bmp.bmWidth, bmp.bmHeight, GL_BGR_EXT, GL_UNSIGNED_BYTE,
bmp.bmBits);

// same code, but different set of values for the position...
glMatrixMode(GL_MODELVIEW);
glViewport(m_xPos, m_yPos, m_width,m_height);
glLoadIdentity();
glDrawPixels(bmp.bmWidth, bmp.bmHeight, GL_BGR_EXT, GL_UNSIGNED_BYTE,
bmp.bmBits);

SwapBuffers(hDC);

Now, the two bitmaps seem to get drawn on the same viewport... I would
appreciate any help anyone can give me regarding this...

Cheers,
xargy

Actually, the bitmaps get drawn on the lower left side of the screen. I
guess I need to do some transformation before drawing the bitmap. I
thought setting the viewport should do that!

I tried using some tricks with glOrtho, but still no luck...

So, in the code here: m_xPos = 500; m_YPos = 200; m_width and m_height
are 200 resp.

So, I do:
glMatrixMode(GL_MODELVIEW);
glViewport(m_xPos, m_yPos, m_width,m_height);
glLoadIdentity();

glOrtho(m_xPos, m_xPos + m_width, m_height, m_height + m_yPos, -1,
1);
glDrawPixels(bmp.bmWidth, bmp.bmHeight, GL_BGR_EXT, GL_UNSIGNED_BYTE,
bmp.bmBits);					

I hope someone can help me here...

Thanks,
xargy

xargon wrote:
> I tried using some tricks with glOrtho, but still no luck...
> 
> So, in the code here: m_xPos = 500; m_YPos = 200; m_width and m_height
> are 200 resp.
> 
> So, I do:
 > glMatrixMode(GL_MODELVIEW);
 > glViewport(m_xPos, m_yPos, m_width,m_height);
 > glLoadIdentity();
 >
 > glOrtho(m_xPos, m_xPos + m_width, m_height, m_height + 
m_yPos, -1,
 > 1);


> glDrawPixels(bmp.bmWidth, bmp.bmHeight, GL_BGR_EXT, GL_UNSIGNED_BYTE,
> bmp.bmBits);					
> 
> I hope someone can help me here...
> 

The "glOrtho" must go in the GL_PROJECTION matrix,
not the GL_MODELVIEW matrix

glViewport(...);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(...);
glMatrixMode(GL_MODELVIEW);

Next you need a call to glRasterPos() before you can
draw a bitmap.

glrasterPos(...);
glDrawPixels(...);


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Hi,

Thanks for the reply! Do you think the arguments to the glOrtho call is
ok?

Thanks,
xargy