Displayin two different images on a window in OpenGL

Question

I am trying to display two different images on a window using OpenGL. Something like what has been shown in the below image.

First image on the left side of window: img [nc x nr]

Second image on the right side of window: img2 [nc x ns]

image

I have written the below code for display routine:

void display(void)
{
   ///////////////////First Image////////////////////////
   glViewport( (GLsizei) 0, (GLsizei) 0, (GLsizei) nc, (GLsizei) nr );
   glClear(GL_COLOR_BUFFER_BIT);
   glPixelStorei(GL_UNPACK_ALIGNMENT, 1);               

   glRasterPos2i(0, 0);                                 
   glDrawPixels(nc,nr, GL_RGB, GL_UNSIGNED_BYTE, img);

   ///////////////////Second Image////////////////////////
   glViewport( (GLsizei) 0, (GLsizei) nc, (GLsizei) nc, (GLsizei) ns );
   glClear(GL_COLOR_BUFFER_BIT);
   glPixelStorei(GL_UNPACK_ALIGNMENT, 1);               

   glRasterPos2i(0, nc);                                    
   glDrawPixels(nc,ns, GL_RGB, GL_UNSIGNED_BYTE, img2); 
   //////////////////////////////////////////////////////

   glutSwapBuffers();                                   

}

When I run the program the window displays nothing; but when I comment out the display code for the second image, I can see image 1 in the left side of window.

Can anyone see what is wrong with my code?

Answer 1

void display(void)
{
   // Size the viewport to be big enough for two images
   glViewport( (GLsizei) 0, (GLsizei) 0, (GLsizei) screen_width, (GLsizei) screen_height );
   glClear(GL_COLOR_BUFFER_BIT);
   glPixelStorei(GL_UNPACK_ALIGNMENT, 1);               

   // Position first image starting at 0, 0
   glRasterPos2i(0, 0);   
   // Get the width and height of image as first two params                              
   glDrawPixels(img.width,img.height, GL_RGB, GL_UNSIGNED_BYTE, img);

   // Position second image starting after the width of the first image
   glRasterPos2i(img.width, 0);   
   // get width and height of second image as first two params                                 
   glDrawPixels(img2.width,img2.height, GL_RGB, GL_UNSIGNED_BYTE, img2); 

   glutSwapBuffers();

}

This is the general idea. Obviously screen_height etc are named differently in your app but the viewport should be set to the size of the screen. The Raster position should be the start position of the images and the first 2 params of DrawPixels should be the width and height of your images. Each image does not need its own viewport, as this would be highly unmanageable(and extremely slow) when the number of images/models grow.

Answer 2

Actually you are defining viewport two times. So the effect of first viewport is no longer in effect. Define only one viewport with height and width of screen.