title: OpenGL resizing a Texture/Quad
body: <p>I'm implementing a pan/zoom viewer for jpegs. I show one image at a time mapped to a texture, then on a key press, swap between images.</p>
  
  <p>My problem is that although the image does change, the size of the quad is fixed to the width and height of the first image loaded and does not update. Here is the code for drawing the quad etc: </p>
  
  <p>note that ROI_WIDTH and ROI_HEIGHT are global variables that do update successfully each time a new image is loaded, however this is not reflected in the output:</p>
  
  <pre><code>void orthogonalStart (void) {
      glMatrixMode(GL_PROJECTION);
      glPushMatrix();
      glLoadIdentity();
      gluOrtho2D(0, ROI_WIDTH, 0, ROI_HEIGHT);
      glScalef(1, -1, 1);
      glTranslatef(0, -ROI_HEIGHT, 0);
      glMatrixMode(GL_MODELVIEW);
  }
  
  void orthogonalEnd (void) {
      glMatrixMode(GL_PROJECTION);
      glPopMatrix();
      glMatrixMode(GL_MODELVIEW);
  }
  
  
  void display (void) {
      glClearColor (1.0,1.0,1.0,0.0);
      glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
      glLoadIdentity();
  
      orthogonalStart();
  
      glEnable( GL_TEXTURE_2D );
      glEnable( GL_DEPTH_TEST );
      glDepthFunc(GL_LESS);
  
      glBindTexture( GL_TEXTURE_2D, texture );
      glRotatef(180.0, 250.0f, 250.0f, 0.0f);
  
      glBegin(GL_QUADS);
      glTexCoord2i(0,0); glVertex2f(0, 0);
      glTexCoord2i(1,0); glVertex2f(0, ROI_WIDTH);
      glTexCoord2i(1,1); glVertex2f(ROI_HEIGHT, ROI_WIDTH);
      glTexCoord2i(0,1); glVertex2f(ROI_HEIGHT, 0);
      glEnd();
  
  
      orthogonalEnd();
      zoomFac();
      glViewport (xView, yView, (GLsizei)(winx*zoomFactor), (GLsizei)(winy*zoomFactor));
      glutSwapBuffers();
  }
  </code></pre>