title: OpenGL Frame Buffer Object for rendering to textures, renders weirdly
body: <p>I'm using python but OpenGL is pretty much done exactly the same way as in any other language.</p>
  
  <p>The problem is that when I try to render a texture or a line to a texture by means of a frame buffer object, it is rendered upside down, too small in the bottom left corner. Very weird. I have these pictures to demonstrate:</p>
  
  <p>This is how it looks,</p>
  
  <p>www.godofgod.co.uk/my_files/Incorrect_operation.png</p>
  
  <p>This is how it did look when I was using pygame instead. Pygame is too slow, I've learnt. My game would be unplayable without OpenGL's speed. Ignore the curved corners. I haven't implemented those in OpenGL yet. I need to solve this issue first.</p>
  
  <p>www.godofgod.co.uk/my_files/Correct_operation.png</p>
  
  <p>I'm not using depth.</p>
  
  <p>What could cause this erratic behaviour. Here's the code (The functions are indented in the actual code. It does show right), you may find useful,</p>
  
  <pre><code>def texture_to_texture(target,surface,offset): #Target is an object of a class which contains texture data. This texture should be the target. Surface is the same but is the texture which should be drawn onto the target. offset is the offset where the surface texture will be drawn on the target texture.
  #This will create the textures if not already. It will create textures from image data or block colour. Seems to work fine as direct rendering of textures to the screen works brilliantly.
  if target.texture == None:
      create_texture(target)
  if surface.texture == None:
      create_texture(surface)
  frame_buffer =  glGenFramebuffersEXT(1)
  glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, frame_buffer)
  glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, target.texture, 0) #target.texture is the texture id from the object
  glPushAttrib(GL_VIEWPORT_BIT)
  glViewport(0,0,target.surface_size[0],target.surface_size[1])
  draw_texture(surface.texture,offset,surface.surface_size,[float(c)/255.0 for c in surface.colour]) #The last part changes the 0-255 colours to 0-1 The textures when drawn appear to have the correct colour. Don't worry about that.
  glPopAttrib()
  glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0)
  glDeleteFramebuffersEXT(1, [int(frame_buffer)]) #Requires the sequence of the integer conversion of the ctype variable, meaning [int(frame_buffer)] is the odd required way to pass the frame buffer id to the function.
  </code></pre>
  
  <p>This function may also be useful,</p>
  
  <pre><code>def draw_texture(texture,offset,size,c):
  glMatrixMode(GL_MODELVIEW)
  glLoadIdentity() #Loads model matrix
  glColor4fv(c)
  glBegin(GL_QUADS)
  glVertex2i(*offset) #Top Left
  glVertex2i(offset[0],offset[1] + size[1]) #Bottom Left
  glVertex2i(offset[0] + size[0],offset[1] + size[1]) #Bottom, Right
  glVertex2i(offset[0] + size[0],offset[1]) #Top, Right
  glEnd()
  glColor4fv((1,1,1,1))
  glBindTexture(GL_TEXTURE_2D, texture)
  glBegin(GL_QUADS)
  glTexCoord2f(0.0, 0.0)
  glVertex2i(*offset) #Top Left
  glTexCoord2f(0.0, 1.0)
  glVertex2i(offset[0],offset[1] + size[1]) #Bottom Left
  glTexCoord2f(1.0, 1.0)
  glVertex2i(offset[0] + size[0],offset[1] + size[1]) #Bottom, Right
  glTexCoord2f(1.0, 0.0)
  glVertex2i(offset[0] + size[0],offset[1]) #Top, Right
  glEnd()
  </code></pre>