CS 184: Discussion Section 1 Notes

Programming in a Windowed Environment

Topics

• Interactive Windows Programming
• Basic Introduction to OpenGL
• Basic Introduction to SLIDE
• Questions about HW1

Interactive Windows Programming

• Tcl/Tk provides a system independent windowing interface.
• Togl is a Tk widget which provides an OpenGL drawing area.
• Dealing with event loops and call backs
  • HandleDisplay()
    The provided rendering code for HandleDisplay (i.e. within the comments "// START: ASSIGNMENT 1: Rendering Code" and "// END  : ASSIGNMENT 1: Rendering Code") is sample OpenGl code. You will need to replace it entirely with your own code; however, if you are unfamiliar with OpenGl, I would see how the code provided draws stuff to the window (comment out parts of it and see the change).
    
  • HandleWrite()
    The provided code will prompt the user for a file name and write out a simple square. Try it...right-click and you should get a 'Save As' prompt. You will need to replace the square writing code in CWindow::WriteSLIDE with your own code.
    
  • HandleMouseButton()
    The provided code does not display the mouse events being captured, but the code to do so is all there - simply set the "cbDisplayEvents" flag (in window.cxx) to true. Then, when you click anywhere within the 'slidedraw' window, the events will be shown on the corresponding console window.
    

Basic Introduction to OpenGL

OpenGL is the set of Graphics Library routines which we will be using throughout the semester. There is an on line OpenGL Reference Page if you do not have the recommended text.

Things to know to do HW #1:

• Double Buffering
  Drawing commands are done to an off screen memory buffer then the whole buffer is swapped to the front making all drawing commands visible at once. This swapping of buffers is done by Togl_SwapBuffers().
• glColor3f(float R, float G, float B)
  This sets what color will used for any drawing primitives which follow.
• glBegin(GLenum MODE)
  glBegin is balanced by a glEnd and will produce geometry with vertices specified by glVertex2f calls in the middle. Depending apon which MODE different types of geometry will be drawn. The different MODES you might want to use are:
  • GL_POLYGON
    
  • GL_LINE_LOOP
    
  • GL_LINE_STRIP
    
  • GL_POINTS
    
• glVertex2f(float X, float Y)
  This specifies the coords of a vertex. This should be called in between calls to glBegin and glEnd.
• glEnd()
  This ends the description of a geometric primitive, at which time another call to glBegin could then happen.

Basic Introduction to SLIDE

# SLIDE Description of a Square

#############################
# Geometry Specification

point p0 ( 0.75 0.75 0 )
endpoint
point p1 ( 0.25 0.75 0 )
endpoint
point p2 ( 0.25 0.25 0 )
endpoint
point p3 ( 0.75 0.25 0 )
endpoint

face fSquare ( p0 p1 p2 p3 )
endface

object oSquare ( fSquare )
  solid SLF_HOLLOW
  shading SLF_WIRE
endobject

#############################
# Viewing Specification

camera cam
  projection SLF_PARALLEL
  frustum ( -0.5 -0.5 -2 )
          ( 0.5 0.5 -0.01 )
endcamera
group gCam
  instance cam
    id iCam
    translate ( 0.5 0.5 1 )
  endinstance
endgroup

window win
endwindow

viewport vp win
endviewport

render vp gCam.iCam.cam oSquare
endrender

Other Questions/Issues about HW1

• The data structure used to store geometry is important because it will be used in both, drawing to the screen and writing to a file. You can use any data structure you'd like (something like a simple linked list will work fine), but make sure you are comfortable with the data structure and you submit everything needed to compile it.
  
• Compiling the code: The provided project settings assume that you have an 'S' drive mapped to the SLIDE libraries on your machine. This is true in the lab computers, but if you are doing the project from home, you will need to change the project settings to change the 'S:' to where SLIDE libraries are installed. The installation instructions talk about this. Please read those carefully. After you compile and run, you should see a window with some cyan (blue-green) things in it - this is a good sign: it means you have compiled properly.