Tutorial 1 - the gemwin

The gemwin object forms the foundation of GEM. Along with the gemhead object, the gemwin provides the base of all render chains. The gemwin is the 'window to the world' that displays the visual information (i.e. pretty pictures) we will create using GEM. The gemwin creates the output window and sets various attributes for both the window (size, placement, fullscreen, etc) and our 3D world (lighting, background color, etc). The following image shows the very minimum required to open a window and start and stop rendering:

This illustration shows two very important messages accepted by the gemwin, create and destroy, and the toggle turns rendering on and off (0 for off, 1 for on). Hitting the create message will open a black display window and create an openGL context for GEM to use for drawing. A critical thing to note is that at this time GEM can only create one window and context at a time, so do not use more than one active gemwin at a time!

Now that the window has opened somewhere on the screen, rendering can begin. Click the toggle button and rendering starts (a message may print in the terminal window stating that rendering has started). Of course nothing will draw in the window at this point because GEM has not received any instructions to draw something.

Here is a list of the messages that the gemwin understands: General:

• create - makes the window for output and an OpenGL rendering context
• destroy - removes the output window and the OpenGL context
• 1 - starts rendering
• 0 - stops rendering
• bang - swaps buffers in double buffered mode; clears the window in single buffered mode
• frame $1 - the number sets the frames per second the render chain executes\
• cursor 0/1 - turns the cursor on (1) or off (0)
• border 0/1 - (1) draws a border around the window, (0) removes it
• offset x y - sets the position where the window is drawn. this is usually the screen coordinates for the top left corner of the window. the units are pixels.
• dimen x y - sets the size of the output window. x is the horizontal dimension in pixels, y is the vertical dimension in pixels.
• fullscreen 0/1 - draws the window as the entire size of the screen.
• title 'name' - puts a title on top of the window where applicable
• color R G B - changes the background color to the mixture of the Red Green and Blue values. The values are floating point numbers between 0 and 1 where 0 0 0 is black and 1 1 1 is white (1 0 0 is Red etc.)

Open the subpatch called positioning and change the dimensions arguments to the 'dimen' message to 320 and 240. Also, set the two numbers for the 'offset' message to 100 and 100. Now, turn off rendering and destroy the gemwin, if it is already open. Recreating the gemwin will update the size and location of the window on the screen.

Open the subpatch labeled color and set the three number boxes to 1 0 0. The gemwin will now turn bright red. Mixing between 0 and 1 for each of the Red Green and Blue color values will give every color the computer can display.