Toggles the pixel shader Starts and stops the scene Advances the scene by a small increment Prompts user to select a new rendering device or display mode Toggles between fullscreen and windowed modes Exits the app. Programming Notes ================= The waving motion of the grass can be accomplished in the vertex shader. Using a traditional method the grass is rendered with randomly placed intersecting quads stored in a single vertex buffer. The quads are texture mapped and rendered with an alpha test. In the vertex shader, the top two vertices of each quad are animated using a combination of four sinusoidal waves. The waves are approximated using a Taylor Series approach. This combination of sine waves using various different frequencies creates a natural waving that does not look like an animation or overly repetitious. When grass blades wave in the wind they also turn and change their orientation with respect to the sunlight. Because this method involves using a textured quad to represent various blades of grass it is impossible to change the lighting on individual grass blades. To simulate the change in color that would occur as the blades twist the wind, the same sine wave that was used to animate the grass is used to oscillate between two colors. In this case, the green channel of the color was changed to make the grass color change from intense green to a more yellowish-brown. The pixel shader combines this color with the grass texture to produce the final result.