The Graphics Pipeline Lecture 5 Mon, Sep 3, 2007

Positioning Objects The pipeline begins with individual vertices (points). Each vertex has a color that was assigned to it by the programmer. The vertices are grouped into line segments or polygons, according to the programmer’s instructions.

Simple Objects Read Run

Colored Objects Read Run

Some Multi-Colored Objects Read Run

Lighting If lighting is enabled, then the brightness of each vertex is calculated, determined by the viewing angle and the angle at which the light source strikes the surface. If the surface has been assigned material properties such as reflectivity and shininess, then they are factored in. If the light source has color, that is added to the color of the vertex.

An Unreflective Red Sphere Read Run

A Reflective Red Sphere Read Run

A Shiny Red Sphere Read Run

A Shiny Red Sphere in Blue Light Read Run

Clipping Now the vertices are transformed into clip coordinates. The scene is clipped. Objects outside of the normalized cube are deleted. Objects that cross the boundaries of the cube are clipped to that part which is inside the cube. Objects within the cube are unchanged.

Clipped Sphere Read Run

Hidden-Surface Removal After conversion to normalized device coordinates, surfaces that are hidden from view by other surfaces are removed.

Rasterization Now the objects are transformed to screen coordinates. They are then rasterized. That is, each line or polygon is converted into a specific set of pixels. The pixels are then colored by interpolating the colors of the vertices. These colors are stored in the framebuffer.

Hidden-Surface Removal The z-coordinate is stored in the depth buffer. If two objects are in the same line of sight, then they will have the same x- and y-coordinates. The one with the higher z-coordinate will be discarded.

A Shaded Rasterized Triangle

Textures The final step is to apply textures. A texture is a bitmap that is pasted onto a surface. For example, the texture can be a geometric pattern or it can be a photograph. It is generally much faster to paste a picture onto a surface than to construct the image geometrically.

A Brick Texture Read Run

A Bitmap Texture Read Run

A Texture Pasted onto a Sphere Read Run