The Programmer's Interface

Tom Kelliher, CS 320

Jan. 30, 1998

Announcements:

From last time:

1. Installed GLUT.

2. Experimented with two OpenGL programs.

Outline:

1. The programmer's interface.

2. Pictorial history.

3. Modeling-Rendering Paradigm.

4. Graphics architectures.

Assignment:

The Programmer's Interface

An API must allow us to specify:

1. Objects --- collections of polygons. API primitives:
   1. Points.

   2. Line segments.

   3. Polygon outlines.

   4. Filled polygons.

   5. Curved surfaces (not supported by all APIs).

      OpenGL example:

      glBegin(GL_POLYGON);
         glVertex3f(0.0, 0.0, 0.0);
         glVertex3f(0.0, 1.0, 0.0);
         glVertex3f(0.0, 0.0, 1.0);
      glEnd();
      

      specifies a triangle.

      Adding additional vertices allows arbitrary polygons.

      Other type parameters: GL_LINE_STRIP, GL_POINTS .

2. The viewer --- through the synthetic camera:
   1. Position.

   2. Orientation.

   3. Focal Length.

   4. Size of film (projection) plane.

3. Light sources:
   1. Location.

   2. Direction.

   3. Strength.

   4. Color.

4. Material properties --- transparency, etc.

A Pictorial History of Graphics

Refer to Plates 25 through 36 in the text:

1. Wireframe images. Complex 3-D objects.

2. Hidden surface removal.

3. Flat shading. Lost 3-D. No light source.

4. Constant shading. Found 3-D. Light source. Still see the polygons.

5. Smooth shading. Polygons less obtrusive.

6. Curved surfaces. Polygons gone.

7. Multiple light sources.

8. Texture mapping.

Modeling-Rendering Paradigm

Alternative to synthetic camera.

Modeler, interface file, renderer.

1. Modeler:
   1. Concerned with design and placement of objects.

   2. Highly interactive process.

   3. Possibly more than one modeler, tailored to each application.

2. Interface file:
   1. Output from modeler, input to renderer.

   2. Basic description of scene.

3. Renderer:
   1. Adds lighting, viewer perspective, material properties (additional components of interface file).

   2. Computationally intensive.

   3. PIXAR's Renderman.

Graphics Architectures

Early Systems

Host, DA converter, CRT.

• Eliminating flicker.

• Re-displaying a scene: computationally expensive.

Display Processors

Host, display processor and display list, CRT.

1. Separate processor.

2. Host sends primitives along, stored in display list.

3. Display processor deals with refresh, re-generation.

Graphics Pipelines

Consider a pipeline for computing large numbers of .

Properties of pipelines:

1. Depth --- latency.

2. Throughput.

Steps in a graphics pipeline:

1. Transformation --- between series of coordinate systems. Matrix multiplications.

2. Clipping --- cut scene down to field of view. Example: Excel.

3. Projection --- Project 3-D objects into 2-D. Matrix multiplication.

4. Rasterization --- Convert 2-D primitives to pixels.