Google Interview Hacks

What are Homogenous coordinates? If w == 1, then the vector (x,y,z,1) is a position in space. If w == 0, then the vector (x,y,z,0) is a direction. (In fact, remember this forever.) What difference does this make ? Well, for a rotation, it doesn't change anything. When you rotate a point or a direction, you get the same result. However, for a translation (when you move the point in a certain direction), things are different. Homogeneous coordinates allow us to use a single mathematical formula to deal with these two cases.

What is Parallel Projection? Simplest type of projection, in which 3D points are mapped to 2D by moving them along a Projection Direction until they hit an image plane. The View that is produced is determined by the choice of projection direction and image plane. Parallel Projections are often used for mechanical and architectural drawings because they keep parallel lines parallel and they preserve the size and shape of planar objects that are parallel to the image plane.

What is Projection Direction? Points on an object are moved along imaginary lines until they hit an Image Plane.

When projection lines are parallel and perpendicular to the image plane, the resulting views are called ....? Orthographic

What is Perspective Projection? Projecting along lines that pass through a single point; the Viewpoint, rather than along parallel lines. In this way objects farther from the viewpoint naturally become smaller when they are projected. A perspective view is determined by the choice of viewpoint (rather than projection direction) and image plane. As with parallel views there are oblique and non-oblique perspective views; the distinction is made based on the projection direction at the center of the image.

What is the difference between Orthographic Projection and Oblique Projection? If the Image Plane is perpendicular to the View Direction, the projection is called Orthographic. If it is not perpendicular to the View Direction, it is called Oblique.

What is Distribution Ray Tracing? A powerful extension to the basic Ray-Tracing idea in which multiple random rays are sent through each pixel in an image to produce images with smooth edges and to simply (yet slowly) produce a wide range of effects from soft shadows to camera depth-of-field.

What is Linear Perspective? The standard approach to make images for Computer Graphics, where 3D objects are projected onto an image plane in such a way that straight lines in the scene become straight lines in the image. A type of perspective used by artists in which the relative size, shape, and position of objects are determined by drawn or imagined lines converging at a point on the horizon.

What is the pseudo-code for the structure of a Ray Tracing program? For each pixel, do Compute Viewing Ray Find 1st object hit by ray and its surface normal n Set pixel color to value computed from hit point, light, and surface normal n.

What is Ray Tracing? An Image-Order Rendering algorithm for making renderings of 3D scenes. Rendering technique that creates photo-realistic images by simulating light's effects on materials.

How does a Ray Tracer work? By computing one pixel at a time, and for each pixel the basic task is to find the object that is seen at that pixel's position in the image. Each pixel "looks" in a different direction, and any object that is seen by a pixel must intersect the Viewing Ray, a line that emanates from the viewpoint in the direction that pixel is looking.

Once an object is found by the Viewing Ray, what happens? A Shading computation uses the: 1. Intersection point 2. Surface normal 3. And other information (depending on the desired type of rendering) to determine the color of the pixel.

What are the 3 parts to a Ray Tracer? 1. Ray Generation: Computes the origin and direction of each pixel's Viewing Ray based on the camera geometry. 2. Ray Intersection: Finds the closest object intersecting the Viewing Ray 3. Shading: Computes the pixel color based on the results of Ray Intersection.

Rendering can be organized in 2 general ways: 1. Object-Order Rendering: Each object is considered in turn, and for each object all the pixels that it influences are found and updated. 2. Image-Order Rendering: Each pixel is considered in turn, and for each pixel, all the objects that influence it are found and the pixel value computed.

Broadly speaking, which of the Order-Rendering methods is simpler to get working and more flexible in the effects that can be produced, but usually takes much more execution time? Answer: Image-Order Rendering

What is Rendering? Taking a Scene (or Model) composed of many geometric objects arranged in 3D space and producing a 2D image that shows the objects as viewed from a particular viewpoint. One of the basic tasks of computer graphics. It is the same operation that has been done for centuries by architects and engineers creating drawings to communicate their designs to others.

Fundamentally, rendering is a process that takes as its input .... and produces as its output .... ? A set of objects. An array of pixels. One way or another, Rendering involves considering how each object contributes to each pixel.

What is Rendering? Taking a Scene (or Model) composed of many geometric objects arranged in 3D space and producing a 2D image that shows the objects as viewed from a particular viewpoint. One of the basic tasks of computer graphics. It is the same operation that has been done for centuries by architects and engineers creating drawings to communicate their designs to others.

By itself, the ability to project points from the world to the image is only good for producing...? Wireframe Renderings - renderings in which only the edges of objects are drawn, and closer surfaces do not occlude more distant surfaces.

Viewing Transformation's can be broken up into a sequence of 3 transformations which are...? 1. Camera Transformation / Eye Transformation 2. Projection Transformation 3. Viewpoint Transformation / Windowing Transformation