CS 70

Homework 3: Add Asciimation Display Functions

Background: How the Animation Works

Animation is a medium in which successive still images are rapidly presented one-after-another to give viewers the impression of smooth movements. To understand how this process works, imagine being presented with a still photograph of an object in motion. Then, a short while later, imagine you were shown another image of the same motion in progress (and then another, and another). As the delay between seeing the photographs decreases, the depicted motion would begin to appear smoother—it would be as if you were watching the original motion itself rather than a series of snapshots. The point at which a viewer perceives smooth motion from successively presented still images is known as the flicker-fusion threshold. It occurs for most humans when these images (known as frames) are presented at a rate of about 10–15 still images per second.

In traditional animation, frames might be drawn directly onto celluloid (“cel” animation), photographed physical objects (as in plasticine or clay animation), or “rendered” with computers (where each frame is computed from various data sources). But for this assignment we will be using the terminal to display our animation.

What's Already Done

We've given you an implementation for the play member function in the Asciimation class. It controls a loop to update and display a movie until the user exits by pressing q. You shouldn't need to modify this code at all, but you should read through it and make sure you understand how it works.

The content that is displayed by play is determined by a few other member functions of the Asciimation class:

  • clearContents wipes out whatever was on the screen in the previous step by stepping through the character array and replacing everything with spaces.
  • updateContents copies characters from the movie's sprite to its character array. It should first call clearContents. Then it should loop through all of the characters in the sprite using its getCharAt function, placing each character at the right spot in the movie's character array.
  • copyToScreen copies characters from the movie's character array to the screen. It should use the ncurses function mvaddch to copy each element of the movie's character array to the right spot on the screen.

Your Task

Complete the implementation of these three functions to make the display system work:

  1. clearContents: This private member function should loop through the entire character array and set each character to a space (' ').

  2. updateContents: This function should:

  3. First call clearContents to clear the display
  4. Then loop through each row and column of the sprite
  5. For each character, check if it would be visible on screen (considering the sprite's position)

  6. If visible, copy the character from the sprite to the appropriate position in the movie's character array

  7. copyToScreen: This function should:

  8. Loop through each position in the movie's character array
  9. Use mvaddch to place each character at the correct screen position

Helpful Hints

  • LHS Cow speaking

    Here are some tips for implementing the display functions!

Using mvaddch

The way you use mvaddch is: mvaddch(row of character to add, column of character to add, character to add);

For example:

mvaddch(5, 10, 'X');  // Places an 'X' at row 5, column 10

Coordinate Calculations

When implementing updateContents, you'll need to:

  • Calculate where each sprite character should go in the movie array
  • Check if the sprite character is within the bounds of the movie display
  • Handle cases where the sprite is partially off-screen

Array Indexing

Remember that both the sprite and movie arrays are one-dimensional. You'll need to convert between 2D coordinates (row, column) and 1D array indices. The formula is:

index = row * width + column

Testing Your Display

Once you've implemented these functions, you can test them by running your program. The sprite should appear on screen (though it won't move yet—that comes in Part 7).

To Complete This Part of the Assignment

You'll know you're done with this part of the assignment when you've done all of the following:

(When logged in, completion status appears here.)