CS2261 LAB 04: Solution

Structs, States, Text, Arrays, and Swap

Provided Files
● gba.c, gba.h
● axolotl.h
● font.c, font.h
● text.h
● print.c, print.h
Files to Add/Edit
● .vscode
○ tasks.json
● main.c
● text.c ● axolotl.c

Instructions
In this lab, you will create a state machine, draw text to the screen, and swap axolotl structs.
Make sure to copy over your .vscode/tasks.json from one of your previous assignments.
TODO 1
For the first part of this lab, we will implement a very basic state machine containing two states. Our states will begin as black backgrounds but will eventually contain more. The state machine for this assignment will have the following states:
➔ REST
◆ Pressing START calls goToAnimate() and takes you to the ANIMATE state.
➔ ANIMATE
◆ Pressing START calls goToRest() and takes you to the REST state.
The following TODOs will walk you through setting up this behavior.
TODO 1.0
● In the main while loop, create the switch-case for the state machine.
○ The state variable that holds the current state and the enum containing the states have already been written for you.
○ You should have a case for each state. For now, each case will just contain a break statement. Soon, you will add your state transition behavior.
TODO 1.1
● Below the already-written initialize function, make the state transition functions for REST and ANIMATE.
○ You should create two separate functions, goToRest() and goToAnimate().
○ For now, each of these functions should just update your state variable to match the state you are transitioning to.
TODO 1.2
● Now that you have made these functions, put the prototypes for them at the top of main.c.
TODO 1.3
● Call your goToRest function in the initialize function so that when the game starts, the REST state is first.
● Additionally, in the switch cases you made in TODO 1.0, transition to the other state if the user presses START.
○ Pressing START in the REST state should take you to the ANIMATE state.
○ Pressing START in the ANIMATE state should take you to the REST state.
○ To change states, you should call the state transition function for the state you want to change to.
Compile and run. You will not notice any new changes on the emulator screen, but you should fix any errors that prevent compilation.
TODO 2
It’s time to add text so we can label each state.
TODO 2.0
● In text.c, complete the drawChar and drawString functions.
● drawString should make use of drawChar, calling it inside of a loop
TODO 2.1
● In main.c, update your state transition functions to draw text to the upper part of the screen (make sure it doesn’t clip past boundaries, and that the color is visible!)
○ For REST, draw “Resting Axolotls” in a color of your choice.
○ For ANIMATE, draw “Animated Axolotls!” in a different color of your choice.
TODO 2.2
○ You should call drawRect and use an area that is just big enough to hide the text from the previous state. You will want to pass in the background color (BLACK).
Compile and run. You should be able to press START to toggle between your REST and ANIMATE states. Each state should be labeled accordingly and text from the previous state should not be visible. If this is not the case, fix your code before moving forward.
TODO 3
TODO 3.0
● In axolotl.c, initialize the axolotlBitmaps array. The array should contain the already defined bitmaps: bitmap1, bitmap2, bitmap3, bitmap4, and bitmap5.
○ bitmap1, bitmap2, etc. are arrays of integers defining how each axolotl is drawn. axolotlBitmaps is an array of integer pointers. It should hold the memory addresses of each of the bitmap arrays.
TODO 3.1
In axolotl.c, find drawAxolotl and complete the switch statement. In this switch statement, we are setting pixels to a particular color based on the retrieved value from the axolotl bitmap. Each axolotl bitmap has 6 possible values, 0, 1, 2, 3, 4, or 5. Create a case for values 1, 2, 3, 4, and 5. The 0 case can be handled by the default statement, as we will not set the pixel any color if the value of the bitmap is 0.
1. For case 1, set the color of the pixel at x + i, y + j to black. ○ BLACK is a macro defined for you in gba.h.
2. For case 2, set the color of the pixel to red.
○ RED is a macro defined for you in gba.h.
3. For case 3, set the color of the pixel to magenta.
○ MAGENTA is a macro defined for you in gba.h.
4. For case 4, set the color of the pixel to the axolotl’s color property.
○ Make use of the axolotl pointer that is passed into the function, and access that axolotl struct’s color member.
○ You can use the arrow operator (->) to access members of struct pointers
like this:
ptr->member (returns the value) ptr->member = value (assigns a new value)
5. For case 5, set the color of the pixel to dark gray.
○ DARKGRAY is a macro defined for you in gba.h.
TODO 3.2
Now we need to update the state machine so we can actually draw the axolotl bitmaps. Each state should be updated with the following functionality (new changes are bolded):
➔ REST
◆ Calls waitForVBlank() and drawGame() in that order
◆ Pressing START calls goToAnimate() and takes you to the ANIMATE state
➔ ANIMATE
◆ Calls updateGame(), waitForVBlank(), and drawGame() in that
order
◆ Pressing START calls goToRest() and takes you to the REST state Add the appropriate function calls to each state.
Compile and run. In addition to your text, you should see the following in each state. If you do not, fix your code before moving forward. If your text overlaps with the axolotl bitmaps, you should fix this as well.

TODO 4
In our ANIMATE state, we want the axolotls to constantly swap. You will implement the swap and reverseAxolotls functions to accomplish this.
TODO 4.0
TODO 4.1
● At the top of main.c, add the function prototype for your swap function.
TODO 4.2
○ Hint: you only need to iterate through half of the array to swap the elements.
○ Hint: there’s no array.length in C! Make use of the AXOLOTLCOUNT macro in axolotl.h instead.
Compile and run your lab. When you enter the ANIMATE state, the axolotls should continuously reverse their order. If you return to the REST state, the axolotls should stay still in the most recent order from the ANIMATE state.
The following images show the two possible orders:


Checklist
Ensure that:
● You can press START to toggle between the REST and ANIMATE states.
● Each state is labeled with the correct text label at the top of the screen.
● The axolotls are drawn properly in each state.
● While in the REST state, the axolotls remain stationary.
● While in the ANIMATE state, the axolotls swap back and forth.
To see what a completed version of the project looks like, see Example.gba.

Tips
● Draw out what your logic for reverseAxolotls actually does. This will help you ensure you’ve implemented the code correctly!
● Follow each TODO in order, and only move forward if everything is correct.

Submission Instructions
Ensure that cleaning and building/running your project still produces the expected results. Please reference the last page of this document for instructions on how to perform a "clean" command.
Zip up your entire project folder, including all source files, the Makefile, and everything produced during compilation (including the .gba file). Submit this zip on Canvas.
Name your submission Lab04_LastnameFirstname, for example:
“Lab04_MinecraftSteve.zip”
It is your responsibility to ensure that all the appropriate files have been submitted, and that your submitted zip can be opened and everything cleans, builds, and runs as expected.
How to Clean
Navigate to the Terminal option at the top of your screen. Click on it, and then select Run Task…, as shown in the image below.

A dropdown menu will appear with the possible tasks to perform. Next, select clean from the options. Note that yours might be in a different order from mine, but the task should be there.

After selecting clean, something similar to the following should appear in your terminal tab (bottom of the screen).

If so, success! You have cleaned. You can now do cmd/ctrl + shift + B to build run (or click Terminal, then Run Build Task… or Run Task… and then build run).