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====== Your first program =======

In this chapter, you're going to learn the basics of compiling and testing a homebrew project targetting the WonderSwan.

===== Creating a project =====

First, set up a new project:

  $ mkdir first-program/ # (1)!
  $ wf-wswantool project new first-program/ # (2)!

  - Create the directory "first-program" in the terminal's current working directory.
  - Create a new wswan target project with the directory and name "first-program".

Next, compile it:

  $ cd first-program/
  $ make

The build script will output lines similar to the following:

  CC      src/main.c
  LD      build/first-program_stage1.elf
  ROM     first-program.wsc
  MERGE   compile_commands.json

  - The C compiler is compiling the source file ''src/main.c''.
  - The ELF file ''build/first-program_stage1.elf'' is being linked. This file will contain all of the program's source code and assets, but not yet placed in the console's ROM and RAM.
  - The ROM file ''first-program.wsc'' is being created, now with the correct memory placements.
  - The ''compile_commands.json'' file is being generated. This is used by your IDE to provide syntax highlighting; as a consequence, it is a good idea to run `make` after adding a new ''.c'' file to the project.

Finally, you can run the ROM file using your emulator of choice.

===== Editing source code =====

The program is not displaying anything - after all, there's no code written yet!

Let's examine the ''src/main.c'' file:

<code C>
// SPDX-License-Identifier: CC0-1.0
//
// SPDX-FileContributor: Adrian "asie" Siekierka, 2023
// (1)!
#include <wonderful.h> // (2)!
#include <ws.h> // (3)!

void main(void) {
    while(1);
}
</code>

  - The default copyright header for the template file. This is required to inform you that you can use the example code contained therein without restrictions. However, before writing your own code, if you wish to put different terms on your code, you should remove it.
  - The ''wonderful.h'' include contains common CPU/target definitions. It's a good idea to put it in essentially every C file.
  - The ''ws.h'' include contains hardware definitions specific to the WonderSwan, as well as many lower-level hardware abstraction functions.

<WRAP round important>
Pay special attention to the `while(1);` at the end - this is an infinite loop.
    
You may be used to ending `main()` with a `return;` of some type. On bare metal, however, one should not return from main, as there's no operating system to return to. Removing it will cause the system to jump to arbitrary code, with unforeseen consequences!
</WRAP>

With only an infinite loop in ''main'', it's clear that the code won't do anything. Let's make it do something!

===== Throwing shade =====

For now, we're going to assume a "mono" program - we'll introduce the color mode in a later chapter. On the "mono" WonderSwan, the palette pipeline that converts tile information to display shades consists of two parts: the //palette//, mapping each of the four possible palette //indexes// to one of eight color values; and a //shade look-up table//, mapping each of the color values to one of the sixteen total shades which the panel can display.

<mermaid>
graph LR
A[Palette index<br><i>one of four colors</i>] -->|palette<br><i>one of sixteen</i>| B[Color value<br><i>one of eight values</i>] 
B -->|shade look-up table<br><i>global</i>| C[Shade<br><i>one of sixteen values</i>]
</mermaid>

First, we need to initialize the shade look-up table. At the beginning of ''main'', add the following function call:

<code C>
    ws_display_set_shade_lut(WS_DISPLAY_SHADE_LUT_DEFAULT);
</code>

This sets a default shade look-up table, with the color value ''0'' corresponding to the brightest shade (''0'') and ''7'' to the darkest shade (''15'').

<WRAP round info>
As the "mono" WonderSwan's panel is a monochrome LCD, it's shades with //lower// values which are brighter. The opposite is true for the WonderSwan Color's RGB values.
</WRAP>

Next, we need to enable the display. We're going to enable the "screen 1" layer - as the WonderSwan's memory is zeroed by default, this should not cause anything to be drawn to the screen, but will enable viewing the background color - which, by default, is the first of eight //color values//:

<code C>
    outportw(WS_DISPLAY_CTRL_PORT, WS_DISPLAY_CTRL_SCR1_ENABLE);
</code>

Finally, we're going to do some changes to the display. Edit the ''while(1)'' loop as follows to cycle the first palette:

<code C>
while (1) {
    outportw(WS_SCR_PAL_0_PORT, inportw(WS_SCR_PAL_0_PORT) + 1); // (1)!
    ws_delay_ms(1000); // (2)!
}
</code>

  - This loads the first palette, adds one to it, and saves it. As the lowest bits constitute the color value for the first palette index, this will cause the background color to change on every execution.
  - As we don't have any interrupts set up yet, the only thing we can do is busy-wait - that is, stall the CPU for a specified number of milliseconds.

That's all! Compile the code using ''make'' and run it in your emulator of choice. If done correctly, you should see the display slowly change colors from brightest to darkest and back again.