Using Meson

Now that we have everything working, let’s take a look at how to use the meson build system. The game directory has a pre-written meson.build file, which you can use if you want to jump right in, but it’s pretty long, so for now, let’s start really simple, with a basic build file:

minrt = dependency('minrt')

elf = executable('guide-01', 'src/main.c',
  include_directories: ['include'],
  dependencies: [minrt],
  name_suffix: 'elf')

makerom = find_program('makerom')

rom = custom_target('guide-01-rom',
  input: elf,
  output: 'guide-01.gba',
  command: [makerom, '@INPUT@', '@OUTPUT@'],
  build_by_default: true)

1. We pull in dependencies (libraries that we want to use in our code) using the dependency() function.
2. We build our program as an ELF file using the executable() function.
3. We find external programs we want to use with find_program().
4. We use custom_target() to add custom build steps (like turning our ELF into a GBA ROM).

Pretty straightforward, right?

Let’s add a library, to help us use the GBA’s hardware, libseven:

# NEW!
libseven = dependency('libseven')
minrt = dependency('minrt')

elf = executable('guide-01', 'src/main.c',
  include_directories: ['include'],
  dependencies: [minrt, libseven], # <- NEW!
  name_suffix: 'elf')

makerom = find_program('makerom')

rom = custom_target('guide-01-rom',
  input: elf,
  output: 'guide-01.gba',
  command: [makerom, '@INPUT@', '@OUTPUT@'],
  build_by_default: true)

And write a basic program, that draws on the screen:

#include <seven/prelude.h>
#include <seven/hw/video.h>
#include <seven/hw/video/bg_bitmap.h>
#include <seven/hw/video/color_constants.h>

int main(void)
{
    // To wait for V-Blank, we need some rudimentary interrupt handling
    irqInitStub();
    irqEnableFull(IRQ_VBLANK);

    // Enable video mode 3, which lets us draw pixels directly to the screen
    REG_DISPCNT = VIDEO_MODE(3) | VIDEO_BG2_ENABLE;

    struct InputState input = inputNew();

    int x = 120;
    int y = 60;

    // Our main game loop runs forever
    while (true)
    {
        // Process inputs
        input = inputPoll(input);
        x += inputAxisX(input);
        y += inputAxisY(input);

        // Make sure x and y stay on the screen (240x160 pixels)
        if (x < 0) x = 0;
        if (x >= 240) x = 239;

        if (y < 0) y = 0;
        if (y >= 160) y = 159;

        // Wait for V-Blank so we can draw to the screen without tearing
        biosVBlankIntrWait();

        // Draw a pixel to the screen
        MODE3_FRAME[y][x] = COLOR_CYAN;
    }
}

And if we run it… hey!