Module 0 checkpoint

Goal

One small ROM that proves you can build, run, read input, and draw a ROM-packed sprite. If this works, foundations are solid.

What you will see

• Text: count value
• A increments (edge-triggered)
• B resets
• Up to 12 star sprites drawn for the current count

Skills exercised

Skill	Lesson
Toolchain + ROM	L01
Update / render + vsync-paced present	L02
Joypad poll + pressed edges	L03
DFS sprite	L04
Mental model of the machine	L05
Debugging loop (any time)	L37 · reference

Build & run

source scripts/env.sh
make -C lessons/m0-checkpoint
# → lessons/m0-checkpoint/m0_checkpoint.z64

Open in Ares (Homebrew mode). Map controls if needed.

Self-check

• [ ] ROM builds without errors
• [ ] Ares shows the UI
• [ ] A increments once per press (not while held forever spamming — we use pressed)
• [ ] B resets to 0
• [ ] Stars appear as the count rises

Optional exercises

1. Change the star art in lessons/m0-checkpoint/assets/star.png.
2. Cap display at 8 stars but allow the counter to go higher (HUD vs icons).
3. Require Start to begin counting (simple two-state: title → play).

Full lesson source

The blocks below are imported from the real repository files at build time (VitePress <<< snippets). They are not hand-copied into this markdown.

lessons/m0-checkpoint/Makefile · lessons/m0-checkpoint/src/main.c

lessons/m0-checkpoint/Makefile

# Module 0 checkpoint — press A to count (+ sprite)
ROMNAME   := m0_checkpoint
ROM_TITLE := "M0 Checkpoint"

MKSPRITE_FLAGS := -f RGBA16

include ../../common/lesson.mk

lessons/m0-checkpoint/src/main.c

/**
 * Module 0 checkpoint
 * ============================================================================
 * Combines L01–L04: loop, joypad edges, DFS sprite.
 * A = +1 count (pressed, not held), B = reset, stars drawn for count.
 * If this ROM works, your foundations are solid.
 * DOCS: docs/guide/m0/checkpoint.md
 */


#include <libdragon.h>
#include <stdio.h>

int main(void)
{
    display_init(RESOLUTION_320x240, DEPTH_16_BPP, 2, GAMMA_NONE,
                 FILTERS_RESAMPLE);
    dfs_init(DFS_DEFAULT_LOCATION);
    rdpq_init();
    rdpq_text_register_font(1, rdpq_font_load_builtin(FONT_BUILTIN_DEBUG_VAR));
    joypad_init();

    sprite_t *star = sprite_load("rom:/star.sprite");
    int count = 0;
    char line[48];

    while (1) {
        joypad_poll();
        joypad_buttons_t pressed = joypad_get_buttons_pressed(JOYPAD_PORT_1);

        if (pressed.a) {
            count++;
        }
        if (pressed.b) {
            count = 0;
        }

        snprintf(line, sizeof(line), "Count: %d", count);

        surface_t *disp = display_get();
        rdpq_attach(disp, NULL);
        rdpq_clear((color_t){ .r = 10, .g = 28, .b = 24, .a = 255 });

        rdpq_text_print(NULL, 1, 24, 30, "Module 0 checkpoint");
        rdpq_text_print(NULL, 1, 24, 56, "A = +1   B = reset");
        rdpq_text_print(NULL, 1, 24, 90, line);

        if (star) {
            rdpq_set_mode_standard();
            rdpq_mode_alphacompare(1);
            /* Draw one star per count (capped so we do not fill the screen). */
            int n = count < 12 ? count : 12;
            for (int i = 0; i < n; i++) {
                float x = 24.0f + (float)(i % 6) * 40.0f;
                float y = 140.0f + (float)(i / 6) * 40.0f;
                rdpq_sprite_blit(star, x, y, NULL);
            }
        }

        rdpq_text_print(NULL, 1, 24, 220, "If this works, foundations are solid.");

        rdpq_detach_show();
    }
}

Next

Module 1 — 3D Literacy.