feat(examples): add Matrix digital-rain SDL2 app

examples/SDL2_Matrix/.gitignore

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+matrix

examples/SDL2_Matrix/Makefile

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+CC       ?= gcc
+CFLAGS   ?= -std=c11 -Wall -Wextra -O2
+PKGS     := sdl2 SDL2_ttf
+PKG_CFLAGS := $(shell pkg-config --cflags $(PKGS))
+PKG_LIBS   := $(shell pkg-config --libs $(PKGS))
+
+TARGET := matrix
+SRC    := main.c
+
+all: $(TARGET)
+
+$(TARGET): $(SRC)
+	$(CC) $(CFLAGS) $(PKG_CFLAGS) $(SRC) -o $(TARGET) $(PKG_LIBS) -lm
+
+clean:
+	rm -f $(TARGET)
+
+.PHONY: all clean

examples/SDL2_Matrix/main.c

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+/*
+ * Matrix digital rain for CardputerZero (320x170, SDL2).
+ *
+ * Ported from the Phoebe LVGL app (app_matrix). Falling columns of green
+ * glyphs on a dark base -- pure eye-candy, no network or sensors. Renders in
+ * the desktop emulator window and on-device via the KMSDRM/Wayland backend.
+ *
+ * Keys: ESC / Q quit.
+ */
+#include <SDL2/SDL.h>
+#include <SDL2/SDL_ttf.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define SCREEN_W 320
+#define SCREEN_H 170
+#define TICK_MS  16
+
+#define FONT_PATH_1 "/usr/share/fonts/truetype/dejavu/DejaVuSansMono.ttf"
+#define FONT_PATH_2 "/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf"
+
+#define GLYPH_W  10   /* column pitch in px */
+#define GLYPH_H  14   /* row pitch in px    */
+#define COLS     (SCREEN_W / GLYPH_W)
+#define ROWS     (SCREEN_H / GLYPH_H + 2)
+
+static const char CHARSET[] =
+    "0123456789ABCDEFGHJKLMNPQRSTUVWXYZ#$%&*+=<>?";
+static const int CHARSET_N = (int)sizeof(CHARSET) - 1;
+
+/* xorshift32 -- same generator the original app used. */
+static uint32_t rng_state = 0x1234abcdu;
+static uint32_t xrand(void) {
+    uint32_t x = rng_state;
+    x ^= x << 13; x ^= x >> 17; x ^= x << 5;
+    rng_state = x;
+    return x;
+}
+
+typedef struct {
+    float head;     /* y of the leading glyph, in rows (may be negative) */
+    float speed;    /* rows per tick */
+    int   len;      /* trail length in rows */
+    char  glyph[ROWS + 4];
+} Column;
+
+static Column cols[COLS];
+
+static void column_reset(Column *c, int seed_above) {
+    c->head  = seed_above ? -(float)(xrand() % (ROWS * 2)) : 0.0f;
+    c->speed = 0.15f + (xrand() % 100) / 300.0f;   /* 0.15 .. ~0.48 rows/tick */
+    c->len   = 5 + (int)(xrand() % (ROWS - 4));
+    for (int i = 0; i < ROWS + 4; i++)
+        c->glyph[i] = CHARSET[xrand() % CHARSET_N];
+}
+
+static void draw_glyph(SDL_Renderer *ren, TTF_Font *font, char ch,
+                       int px, int py, SDL_Color c) {
+    if (!font) return;
+    char s[2] = { ch, 0 };
+    SDL_Surface *surf = TTF_RenderUTF8_Blended(font, s, c);
+    if (!surf) return;
+    SDL_Texture *tex = SDL_CreateTextureFromSurface(ren, surf);
+    SDL_Rect dst = { px, py, surf->w, surf->h };
+    SDL_FreeSurface(surf);
+    if (!tex) return;
+    SDL_RenderCopy(ren, tex, NULL, &dst);
+    SDL_DestroyTexture(tex);
+}
+
+int main(int argc, char **argv) {
+    (void)argc; (void)argv;
+
+    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_EVENTS) != 0) {
+        fprintf(stderr, "SDL_Init: %s\n", SDL_GetError());
+        return 1;
+    }
+    if (TTF_Init() != 0) {
+        fprintf(stderr, "TTF_Init: %s\n", TTF_GetError());
+        SDL_Quit();
+        return 1;
+    }
+
+    SDL_Window *win = SDL_CreateWindow("Matrix",
+        SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
+        SCREEN_W, SCREEN_H, SDL_WINDOW_BORDERLESS);
+    if (!win) { fprintf(stderr, "SDL_CreateWindow: %s\n", SDL_GetError());
+                TTF_Quit(); SDL_Quit(); return 1; }
+
+    SDL_Renderer *ren = SDL_CreateRenderer(win, -1, SDL_RENDERER_SOFTWARE);
+    if (!ren) { fprintf(stderr, "SDL_CreateRenderer: %s\n", SDL_GetError());
+                SDL_DestroyWindow(win); TTF_Quit(); SDL_Quit(); return 1; }
+
+    TTF_Font *font = TTF_OpenFont(FONT_PATH_1, 12);
+    if (!font) font = TTF_OpenFont(FONT_PATH_2, 12);
+    if (!font) fprintf(stderr, "TTF_OpenFont: %s\n", TTF_GetError());
+
+    for (int i = 0; i < COLS; i++) column_reset(&cols[i], 1);
+
+    int running = 1;
+    while (running) {
+        Uint32 now = SDL_GetTicks();
+        SDL_Event ev;
+        while (SDL_PollEvent(&ev)) {
+            if (ev.type == SDL_QUIT) running = 0;
+            else if (ev.type == SDL_KEYDOWN) {
+                SDL_Keycode k = ev.key.keysym.sym;
+                if (k == SDLK_ESCAPE || k == SDLK_q) running = 0;
+            }
+        }
+
+        /* advance + draw */
+        SDL_SetRenderDrawColor(ren, 0x00, 0x10, 0x05, 255); /* dark green base */
+        SDL_RenderClear(ren);
+
+        for (int i = 0; i < COLS; i++) {
+            Column *c = &cols[i];
+            c->head += c->speed;
+            /* occasionally mutate a glyph so columns shimmer */
+            if ((xrand() & 0x1f) == 0)
+                c->glyph[xrand() % (ROWS + 4)] = CHARSET[xrand() % CHARSET_N];
+
+            int px = i * GLYPH_W + 1;
+            int head_row = (int)c->head;
+            for (int t = 0; t < c->len; t++) {
+                int row = head_row - t;
+                if (row < 0 || row >= ROWS) continue;
+                SDL_Color col;
+                if (t == 0) {
+                    col = (SDL_Color){ 0xCC, 0xFF, 0xCC, 255 }; /* bright head */
+                } else {
+                    int fade = 255 - (t * 220 / c->len);
+                    if (fade < 30) fade = 30;
+                    col = (SDL_Color){ 0x22, (Uint8)(0x88 + fade / 4),
+                                       0x44, (Uint8)fade };
+                }
+                char ch = c->glyph[(row + i) % (ROWS + 4)];
+                draw_glyph(ren, font, ch, px, row * GLYPH_H, col);
+            }
+            if (head_row - c->len > ROWS) column_reset(c, 0);
+        }
+
+        SDL_RenderPresent(ren);
+
+        Uint32 elapsed = SDL_GetTicks() - now;
+        if (elapsed < TICK_MS) SDL_Delay(TICK_MS - elapsed);
+    }
+
+    if (font) TTF_CloseFont(font);
+    SDL_DestroyRenderer(ren);
+    SDL_DestroyWindow(win);
+    TTF_Quit();
+    SDL_Quit();
+    return 0;
+}

examples/SDL2_Matrix/packaging/build.sh

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+#!/usr/bin/env bash
+set -euo pipefail
+make

examples/SDL2_Matrix/packaging/ci-deps.sh

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+#!/usr/bin/env bash
+set -euo pipefail
+apt-get install -y libsdl2-dev libsdl2-ttf-dev

examples/SDL2_Matrix/packaging/meta.env

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+PKG_NAME=sdl2-matrix
+PKG_VERSION=0.1
+PKG_REVISION=m5stack1
+PKG_DESC="Matrix digital-rain screensaver for CardputerZero (SDL2)"
+PKG_DEPENDS="libsdl2-2.0-0, libsdl2-ttf-2.0-0, libwayland-client0, fonts-dejavu-core"
+APP_NAME="Matrix"
+APP_EXEC=/usr/share/APPLaunch/bin/sdl2-matrix
+APP_TERMINAL=false
+APP_ICON=share/images/sdl2-matrix.png

examples/SDL2_Matrix/packaging/stage.sh

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+#!/usr/bin/env bash
+set -euo pipefail
+
+install -D -m 0755 matrix "$STAGE$APP_INSTALL_DIR/matrix"
+
+# Wayland/KMSDRM launcher wrapper: CM0 runs a labwc Wayland compositor that
+# owns /dev/dri/card0, so probe for a live Wayland socket first, then fall
+# back kmsdrm -> offscreen. See SDL2_HelloWorld for the rationale.
+cat >"$STAGE$INSTALL_PREFIX/bin/$PKG_NAME" <<EOF
+#!/bin/sh
+LOG=/tmp/$PKG_NAME.log
+: >"\$LOG" 2>/dev/null || LOG=/dev/null
+
+if [ -z "\${XDG_RUNTIME_DIR:-}" ]; then
+    _uid=\$(id -u 2>/dev/null || echo 1000)
+    if [ -d "/run/user/\$_uid" ]; then
+        XDG_RUNTIME_DIR="/run/user/\$_uid"
+    elif [ -d "/run/user/1000" ]; then
+        XDG_RUNTIME_DIR="/run/user/1000"
+    fi
+    [ -n "\$XDG_RUNTIME_DIR" ] && export XDG_RUNTIME_DIR
+fi
+
+_wl_ok=0
+if [ -n "\${WAYLAND_DISPLAY:-}" ] && [ -n "\${XDG_RUNTIME_DIR:-}" ] && \\
+   [ -S "\$XDG_RUNTIME_DIR/\$WAYLAND_DISPLAY" ]; then
+    _wl_ok=1
+elif [ -n "\${XDG_RUNTIME_DIR:-}" ]; then
+    for _c in wayland-0 wayland-1; do
+        if [ -S "\$XDG_RUNTIME_DIR/\$_c" ]; then
+            WAYLAND_DISPLAY=\$_c
+            export WAYLAND_DISPLAY
+            _wl_ok=1
+            break
+        fi
+    done
+fi
+
+if [ -z "\${SDL_VIDEODRIVER:-}" ]; then
+    if [ "\$_wl_ok" = 1 ]; then
+        SDL_VIDEODRIVER=wayland
+    elif [ -e /dev/dri/card0 ]; then
+        SDL_VIDEODRIVER=kmsdrm
+    else
+        SDL_VIDEODRIVER=offscreen
+    fi
+    export SDL_VIDEODRIVER
+fi
+
+echo "[$PKG_NAME] driver=\$SDL_VIDEODRIVER WAYLAND_DISPLAY=\${WAYLAND_DISPLAY:-} XDG_RUNTIME_DIR=\${XDG_RUNTIME_DIR:-} uid=\$(id -u)" >>"\$LOG" 2>&1
+exec $APP_INSTALL_DIR/matrix "\$@" >>"\$LOG" 2>&1
+EOF
+chmod 0755 "$STAGE$INSTALL_PREFIX/bin/$PKG_NAME"