Support Linux framebuffer as new backend

Author: shengwen-tw

.gitignore

@@ -1,8 +1,8 @@
 # Generated
 *.o
 *.o.d
-demo-sdl
-.demo-sdl
+demo-*
+.demo-*
 libtwin.a
 .libtwin.a
 libbackend.a

Makefile

@@ -93,6 +93,13 @@ libtwin.a_cflags-y += $(shell sdl2-config --cflags)
 TARGET_LIBS += $(shell sdl2-config --libs)
 endif
 
+ifeq ($(CONFIG_BACKEND_FBDEV), y)
+BACKEND = fbdev
+libtwin.a_files-y += backend/fbdev.c
+libtwin.a_cflags-y += $(shell sdl2-config --cflags)
+TARGET_LIBS += $(shell sdl2-config --libs)
+endif
+
 # Standalone application
 
 ifeq ($(CONFIG_DEMO_APPLICATIONS), y)

backend/fbdev.c

@@ -0,0 +1,187 @@
+/*
+ * Twin - A Tiny Window System
+ * Copyright (c) 2024 National Cheng Kung University, Taiwan
+ * All rights reserved.
+ */
+
+#include <fcntl.h>
+#include <linux/fb.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <twin.h>
+#include <unistd.h>
+
+#include "twin_backend.h"
+
+typedef struct {
+    int fd;
+    int depth;
+    int image_y;
+    int *pixels;
+    int *fbdev_raw;
+    twin_screen_t *screen;
+    twin_coord_t width, height;
+} twin_fbdev_t;
+
+#define FBDEV_ENVVAR "FRAMEBUFFER"
+#define SCREEN(x) ((twin_context_t *) x)->screen
+#define PRIV(x) ((twin_fbdev_t *) ((twin_context_t *) x)->priv)
+
+static void _twin_fbdev_put_begin(twin_coord_t left,
+                               twin_coord_t top,
+                               twin_coord_t right,
+                               twin_coord_t bottom,
+                               void *closure)
+{
+    twin_fbdev_t *tx = PRIV(closure);
+    tx->width = right - left;
+    tx->height = bottom - top;
+    tx->image_y = top;
+}
+
+static void _twin_fbdev_put_span(twin_coord_t left,
+                              twin_coord_t top,
+                              twin_coord_t right,
+                              twin_argb32_t *pixels,
+                              void *closure)
+{
+    twin_screen_t *screen = SCREEN(closure);
+    twin_fbdev_t *tx = PRIV(closure);
+
+    for (twin_coord_t ix = left, iy = top; ix < right; ix++) {
+        twin_argb32_t pixel = *pixels++;
+        tx->pixels[iy * screen->width + ix] = pixel;
+    }
+    if ((top + 1 - tx->image_y) == tx->height) {
+        /* Update the pixels to the framebuffer */
+        memcpy(tx->fbdev_raw, tx->pixels,
+               sizeof(uint32_t) * screen->width * screen->height);
+    }
+}
+
+static void twin_fbdev_get_screen_size(twin_fbdev_t *tx, int *width, int *height)
+{
+    struct fb_var_screeninfo info;
+    ioctl(tx->fd, FBIOGET_VSCREENINFO, &info);
+    *width = info.xres;
+    *height = info.yres;
+}
+
+static void twin_fbdev_damage(twin_screen_t *screen, twin_fbdev_t *tx)
+{
+    int width, height;
+    twin_fbdev_get_screen_size(tx, &width, &height);
+    twin_screen_damage(tx->screen, 0, 0, width, height);
+}
+
+static bool twin_fbdev_read_events(int file maybe_unused,
+                                twin_file_op_t ops maybe_unused,
+                                void *closure)
+{
+    /* TODO: Implement events handling for mouse, keyboard, etc. */
+    return true;
+}
+
+static bool twin_fbdev_work(void *closure)
+{
+    twin_screen_t *screen = SCREEN(closure);
+
+    if (twin_screen_damaged(screen))
+        twin_screen_update(screen);
+    return true;
+}
+
+twin_context_t *twin_fbdev_init(int width, int height)
+{
+    char *fbdev_path = getenv(FBDEV_ENVVAR);
+    if(!fbdev_path) {
+        printf("error : environment variable $FRAMEBUFFER not set\n");
+        return NULL;
+    }
+
+    twin_context_t *ctx = calloc(1, sizeof(twin_context_t));
+    if (!ctx)
+        return NULL;
+    ctx->priv = calloc(1, sizeof(twin_fbdev_t));
+    if (!ctx->priv)
+        return NULL;
+
+    twin_fbdev_t *tx = ctx->priv;
+
+    /* Open the framebuffer device */
+    tx->fd = open(fbdev_path, O_RDWR);
+    if (tx->fd == -1) {
+        printf("error : failed opening %s\n", fbdev_path);
+        goto bail;
+    }
+
+    /* Read framebuffer information */
+    struct fb_var_screeninfo info;
+    if (ioctl(tx->fd, FBIOGET_VSCREENINFO, &info) == -1) {
+        printf("error : failed getting framebuffer information\n");
+        goto bail_fd;
+    }
+    width = info.xres;
+    height = info.yres;
+
+    /* Create memory mapping for accessing the framebuffer */
+    tx->fbdev_raw = mmap(NULL, width * height * info.bits_per_pixel / 8,
+                      PROT_READ | PROT_WRITE, MAP_SHARED, tx->fd, 0);
+    if (tx->fbdev_raw == MAP_FAILED) {
+        printf("error : failed calling mmap()\n");
+        goto bail_fd;
+    }
+
+    /* Create buffer space for TWIN */
+    tx->pixels = malloc(width * height * sizeof(uint32_t));
+    if (!tx->pixels) {
+        printf("error : failed calling malloc()\n");
+        goto bail_fd;
+    }
+    memset(tx->pixels, 255, width * height * sizeof(uint32_t));
+
+    /* Create TWIN screen */
+    ctx->screen = twin_screen_create(width, height, _twin_fbdev_put_begin,
+                                     _twin_fbdev_put_span, ctx);
+
+    /* Setup file handler and work function for framebuffer backend */
+    twin_set_file(twin_fbdev_read_events, 0, TWIN_READ, ctx);
+    twin_set_work(twin_fbdev_work, TWIN_WORK_REDISPLAY, ctx);
+
+    return ctx;
+
+bail_fd:
+    close(tx->fd);
+bail:
+    free(ctx->priv);
+    free(ctx);
+    return NULL;
+}
+
+static void twin_fbdev_configure(twin_context_t *ctx)
+{
+    int width, height;
+    twin_fbdev_t *tx = ctx->priv;
+    twin_fbdev_get_screen_size(tx, &width, &height);
+    twin_screen_resize(ctx->screen, width, height);
+}
+
+static void twin_fbdev_exit(twin_context_t *ctx)
+{
+    if (!ctx)
+        return;
+    close(PRIV(ctx)->fd);
+    free(PRIV(ctx)->pixels);
+    free(ctx->priv);
+    free(ctx);
+}
+
+/* Register the Linux framebuffer backend */
+
+const twin_backend_t g_twin_backend = {
+    .init = twin_fbdev_init,
+    .configure = twin_fbdev_configure,
+    .exit = twin_fbdev_exit,
+};