terminal: add unifont font-handling

The unifont layer of libsystemd-terminal provides a fallback font for
situations where no system-fonts are available, or if you don't want to
deal with traditional font-formats for some reasons.

The unifont API mmaps a pre-compiled bitmap font that was generated out of
GNU-Unifont font-data. This guarantees, that all users of the font will
share the pages in memory. Furthermore, the layout of the binary file
allows accessing glyph data in O(1) without pre-rendering glyphs etc. That
is, the OS can skip loading pages for glyphs that we never access.

Note that this is currently a test-run and we want to include the binary
file in the GNU-Unifont package. However, until it was considered stable
and accepted by the maintainers, we will ship it as part of systemd. So
far it's only enabled with the experimental --enable-terminal, anyway.

1 files changed, 211 insertions, 0 deletions

diff --git a/src/libsystemd-terminal/unifont.c b/src/libsystemd-terminal/unifont.c
new file mode 100644
index 0000000000..9e0f718665
--- /dev/null
+++ b/src/libsystemd-terminal/unifont.c
@@ -0,0 +1,211 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright (C) 2014 David Herrmann <dh.herrmann@gmail.com>
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+/*
+ * Unifont
+ * This implements the unifont glyph-array parser and provides it via a simple
+ * API to the caller. No heavy transformations are performed so glyph-lookups
+ * stay as fast as possible.
+ */
+
+#include <endian.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include "macro.h"
+#include "unifont-def.h"
+#include "unifont-internal.h"
+#include "util.h"
+
+struct unifont {
+        unsigned long ref;
+
+        int fd;
+        const uint8_t *map;
+        size_t size;
+
+        unifont_header header;
+        const void *glyphs;     /* unaligned! */
+        size_t n_glyphs;
+        size_t glyphsize;
+};
+
+static int unifont_fetch_header(unifont *u) {
+        unifont_header h = { };
+        uint64_t glyphsize;
+
+        if (u->size < UNIFONT_HEADER_SIZE_MIN)
+                return -EBFONT;
+
+        assert_cc(sizeof(h) >= UNIFONT_HEADER_SIZE_MIN);
+        memcpy(&h, u->map, UNIFONT_HEADER_SIZE_MIN);
+
+        h.compatible_flags = le32toh(h.compatible_flags);
+        h.incompatible_flags = le32toh(h.incompatible_flags);
+        h.header_size = le32toh(h.header_size);
+        h.glyph_header_size = le16toh(h.glyph_header_size);
+        h.glyph_stride = le16toh(h.glyph_stride);
+        h.glyph_body_size = le64toh(h.glyph_body_size);
+
+        if (memcmp(h.signature, "DVDHRMUF", 8))
+                return -EBFONT;
+        if (h.incompatible_flags != 0)
+                return -EBFONT;
+        if (h.header_size < UNIFONT_HEADER_SIZE_MIN || h.header_size > u->size)
+                return -EBFONT;
+        if (h.glyph_header_size + h.glyph_body_size < h.glyph_header_size)
+                return -EBFONT;
+        if (h.glyph_stride * 16ULL > h.glyph_body_size)
+                return -EBFONT;
+
+        glyphsize = h.glyph_header_size + h.glyph_body_size;
+
+        if (glyphsize == 0 || glyphsize > u->size - h.header_size) {
+                u->n_glyphs = 0;
+        } else {
+                u->glyphs = u->map + h.header_size;
+                u->n_glyphs = (u->size - h.header_size) / glyphsize;
+                u->glyphsize = glyphsize;
+        }
+
+        memcpy(&u->header, &h, sizeof(h));
+        return 0;
+}
+
+static int unifont_fetch_glyph(unifont *u, unifont_glyph_header *out_header, const void **out_body, uint32_t ucs4) {
+        unifont_glyph_header glyph_header = { };
+        const void *glyph_body = NULL;
+        const uint8_t *p;
+
+        if (ucs4 >= u->n_glyphs)
+                return -ENOENT;
+
+        p = u->glyphs;
+
+        /* copy glyph-header data */
+        p += ucs4 * u->glyphsize;
+        memcpy(&glyph_header, p, MIN(sizeof(glyph_header), u->header.glyph_header_size));
+
+        /* copy glyph-body pointer */
+        p += u->header.glyph_header_size;
+        glyph_body = p;
+
+        if (glyph_header.width < 1)
+                return -ENOENT;
+        if (glyph_header.width > u->header.glyph_stride)
+                return -EBFONT;
+
+        memcpy(out_header, &glyph_header, sizeof(glyph_header));
+        *out_body = glyph_body;
+        return 0;
+}
+
+int unifont_new(unifont **out) {
+        _cleanup_(unifont_unrefp) unifont *u = NULL;
+        struct stat st;
+        int r;
+
+        assert_return(out, -EINVAL);
+
+        u = new0(unifont, 1);
+        if (!u)
+                return -ENOMEM;
+
+        u->ref = 1;
+        u->fd = -1;
+        u->map = MAP_FAILED;
+
+        u->fd = open(UNIFONT_PATH, O_RDONLY | O_CLOEXEC | O_NOCTTY);
+        if (u->fd < 0)
+                return -errno;
+
+        r = fstat(u->fd, &st);
+        if (r < 0)
+                return -errno;
+
+        u->size = st.st_size;
+        u->map = mmap(NULL, u->size, PROT_READ, MAP_PRIVATE, u->fd, 0);
+        if (u->map == MAP_FAILED)
+                return -errno;
+
+        r = unifont_fetch_header(u);
+        if (r < 0)
+                return r;
+
+        *out = u;
+        u = NULL;
+        return 0;
+}
+
+unifont *unifont_ref(unifont *u) {
+        if (!u || !u->ref)
+                return NULL;
+
+        ++u->ref;
+
+        return u;
+}
+
+unifont *unifont_unref(unifont *u) {
+        if (!u || !u->ref || --u->ref)
+                return NULL;
+
+        if (u->map != MAP_FAILED)
+                munmap((void*)u->map, u->size);
+        u->fd = safe_close(u->fd);
+        free(u);
+
+        return NULL;
+}
+
+unsigned int unifont_get_stride(unifont *u) {
+        assert(u);
+
+        return u->header.glyph_stride;
+}
+
+int unifont_lookup(unifont *u, unifont_glyph *out, uint32_t ucs4) {
+        unifont_glyph_header h = { };
+        const void *b = NULL;
+        unifont_glyph g = { };
+        int r;
+
+        assert_return(u, -EINVAL);
+
+        r = unifont_fetch_glyph(u, &h, &b, ucs4);
+        if (r < 0)
+                return r;
+
+        g.width = h.width * 8U;
+        g.height = 16U;
+        g.stride = u->header.glyph_stride;
+        g.cwidth = h.width;
+        g.data = b;
+
+        if (out)
+                memcpy(out, &g, sizeof(g));
+        return 0;
+}