Add experimental raw vt100 UI backend

The intention of this is not to slowly reimplement curses but to provide
a minimal working terminal UI backend which can also be used for debugging,
fuzzing and in environments where curses is not available.

Currently no attempt is made to optimize terminal output. The amount of
flickering will depend on the smartness of your terminal emulator.

8 files changed, 273 insertions, 31 deletions

diff --git a/Makefile b/Makefile
index 5c92cda..3f261ae 100644
--- a/Makefile
+++ b/Makefile
@@ -21,6 +21,7 @@ MANPREFIX ?= ${PREFIX}/man
 VERSION = $(shell git describe --always --dirty 2>/dev/null || echo "0.2-git")
 
 CONFIG_HELP ?= 1
+CONFIG_CURSES ?= 1
 CONFIG_LUA ?= 1
 CONFIG_LPEG ?= 0
 CONFIG_TRE ?= 0
@@ -36,6 +37,7 @@ CFLAGS_VIS = $(CFLAGS_AUTO) $(CFLAGS_TERMKEY) $(CFLAGS_CURSES) $(CFLAGS_ACL) \
 
 CFLAGS_VIS += -DVIS_PATH=\"${SHAREPREFIX}/vis\"
 CFLAGS_VIS += -DCONFIG_HELP=${CONFIG_HELP}
+CFLAGS_VIS += -DCONFIG_CURSES=${CONFIG_CURSES}
 CFLAGS_VIS += -DCONFIG_LUA=${CONFIG_LUA}
 CFLAGS_VIS += -DCONFIG_LPEG=${CONFIG_LPEG}
 CFLAGS_VIS += -DCONFIG_TRE=${CONFIG_TRE}
diff --git a/README.md b/README.md
index 7254b77..a24b1e8 100644
--- a/README.md
+++ b/README.md
@@ -49,9 +49,8 @@ In order to build vis you will need a
 compiler, a [POSIX.1-2008](http://pubs.opengroup.org/onlinepubs/9699919799/)
 compatible environment as well as:
 
- * [libcurses](http://www.gnu.org/software/ncurses/), preferably in the
-   wide-character version
  * [libtermkey](http://www.leonerd.org.uk/code/libtermkey/)
+ * [curses](https://en.wikipedia.org/wiki/Curses_(programming_library)) (recommended)
  * [Lua](http://www.lua.org/) >= 5.2 (optional)
  * [LPeg](http://www.inf.puc-rio.br/~roberto/lpeg/) >= 0.12
    (optional runtime dependency required for syntax highlighting)
diff --git a/configure b/configure
index 2c689db..29bb5c5 100755
--- a/configure
+++ b/configure
@@ -23,6 +23,7 @@ Fine tuning of the installation directories:
   --mandir=DIR            man pages [PREFIX/share/man]
 
 Optional features:
+  --enable-curses         build with Curses terminal output [yes]
   --enable-lua            build with Lua support [auto]
   --enable-lpeg           build with support for statically linking to LPeg [auto]
   --enable-tre            build with TRE regex support [auto]
@@ -116,6 +117,7 @@ SHAREDIR='$(PREFIX)/share'
 MANDIR='$(PREFIX)/share/man'
 
 help=yes
+curses=yes
 lua=auto
 lpeg=auto
 tre=auto
@@ -135,6 +137,8 @@ case "$arg" in
 --static) static=yes ;;
 --enable-help|--enable-help=yes) help=yes ;;
 --disable-help|--enable-help=no) help=no ;;
+--enable-curses|--enable-curses=yes) curses=yes ;;
+--disable-curses|--enable-curses=no) curses=no ;;
 --enable-lua|--enable-lua=yes) lua=yes ;;
 --disable-lua|--enable-lua=no) lua=no ;;
 --enable-lpeg|--enable-lpeg=yes) lpeg=yes ;;
@@ -293,9 +297,12 @@ else
 	CONFIG_HELP=0
 fi
 
-# libcurses is a mandatory dependency
+CONFIG_CURSES=0
+
+if test "$curses" != "no" ; then
+
+	printf "checking for libcurses...\n"
 
-printf "checking for libcurses...\n"
 cat > "$tmpc" <<EOF
 #include <curses.h>
 
@@ -306,36 +313,37 @@ int main(int argc, char *argv[]) {
 }
 EOF
 
-CONFIG_CURSES=0
+	for libcurses in ncursesw ncurses libcurses; do
+		printf " checking for %s... " "$libcurses"
 
-for curses in ncursesw ncurses curses; do
-	printf " checking for %s... " "$curses"
+		if test "$have_pkgconfig" = "yes" ; then
+			CFLAGS_CURSES=$(pkg-config --cflags $libcurses 2>/dev/null)
+			LDFLAGS_CURSES=$(pkg-config --libs $libcurses 2>/dev/null)
+			if test $? -eq 0 && $CC $CFLAGS $CFLAGS_CURSES "$tmpc" \
+				$LDFLAGS $LDFLAGS_CURSES -o "$tmpo" >/dev/null 2>&1 ; then
+				CONFIG_CURSES=1
+				printf "yes\n"
+				break
+			fi
+		fi
 
-	if test "$have_pkgconfig" = "yes" ; then
-		CFLAGS_CURSES=$(pkg-config --cflags $curses 2>/dev/null)
-		LDFLAGS_CURSES=$(pkg-config --libs $curses 2>/dev/null)
-		if test $? -eq 0 && $CC $CFLAGS $CFLAGS_CURSES "$tmpc" \
+		CFLAGS_CURSES=""
+		LDFLAGS_CURSES="-l$libcurses"
+
+		if $CC $CFLAGS $CFLAGS_CURSES "$tmpc" \
 			$LDFLAGS $LDFLAGS_CURSES -o "$tmpo" >/dev/null 2>&1 ; then
 			CONFIG_CURSES=1
 			printf "yes\n"
 			break
+		else
+			CFLAGS_CURSES=""
+			LDFLAGS_CURSES=""
+			printf "no\n"
 		fi
-	fi
-
-	CFLAGS_CURSES=""
-	LDFLAGS_CURSES="-l$curses"
-
-	if $CC $CFLAGS $CFLAGS_CURSES "$tmpc" \
-		$LDFLAGS $LDFLAGS_CURSES -o "$tmpo" >/dev/null 2>&1 ; then
-		CONFIG_CURSES=1
-		printf "yes\n"
-		break
-	else
-		printf "no\n"
-	fi
-done
+	done
 
-test $CONFIG_CURSES -ne 1 && fail "$0: cannot find libcurses"
+	test "$curses" = "yes" -a $CONFIG_CURSES -ne 1 && fail "$0: cannot find libcurses"
+fi
 
 # libtermkey is a mandatory dependency
 
@@ -356,7 +364,7 @@ fi
 
 if test -z "$LDFLAGS_TERMKEY"; then
 	CFLAGS_TERMKEY=""
-	LDFLAGS_TERMKEY="-ltermkey"
+	LDFLAGS_TERMKEY="-ltermkey -lncursesw"
 fi
 
 if $CC $CFLAGS $CFLAGS_TERMKEY "$tmpc" $LDFLAGS $LDFLAGS_TERMKEY $LDFLAGS_CURSES \
@@ -591,11 +599,12 @@ printf "completing config.mk... "
 exec 3>&1 1>>config.mk
 
 cat << EOF
-CFLAGS_CURSES = $CFLAGS_CURSES
-LDFLAGS_CURSES = $LDFLAGS_CURSES
+CONFIG_HELP = $CONFIG_HELP
 CFLAGS_TERMKEY = $CFLAGS_TERMKEY
 LDFLAGS_TERMKEY = $LDFLAGS_TERMKEY
-CONFIG_HELP = $CONFIG_HELP
+CONFIG_CURSES = $CONFIG_CURSES
+CFLAGS_CURSES = $CFLAGS_CURSES
+LDFLAGS_CURSES = $LDFLAGS_CURSES
 REGEX_SRC = $REGEX_SRC
 CONFIG_TRE = $CONFIG_TRE
 CFLAGS_TRE = $CFLAGS_TRE
diff --git a/main.c b/main.c
index db6b994..c154eac 100644
--- a/main.c
+++ b/main.c
@@ -2061,7 +2061,8 @@ int main(int argc, char *argv[]) {
 		} else if (strcmp(argv[i], "--") == 0) {
 			break;
 		} else if (strcmp(argv[i], "-v") == 0) {
-			printf("vis %s%s%s%s%s%s\n", VERSION,
+			printf("vis %s%s%s%s%s%s%s\n", VERSION,
+			       CONFIG_CURSES ? " +curses" : "",
 			       CONFIG_LUA ? " +lua" : "",
 			       CONFIG_LPEG ? " +lpeg" : "",
 			       CONFIG_TRE ? " +tre" : "",
diff --git a/ui-terminal-vt100.c b/ui-terminal-vt100.c
new file mode 100644
index 0000000..8a73bb7
--- /dev/null
+++ b/ui-terminal-vt100.c
@@ -0,0 +1,211 @@
+/* This file is included from ui-terminal.c
+ *
+ * The goal is *not* to reimplement curses. Instead we aim to provide the
+ * simplest possible drawing backend for VT-100 compatible terminals.
+ * This is useful for debugging and fuzzing purposes as well as for environments
+ * with no curses support.
+ *
+ * Currently no attempt is made to optimize terminal output. The amount of
+ * flickering will depend on the smartness of your terminal emulator.
+ *
+ * The following terminal escape sequences are used:
+ *
+ *  - CSI ? 1049 h             Save cursor and use Alternate Screen Buffer (DECSET)
+ *  - CSI ? 1049 l             Use Normal Screen Buffer and restore cursor (DECRST)
+ *  - CSI ? 25 l               Hide Cursor (DECTCEM)
+ *  - CSI ? 25 h               Show Cursor (DECTCEM)
+ *  - CSI 2 J                  Erase in Display (ED)
+ *  - CSI row ; column H       Cursor Position (CUP)
+ *  - CSI ... m                Character Attributes (SGR)
+ *    - CSI 0 m                     Normal
+ *    - CSI 1 m                     Bold
+ *    - CSI 3 m                     Italicized
+ *    - CSI 4 m                     Underlined
+ *    - CSI 5 m                     Blink
+ *    - CSI 7 m                     Inverse
+ *    - CSI 22 m                    Normal (not bold)
+ *    - CSI 23 m                    Not italicized
+ *    - CSI 24 m                    Not underlined
+ *    - CSI 25 m                    Not blinking
+ *    - CSI 27 m                    Not inverse
+ *    - CSI 30-37,39                Set foreground color
+ *    - CSI 38 ; 2 ; R ; G ; B m    Set RGB foreground color
+ *    - CSI 40-47,49                Set background color
+ *    - CSI 48 ; 2 ; R ; G ; B m    Set RGB background color
+ *
+ * See http://invisible-island.net/xterm/ctlseqs/ctlseqs.txt
+ * for further information.
+ */
+#include <stdio.h>
+#include "buffer.h"
+
+#define ui_term_backend_init ui_vt100_init
+#define ui_term_backend_blit ui_vt100_blit
+#define ui_term_backend_clear ui_vt100_clear
+#define ui_term_backend_colors ui_vt100_colors
+#define ui_term_backend_resize ui_vt100_resize
+#define ui_term_backend_save ui_vt100_save
+#define ui_term_backend_restore ui_vt100_restore
+#define ui_term_backend_suspend ui_vt100_suspend
+#define ui_term_backend_resume ui_vt100_resume
+#define ui_term_backend_new ui_vt100_new
+#define ui_term_backend_free ui_vt100_free
+
+#define CELL_COLOR_BLACK   (CellColor){ .index = 0 }
+#define CELL_COLOR_RED     (CellColor){ .index = 1 }
+#define CELL_COLOR_GREEN   (CellColor){ .index = 2 }
+#define CELL_COLOR_YELLOW  (CellColor){ .index = 3 }
+#define CELL_COLOR_BLUE    (CellColor){ .index = 4 }
+#define CELL_COLOR_MAGENTA (CellColor){ .index = 5 }
+#define CELL_COLOR_CYAN    (CellColor){ .index = 6 }
+#define CELL_COLOR_WHITE   (CellColor){ .index = 7 }
+#define CELL_COLOR_DEFAULT (CellColor){ .index = 9 }
+
+#define CELL_ATTR_NORMAL    0
+#define CELL_ATTR_UNDERLINE (1 << 0)
+#define CELL_ATTR_REVERSE   (1 << 1)
+#define CELL_ATTR_BLINK     (1 << 2)
+#define CELL_ATTR_BOLD      (1 << 3)
+#define CELL_ATTR_ITALIC    (1 << 4)
+
+typedef struct {
+	UiTerm uiterm;
+	Buffer buf;
+} UiVt100;
+	
+static CellColor color_rgb(UiTerm *ui, uint8_t r, uint8_t g, uint8_t b) {
+	return (CellColor){ .r = r, .g = g, .b = b, .index = (uint8_t)-1 };
+}
+
+static CellColor color_terminal(UiTerm *ui, uint8_t index) {
+	return (CellColor){ .r = 0, .g = 0, .b = 0, .index = index };
+}
+
+
+static void output(const char *data, size_t len) {
+	fwrite(data, len, 1, stderr);
+	fflush(stderr);
+}
+
+static void output_literal(const char *data) {
+	output(data, strlen(data));
+}
+
+static void screen_alternate(bool alternate) {
+	output_literal(alternate ? "\x1b[?1049h" : "\x1b[0m" "\x1b[?1049l");
+}
+
+static void cursor_visible(bool visible) {
+	output_literal(visible ? "\x1b[?25h" : "\x1b[?25l");
+}
+
+static void ui_vt100_blit(UiTerm *tui) {
+	Buffer *buf = &((UiVt100*)tui)->buf;
+	buffer_clear(buf);
+	CellAttr attr = CELL_ATTR_NORMAL;
+	CellColor fg = CELL_COLOR_DEFAULT, bg = CELL_COLOR_DEFAULT;
+	int w = tui->width, h = tui->height;
+	Cell *cell = tui->cells;
+	/* erase screen, reposition cursor, reset attributes */
+	buffer_append0(buf, "\x1b[2J" "\x1b[H" "\x1b[0m");
+	for (int y = 0; y < h; y++) {
+		for (int x = 0; x < w; x++) {
+			CellStyle *style = &cell->style;
+			if (style->attr != attr) {
+
+				static struct {
+					CellAttr attr;
+					char on[4], off[4];
+				} cell_attrs[] = {
+					{ CELL_ATTR_BOLD, "1", "22" },
+					{ CELL_ATTR_ITALIC, "3", "23" },
+					{ CELL_ATTR_UNDERLINE, "4", "24" },
+					{ CELL_ATTR_BLINK, "5", "25" },
+					{ CELL_ATTR_REVERSE, "7", "27" },
+				};
+
+				for (size_t i = 0; i < LENGTH(cell_attrs); i++) {
+					CellAttr a = cell_attrs[i].attr;
+					if ((style->attr & a) == (attr & a))
+						continue;
+					buffer_appendf(buf, "\x1b[%sm",
+					               style->attr & a ? 
+					               cell_attrs[i].on :
+					               cell_attrs[i].off);
+				}
+
+				attr = style->attr;
+			}
+
+			if (!cell_color_equal(fg, style->fg)) {
+				fg = style->fg;
+				if (fg.index != (uint8_t)-1) {
+					buffer_appendf(buf, "\x1b[%dm", 30 + fg.index);
+				} else {
+					buffer_appendf(buf, "\x1b[38;2;%d;%d;%dm",
+					               fg.r, fg.g, fg.b);
+				}
+			}
+
+			if (!cell_color_equal(bg, style->bg)) {
+				bg = style->bg;
+				if (bg.index != (uint8_t)-1) {
+					buffer_appendf(buf, "\x1b[%dm", 40 + bg.index);
+				} else {
+					buffer_appendf(buf, "\x1b[48;2;%d;%d;%dm",
+					               bg.r, bg.g, bg.b);
+				}
+			}
+
+			buffer_append0(buf, cell->data);
+			cell++;
+		}
+	}
+	output(buffer_content(buf), buffer_length0(buf));
+}
+
+static void ui_vt100_clear(UiTerm *tui) { }
+
+static void ui_vt100_resize(UiTerm *tui, int width, int height) { }
+
+static void ui_vt100_save(UiTerm *tui) {
+	cursor_visible(true);
+}
+
+static void ui_vt100_restore(UiTerm *tui) {
+	cursor_visible(false);
+}
+
+static int ui_vt100_colors(Ui *ui) {
+	char *term = getenv("TERM");
+	return (term && strstr(term, "-256color")) ? 256 : 16;
+}
+
+static void ui_vt100_suspend(UiTerm *term) {
+	cursor_visible(true);
+	screen_alternate(false);
+}
+
+static void ui_vt100_resume(UiTerm *term) {
+	screen_alternate(true);
+	cursor_visible(false);
+}
+
+static bool ui_vt100_init(UiTerm *tui, const char *term) {
+	ui_vt100_resume(tui);
+	return true;
+}
+
+static UiTerm *ui_vt100_new(void) {
+	UiVt100 *vtui = calloc(1, sizeof *vtui);
+	if (!vtui)
+		return NULL;
+	buffer_init(&vtui->buf);
+	return (UiTerm*)vtui;
+}
+
+static void ui_vt100_free(UiTerm *tui) {
+	UiVt100 *vtui = (UiVt100*)tui;
+	ui_vt100_suspend(tui);
+	buffer_release(&vtui->buf);
+}
diff --git a/ui-terminal.c b/ui-terminal.c
index 67cabba..3b9ac3b 100644
--- a/ui-terminal.c
+++ b/ui-terminal.c
@@ -62,7 +62,11 @@ struct UiTermWin {
 	enum UiOption options;    /* display settings for this window */
 };
 
+#if CONFIG_CURSES
 #include "ui-terminal-curses.c"
+#else
+#include "ui-terminal-vt100.c"
+#endif
 
 __attribute__((noreturn)) static void ui_die(Ui *ui, const char *msg, va_list ap) {
 	UiTerm *tui = (UiTerm*)ui;
diff --git a/ui.h b/ui.h
index 41ef975..ee434fc 100644
--- a/ui.h
+++ b/ui.h
@@ -50,12 +50,27 @@ enum UiStyle {
 	UI_STYLE_MAX,
 };
 
+#if CONFIG_CURSES
 typedef uint64_t CellAttr;
 typedef short CellColor;
 
 static inline bool cell_color_equal(CellColor c1, CellColor c2) {
 	return c1 == c2;
 }
+#else
+typedef uint8_t CellAttr;
+typedef struct {
+	uint8_t r, g, b;
+	uint8_t index;
+} CellColor;
+
+static inline bool cell_color_equal(CellColor c1, CellColor c2) {
+	if (c1.index != (uint8_t)-1 || c2.index != (uint8_t)-1)
+		return c1.index == c2.index;
+	return c1.r == c2.r && c1.g == c2.g && c1.b == c2.b;
+}
+
+#endif
 
 typedef struct {
 	CellAttr attr;
diff --git a/vis-cmds.c b/vis-cmds.c
index 4f1512f..f38a96f 100644
--- a/vis-cmds.c
+++ b/vis-cmds.c
@@ -755,6 +755,7 @@ static bool cmd_help(Vis *vis, Win *win, Command *cmd, const char *argv[], Curso
 		const char *name;
 		bool enabled;
 	} configs[] = {
+		{ "Curses support: ", CONFIG_CURSES },
 		{ "Lua support: ", CONFIG_LUA },
 		{ "Lua LPeg statically built-in: ", CONFIG_LPEG },
 		{ "TRE based regex support: ", CONFIG_TRE },