Add support for mirrored text (mirror both text and characters for right-to-left)

Signed-off-by: Mattias Andrée <maandree@kth.se>

4 files changed, 39 insertions, 4 deletions

diff --git a/common.h b/common.h
index 5caf373..79f5507 100644
--- a/common.h
+++ b/common.h
@@ -2,6 +2,7 @@
 
 #include <sys/mman.h>
 #include <sys/stat.h>
+#include <alloca.h>
 #include <endian.h>
 #include <errno.h>
 #include <math.h>
diff --git a/demo.c b/demo.c
index 0e9a6d4..dbc20c7 100644
--- a/demo.c
+++ b/demo.c
@@ -17,8 +17,8 @@ main(void)
 
 	rendering.smoothing           = LIBSKRIFT_SUBPIXEL;
 	rendering.subpixel_order      = LIBSKRIFT_NONE;
-	rendering.flags               = LIBSKRIFT_MIRROR_CHARS * 0;
-	rendering.interletter_spacing = -5;
+	rendering.flags               = LIBSKRIFT_MIRROR_CHARS | LIBSKRIFT_MIRROR_TEXT;
+	rendering.interletter_spacing = 2;
 
 	if (libskrift_open_font_file(&font, DEMO_FONT)) {
 		perror("libskrift_open_font_file");
diff --git a/libskrift_create_context.c b/libskrift_create_context.c
index c1732c0..18cf961 100644
--- a/libskrift_create_context.c
+++ b/libskrift_create_context.c
@@ -6,6 +6,7 @@
                       LIBSKRIFT_NO_AUTOKERNING)
 
 #define IMPLEMENTED_FLAGS (LIBSKRIFT_REMOVE_GAMMA |\
+                           LIBSKRIFT_MIRROR_TEXT  |\
                            LIBSKRIFT_MIRROR_CHARS |\
                            FORCED_FLAGS) /* libschrift does not add gamma, so not handling is required */
 
diff --git a/libskrift_draw_text.c b/libskrift_draw_text.c
index 05f278c..cce2991 100644
--- a/libskrift_draw_text.c
+++ b/libskrift_draw_text.c
@@ -1,28 +1,61 @@
 /* See LICENSE file for copyright and license details. */
 #include "common.h"
 
+static void
+reverse_text(const char *text, char *s, size_t off)
+{
+	size_t n;
+	s[off] = '\0';
+	for (; *text; text += n) {
+		off -= n = grapheme_len(text);
+		memcpy(&s[off], text, n);
+	}
+}
+
 int
 libskrift_draw_text(LIBSKRIFT_CONTEXT *ctx, const char *text, const struct libskrift_colour *colour,
                     int16_t x, int16_t y, struct libskrift_image *image)
 {
 	struct libskrift_saved_grapheme saved = LIBSKRIFT_NO_SAVED_GRAPHEME;
 	struct libskrift_glyph *glyph;
+	char *buffer = NULL;
 	double xpos = 0, ypos = 0;
 	ssize_t len;
+	size_t n;
 	int r;
 
+	if (ctx->rendering.flags & LIBSKRIFT_MIRROR_TEXT) {
+		n = strlen(text);
+		if (n < 1024) {
+			buffer = alloca(n + 1);
+		} else {
+			buffer = malloc(n + 1);
+			if (!buffer)
+				return -1;
+		}
+		reverse_text(text, buffer, n);
+		text = buffer;
+		if (n < 1024)
+			buffer = NULL;
+	}
+
 	for (; *text; text += len) {
 		len = libskrift_get_cluster_glyph(ctx, text, &saved, xpos, ypos, &glyph);
-		if (len < 0)
+		if (len < 0) {
+			free(buffer);
 			return -1;
+		}
 
 		r = libskrift_apply_glyph(ctx, glyph, colour, x, y, image);
 		xpos += (glyph->advance + ctx->rendering.interletter_spacing) * ctx->x_advancement;
 		ypos += (glyph->advance + ctx->rendering.interletter_spacing) * ctx->y_advancement;
 		free(glyph);
-		if (r)
+		if (r) {
+			free(buffer);
 			return -1;
+		}
 	}
 
+	free(buffer);
 	return 0;
 }