Add libfonts_get_subpixel_expansion

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

3 files changed, 81 insertions, 4 deletions

diff --git a/Makefile b/Makefile
index c3dc40a..32ad9a5 100644
--- a/Makefile
+++ b/Makefile
@@ -34,6 +34,7 @@ PUBLIC_OBJ =\
 	libfonts_get_font_root_dirs.o\
 	libfonts_get_output_dpi.o\
 	libfonts_get_output_rendering_settings.o\
+	libfonts_get_subpixel_expansion.o\
 	libfonts_get_subpixel_order_class.o\
 	libfonts_parse_alias_line.o\
 	libfonts_parse_dir_line.o\
diff --git a/libfonts.h b/libfonts.h
index 7224c9a..3ecd123 100644
--- a/libfonts.h
+++ b/libfonts.h
@@ -303,7 +303,8 @@ enum libfonts_subpixel_order_class {
 	 *
 	 * Cells 2 and 3 have the aspect ratio
 	 * (width to height) 3:4 and cell 1 has
-	 * the aspect ratio 6:2
+	 * the aspect ratio 6:2; cell 1 occupies
+	 * a third of the pixel's height
 	 */
 	LIBFONTS_SUBPIXEL_ORDER_CLASS_BALANCED_11_23,
 
@@ -322,7 +323,8 @@ enum libfonts_subpixel_order_class {
 	 *
 	 * Cells 2 and 3 have the aspect ratio
 	 * (width to height) 4:3 and cell 1 has
-	 * the aspect ratio 2:6
+	 * the aspect ratio 2:6; cell 1 occupies
+	 * a third of the pixel's width
 	 */
 	LIBFONTS_SUBPIXEL_ORDER_CLASS_BALANCED_21_31,
 
@@ -341,7 +343,8 @@ enum libfonts_subpixel_order_class {
 	 *
 	 * Cells 2 and 3 have the aspect ratio
 	 * (width to height) 3:4 and cell 1 has
-	 * the aspect ratio 6:2
+	 * the aspect ratio 6:2; cell 1 occupies
+	 * a third of the pixel's height
 	 */
 	LIBFONTS_SUBPIXEL_ORDER_CLASS_BALANCED_32_11,
 
@@ -360,7 +363,8 @@ enum libfonts_subpixel_order_class {
 	 *
 	 * Cells 2 and 3 have the aspect ratio
 	 * (width to height) 4:3 and cell 1 has
-	 * the aspect ratio 2:6
+	 * the aspect ratio 2:6; cell 1 occupies
+	 * a third of the pixel's width
 	 */
 	LIBFONTS_SUBPIXEL_ORDER_CLASS_BALANCED_13_12
 };
@@ -2441,5 +2445,25 @@ int libfonts_unget_subpixel_order_class(enum libfonts_subpixel_order *,
                                         enum libfonts_subpixel_colour,
                                         enum libfonts_subpixel_colour);
 
+/**
+ * Get the width and height multipliers needed to
+ * turn a raster of pixel cells into a raster of
+ * subpixel cells
+ *
+ * `*widthmulp` * `*heightmulp` will never exceed
+ * `SIZE_MAX` (or even be close to it)
+ * 
+ * @param   layout      The subpixel layout
+ * @param   widthmulp   Output parameter for the width multiplier,
+ *                      this value is always positive
+ * @param   heightmulp  Output parameter for the height multiplier,
+ *                      this value is always positive
+ * @return              0 on success, -1 on failure
+ * 
+ * @throws  EINVAL  `layout` is `LIBFONTS_SUBPIXEL_ORDER_CLASS_OTHER`
+ * @throws  EINVAL  `layout` is unrecognised
+ */
+int libfonts_get_subpixel_expansion(enum libfonts_subpixel_order_class, size_t *restrict, size_t *restrict);
+
 
 #endif
diff --git a/libfonts_get_subpixel_expansion.c b/libfonts_get_subpixel_expansion.c
new file mode 100644
index 0000000..99f72ba
--- /dev/null
+++ b/libfonts_get_subpixel_expansion.c
@@ -0,0 +1,52 @@
+/* See LICENSE file for copyright and license details. */
+#include "common.h"
+#ifndef TEST
+
+
+int
+libfonts_get_subpixel_expansion(enum libfonts_subpixel_order_class layout, size_t *restrict widthmulp, size_t *restrict heightmulp)
+{
+	size_t w, h;
+
+	if (layout == LIBFONTS_SUBPIXEL_ORDER_CLASS_123) {
+		w = 3;
+		h = 1;
+	} else if (layout == LIBFONTS_SUBPIXEL_ORDER_CLASS_1_2_3) {
+		w = 1;
+		h = 3;
+	} else if (layout >= LIBFONTS_SUBPIXEL_ORDER_CLASS_11_23 &&
+		   layout <= LIBFONTS_SUBPIXEL_ORDER_CLASS_13_12) {
+		w = 2;
+		h = 2;
+	} else if (layout == LIBFONTS_SUBPIXEL_ORDER_CLASS_BALANCED_11_23 ||
+		   layout == LIBFONTS_SUBPIXEL_ORDER_CLASS_BALANCED_32_11) {
+		w = 2;
+		h = 3;
+	} else if (layout == LIBFONTS_SUBPIXEL_ORDER_CLASS_BALANCED_21_31 ||
+		   layout == LIBFONTS_SUBPIXEL_ORDER_CLASS_BALANCED_13_12) {
+		w = 3;
+		h = 2;
+	} else {
+		errno = EINVAL;
+		return -1;
+	}
+
+	if (widthmulp)
+		*widthmulp = w;
+	if (heightmulp)
+		*heightmulp = h;
+	return 0;
+}
+
+
+#else
+
+
+int
+main(void)
+{
+	return 0;
+}
+
+
+#endif