Add libglitter_reorder_rasters

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

3 files changed, 59 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index 3afe4af..8ae2b95 100644
--- a/Makefile
+++ b/Makefile
@@ -34,6 +34,7 @@ OBJ =\
 	libglitter_get_colour_space_conversion_matrix_float.o\
 	libglitter_per_channel_desaturate_double.o\
 	libglitter_per_channel_desaturate_float.o\
+	libglitter_reorder_rasters.o\
 	libglitter_split_uint32_raster.o\
 	libglitter_split_uint64_raster.o\
 	libglitter_update_render_context.o
diff --git a/libglitter.h b/libglitter.h
index 4e339e7..79af0fd 100644
--- a/libglitter.h
+++ b/libglitter.h
@@ -79,6 +79,27 @@ typedef struct libglitter_render_context LIBGLITTER_RENDER_CONTEXT;
 
 
 /**
+ * Output primary colour
+ */
+enum libglitter_colour {
+	/**
+	 * Red primary colour
+	 */
+	LIBGLITTER_CHANNEL_RED = 0,
+
+	/**
+	 * Green primary colour
+	 */
+	LIBGLITTER_CHANNEL_GREEN = 1,
+
+	/**
+	 * Blue primary colour
+	 */
+	LIBGLITTER_CHANNEL_BLUE = 2
+};
+
+
+/**
  * Attempt to enable hardware acceleration
  * 
  * Currently this function doesn't do anything but call the
@@ -251,7 +272,28 @@ void libglitter_compose_uint8(uint8_t **, const uint8_t *restrict, size_t, size_
                               size_t, size_t, const LIBGLITTER_RENDER_CONTEXT *);
 
 
-/* TODO add function for reordering rasters according to the subpixel layout */
+/**
+ * Reorders a set of three rasters
+ * 
+ * When the function `libglitter_create_render_context` is called,
+ * the parameter named `cellmap` contains the values 0, 1, and 2,
+ * representing different channels: indices in the raster array.
+ * The values are not necessarily 0 for red, 1 for green, and 2 for blue,
+ * but this function lets the user reorder the rasters so that before
+ * calling this function the rasters may be in this order, but when
+ * call a `libglitter_compose_*` function after calling this function,
+ * that function will write to the correct rasters
+ * 
+ * @param  rasters  The array of the three rasters, on input the rasters
+ *                  shall be in the order (0) red, (1) green, (2) blue;
+ *                  the function will reorder them
+ * @param  colour1  The colour of the channel value 0 represents in `cellmap`
+ * @param  colour2  The colour of the channel value 1 represents in `cellmap`
+ * @param  colour3  The colour of the channel value 2 represents in `cellmap`
+ *
+ * The values `colour1`, `colour2`, `colour3` must be valid but distinct
+ */
+void libglitter_reorder_rasters(void **, enum libglitter_colour, enum libglitter_colour, enum libglitter_colour);
 
 
 /**
diff --git a/libglitter_reorder_rasters.c b/libglitter_reorder_rasters.c
new file mode 100644
index 0000000..5df590e
--- /dev/null
+++ b/libglitter_reorder_rasters.c
@@ -0,0 +1,15 @@
+/* See LICENSE file for copyright and license details. */
+#include "common.h"
+
+
+void
+libglitter_reorder_rasters(void **rasters, enum libglitter_colour colour1,
+                           enum libglitter_colour colour2, enum libglitter_colour colour3)
+{
+	void *channel1 = rasters[colour1];
+	void *channel2 = rasters[colour2];
+	void *channel3 = rasters[colour3];
+	rasters[0] = channel1;
+	rasters[1] = channel2;
+	rasters[2] = channel3;
+}