7 files changed, 92 insertions, 0 deletions
diff --git a/include/sway/commands.h b/include/sway/commands.h
index 4be40870..c6f5c2e0 100644
--- a/include/sway/commands.h
+++ b/include/sway/commands.h
@@ -284,6 +284,7 @@ sway_cmd output_cmd_max_render_time;
 sway_cmd output_cmd_mode;
 sway_cmd output_cmd_modeline;
 sway_cmd output_cmd_position;
+sway_cmd output_cmd_render_bit_depth;
 sway_cmd output_cmd_scale;
 sway_cmd output_cmd_scale_filter;
 sway_cmd output_cmd_subpixel;
diff --git a/include/sway/config.h b/include/sway/config.h
index 660245c1..aa71209d 100644
--- a/include/sway/config.h
+++ b/include/sway/config.h
@@ -247,6 +247,12 @@ enum scale_filter_mode {
 	SCALE_FILTER_SMART,
 };
 
+enum render_bit_depth {
+	RENDER_BIT_DEPTH_DEFAULT, // the default is currently 8
+	RENDER_BIT_DEPTH_8,
+	RENDER_BIT_DEPTH_10,
+};
+
 /**
  * Size and position configuration for a particular output.
  *
@@ -266,6 +272,7 @@ struct output_config {
 	enum wl_output_subpixel subpixel;
 	int max_render_time; // In milliseconds
 	int adaptive_sync;
+	enum render_bit_depth render_bit_depth;
 
 	char *background;
 	char *background_option;
diff --git a/sway/commands/output.c b/sway/commands/output.c
index d8ef2885..42230bd7 100644
--- a/sway/commands/output.c
+++ b/sway/commands/output.c
@@ -18,6 +18,7 @@ static const struct cmd_handler output_handlers[] = {
 	{ "modeline", output_cmd_modeline },
 	{ "pos", output_cmd_position },
 	{ "position", output_cmd_position },
+	{ "render_bit_depth", output_cmd_render_bit_depth },
 	{ "res", output_cmd_mode },
 	{ "resolution", output_cmd_mode },
 	{ "scale", output_cmd_scale },
diff --git a/sway/commands/output/render_bit_depth.c b/sway/commands/output/render_bit_depth.c
new file mode 100644
index 00000000..c419321e
--- /dev/null
+++ b/sway/commands/output/render_bit_depth.c
@@ -0,0 +1,29 @@
+#include <drm_fourcc.h>
+#include <strings.h>
+#include "sway/commands.h"
+#include "sway/config.h"
+
+struct cmd_results *output_cmd_render_bit_depth(int argc, char **argv) {
+	if (!config->handler_context.output_config) {
+		return cmd_results_new(CMD_FAILURE, "Missing output config");
+	}
+	if (!argc) {
+		return cmd_results_new(CMD_INVALID, "Missing bit depth argument.");
+	}
+
+	if (strcmp(*argv, "8") == 0) {
+		config->handler_context.output_config->render_bit_depth =
+			RENDER_BIT_DEPTH_8;
+	} else if (strcmp(*argv, "10") == 0) {
+		config->handler_context.output_config->render_bit_depth =
+			RENDER_BIT_DEPTH_10;
+	} else {
+		return cmd_results_new(CMD_INVALID,
+			"Invalid bit depth. Must be a value in (8|10).");
+	}
+
+	config->handler_context.leftovers.argc = argc - 1;
+	config->handler_context.leftovers.argv = argv + 1;
+	return NULL;
+}
+
diff --git a/sway/config/output.c b/sway/config/output.c
index 6d39c2f5..63c81382 100644
--- a/sway/config/output.c
+++ b/sway/config/output.c
@@ -1,5 +1,6 @@
 #define _POSIX_C_SOURCE 200809L
 #include <assert.h>
+#include <drm_fourcc.h>
 #include <stdbool.h>
 #include <string.h>
 #include <sys/socket.h>
@@ -67,6 +68,7 @@ struct output_config *new_output_config(const char *name) {
 	oc->subpixel = WL_OUTPUT_SUBPIXEL_UNKNOWN;
 	oc->max_render_time = -1;
 	oc->adaptive_sync = -1;
+	oc->render_bit_depth = RENDER_BIT_DEPTH_DEFAULT;
 	return oc;
 }
 
@@ -113,6 +115,9 @@ void merge_output_config(struct output_config *dst, struct output_config *src) {
 	if (src->adaptive_sync != -1) {
 		dst->adaptive_sync = src->adaptive_sync;
 	}
+	if (src->render_bit_depth != RENDER_BIT_DEPTH_DEFAULT) {
+		dst->render_bit_depth = src->render_bit_depth;
+	}
 	if (src->background) {
 		free(dst->background);
 		dst->background = strdup(src->background);
@@ -351,6 +356,23 @@ static int compute_default_scale(struct wlr_output *output) {
 	return 2;
 }
 
+/* Lists of formats to try, in order, when a specific render bit depth has
+ * been asked for. The second to last format in each list should always
+ * be XRGB8888, as a reliable backup in case the others are not available;
+ * the last should be DRM_FORMAT_INVALID, to indicate the end of the list. */
+static const uint32_t *bit_depth_preferences[] = {
+	[RENDER_BIT_DEPTH_8] = (const uint32_t []){
+		DRM_FORMAT_XRGB8888,
+		DRM_FORMAT_INVALID,
+	},
+	[RENDER_BIT_DEPTH_10] = (const uint32_t []){
+		DRM_FORMAT_XRGB2101010,
+		DRM_FORMAT_XBGR2101010,
+		DRM_FORMAT_XRGB8888,
+		DRM_FORMAT_INVALID,
+	},
+};
+
 static void queue_output_config(struct output_config *oc,
 		struct sway_output *output) {
 	if (output == root->noop_output) {
@@ -437,6 +459,22 @@ static void queue_output_config(struct output_config *oc,
 			oc->adaptive_sync);
 		wlr_output_enable_adaptive_sync(wlr_output, oc->adaptive_sync == 1);
 	}
+
+	if (oc && oc->render_bit_depth != RENDER_BIT_DEPTH_DEFAULT) {
+		const uint32_t *fmts = bit_depth_preferences[oc->render_bit_depth];
+		assert(fmts);
+
+		for (size_t i = 0; fmts[i] != DRM_FORMAT_INVALID; i++) {
+			wlr_output_set_render_format(wlr_output, fmts[i]);
+			if (wlr_output_test(wlr_output)) {
+				break;
+			}
+
+			sway_log(SWAY_DEBUG, "Preferred output format 0x%08x "
+				"failed to work, falling back to next in "
+				"list, 0x%08x", fmts[i], fmts[i + 1]);
+		}
+	}
 }
 
 bool apply_output_config(struct output_config *oc, struct sway_output *output) {
diff --git a/sway/meson.build b/sway/meson.build
index 1402db15..8eab31a2 100644
--- a/sway/meson.build
+++ b/sway/meson.build
@@ -188,6 +188,7 @@ sway_sources = files(
 	'commands/output/max_render_time.c',
 	'commands/output/mode.c',
 	'commands/output/position.c',
+	'commands/output/render_bit_depth.c',
 	'commands/output/scale.c',
 	'commands/output/scale_filter.c',
 	'commands/output/subpixel.c',
diff --git a/sway/sway-output.5.scd b/sway/sway-output.5.scd
index 55d8f719..4159a851 100644
--- a/sway/sway-output.5.scd
+++ b/sway/sway-output.5.scd
@@ -157,6 +157,21 @@ must be separated by one space. For example:
 	adaptive sync can improve latency, but can cause flickering on some
 	hardware.
 
+*output* <name> render_bit_depth 8|10
+	Controls the color channel bit depth at which frames are rendered; the
+	default is currently 8 bits per channel.
+
+	Setting higher values will not have an effect if hardware and software lack
+	support for such bit depths. Successfully increasing the render bit depth
+	will not necessarily increase the bit depth of the frames sent to a display.
+	An increased render bit depth may provide smoother rendering of gradients,
+	and screenshots which can more precisely store the colors of programs
+	which display high bit depth colors.
+
+	Warnings: this can break screenshot/screencast programs which have not been
+	updated to work with different bit depths. This command is experimental,
+	and may be removed or changed in the future.
+
 # SEE ALSO
 
 *sway*(5) *sway-input*(5)