backend-headless: Improve documentation

Add a section about the headless backend to the main Weston manual
page and describe the current CLI options as well the new
`--refresh-rate` one.

Fix the incorrect list of supported transforms in the CLI usage.

Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>

frontend/main.c

@@ -748,7 +748,8 @@ usage(int error_code)
 		"  --height=HEIGHT\tHeight of memory surface\n"
 		"  --scale=SCALE\t\tScale factor of output\n"
 		"  --transform=TR\tThe output transformation, TR is one of:\n"
-		"\tnormal 90 180 270 flipped flipped-90 flipped-180 flipped-270\n"
+		"\tnormal rotate-90 rotate-180 rotate-270 flipped flipped-rotate-90 flipped-rotate-180\n"
+		"\tflipped-rotate-270\n"
 		"  --use-pixman\t\tUse the pixman (CPU) renderer (deprecated alias for --renderer=pixman)\n"
 		"  --use-gl\t\tUse the GL renderer (deprecated alias for --renderer=gl)\n"
 		"  --no-outputs\t\tDo not create any virtual outputs\n"

man/weston.man

@@ -57,6 +57,10 @@ if installed.
 The PipeWire backend runs in memory without the need of graphical hardware and
 creates a PipeWire node for each output. It can be used to capture Weston
 outputs for processing with another application.
+.TP
+.I headless
+The headless backend runs in memory. It can be used to capture Weston outputs
+or to test client applications.
 .
 .\" ***************************************************************
 .SH SHELLS
@@ -289,6 +293,32 @@ See
 See
 .BR weston-vnc (7).
 .
+.SS headless backend options:
+.TP
+\fB\-\-width\fR=\fIW\fR, \fB\-\-height\fR=\fIH\fR
+Make the default size of each output
+.IR W x H " pixels."
+.TP
+.B \-\-scale\fR=\fIN\fR
+Give all outputs a scale factor of
+.IR N "."
+.TP
+\fB\-\-transform\fR=\fItransform\fR
+Transform for the output, which can be rotated in 90-degree steps
+and possibly flipped. Possible values are
+.BR normal ", " rotate-90 ", " rotate-180 ", " rotate-270 ", "
+.BR flipped ", " flipped-rotate-90 ", " flipped-rotate-180 ", and "
+.BR flipped-rotate-270 .
+.TP
+.B \-\-no\-outputs
+Do not create any virtual outputs.
+.TP
+.B \-\-refresh\-rate\fR=\fIN\fR
+Give all outputs a refresh rate of
+.IR N " mHz (60,000 mHz by default)."
+Supported values range from 0 mHz to 1,000,000 mHz. 0 is a special value
+that repaints as soon as possible on capture requests only, not on damages.
+.
 .
 .\" ***************************************************************
 .SH FILES