Add a --scale-from option

A typical case for wanting to specify a scale on an output is making your
framebuffer be one size and scaling it to fill an output of a different size.
Instead of making the user calculate the scaling factors to be specified by
--scale, add a new option, --scale-from, that lets the user specify the
framebuffer size directly.  Compute the appropriate transform to achieve the
desired target size.

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
Reviewed-by: Andy Ritger <aritger@nvidia.com>

2 files changed, 45 insertions, 0 deletions

diff --git a/man/xrandr.man b/man/xrandr.man
index ba36ae3..ddc2804 100644
--- a/man/xrandr.man
+++ b/man/xrandr.man
@@ -41,6 +41,7 @@ xrandr \- primitive command line interface to RandR extension
 .br
 [\-\-panning \fIwidth\fPx\fIheight\fP[+\fIx\fP+\fIy\fP[/\fItrack_width\fPx\fItrack_height\fP+\fItrack_x\fP+\fItrack_y\fP[/\fIborder_left\fP/\fIborder_top\fP/\fIborder_right\fP/\fIborder_bottom\fP]]]]
 [\-\-scale \fIx\fPx\fIy\fP]
+[\-\-scale-from \fIw\fPx\fIh\fP]
 [\-\-transform \fIa\fP,\fIb\fP,\fIc\fP,\fId\fP,\fIe\fP,\fIf\fP,\fIg\fP,\fIh\fP,\fIi\fP]
 [\-\-primary]
 .br
@@ -199,6 +200,10 @@ Changes the dimensions of the output picture. Values superior to 1 will lead to
 a compressed screen (screen dimension bigger than the dimension of the output
 mode), and values below 1 leads to a zoom in on the output. This option is
 actually a shortcut version of the \fI\-\-transform\fP option.
+.IP "\-\-scale-from \fIw\fPx\fIh\fP"
+Specifies the size in pixels of the area of the framebuffer to be displayed on
+this output.
+This option is actually a shortcut version of the \fI\-\-transform\fP option.
 .IP \-\-primary
 Set the output as primary.
 It will be sorted first in Xinerama and RANDR geometry requests.
diff --git a/xrandr.c b/xrandr.c
index b7f468b..6683ceb 100644
--- a/xrandr.c
+++ b/xrandr.c
@@ -128,6 +128,7 @@ usage(void)
     fprintf(stderr, "      --same-as <output>\n");
     fprintf(stderr, "      --set <property> <value>\n");
     fprintf(stderr, "      --scale <x>x<y>\n");
+    fprintf(stderr, "      --scale-from <w>x<h>\n");
     fprintf(stderr, "      --transform <a>,<b>,<c>,<d>,<e>,<f>,<g>,<h>,<i>\n");
     fprintf(stderr, "      --off\n");
     fprintf(stderr, "      --crtc <crtc>\n");
@@ -324,6 +325,7 @@ struct _output {
     XRRPanning      panning;
 
     Bool    	    automatic;
+    int     	    scale_from_w, scale_from_h;
     transform_t	    transform;
 
     struct {
@@ -1166,6 +1168,30 @@ set_output_info (output_t *output, RROutput xid, XRROutputInfo *output_info)
 	    copy_transform (&output->transform, &output->crtc_info->current_transform);
 	else
 	    init_transform (&output->transform);
+    } else {
+	/* transform was already set for --scale or --transform */
+
+	/* for --scale-from, figure out the mode size and compute the transform
+	 * for the target framebuffer area */
+	if (output->scale_from_w > 0 && output->mode_info) {
+	    double sx = (double)output->scale_from_w /
+				output->mode_info->width;
+	    double sy = (double)output->scale_from_h /
+				output->mode_info->height;
+	    if (verbose)
+		printf("scaling %s by %lfx%lf\n", output->output.string, sx,
+		       sy);
+	    init_transform (&output->transform);
+	    output->transform.transform.matrix[0][0] = XDoubleToFixed (sx);
+	    output->transform.transform.matrix[1][1] = XDoubleToFixed (sy);
+	    output->transform.transform.matrix[2][2] = XDoubleToFixed (1.0);
+	    if (sx != 1 || sy != 1)
+		output->transform.filter = "bilinear";
+	    else
+		output->transform.filter = "nearest";
+	    output->transform.nparams = 0;
+	    output->transform.params = NULL;
+	}
     }
 
     /* set primary */
@@ -2490,6 +2516,20 @@ main (int argc, char **argv)
 	    output->changes |= changes_transform;
 	    continue;
 	}
+	if (!strcmp ("--scale-from", argv[i]))
+	{
+	    int w, h;
+	    if (!output) usage();
+	    if (++i>=argc) usage();
+	    if (sscanf (argv[i], "%dx%d", &w, &h) != 2)
+		usage ();
+	    if (w <=0 || h <= 0)
+		usage ();
+	    output->scale_from_w = w;
+	    output->scale_from_h = h;
+	    output->changes |= changes_transform;
+	    continue;
+	}
 	if (!strcmp ("--transform", argv[i])) {
 	    double  transform[3][3];
 	    int	    k, l;