Convert test to doc figure for grdmix (#8011)

Author: PaulWessel

doc/rst/source/grdmix.rst

@@ -47,6 +47,15 @@ All *raster?*, *alpha*, *intensity* and *weights* files must have the same
 dimensions. The optional *alpha*, *intensity* and *weights* files may be
 replaced by constant values instead.
 
+.. figure:: /_images/GMT_mixing.*
+    :width: 600 px
+    :align: center
+
+    Breaking the NASA blue marble image into its red, green, and blue
+    components, taking the gradient of the topography at the same
+    spatial resolution (gray), and combining them to obtained a blue
+    marble image with slope shading.
+
 Required Arguments
 ------------------
 

test/grdmix/mixcompose.sh renamed to doc/scripts/GMT_mixing.sh

@@ -2,13 +2,13 @@
 # Test grdmix by deconstructing an image into r,g,b grids the
 # reassembly to another image.
 
-gmt begin mixcompose
-	gmt set MAP_FRAME_TYPE plain PS_MEDIA letter
+gmt begin GMT_mixing
+	gmt set MAP_FRAME_TYPE plain FONT_ANNOT_PRIMARY 7p,Helvetica,black
+	gmt grdgradient @earth_relief_20m_p -A45 -Nt1 -Gint.grd
+	gmt grdimage @earth_day_20m_p -JQ9c -B0 -Iint.grd
 	gmt grdmix @earth_day_01d -D -Glayer_%c.grd
-	gmt grdmix layer_R.grd layer_G.grd layer_B.grd -Ni -C -Gearth_day.tif
-	gmt grdimage earth_day.tif -JQ18c -B
-	gmt subplot begin 2x2 -Fs8.5c/4.25c -JQ8.5c -Rd -Srl -Scb -Y10c -M10p/4p -T"Deconstruct/construct Earth Day"
-		gmt grdimage @earth_day_01d -c
+	gmt subplot begin 2x2 -Fs4.2c/2.125c -JQ4.25c -Rd -Srr -Scb -B0 -M1p/0.5p -X9.3c
+		gmt grdimage int.grd -Cgray -c
 		gmt makecpt -T0/255 -Cwhite,red -H > t.cpt
 		gmt grdimage layer_R.grd -Ct.cpt -c
 		gmt makecpt -T0/255 -Cwhite,green -H > t.cpt

doc/scripts/images/GMT_mixing.ps.dvc

@@ -0,0 +1,5 @@
+outs:
+- md5: 2034c03edb88cfe33f2ceeffcc040bce
+  size: 2225728
+  hash: md5
+  path: GMT_mixing.ps

test/baseline/grdmix.dvc

@@ -1,5 +1,6 @@
 outs:
-- md5: 34cbcc424bd5ec8c24e637bb6b7c4525.dir
-  size: 241450
-  nfiles: 2
+- md5: 59f039fd8f4375bbdb65d34bbd09d9cc.dir
+  size: 31145
+  nfiles: 1
   path: grdmix
+  hash: md5