Picture film inside a mask layer

The manual described film in a mask layer (6b99f67) with no picture of
it, and the paragraph named the control `Print exposure` where the
panel says `Print Exposure`.

A new scene, film_local, sets Kodak Ektar 100 on an upright alpine
frame — a negative, so it is printed and has a print exposure — then
adds a linear gradient, turns it by its rotate handle to fall from the
top, moves it onto the sky, shows the mask as its edge so the print
stays visible, and raises the layer's Print Exposure to burn the sky
in. Done Masking, then Before held. It puts the masks back to Tint
before undoing, as the other scenes expect.

The picture follows the film list's, under the paragraph it
illustrates. The bundled manual is regenerated to match.

tools/manual/scenes.py

@@ -57,6 +57,7 @@ TEAPOT = '_MG_4918'
 PANO_FIRST, PANO_LAST = '_MG_8320', '_MG_8331'
 NY_FIRST, NY_LAST = '_MG_8393', '_MG_8397'
 ALPS_ROW = ['_MG_8322', '_MG_8328']   # the second row of the alps, first and last
+ALPS_SKY = '_MG_8330'       # an upright alpine frame, its top third sky and cloud
 TOWER = '_MG_8693'          # towers shot looking up: verticals that converge
 ROAD = '_MG_8672'           # a road under a sky, with marks on it: masks and repair
 ROAD_MARK = (0.305, 0.794)  # a dark mark on its tarmac
@@ -1005,6 +1006,64 @@ def film():
     undo_all()
 
 
+FILM_LOCAL = 'Kodak Ektar 100'   # a negative, so it is printed and has a print exposure
+
+
+def choose_film(stock):
+    """`stock` chosen from the film list, which is open at its top."""
+    px, py, _, _ = film_list_origin()
+    vx0, vy0, vx1, vy1 = dr.rect(f'{stock}@Text')
+    dr.click(px + (vx0 + vx1) // 2, py + (vy0 + vy1) // 2)
+    pause(3)
+
+
+def gradient_over_top(to_fy):
+    """The linear gradient just added, turned to fall from the top of the
+    frame and its middle moved to `to_fy`. A new one is laid across the
+    middle facing right, its rotate handle below the centre: that handle,
+    dragged round to the right, turns it a quarter to face up."""
+    cx, cy = dr.photo(0.5, 0.5)
+    handles = [(int(h['x'] + h['w'] / 2), int(h['y'] + h['h'] / 2))
+               for h in dr.matches('id:GradientHandles::drag')]
+    rx, ry = max(handles, key=lambda p: p[1])
+    dr.drag(rx, ry, cx + (ry - cy), cy, 25)
+    pause(1.0)
+    dr.drag(cx, cy, *dr.photo(0.5, to_fy), 25)
+    pause(1.2)
+
+
+@scene(media=['film-local.gif'], sources=MASK_SRC + ['core/dr-film/src/**', 'core/dr-pipeline/src/ops/film_sim.rs'])
+def film_local():
+    """A negative stock on the whole photograph, then a gradient over the
+    sky whose Print Exposure burns it in, as a printer would under the
+    enlarger, the mask drawn as its edge so the print shows through; Done
+    Masking, then Before held."""
+    at_develop(ALPS_SKY)
+    in_column('Film@Button')
+    film_list_open()
+    choose_film(FILM_LOCAL)
+    tool('Local')
+    rec('film-local')
+    pause(0.6)
+    dr.click(*in_column('Linear@Button'))
+    pause(1.5)
+    gradient_over_top(0.36)
+    dr.click(*in_column('Edge@RadioButton'))   # an outline, so the tint hides nothing
+    pause(1.2)
+    slide('Print Exposure', 28, 30)
+    pause(2.0)
+    dr.click_on('Done Masking@Button')
+    pause(2.0)
+    hold_before(1.6)
+    pause(1.0)
+    cut()
+    tool('Local')           # masks shown tinted again, as the other scenes
+    dr.click(*in_column('Tint@RadioButton'))    # expect; offered while one exists
+    pause(0.6)
+    tool('Photo')
+    undo_all()
+
+
 FILM_LAST = 'Ilford HP5 Plus'   # the last stock `DevelopSession::film_choices` lists
 FILM_ROWS = 28                  # None and the 27 camera stocks
 FILM_ROW, FILM_LIST_MAX = 32, 320