drop shadows! they're a thing now.

Fixes #306, #264

samples/shadows/_blend_ops.rb

@@ -0,0 +1,20 @@
+require 'squib'
+
+orig = Cairo::ImageSurface.new(100,100)
+orig_cc = Cairo::Context.new(orig)
+orig_cc.circle(50,50, 30)
+orig_cc.set_source_color(:red)
+orig_cc.fill
+
+orig.write_to_png '_output/blend_orig.png'
+
+new_img = Cairo::ImageSurface.new(120, 120)
+new_cc = Cairo::Context.new(new_img)
+new_cc.set_source_color(:black)
+new_cc.rectangle(0,0,120,120)
+new_cc.fill
+new_cc.set_source orig
+new_cc.operator = :dest_in
+new_cc.paint
+
+new_img.write_to_png '_output/blend_new.png'

samples/shadows/_shadow.rb

@@ -0,0 +1,77 @@
+require_relative '../../lib/squib'
+# require 'squib'
+# The save_png method supports drop shadows on the final save
+# This is useful for when you want to generate images for your rulebook
+
+Squib::Deck.new(width: 100, height: 150) do
+  background color: '#abc'
+  svg file: '../spanner.svg',
+      x: 'middle - 25', y: 'middle - 25',
+      width: 50, height: 50
+
+  # Shadows off by default, i.e. shadow_radius is nil
+  # So our final dimensions are 100 - 2*15 and 150-2*15
+  save_png prefix: 'no_shadow_', trim: 15, trim_radius: 15
+
+  # Here's a nice-looking drop shadow
+  # Defaults are designed to be generally good, so I recommend just
+  # trying out a shadow_radius of 3 to 10 and see how it looks first
+  save_png prefix: 'with_shadow_', trim: 15, trim_radius: 15,
+           shadow_radius: 8,
+           shadow_offset_x: 3, shadow_offset_y: 3,  # about r / 2.5 looks good
+           shadow_trim: 2.5, # about r/ 3 looks good
+           shadow_color: '#101010aa' #tip: start the shadow color kinda transparent
+
+  # Don't want a blur? Use a radius of 0
+  save_png prefix: 'no_blur_', trim: 15, trim_radius: 15,
+           shadow_radius: 0
+
+  # Ok this next stop is crazytown, but it does give you ultimate control
+  # Remember that all Squib colors can also be gradients.
+  # They can be clunky but they do work here.
+  #   - x,y's are centered in the card itself
+  #   - stops go from fully empty to fully black
+  #   - we need to still turn on radius to get the effect
+  #   - but, this makes the upper-left corner not have a glowing effect and
+  #     have a harder edge, which (to my eye at least) feels more realistic
+  #     since the card would obscure the upper-left shadow at that angle
+  #   - this also allows you have a larger, softer blur without making it look
+  #     like it's glowing
+  #
+  # Oh just because it's easier to write we can use a ruby heredoc
+  save_png prefix: 'gradient_blur_', trim: 15, trim_radius: 15,
+           shadow_radius: 10,
+           shadow_color: <<~EOS
+              (25,25)
+              (175,175)
+              #0000@0.0
+              #000f@1.0
+           EOS
+
+  # This one looks weird I know but it's for regression testing
+  save_png prefix: 'with_shadow_test_',
+           trim: 15, trim_radius: 15, rotate: :clockwise,
+           shadow_offset_x: 5, shadow_offset_y: 25, shadow_radius: 10,
+           shadow_trim: 10,
+           shadow_color: '#123'
+end
+
+Squib::Deck.new(width:50, height: 50) do
+
+  # What if we had a transparent card but just some shapes?
+  # Like chits or something
+
+  # background defaults to fully transparent here
+
+  # star x: 50, y: 50, inner_radius: 15, outer_radius: 35,
+  #      fill_color: :red, stroke_color: :red
+
+  png file: 'doodle.png'
+
+  # save_png prefix: 'no_bg_shadow_', shadow_radius: 8, shadow_offset_x: 3, shadow_offset_y: 3
+  save_png prefix: 'transparent_bg_shadow_',
+           shadow_radius: 2,
+           shadow_offset_x: 2, shadow_offset_y: 2,
+           shadow_color: :black
+
+end