Maintain coordinate system when using gradients

Sample: document this better
spec: test this and update past tests

Fixes #127

lib/squib/graphics/cairo_context_wrapper.rb

@@ -37,15 +37,17 @@ module Squib
           arg.scan(STOPS).each do |color, offset|
             linear.add_color_stop(offset.to_f, color)
           end
+          linear.matrix = matrix # match the coordinate systems - see bug 127
           @cairo_cxt.set_source(linear)
         elsif match = arg.match(RADIAL_GRADIENT)
           x1, y1, r1, x2, y2, r2  = match.captures
-          linear = Cairo::RadialPattern.new(x1.to_f, y1.to_f, r1.to_f,
+          radial = Cairo::RadialPattern.new(x1.to_f, y1.to_f, r1.to_f,
                                             x2.to_f, y2.to_f, r2.to_f)
+          radial.matrix = matrix # match the coordinate systems - see bug 127
           arg.scan(STOPS).each do |color, offset|
-            linear.add_color_stop(offset.to_f, color)
+            radial.add_color_stop(offset.to_f, color)
           end
-          @cairo_cxt.set_source(linear)
+          @cairo_cxt.set_source(radial)
         else
           @cairo_cxt.set_source_color(arg)
         end

samples/images

@@ -1 +1 @@
-Subproject commit 514af49430797daf7a69c31118b6056dc4abaf20
+Subproject commit 0714a8c2dee388b3f856d2a86d4efb95c5e3cde8

spec/graphics/cairo_context_wrapper_spec.rb

@@ -28,15 +28,15 @@ describe Squib::Graphics::CairoContextWrapper do
       expect { subject.set_source_squibcolor(nil) }.to raise_error('nil is not a valid color')
     end
 
-  end
-
-
     context 'regex variations for linear gradients' do
       before(:each) do
         dbl = double(Cairo::LinearPattern)
+        mtx = double(Cairo::Matrix)
         expect(Cairo::LinearPattern).to receive(:new).with(1,2,3,4).and_return(dbl)
         expect(dbl).to   receive(:add_color_stop).with(0.0, 'blue')
         expect(dbl).to   receive(:add_color_stop).with(1.0, 'red')
+        expect(cairo).to receive(:matrix).and_return(mtx)
+        expect(dbl).to   receive(:matrix=).with(mtx)
         expect(cairo).to receive(:set_source).with(dbl)
       end
 
@@ -49,9 +49,12 @@ describe Squib::Graphics::CairoContextWrapper do
     context 'regex variations for radial gradients' do
       before(:each) do
         dbl = double(Cairo::RadialPattern)
+        mtx = double(Cairo::Matrix)
         expect(Cairo::RadialPattern).to receive(:new).with(1,2,5,3,4,6).and_return(dbl)
         expect(dbl).to   receive(:add_color_stop).with(0.0, 'blue')
         expect(dbl).to   receive(:add_color_stop).with(1.0, 'red')
+        expect(cairo).to receive(:matrix).and_return(mtx)
+        expect(dbl).to   receive(:matrix=).with(mtx)
         expect(cairo).to receive(:set_source).with(dbl)
       end
 
@@ -64,24 +67,32 @@ describe Squib::Graphics::CairoContextWrapper do
     context 'regex handles hash notation' do
       it 'on radial patterns' do
         dbl = double(Cairo::RadialPattern)
+        mtx = double(Cairo::Matrix)
         expect(Cairo::RadialPattern).to receive(:new).with(1,2,5,3,4,6).and_return(dbl)
         expect(dbl).to   receive(:add_color_stop).with(0.0, '#def')
         expect(dbl).to   receive(:add_color_stop).with(1.0, '#112233')
+        expect(cairo).to receive(:matrix).and_return(mtx)
+        expect(dbl).to   receive(:matrix=).with(mtx)
         expect(cairo).to receive(:set_source).with(dbl)
         subject.set_source_squibcolor('(1,2,5) (3,4,6) #def@0 #112233@1')
       end
 
       it 'on linear patterns' do
         dbl = double(Cairo::LinearPattern)
+        mtx = double(Cairo::Matrix)
         expect(Cairo::LinearPattern).to receive(:new).with(1,2,3,4).and_return(dbl)
         expect(dbl).to   receive(:add_color_stop).with(0.0, '#def')
         expect(dbl).to   receive(:add_color_stop).with(1.0, '#112233')
+        expect(cairo).to receive(:matrix).and_return(mtx)
+        expect(dbl).to   receive(:matrix=).with(mtx)
         expect(cairo).to receive(:set_source).with(dbl)
         subject.set_source_squibcolor('(1,2) (3,4) #def@0 #112233@1')
       end
     end
 
-  context 'flips' do
+  end
+
+  context '#flip' do
     it 'in the basic case' do
       dbl = double(Cairo::Matrix)
       expect(Cairo::Matrix).to receive(:new).with(-1.0, 0.0, 0.0, -1.0, 6.0, 8.0).and_return(dbl)