make TransformationMatrix#horizontal_displacement_multiply! public

* allows callers to use this method directly if they know it is
  applicable, avoid the processing cost of the multiply! method

lib/pdf/reader/page_state.rb

@@ -323,14 +323,11 @@ def process_glyph_displacement(w0, tj, word_boundary)
         # TODO: I'm pretty sure that tx shouldn't need to be divided by
         #       ctm[0] here, but this gets my tests green and I'm out of
         #       ideas for now
+        # TODO: support ty > 0
         if ctm.a == 1
-          @text_matrix.multiply!(1,  0,
-                                 0,  1,
-                                 tx, ty)
+          @text_matrix.horizontal_displacement_multiply!(tx)
         else
-          @text_matrix.multiply!(1,  0,
-                                 0,  1,
-                                 tx/ctm.a, ty)
+          @text_matrix.horizontal_displacement_multiply!(tx/ctm.a)
         end
         @font_size = @text_rendering_matrix = nil # invalidate cached value
       end

lib/pdf/reader/transformation_matrix.rb

@@ -63,7 +63,7 @@ def multiply!(a,b=nil,c=nil, d=nil,e=nil,f=nil)
         @f = f
       elsif a == 1 && b == 0 && c == 0 && d == 1 && f == 0
         # the other matrix is a horizontal displacement
-        horizontal_displacement_multiply!(a,b,c,d,e,f)
+        horizontal_displacement_multiply!(e)
       elsif @a == 1 && @b == 0 && @c == 0 && @d == 1 && @f == 0
         # I'm a horizontal displacement
         horizontal_displacement_multiply_reversed!(a,b,c,d,e,f)
@@ -79,21 +79,21 @@ def multiply!(a,b=nil,c=nil, d=nil,e=nil,f=nil)
       self
     end
 
-    private
-
     # Optimised method for when the second matrix in the calculation is
     # a simple horizontal displacement.
     #
     # Like this:
     #
-    #   [ 1 2 0 ]   [ 1 0 0 ]
-    #   [ 3 4 0 ] x [ 0 1 0 ]
-    #   [ 5 6 1 ]   [ 5 0 1 ]
+    #   [ 1 2 0 ]   [ 1  0 0 ]
+    #   [ 3 4 0 ] x [ 0  1 0 ]
+    #   [ 5 6 1 ]   [ e2 0 1 ]
     #
-    def horizontal_displacement_multiply!(a2,b2,c2, d2,e2,f2)
+    def horizontal_displacement_multiply!(e2)
       @e = @e + e2
     end
 
+    private
+
     # Optimised method for when the first matrix in the calculation is
     # a simple horizontal displacement.
     #

spec/transformation_matrix_spec.rb

@@ -5,7 +5,7 @@
 # The results in these specs were generated at
 # http://www.calcul.com/matrix-multiply-3x3-3x3 to ensure correctness.
 
-describe PDF::Reader::TransformationMatrix, "#multiply_with_an_object!" do
+describe PDF::Reader::TransformationMatrix, "#multiply!" do
   class PDF::Reader::TransformationMatrix
     # a helper method for tests
     def multiply_with_an_object!(m2)
@@ -167,3 +167,20 @@ def multiply_with_an_object!(m2)
   end
 
 end
+
+describe PDF::Reader::TransformationMatrix, "#horizontal_displacement_multiply!" do
+  context "with [2,3,0   4,5,0   6 7 1]" do
+    let(:matrix_one) { PDF::Reader::TransformationMatrix.new(2,3,4,5,6,7)}
+
+    context "and a horizontal displacement" do
+      let(:displacement) { 10 }
+
+      it "should set the new matrix values" do
+        matrix_one.horizontal_displacement_multiply!(displacement)
+
+        matrix_one.to_a.should == [2,3,0,  4,5,0,  16,7,1]
+      end
+
+    end
+  end
+end