[cairo-commit] cairo/src cairo_pattern.c,1.6,1.7

[David Reveman]

Committed by: davidr

Update of /cvs/cairo/cairo/src
In directory pdx:/tmp/cvs-serv3596/src

Modified Files:
	cairo_pattern.c 
Log Message:
Corrected some confusing comments about the math used for radial gradients

Index: cairo_pattern.c
===================================================================
RCS file: /cvs/cairo/cairo/src/cairo_pattern.c,v
retrieving revision 1.6
retrieving revision 1.7
diff -C2 -d -r1.6 -r1.7
*** a/cairo_pattern.c	30 Apr 2004 03:26:56 -0000	1.6
--- b/cairo_pattern.c	4 May 2004 11:01:18 -0000	1.7
***************
*** 621,638 ****
  		factor = (sqrt (ex * ex + ey * ey) - r0) * r1;
  	    } else {
! 	    /* Here we need to calulate distance c0 -> x; the distance from
! 	       the inner circle center c0, through point (ex, ey) to
! 	       point x where it crosses the outer circle. The gradient offset
! 	       can then be calculated within the distance of the inner and
! 	       outer circles.
! 	       
!                         y    y_x  (ex, ey)        
                 c0 -------------------+---------- x
                    \     |                  __--
                     \    |              __--
!                  r0 \   | c1_y     __--
                       \  |      __-- r1
                        \ |  __--
                        c1 --
  	       */
  
--- 621,646 ----
  		factor = (sqrt (ex * ex + ey * ey) - r0) * r1;
  	    } else {
! 	    /*
! 	                y         (ex, ey)
                 c0 -------------------+---------- x
                    \     |                  __--
                     \    |              __--
!                     \   |          __--
                       \  |      __-- r1
                        \ |  __--
                        c1 --
+ 
+ 	       We need to calulate distance c0->x; the distance from
+ 	       the inner circle center c0, through fragment position
+ 	       (ex, ey) to point x where it crosses the outer circle.
+ 
+ 	       From points c0, c1 and (ex, ey) we get angle C0. With
+ 	       angle C0 we calculate distance c1->y and c0->y and by
+ 	       knowing c1->y and r1, we also know y->x. Adding y->x to
+ 	       c0->y gives us c0->x. The gradient offset can then be
+ 	       calculated as:
+ 	       
+ 	       offset = (c0->e - r0) / (c0->x - r0)
+ 	       
  	       */