<div dir="ltr">Is the problem that you need to use (more) absolute coordinates in the coordinate arguments to linear-gradient% (either that or set the origin of the dc, in the case that you wanted to create the brush only once)?<div> </div><div>Robby</div><div> </div></div><div class="gmail_extra"> <div class="gmail_quote">On Tue, Feb 11, 2014 at 10:49 AM, Jens Axel Søgaard <<a href="mailto:jensaxel@soegaard.net" target="_blank">jensaxel@soegaard.net</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">The intent of hc-append is that (hc-append p1 p2) draws p1 and p2 beside each other. The question is whether (hc-append p p) should draw to identical picts? When I use a non-solid brush I get the two ps are drawn differently. In (hc-append p1 p2) I was expecting a transformation (translation) on the brush. As a demonstration I offer the following program (a bit long, but hopefully clear. See a syntax-highligthed version here: <a href="http://pasterack.org/pastes/7953" target="_blank">http://pasterack.org/pastes/7953</a> The DrRacket output is here: <a href="http://imgur.com/5BRiY0Z" target="_blank">http://imgur.com/5BRiY0Z</a> /Jens Axel #lang racket (require pict) ; debug : value pict -> pict ; return a pict, that when drawn prints the ; brush and drawing context transformation (define (debug who pict) (dc (lambda (dc x y) (define b (send dc get-brush)) (define bt (send b get-transformation)) (define dct (send dc get-transformation)) (displayln (list who 'x x 'y y 'brush: bt 'dc: dct)) (draw-pict pict dc x y)) (pict-width pict) (pict-height pict))) (define r 20) ; use same box side for the entire example ; a black filled rectangle (define (rect) (filled-rectangle r r)) ;;; Examine whether hc-append does any transformation. "Expected Image: Two squares a black and a red" "Expected Transformation: Same for A and B. Some difference for C." (debug 'A (hc-append (debug 'B (rect)) (debug 'C (colorize (rect) "red" )))) ;;; -------------------------------------------------------------- (require racket/draw) ; colors (define (color: name) (send the-color-database find-color name)) (define red (color: "red")) (define green (color: "green")) (define blue (color: "blue")) ; square-path : real real real real -> path% ; make square with side r and upper left corner (x,y) (define (square-path x y w h) (define p (new dc-path%)) (send p move-to x y) (send p line-to x (+ y h)) (send p line-to (+ x w)(+ y h)) (send p line-to (+ x w)(+ y 0)) (send p line-to (+ x 0)(+ y 0)) p) ; fill : pict -> pict ; draw a path around pict using current pen and brush (define (fill pict) (define w (pict-width pict)) (define h (pict-height pict)) (dc (lambda (dc x y) (draw-pict pict dc x y) (send dc draw-path (square-path x y w h))) w h)) ; shady : pict -> pict ; Draws pict with a brush given by a linear, horizontal ; gradient from (0,0) to (0,2r). The colors are red->green->blue. (define (shady pict) (dc (lambda (dc x y) ; get old brush (define b (send dc get-brush)) ; make new brush, only change gradient (define new-brush (new brush% [color (send b get-color)] [style (send b get-style)] [stipple (send b get-stipple)] [gradient (new linear-gradient% [x0 0] [y0 0] [x1 (* 2 r)] [y1 0] ; horizontal gradient [stops (list (list 0 red) ; (0,0) to ( r,0) red->green (list 1/2 green) ; (r,0) to (2r,0) green->blue (list 1 blue))])] [transformation (send b get-transformation)])) ; use new brush to draw the pict (send dc set-brush new-brush) (draw-pict pict dc x y) ; restore old brush (send dc set-brush b)) (pict-width pict) (pict-height pict))) (define-syntax (echo stx) (syntax-case stx () [(_ expr) #'(values 'expr expr)])) (newline) (newline) "Expected: A (black) rectangle" (echo (rect)) "Expected: A rectangle filled with nothing (default brush is empty)" (echo (fill (rect))) "Expected: A rectangle filled with linear gradient (red to green)" (echo (shady (fill (rect)))) "Expected: Two red-to-green rectangles" (echo (hc-append (shady (fill (rect))) (shady (fill (rect))))) "Expected: Two red-to-green rectangles" (echo (let () (define p (shady (fill (rect)))) (hc-append p p))) -- Jens Axel Søgaard ____________________ Racket Users list: <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> </blockquote></div> </div>