Thanks very much for looking into this. I'm sure the docs will benefit from what you figure out!
Robby On Tue, Feb 11, 2014 at 3:54 PM, Jens Axel Søgaard <[email protected]>wrote: > 2014-02-11 20:07 GMT+01:00 Robby Findler <[email protected]>: > > I'm not sure I can give you more than just hints (and certainly not a > > specification) > > I suddenly realized I should look in the Cairo docs, to see their > intended usage. > > > but probably the difference is that pict->bitmap is drawing > > the pict at (0,0) in the DC and scribble is drawing it at some random > place. > > But yeah, I'm sorry, that's still just a guess. > > After some experiments I think the reason is that Cairo has both user > space coordinates (aka logical coordinates) and pattern space. When a > pattern is > created it has the same coordinate system has the user space, but if > a transformation is applied (to user space) the spaces become different. > > I haven't yet fully grokked what the implications are. > > It is still odd that DrRacket and Scribble render the same pict > differently though. > If I call (convert the-pict 'png-bytes) in DrRacket I get the correct > image, and > Scribble doesn't do anything more. > > > And the examples at that link are really fantastic! > > Thanks! > > > On Tue, Feb 11, 2014 at 1:03 PM, Jens Axel Søgaard < > [email protected]> > > wrote: > >> > >> 2014-02-11 19:39 GMT+01:00 Robby Findler <[email protected]>: > >> > 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)? > >> > >> The problem is that it is unspecified (as far as I know) whether brushes > >> used in picts are specified using absolute or relative coordinates. For > >> solid > >> brushes this makes no difference. For non-solid brushes (gradients and > >> textures) there is a choice to be made. I got surprised by the > >> behavior and thought > >> of it as a bug (I was looking for one - I have an example where a pict > >> shows up perfectly in DrRacket but renders differently in Scribble). > >> > >> If I in shady make a new gradient each time the pict is to be drawn, I > get > >> the > >> behavior I want: > >> > >> (new linear-gradient% > >> [x0 x] [y0 y] [x1 (+ x (* 2 r))] [y1 > >> y] ; 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))]) > >> > >> Since the pict constructors such as filled-rectangle use the pen, there > >> were no way to figure out what was intended. > >> > >> The last example here: shows that Scribble converts p and (pict->bitmap > p) > >> differently. I am still puzzled by this. > >> > >> > >> > http://soegaard.github.io/docs/metapict/metapict.html#%28part._example-rgb-triangle%29 > >> > >> /Jens Axel > >> > >> > >> > On Tue, Feb 11, 2014 at 10:49 AM, Jens Axel Søgaard > >> > <[email protected]> > >> > wrote: > >> >> > >> >> 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: > http://pasterack.org/pastes/7953 > >> >> The DrRacket output is here: http://imgur.com/5BRiY0Z > >> >> > >> >> /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: > >> >> http://lists.racket-lang.org/users > >> > > >> > > >> > >> > >> > >> -- > >> -- > >> Jens Axel Søgaard > > > > > > > > -- > -- > Jens Axel Søgaard >
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