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 ____________________ Racket Users list: http://lists.racket-lang.org/users
