[Haskell-cafe] Ridiculously slow FFI, or cairo binding?

[Eugene Kirpichov]

Hello,

I've got two very simple programs that draw a very simple picture using
cairo, doing a couple hundred thousand of cairo calls.
One program is in C++. The other is in Haskell and uses the cairo library
bindings.

The C++ program completes in a fraction of a second, the Haskell program
takes about 7-8 seconds to run. They produce exactly the same output.

What could be at fault here? Why are the cairo bindings working so slow? (I
suppose there isn't too much cairo-specific stuff here, perhaps it's a
general FFI question?)

#include "cairo.h"
int main() {
   cairo_surface_t *surface =
cairo_image_surface_create(CAIRO_FORMAT_ARGB32, 1024, 768);
   cairo_t *cr = cairo_create(surface);
   cairo_set_source_rgb(cr, 0, 255, 0);
   for(int x = 0; x < 1024; x += 2) for(int y = 0; y < 768; y += 2) {
       cairo_rectangle(cr, x, y, 1, 1);
       cairo_fill(cr);
   }
   cairo_surface_write_to_png(surface, "picture.png");
   return 0;
}

module Main where

import qualified Graphics.Rendering.Cairo as C
import Control.Monad

main = C.withImageSurface C.FormatARGB32 1024 768 $ \s -> do
 C.renderWith s $ do
   C.setSourceRGBA 0 255 0 255
   forM_ [0,2..1024] $ \x -> do
     forM_ [0,2..768] $ \y -> do
       C.rectangle x y 1 1
       C.fill
 C.surfaceWriteToPNG s "picture.png"

-- 
Eugene Kirpichov
Principal Engineer, Mirantis Inc. http://www.mirantis.com/
Editor, http://fprog.ru/
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