Fwd: New example to illustrate data buffer manipulation

Steve Moreau <[email protected]> Tue, 6 Nov 2012 11:50:59 +0100

Newsgroups	gmane.comp.lib.cairo
Message-ID	<CAD9K4eCjJAjiB1W+Arf+tf7aXyB5BcPERy7gXAixrrZZnXx-Sw@mail.gmail.com>

Hi all,

Following the question I asked here :
http://lists.freedesktop.org/archives/cairo/2012-November/023716.html, I
tried to make an example to illustrate :
- several layers flattening with transparency
- direct data buffer manipulation

As far I know, there is no example to do that (
http://cairographics.org/samples/ ?), so feel free to made it available if
you think it could help someone.

$ gcc -Wall -I/usr/include/cairo -o DirectBufferManipulation
DirectBufferManipulation.c -lcairo &&  ./DirectBufferManipulation

or

$ gcc -Wall `pkg-config --cflags cairo` -o DirectBufferManipulation
DirectBufferManipulation.c `pkg-config --libs cairo` &&
./DirectBufferManipulation

See you,

Steve

[image: Images intégrées 3]

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image.png (image/png, 2.1 KB) - not displayed

DirectBufferManipulation.c (text/x-csrc, 2.3 KB)

#include <stdlib.h>
#include <cairo.h>

int main(int argc, char* argv[])
{
  int width = 350;
  int height = 300;
  int stride;
  int x, y;
  unsigned char r, g, b, alpha;
  unsigned char* pDataBuf;
  unsigned char* pImageBuffer;
  
  cairo_surface_t* pLayer0Surface;
  cairo_t* pLayer0Context;

  cairo_surface_t* pLayer1Surface;
  cairo_t* pLayer1Context;

  cairo_surface_t* pLayer2Surface;  
  
  /* ---------- LAYER 0 : draw a white background fo example ---------- */
  pLayer0Surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, width, height);
  pLayer0Context = cairo_create(pLayer0Surface);
  stride = cairo_image_surface_get_stride(pLayer0Surface);

  /* ---------- LAYER 1 : draw a dark blue rectangle ---------- */
  pLayer1Surface = cairo_surface_create_similar(cairo_get_target(pLayer0Context), CAIRO_CONTENT_COLOR_ALPHA, width, height);
  pLayer1Context = cairo_create(pLayer1Surface);
  cairo_set_source_rgba(pLayer1Context, 0, 0, 0.4, 1);
  cairo_rectangle(pLayer1Context, 50, 0, 250, 250);
  cairo_fill(pLayer1Context);

  /* ---------- LAYER 2 // DIRECT BUFFER MANIPULATION : draw a green to transparent gradient manually ---------- */
  pDataBuf = (unsigned char*) malloc(stride*height);
  pLayer2Surface = cairo_image_surface_create_for_data (pDataBuf, CAIRO_FORMAT_ARGB32, width, height, stride);
  for (y=0; y<height; y++)
  {
    for (x=0; x<width; x++)
    {
      r = 0;
      g = 0x80;
      b = 0;
      alpha = y*255/height;
      
      r = r*alpha/255;
      g = g*alpha/255;
      b = b*alpha/255;
      
      *((unsigned int*) &pDataBuf[y*stride + x*4]) = alpha << 24 | r << 16 | g << 8 | b;
    }
  }
  
  cairo_set_source_surface(pLayer1Context, pLayer2Surface, 0, 0);
  cairo_paint(pLayer1Context);

  cairo_set_source_surface(pLayer0Context, pLayer1Surface, 0, 0);
  cairo_paint(pLayer0Context);
  
  /* ---------- FINALIZE // dump to PNG or access final buffer ---------- */
  pImageBuffer = cairo_image_surface_get_data(pLayer0Surface);
  /* ... do whatever with pImageBuffer */

  cairo_surface_write_to_png(pLayer0Surface, "image.png");
  
  cairo_surface_destroy(pLayer0Surface);
  cairo_surface_destroy(pLayer1Surface);
  cairo_surface_destroy(pLayer2Surface);
  free(pDataBuf);
  
  cairo_destroy(pLayer0Context);
  cairo_destroy(pLayer1Context);
  
  return 0;
}