Created attachment 116078 [details]
Error output image

Hi,

I'm using version on debian Wheezy (1.12.2) or debian Jessie (1.14.0). Problem "works" on both version. As i use cairomm or vala, this problem is in cairo (vala doing precompilation source to C source).

I'm working with two image surfaces with format RGB16_565. One as source, and one as target. Sometimes using surface work fine, sometimes cairo gets another part of surface memmory, so get's another source part which I want.

Here is test in Vala language:
// start of Vala test
// modules: Cairo

const uint16 WIDTH = 720;
const uint16 HEIGHT = 360;

public Cairo.ImageSurface get_source () {
    Cairo.ImageSurface surface = new Cairo.ImageSurface (
                Cairo.Format.RGB16_565,
                WIDTH,
                HEIGHT);

    Cairo.Context cr = new Cairo.Context (surface);
    cr.set_antialias (Cairo.Antialias.NONE);
    cr.set_line_width (1.0);

    cr.rectangle (0, 0, WIDTH, HEIGHT);
    cr.set_source_rgb(0.5, 0.5, 0.5);
    cr.fill();

   for (uint16 y = 0; y < HEIGHT; y+=5) {
        cr.set_source_rgb (0.0, 0.0, y/(double)HEIGHT);
        cr.move_to(0, y);
        cr.line_to(WIDTH, y);
        cr.stroke();
    }

    for (uint16 x = 0; x < WIDTH; x+=10) {
        cr.set_source_rgb (0.0, x/(double)WIDTH, 0.0);
        cr.move_to (x, 0);
        cr.line_to (x, HEIGHT);
        cr.stroke();
    }

    surface.write_to_png ("source.png");
    return surface;
}

public void use_source (Cairo.ImageSurface source) {
    Cairo.ImageSurface surface = new Cairo.ImageSurface (
                Cairo.Format.RGB16_565,
                162,
                115);

    Cairo.Context cr = new Cairo.Context (surface);
    cr.set_antialias (Cairo.Antialias.NONE);
    cr.set_line_width (1.0);
    cr.set_source_surface (source, -166, -139);

    cr.arc(80, 60, 30, 0, 6.28);    // bad part
    cr.fill();

    cr.rectangle(0,0,162,30);       // right part
    cr.fill();

    surface.write_to_png ("target.png");
}

public int main (string [] args) {
    Cairo.ImageSurface source = get_source();
    use_source (source);

    return 0;
} // end of vala test

To compile, type:
 ~$ valac --pkg=cairo cairo-bug.vala

And Here is c++ test:

// Start of c++ test
#include <stdint.h>

#include <cairomm/surface.h>
#include <cairomm/context.h>

const uint16_t WIDTH = 720;
const uint16_t HEIGHT = 360;

Cairo::RefPtr<Cairo::ImageSurface> get_source () {
    Cairo::RefPtr<Cairo::ImageSurface> surface = Cairo::ImageSurface::create(
                Cairo::FORMAT_RGB16_565,
                WIDTH,
                HEIGHT);

    Cairo::RefPtr<Cairo::Context> cr = Cairo::Context::create(surface);
    cr->set_line_width(1.0);
    cr->set_antialias (Cairo::Antialias::ANTIALIAS_NONE);

    cr->rectangle (0, 0, WIDTH, HEIGHT);
    cr->set_source_rgb(0.5, 0.5, 0.5);
    cr->fill();

    for (uint16_t y = 0; y < HEIGHT; y+=5) {
        cr->set_source_rgb (0.0, 0.0, y/(double)HEIGHT);
        cr->move_to(0, y);
        cr->line_to(WIDTH, y);
        cr->stroke();
    }

    for (uint16_t x = 0; x < WIDTH; x+=10) {
        cr->set_source_rgb (0.0, x/(double)WIDTH, 0.0);
        cr->move_to (x, 0);
        cr->line_to (x, HEIGHT);
        cr->stroke();
    }

    surface->write_to_png ("source.png");
    return surface;
}

void use_source (Cairo::RefPtr<Cairo::ImageSurface> source) {
     Cairo::RefPtr<Cairo::ImageSurface> surface = Cairo::ImageSurface::create(
                Cairo::FORMAT_RGB16_565,
                162,
                115);

    Cairo::RefPtr<Cairo::Context> cr = Cairo::Context::create(surface);
    cr->set_line_width(1.0);
    cr->set_antialias (Cairo::Antialias::ANTIALIAS_NONE);
    cr->set_source (source, -166, -139);

    cr->arc(80, 60, 30, 0, 6.28);   // bad part
    cr->fill();

    cr->rectangle(0,0,162,30);      // right part
    cr->fill();

    surface->write_to_png ("target.png");
}

int main (int argv, char ** argc) {
    Cairo::RefPtr<Cairo::ImageSurface> source = get_source();
    use_source (source);

    return 0;
} // End of c++ test


To compile cairomm test, type:
 ~$ g++ `pkg-config --libs --cflags cairomm-1.0` -std=c++11 cairo-bug.cc -o cairo-bug

In attachment image you can see what fails. If I use RGB24 format, all works fine :)