Re: Horizontal artifacts rendering to an image surface

[email protected] (Søren Sandmann) Fri, 27 Jul 2012 23:43:00 +0200

Newsgroups	gmane.comp.lib.cairo
Message-ID	<[email protected]>

Floyd May <[email protected]> writes:

> I've been able to boil this down to a reproducible, small case.
> Basically, two four-point polygons where one edge from each is
> collinear.  Using even-odd rendering, I'm getting these artifacts:
>
> http://imagebin.org/222354
>
> Again, this is based on v 1.10.2, on Windows (both x86 and x64 exhibit
> the issue), based on a recent download of GTK+ binaries.
>
> Here is C# source (using Mono.Cairo; should be able to adapt to C code
> relatively easily):

FWIW, here is a C variant that shows the same artefact and also
demonstrates that it doesn't happen with the X backend. (To use the X
backend, set the "const int image" variable to 0).


Soren

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artefacts.c (text/x-csrc, 2.6 KB)

#include <math.h>
#include <gtk/gtk.h>
#include <stdio.h>

static void
path_quad (cairo_t *cr,
           double x1, double y1, double x2, double y2,
           double x3, double y3, double x4, double y4)
{
    cairo_move_to (cr, x1, y1);
    cairo_line_to (cr, x2, y2);
    cairo_line_to (cr, x3, y3);
    cairo_line_to (cr, x4, y4);
    cairo_close_path (cr);
}

const int image = 1;

static gboolean
on_expose (GtkWidget *widget, GdkEvent *event, gpointer data)
{
    if (GTK_WIDGET_DRAWABLE (widget))
    {
        cairo_t *cr;
        int w, h;
        cairo_surface_t *surface;

        gdk_drawable_get_size (widget->window, &w, &h);
	printf ("size: %d %d\n", w, h);

        if (image)
        {
            surface = cairo_image_surface_create (CAIRO_FORMAT_RGB24, w, h);
            cr = cairo_create (surface);
        }
        else
        {
            cr = gdk_cairo_create (widget->window);
        }

        cairo_rectangle (cr, 0, 0, w, h);
        cairo_set_source_rgba (cr, 1, 1, 1, 1.0);
        cairo_fill (cr);

	cairo_set_fill_rule (cr, CAIRO_FILL_RULE_EVEN_ODD);
	
        cairo_push_group (cr);

        cairo_set_operator (cr, CAIRO_OPERATOR_OVER);

	path_quad (cr,
		   448.948314981535, 264.938083162531,
		   448.51546072308, 220.797386273742,
		   530, 220,
		   561.332719124854, 261.581040261313);

        path_quad (cr,
                   339.794010419399, 236.296868257225,
		   346.503195904195, 229.764422696084,
		   448.474225856364, 216.590856667608,
		   448.948314981535, 264.938083162531);

	cairo_set_source_rgb (cr, 0, 0.5, 1);
	cairo_fill_preserve (cr);
	cairo_set_source_rgb (cr, 0, 0, 0);
	cairo_stroke (cr);

        cairo_pop_group_to_source (cr);

        cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
        cairo_paint (cr);

        cairo_destroy (cr);

        if (image)
        {
            cr = gdk_cairo_create (widget->window);

            cairo_set_source_surface (cr, surface, 0, 0);

            cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);

            cairo_paint (cr);

            cairo_destroy (cr);
        }
    }

    return TRUE;
}

int
main (int argc, char **argv)
{
    GtkWindow *window;
    GtkDrawingArea *area;

    gtk_init (&argc, &argv);

    window = GTK_WINDOW  (gtk_window_new (GTK_WINDOW_TOPLEVEL));
    area = GTK_DRAWING_AREA (gtk_drawing_area_new ());

    gtk_container_add (GTK_CONTAINER (window), GTK_WIDGET (area));

    gtk_window_set_default_size (window, 800, 600);

    gtk_widget_show_all (GTK_WIDGET (window));

    g_signal_connect (area, "expose_event", G_CALLBACK (on_expose), NULL);

    gtk_main ();
    return 0;
}