[cairo] cairo_show_surface (), bug ?

Ravindra rkumar at novell.com
Tue Apr 13 05:45:49 PDT 2004

There seems to be a bug in cairo_show_surface API of cairo as mentioned
in cairo_gstate.c: line 1836 also.
Below is a testcase to reproduce the possible bug in cairo. This
function draws an image and its reflection along X-axis side by side.
The output gets the unwanted space of 1-2 pixels between the image and
its reflection. Either my approach my wrong or I found a bug in cairo
Please let me know, if my approach for flipping an image is not correct.


/*======================== CODE ==========================*/
/* NOTE: Please make sure that image background color and window
background color are different. */

/* Provide a surface of the image to be flipped */
void draw_tile_flipX (cairo_t *ct, cairo_surface_t *original, int width,
int height)
	cairo_surface_t *flip;
	cairo_pattern_t *pat;
	GpMatrix *matrix = cairo_matrix_create ();

	/* clear the repeat flag, if already set */
	cairo_surface_set_repeat (original, 0);

	/* texture surface to be created */
	flip = cairo_surface_create_similar (original,
                                             2 * width, height);

	cairo_save (ct);
		cairo_identity_matrix (ct);

		cairo_set_target_surface (ct, flip);
		/* Draw original surface */
		cairo_show_surface (ct, original, width, height);

		/* Draw reflection */
		cairo_matrix_translate (matrix, 2 * width, 0);
		/* scale in -X direction to flip along X */
		cairo_matrix_scale (matrix, -1.0, 1.0);
		cairo_surface_set_matrix (original, matrix);
		cairo_show_surface (ct, original, width, height);
	cairo_restore (ct);

	cairo_surface_set_repeat (flip, 1);
	pat = cairo_pattern_create_for_surface (flip);
	cairo_set_pattern (ct, pat);

	cairo_matrix_destroy (matrix);
	cairo_pattern_destroy (pat);
	cairo_surface_destroy (flip);

void fill_window (cairo_t *ct,  win_t *win)
	cairo_save (ct);

	cairo_t *surf;
	int width, height;
	// TODO: create a surface here
	draw_tile_flipX (ct, s, width, height);
        cairo_rectangle (ct, 0, 0, win->width,win->height);
        cairo_fill (ct);

        cairo_restore (ct);

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