[cairo] how to scale an image - correction

[Bertram Felgenhauer]

Kelvin Cheng wrote:
> Hi,
> This is a correction to my previous question. The cairo_matrix_init_scale 
> should be 2.0 instead of 0.5.
> Even when it is 2.0,   the code still does reduce the image by 50%. Any 
> idea ?

Isn't that what you wanted?

> I am trying to scale an image by 50 %. 

Try this:

    cairo_save(cr);
    cairo_translate(cr, target_x, target_y);
    cairo_scale(cr, 0.5, 0.5);
    // note: it's important to set the source after setting up the
    // user space transformation.
    cairo_set_source_surface(cr, local_surf, 0, 0);
    cairo_paint(cr);
    cairo_restore(cr);

> I tried with the following code but it does not work: 
> 
>         cairo_save(cr); 
>         cairo_set_source_surface(cr, local_surf, target_x, target_y); 
> 
>         // these 2 lines are used for scaling 
>         cairo_pattern_set_matrix (cairo_get_source(board->cr), &matrix); 

What is 'matrix' here?

In any case, the pattern matrix transforms coordinates from user space
to pattern space; multiplying the coordinates by 2 will result in the
appearance of the pattern to shrink to 50% its original size.

HTH,

Bertram